Multi-interface engineering of nickel-based electrocatalysts for alkaline hydrogen evolution reaction
0 
Abstract
High gravimetric energy density and zero carbon emission of hydrogen have motivated hydrogen energy to be an attractive alternative to fossil fuels. Electrochemical water splitting in alkaline medium, driven by green electricity from renewable sources, has been mentioned as a potential solution for sustainable hydrogen production. Hydrogen evolution reaction (HER), as a cathodic half-reaction of water splitting, requires additional overpotential to obtain protons via water adsorption/dissociation, suffering from slow kinetics in alkaline solution. Robust and active nickel (Ni)-based electrocatalyst is a promising candidate for achieving precious-metal comparable performance owing to its platinum-like electronic structures with more efficient electrical power consumption. Various modification strategies have been explored on Ni-based catalysts, among which multi-interface engineering is one of the most effective routines to optimize both the intrinsic activity of Ni-based electrocatalysts and the extrinsic stacked component limitations. Herein, we systematically summarize the recent progress of multi-interface engineering of Ni-based electrocatalysts to improve their alkaline HER catalytic activity. The origin of sluggish alkaline HER kinetics is first discussed. Subsequently, three kinds of interfaces, geometrically and reactively, conductive substrate/electrocatalyst interface, electrocatalyst internal heterointerface, and electrocatalyst/electrolyte interface, were cataloged and discussed on their contribution mechanisms toward alkaline HER. Particular focuses lie on the microstructural and electronic modulation of key intermediates with energetically favorable adsorption/desorption behaviors via rationally designed interfaces. Finally, challenges and perspectives for multi-interface engineering are discussed. We hope that this review will be inspiring and beneficial for the exploration of efficient Ni-based electrocatalysts for alkaline water electrolysis.
Keywords
INTRODUCTION
The scalable and sustainable production of hydrogen is essential to alleviating the environmental and energy crises[1-5]. In addition to holding a significantly higher energy density than conventional fossil fuels, hydrogen emits no greenhouse gases, endowing it as a cleaner energy source[6]. In light of these characteristics, it offers a vast range of applications in smart grids, residential heating systems, hydrogen vehicles, and fuel cell systems. Currently, coal gasification and steam reforming account for more than 96% of the world's annual hydrogen output, during which excessive energy would be consumed and vast amounts of greenhouse gases would be inevitably released into the atmosphere[7,8]. Therefore, it is attractive and desirable to upgrade the hydrogen production method from conventional techniques to the innovative technology, e.g., ion exchange membrane-based water electrolysis, to further fulfill the ambitious carbon neutral goals and facilitate the transition toward low-carbon power systems[9]. Specifically, the proton exchange membrane (PEM) can be assembled into membrane electrode assemblies (MEAs) as a water electrolyzer to directly produce high-purity hydrogen from water. More significantly, PEM could be further coupled with renewable and intermittent energy (solar, wind, tidal, etc.) to store the energy/electricity into chemical forms and integrated within the power grid (acting as load) to relieve network bottlenecks with improved system flexibility[10]. Despite these unique benefits, the practical applications of these devices face obstacles due to the expensive electrolyte-tolerant parts and catalysts. Typically, precious metal (oxides)-based catalysts and titanium alloy/stainless-steel components are essential for the stable operation of PEM electrolyzers in acidic medium. Comparatively, an anion exchange membrane (AEM) electrolyzer, in which alkaline electrolyte is employed as the ion diffusion and reactive media, can introduce earth-abundant metals (Ni/Co/Fe, etc.) as catalyst materials, enabling promising application perspectives with great advantages than PEM electrolyzers[11]. Nevertheless, the unsatisfactory performance of these non-precious metal catalysts generally results in high energy barriers and low energy efficiency. Consequently, the pursuit of cost-effective, reliable, and high-performing catalysts has emerged as a significant research frontier for alkaline water splitting technology[12,13].
Principally, electrocatalytic water splitting includes hydrogen evolution reaction (HER) for the cathode and oxygen evolution reaction (OER) for the anode, respectively[14]. Unlike the abundant protons supplied in acidic electrolyte, the HER undergoes a sequential two-step process in alkaline conditions, during which the protons are generated via the water dissociation firstly and transformed into hydrogen molecular subsequently[15,16]. This additional water adsorption/dissociation step in alkaline electrolyte accounts for more than 2-3 orders of magnitude slower kinetics than that of acidic conditions[17,18]. Moreover, the inclusion of extra steps would also result in extra energy consumption, defined as the overpotentials beyond the thermodynamic energy. Therefore, the advancement of electrocatalysts is crucial in order to diminish these excessive overpotentials and accelerate the reaction kinetics[19]. It is widely acknowledged that platinum (Pt)-based materials have the best HER electrocatalytic performance[20,21]. However, their application is hindered by the high cost and scarce storage[22]. In order to address these issues, earth-abundant non-precious metal materials have triggered extensive attention, among which nickel (Ni)-based materials have exhibited great potentials owing to their earth abundance, cost-effectiveness, and, most importantly, holding similar electronic properties to Pt[23]. Unfortunately, Ni-based electrocatalysts currently still cannot completely replace Pt due to their relatively strong H adsorption, insufficient active sites, and high energy barriers for water adsorption/dissociation in alkaline conditions, which hampered their practical application. Therefore, the dilemma of conventional Ni-based catalysts lies in that the sole Ni content cannot simultaneously promote the water dissociation and the desorption of adsorbed hydrogen intermediate (Had) in alkaline medium, not to mention the potential modulation of hydroxy groups. Therefore, rationally designing and fabricating Ni-based electrocatalysts with excellent intrinsic activity is still a grand challenge at present[24].
During the last decade, growing interests have been attracted in the construction of multi-component composite systems to intentionally overcome the limitations of sole Ni catalyst via different strategies, e.g., (Ni) metal alloying/dealloying[25-27], heteroatom doping[28-30], strain engineering[31-33], multi-interface engineering[34-38], etc. Among them, the multi-interface engineering has exhibited substantial potential to synergistically optimize the entire HER systems from different perspectives: geometrically and chronologically, three interfaces, including (1) conductive substrate/electrocatalyst interface; (2) internal interface of electrocatalyst; and (3) electrocatalyst/electrolyte interface, could be optimized to fundamentally facilitate the alkaline HER performance. Specifically, close and flawless contact between the conductive substrate and electrocatalyst could effectively minimize the charge transfer resistance and benefit the HER kinetics with smaller overpotential. Secondly, multi-component Ni-based catalysts with wisely heterointerface engineering (e.g., ensemble effect and electronic modulation) enable the optimization of both the thermodynamics and kinetics of HER processes. Thirdly, a robust electrocatalyst/electrolyte interface is significant for achieving a stable HER performance, particularly for high current density conditions. The generated gas bubbles could induce great inner pressure at the interface and lead to severe catalyst damage or structure failure. During high current density and prolonged operation, the accumulation of bubbles and generation of joule heat can cause the electrocatalyst to easily detach from the conductive substrate. By optimizing the substrate/electrocatalyst interface, the binding strength between the electrocatalyst and the substrate can be enhanced, resulting in improved stability of the electrocatalyst. By introducing defect sites or constructing heterostructures to optimize the internal interface of electrocatalyst, the intrinsic catalytic activity of the electrocatalyst can be enhanced, leading to higher conversion efficiency of reactant species and promoting long-term stable operation of the electrocatalyst. Additionally, by adjusting the wettability of electrocatalyst/electrolyte interface, the wetting properties of the electrolyte and the bubble detachment rate can be improved, allowing the electrocatalyst to exhibit superior performance during prolonged catalytic processes. Therefore, reasonable multi-interface design can significantly break the activity limitation of electrocatalysts.
Recent advances of interface engineering for alkaline HER electrocatalysts have been summarized in several reviews. Xu et al. thoroughly summarized the atomic heterointerface engineering for improving the catalytic performance of electrocatalysts[39]. Wei et al. focused on the advances in building heterostructured catalysts for accelerating the Volmer step in alkaline conditions[40]. Huang et al. discussed a series of representative heteroatom‐modified electrocatalysts with properly designed multi-component interfaces and highlighted the optimized HER reaction pathway[41]. These reviews mostly focus on the interface engineering of the electrocatalyst itself, whereas the other two types of interface with both conductive substrate and electrolyte still lack detailed discussion, especially based on the electrocatalytic HER mechanism. Herein, the multi-component functions, design protocols and synthesis approaches of multi-interface engineering are summarized and discussed for exploring efficient Ni-based alkaline HER electrocatalysts [Figure 1]. We first summed up the alkaline HER mechanism, the origin of the sluggish kinetics for elementary steps, and the critical electrochemical parameters to evaluate the HER performance. Afterward, detailed discussions on the aforementioned three types of interfaces are organized, focusing on the internal interface of electrocatalyst to modulate the HER elementary process thermodynamically and kinetically. Finally, the challenges and prospects of multi-interface engineering for the design of alkaline HER electrocatalysts are discussed.
Figure 1. Schematic illustration of multi-interface structure and engineering strategies.
FUNDAMENTAL MECHANISMS OF ALKALINE HER
A typical water electrolyzer consists of three stacked components: a cathode, an anode, and an electrolyte. Two half reactions, HER and OER, occur at the cathode and anode, respectively. Although the reaction of splitting water into hydrogen and oxygen was discovered in acidic electrolyte, the water splitting in alkaline electrolyte has been commercialized on a large scale for a century owing to its more economic efficiency with robust electrocatalysts. The cathodic HER is recognized as a relatively basic catalytic reaction involving a two‐electron transfer process, which could be divided into two elementary steps regardless of whether it occurs in acidic or alkaline electrolyte: (i) hydrogen adsorption step (Volmer step), during which a proton (H+) combines an electron on the active sites to generate an adsorbed hydrogen intermediate; (ii) hydrogen desorption step (Heyrovsky/Tafel step), during which the obtained Had would form hydrogen molecule and desorb from the catalyst surface via either Heyrovsky or Tafel step. The detailed HER process is illustrated as the following elementary steps [Figure 2].
Figure 2. Schematicillustrationforthe elementaryHERstep: Volmer step and Heyrovsky step/Tafel step. balls in blue: active sites; grey: O atom; orange: H atom, respectively.
For acidic HER, the generation of hydrogen molecules is associated with the hydrogen adsorption free energy (ΔGH) on the active sites. The well-established Sabatier principle indicates that the interaction between an optimal catalyst and the reactive intermediates should not be too strong or weak. Therefore,
ELECTROCHEMICAL PARAMETERS OF HER
The performance of a given HER electrocatalyst is commonly assessed using a few key electrochemical parameters, including overpotential (η), Tafel plot, electrochemical impedance spectroscopy (EIS), turnover frequency (TOF), stability, etc. Through these parameters, the detailed reaction thermodynamics and kinetics information could be extracted. In this section, a concise overview of these parameters will be provided.
Overpotential
The representative polarization curves are obtained by graphing the geometric current density against the applied potential. The η is described as the potential gap between the actual applied potential for triggering the reaction and the thermodynamic equilibrium potential. A larger η indicates an increased electricity consumption, thereby resulting in a limited energy conversion efficiency. A satisfactory electrocatalyst should exhibit a higher current density at a low overpotential. Nernst equation elucidates the relationship between the HER equilibrium potential (EHER) and the standard hydrogen electrode potential (ESHE) which is defined as 0 V at any temperature.
where R is the gas constant, T represents the temperature in kelvins, z denotes the number of electrons transferred (z = 2 for HER), F is the Faraday constant (96,485 C mol-1),
The origins of η include the activation barriers of electrochemical reactions, ion migration, and internal resistance of the measurement system (RS). An excellent catalyst can reduce the activation energy barriers required for initiating the reaction. Ion migration and series resistances are mostly dependent on external testing system configurations. The ohmic potential drop caused by RS can be corrected by iR compensation. Therefore, the terminal E can be given by
Generally, the overpotential needed to achieve a current density of 10 mA cm-2 (geometric current density)
Tafel plot
Tafel plot can be well employed to investigate the inherent kinetics information of the electrocatalyst, which is derived from the experimentally measured polarization curves. When the solution concentration at the electrode surface is comparable to that of the bulk solution, the overpotential connected with the electrode kinetics can be significantly correlated with the current density by the Butler-Volmer equation, denoted as
where i represents the current density, i0 is the exchange current density under reversible conditions, α is the charge transfer coefficient, and f equals to F/RT. In the region of high overpotential, Eq. 5 can be simplified to
According to Eq. 6, the relationship between overpotential and Tafel slope (b) can be expressed as
where i0 is the rate of charges entering or leaving the electrocatalyst surface under reversible conditions in an electrolyte, which can be extracted at the overpotential of zero. A high i0 indicates the easier polarization of the electrocatalyst, and a lower activation overpotential to trigger the electrode reaction. The possible reaction mechanisms can be inferred from the value of the Tafel slope. For example, the Tafel slope of
Charge transfer resistance
For an electrochemical reaction, the charge transfer characteristics are an important descriptor of an electrocatalyst activity, which can be evaluated from the EIS measurement technique within a reasonable frequency band. Generally, EIS measurements are conducted at the amplitude of perturbation voltage of
where n is the number of transferred electrons. Smaller values of Rct indicate faster reaction kinetics and potentially better catalytic performance.
Turnover frequency
TOF is defined as the number of the desired product per active site in unit time (second, Eq. 9) at a predefined applied potential, which is an important parameter for measuring the intrinsic activity of an electrocatalyst. Nevertheless, the exact value of TOF is difficult to measure because the actual population of active sites cannot be accurately determined for heterogeneous catalysis. In some instances, the TOF can be obtained by calculating the total catalyst loadings, no matter whether they are truly involved in the catalytic process. In other cases, many researchers reported that the sole surface atoms or the easily accessible surface catalytic sites of the electrocatalysts participate in the catalytic process and generated the TOFs accordingly. Nonetheless, such results are meaningful when similar electrocatalysts are compared.
For HER, assuming that Faradaic efficiency is 100%, and the number of H2 can be can be expressed as
Consequently, Eq. 10 can be simplified to
where I is current (A), z represents the quantity of electron transferred per molecule (z = 2, for HER), and
Stability
Besides the intrinsic activity, the time-dependent stability is also a very important parameter for potential applications, especially under high current conditions. Two approaches exist for evaluating the durability of an HER electrocatalyst, including the chronopotentiometry (CP)/chronoamperometry (CA) and accelerated cyclic voltammetry (CV) tests. CP/CA test is conducted by recording the curve of potential/current over time under a fixed current/potential, respectively. For CP or CA test, most reported works are performed at a current density lower than 200 mA cm-2. In fact, for practical application, durability test at higher current densities is encouraged for mimicking the real working conditions in AEM. In CV test, generally, larger than 1,000 CV cycles are repeated by recording the potential with the current response. By comparing the polarization curves before and after CV cycles, it can be seen that the less η increment, the better the stability of the electrocatalysts.
MULTI-INTERFACE ENGINEERING OF ALKALINE HER ELECTROCATALYSTS
For a complete electrocatalytic HER process, electrons from the external power source would structurally and chronologically go across three interfaces to reach the active site and participate in the reaction, including conductive substrate/electrocatalyst, electrocatalyst internal and electrocatalyst/electrolyte interfaces. Therefore, engineering these multi-interfaces is very important to optimize the overall electrocatalytic performance, which will be meticulously reviewed in this section.
Conductive substrate/electrocatalyst interface
In order to enhance electron transport efficiency with minimal charge resistance and avoid the electroheat energy waste, a geometric and electric close interfacial contact between an active electrocatalyst and a conductive substrate is essential. Most commercial and experimental electrodes are currently made by coating active catalyst materials onto a conductive substrate with the assistance of polymer binders, inevitably resulting in a vulnerable interfacial adhesion and hindrance to electron transport. In order to strengthen this interface, in-situ synthesizing catalytically active materials on conductive substrates or directly preparing self-supported freestanding electrode/electrocatalyst has been documented to address these interface issues.
Conductive substrate
The commonly used conductive substrates mainly include nickel (NF)/copper foam, Ni-based alloy foam, carbon cloth, carbon paper, etc., among which the NF has been reported as the most popular electrode substrate. On the choice of the conductive substrate, NF has enjoyed widespread application as its distinctive interlinked third-dimensional (3D) microstructure provides merits as light weight, high porosity, reliable mechanical strength, chemical stability, and promising electrical conductivity. Moreover, its employment could also act as the nickel source during the synthesis, offering further opportunities for constructing Ni-based compounds with multi-interface. For example, through a two-step synthetic procedure, specifically, the 1st step preparation of NiMoO4·xH2O nanowire arrays followed by the 2nd step pyrolysis process, Liu et al. constructed MoO2-Ni nanowire arrays supported on NF as an efficient HER catalyst [Figure 3A-J]. Benefiting from the in-situ grown MoO2-Ni heterostructure with an atomically infused interface, the HER kinetics was enhanced by the upraised atomic d orbital[42]. The optimized MoO2-Ni@NF electrocatalyst exhibited exceptional Pt-like HER performance in 1 M KOH[42]. Chang et al. electrodeposited amorphous Ni-Co-Fe ternary phosphides (Ni4Co4Fe1-P) on NF as a self-supported catalytic electrode for alkaline HER. The integration of multimetallic phosphide on the NF surface allows sufficient exposure of surface sites[43]. Therefore, the Ni4Co4Fe1-P electrode presented good HER catalytic performance (-61 mV at -20 mA cm-2)[43]. Ni-Cu-P@Ni-Cu catalyst was also prepared using electrodeposition as an efficient electrode for HER. During electrodeposition, NF provided sufficient active sites for the growth of dendrites with unique structures. Its high active electrochemical area, the convenient mass transfer channels provided by the porous structure, and the synergistic effect between Cu and Ni led to the excellent electrocatalytic activity (-70 mV at 10 mA cm-2) of the catalyst[44]. Deng et al. designed a definite metal-support interfacial bond to enhance the intrinsic activity of noble metals (Ru, Ir, and Pd)[45]. Through a spontaneous redox strategy, three kinds of quantum-sized metal nanoparticles propped against Ni-based metal-organic framework (Ni-MOF) nanohybrids (Ru@Ni-MOF, Ir@Ni-MOF, and Pd@Ni-MOF) were rationally prepared. As shown in Figure 3K-N, Ru3+ and metallic Ni on the NF surface spontaneously underwent a redox reaction, during which Ni2+ ions were also coordinated with 1,4-benzenedicarboxylic acid (H2BDC) to shape Ni-MOF nanosheets. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images demonstrated the uniform distribution of Ru nanoparticles anchored (2-4 nm) on the Ni-MOF surface. The strong interfacial interaction between the nanoparticles and Ni-MOF ensured not only the structural stability but also adequate exposure of active sites. More significantly, the electronic structure of hybrid materials was successfully modulated by the charge exchange in the formed Ni-O-M (Ru, Ir, Pd) bridge bond with enhanced HER kinetics. Consequently, the Ru@Ni-MOF catalyst exhibited superior HER performance, even superior to commercial Pt/C. Theoretical calculation demonstrated that the interfacial-bond-induced electron transfer resulted in the optimized adsorption of
Figure 3. (A and B) SEM images of MoO2-Ni on NF. (C) TEM, (D) HRTEM, (E-J) HAADF-STEM images and elemental analysis results of MoO2-Ni nanowires. (K) Schematic illustration of the formation of Ru@Ni-MOF grown on NF. (L, M) SEM and (N) TEM images of Ru@Ni-MOF. This figure is quoted with permission from Liu et al.[42] and Deng et al.[45].
Ni-based alloy foams could provide more growth sites when the conductive substrate is combined with active substance by hydrothermal methods. For instance, a HER electrocatalyst (NiFeCoSx@FeNi3) consisting of Co3S4 and Ni-Fe sulfide on FeNi3 foam was prepared. The synergistic interaction among multi-elements and the unique structure together gave the catalyst outstanding catalytic performance. In alkaline solution, the η10 of NiFeCoSx@FeNi3 is 88 mV[51]. In addition to Ni-based conductive substrates, copper substrates could also serve as good conductive substrates. A dynamic hydrogen bubble template (DHBT) method is a practical approach to fabricating the porous alloy electrodes. The porous Ni-Co catalyst on a copper substrate electrode was prepared using the DHBT method and exhibited outstanding stability[52]. Zhang et al. prepared an efficient HER electrocatalyst by coating metallic Ni onto Cu2S nanoarrays using the commercial copper foam as a substrate and unveiled a preferable HER activity (η < 200 mV at 500 mA cm-2). Finally, theoretical analyses indicated that the Ni-S interaction between metallic Ni and Cu2S interface can optimize the adsorption energy of hydrogen and thus promote HER kinectics[53].
Moreover, carbon cloth has been widely used as a conductive substrate for HER because of its superior electric conductivity, low cost, and robust mechanical flexibility. Yang et al. prepared an electrocatalyst containing W2C nanowires decorated with Ni nanoparticles on carbon cloth[54]. It only required a low overpotential of 37 mV to obtain current densities of 10 mA cm-2, which was comparable to the commercial Pt/C catalyst. Moreover, the experimental results indicated that the close interaction between Ni nanoparticles and W2C nanowires can effectively accelerate electron transport[54]. A NiO/Ni heterostructure on carbon cloth (NiO/Ni@CC) was fabricated by in-situ electrochemical oxidation after electrodepositing metallic Ni on the surface of carbon cloth. The existence of heterostructure and the superior electric conductivity of carbon cloth made the catalyst exhibit a low η10 of 40 mV for alkaline HER[55]. Theoretical calculations by Wang et al. predicted that coupling Ni3C with metallic Ni can balance H and H2O adsorption energies. Subsequently, they fabricated an integrated heterostructure catalyst consisting of Ni3C nanosheets and Ni nanoparticles on carbon cloth, demonstrating excellent electrocatalytic HER activity
Freestanding electrocatalyst/electrode
In addition to preparing binder-free electrocatalysts by off-the-shelf substrates, self-supported electrocatalysts could also be directly prepared using the bottom-up approach, namely freestanding electrocatalysts. The freestanding electrocatalyst with the absence of an interface, or denoted as the integrated catalyst electrode, enables a faster electron transfer rate through the interior of the electrodes.
The electrospinning technique is efficient in preparing freestanding electrocatalysts. For instance, Yang et al. fabricated novel Ni/NiO-carbon nanotubes (CNTs) composite nanofibers by electrospinning and followed thermal treatment[59]. Without extra reducing agents and carbon source, the Ni(Ac)2/polyvinylpyrrolidone (PVP) precursor can decompose to reductive gaseous H2, CO, CH4 during the vacuum heat treatment, which could facilitate the NiO reduction and CNT growth. The optimized Ni/NiO-CNTs composite can deliver an excellent HER activity (η10 = 98 mV) in 1 M KOH[59]. The freestanding CNF-Ni/NiO-Pd electrode was also prepared by Barhoum et al. via electrospinning, pyrolysis, and atomic layer deposition, sequentially[60]. This self-supported composite was employed as a highly efficient HER electrocatalyst. The surface graphitic layers can keep the Ni/NiO from corrosion, and the synergistic effect of different substances at the interfaces attributed the catalyst to excellent performance. The optimized CNF-Ni/NiO-Pd electrocatalyst exhibited a low overpotential (η10 = 63 mV) and a remarkably small Tafel slope of
Figure 4. (A) Schematic illustration of the synthesis process of Ni/CeO2@N-CNFs. (B) Schematic representation of the preparation of NiCuDSS electrocatalysts. (C-E) SEM images of prepared Ni0.95Cu0.05DSS at different magnifications. This figure is quoted with permission from Li et al.[61] and Zhang et al.[63].
Briefly, the interfacial charge transfer resistance between electrocatalyst and conductive substrate can greatly affect the overall catalytic performance of electrocatalyst. The electron transfer between the conductive substrate and electrocatalyst can be facilitated by chemically in-situ growth of active species on a conductive substrate. In addition, the intrinsic conductivity of freestanding electrocatalysts without a conductive substrate needs special attention.
Internal interface of electrocatalyst
For enhancing the intrinsic catalytic activity of materials, an efficient approach is to create atomic-level or phase-level heterogeneous interfaces inside the electrocatalysts. Multi-interface catalysts in the electrocatalytic field, defined as the catalysts containing interfaces between different components, have received a lot of attention. Interesting physicochemical features could be induced towards the multi-interface catalysts owing to the differences in the geometric and electronic structures of the unequal components. The preferred combination of different components thus can modulate the electrocatalytic reaction pathways and improve reactive kinetics. Although interfaces with variable atomic arrangements can lead to different electron transfer or interfacial resistances, two distinctive interfacial effects have been well identified, namely the ensemble and electron effects. The former originates from the multi-component heterointerfaces, where the interconnected active sites with different local electronic structures can regulate and facilitate the adsorption/desorption procedure of various reactive intermediate species. Therefore, the multi-interface can offer an energetically favorable pathway for a multi-step catalytic process when the individual elementary reaction occurs on its preferred component and so greatly enhances the overall reaction efficiency. Comparatively, the latter (electron effect) means that the different components have electronic interaction at the interface, which could further trigger an interfacial charge redistribution. As a consequence, the adsorption behaviors of key intermediates could be modulated by coupling their electronic structures via electron effect. It may be noted that in a composite electrocatalyst, the ensemble effect and electron effect could hardly be clearly separated; actually, they synergistically accelerate the HER process. Therefore, the rational multi-interface engineering holds great promise to maximize these effects. In order to achieve the atomic design of multi-interfaces, several innovative preparation methods have been explored, e.g., defecting engineering, vacancy or heteroatom doping, the phase-level heterostructure engineering, etc.
Atomic interface via defect engineering
The defect can be defined as the nonuniform composition in a material, including vacancies, heteroatom dopants, etc., which could significantly affect the electron distribution around the defective sites. The electronic arrangement of the catalyst is closely related to its catalytic activity; consequently, atomic defect engineering could effectively tune the electronic configuration of catalysts, which, in turn, is used to regulate its electrocatalytic performance.
The rational design of non-metallic element vacancies has been revealed as a convenient defect engineering strategy to enhance catalytic activity. For instance, by introducing sulfur vacancies to Ni3S2, Jia et al. successfully tuned the hydrogen adsorption behaviors on Ni sites to improve HER activity (η10 = 88 mV) in
Metal ion doping has also been shown to be another effective approach to modulating the electronic configuration of catalysts. For example, based on Ni/Co-doped MoSe2 catalysts, Mao et al. revealed that doping Ni/Co atoms could effectively modulate the electronic structure of MoSe2[68]. Experimental and theoretical analyses showed that the doped Ni/Co atoms can regulate the position of the d-band center and optimize electrical conductivity of catalyst, which, in turn, adjusts the strength of the interactions between adsorbed hydroxyl (OHad) and active sites. The optimal hydroxyl adsorption strength would facilitate the Volmer step, thus enhancing the overall alkaline HER kinetics [Figure 5A-E][68]. As shown in Figure 5F, by controlling the reaction conditions, Zhong et al. synthesized Ni-doped CoSe with and without Co vacancies, respectively[69]. Theoretical and experimental results demonstrated that the Co vacancy and Ni atom located in the vicinity of Se atoms synergistically affect its electron distribution, leading to the upshift of Se 4p(z) orbital. Consequently, the ΔGH of Se atoms was significantly optimized, resulting in an advanced HER activity[69]. Jiao et al. designed an effective strategy for increasing quantity of active sites by annealing Ni-MOF at different temperatures. The incorporation of trivalent Ni3+ resulted in a delicate atomic rearrangement and provided more catalytic active sites. Therefore, the as-prepared Ni/NiO nanoparticles displayed excellent HER performance (η10 = 41 mV)[70]. Tang et al. prepared a heterostructure catalyst consisting of V-doped NiFe layered double hydroxide (LDH) and Ni nanoparticles, possessing excellent HER catalytic performance (η10 = 19 mV)[71].
Figure 5. (A) The TDOS charts of MoSe2, Co-MoSe2, and Ni-MoSe2. (B) The PDOS charts of Co-MoSe2. (C) The comparison of d-band centers (εd) of MoSe2, Co-MoSe2, and Ni-MoSe2. (D) The Gibbs free energy of OHad. (E) Schematic diagram of catalytic action of OHad transfer in alkaline HER process. (F) Schematic diagram of the synthesis method of (Co1-xNix)2Se2 with and without vacancies. This figure is quoted with permission from Mao et al.[68] and Zhong et al.[69].
Introducing vacancies or heteroatom dopants into electrocatalysts has been confirmed as useful atomic interface engineering to enhance the electrocatalytic performance. However, some problems still need to be solved. For instance, there remains a need for a greater focus on the stability and in-situ reconstruction of defect-rich catalysts. Additionally, the precise control of the coordination environment of the doping site has yet to be available.
Interface at heterostructures
The unique physicochemical properties of heterostructured electrocatalysts lead to their excellent HER performance. Heterostructured electrocatalysts composed of different components usually have higher catalytic activity than a single-component catalyst due to the aforementioned synergistic ensemble and electron effects. Therefore, developing heterostructured electrocatalysts with distinctive ensemble effect/electron effect is considered an effectual approach to obtain satisfactory HER performance.
The different multi-components usually have specific catalytic activities for different elementary steps (for distinct intermediates). When these active sites are rationally combined, the overall reaction kinetics thus can be synergistically enhanced. For example, nickel oxide could effectively expedite the water adsorption and dissociation step to generate protons, while metallic nickel can further facilitate hydrogen desorption to generate hydrogen molecules. Based on this dual active site conception, Huang et al. developed heterostructured efficient HER catalysts (Mo-NiO/Ni) by doping metal Mo atoms into NiO and coupled with metallic Ni[72]. Theoretical and experimental analyses have been used to comprehensively investigate its catalytic mechanisms. Doping Mo heteroatoms into NiO could not only accelerate the water dissociation and rapid transfer of H to the adjacent Ni sites to generate H2 but also maintain the structural stability of NiO crystal [Figure 6A-C]. As a consequence, the Mo-NiO/Ni catalyst exhibited an excellent HER performance with η10 of 50 mV and the Tafel slope of 86 mV dec-1[72]. Gu et al. synthesized a 3D sponge built via graphene nanocages in which Ni nanoparticles and single atoms coexisted using a facile one-pot strategy[73]. The H2O molecule was preferentially adsorbed on the atomic Ni sites within the graphene cage, then dissociated into OHad and Had. Subsequently, Ni nanoparticles provided active sites for H adsorption to produce molecular hydrogen. The synergistic catalytic effect between Ni nanoparticles and atomic Ni sites endowed the composite catalyst with excellent HER performance (η10 = 27 mV)[73]. Pt electrodes have excellent catalytic HER performance under acidic conditions, while their HER performance under alkaline conditions is unsatisfactory owing to the lack of water adsorption/dissociation sites. To enhance the HER activity of Pt electrodes in alkaline conditions, Xue et al. modified the electrode with Ni-Fe clusters. This heterostructured catalyst exhibited an excellent HER performance, which mostly originated from the synergistic promotion of the facilitated water dissociation ability of Ni-Fe clusters and the optimized hydrogen adsorption ability of Pt[74]. Additionally, a special heterostructured HER catalyst (Ni/NiFe-LDO), comprising Ni nanoparticles and NiFe-layered double oxide (LDO) on NF, was successfully constructed, which exhibited η10= 29 mV in 1.0 M KOH electrolyte. Detail characterizations indicated that the synergistic interface effect between NiFe-LDO nanosheets and Ni nanoparticles improved its HER activity. The metal oxides were beneficial for water activation because of their strong H2O adsorption ability; subsequently, OH was adsorbed on NiO active sites; meanwhile, Ni nanoparticle active sites were responsible for the adsorption of H. In summary, it has been widely acknowledged that properly constructing a multi-component interface could significantly enhance the kinetics of Volmer-step reaction via the distinctive ensemble effect as decoupling the generation and desorption of hydrogen intermediate[75].
Figure 6. (A) Calculated H2O dissociation barriers and (B) Gibbs free energies of H adsorption on different theoretical models. (C) Summary of adsorption energy of various reactive intermediates on the three surfaces. (D) Schematic diagram of the catalyst preparation and the representation of the alkaline HER process on the Ni-γ-Fe2O3 interface. This figure is quoted with permission from Huang et al.[72] and Suryanto et al.[76].
In heterogeneous catalysts, interfacial electron transfer could be initiated between different components due to their unequal energy band structures, leading to changes in the adsorption and desorption behavior of intermediates, which is strongly associated with the HER activity of the electrocatalyst. Therefore, the rational design of efficient alkaline HER electrocatalysts could also be realized by modulating the electronic interactions at the interface. For instance, a nanoparticle catalyst with abundant metallic Ni/γ-Fe2O3 interfaces was developed as an efficient HER electrocatalyst, as shown in Figure 6D. Theoretical calculations indicated that the strong electronic interactions at the Ni/γ-Fe2O3 interfaces resulted in its good HER catalytic activity[76]. Sun et al. developed a series of hybrid electrocatalysts via implanting bixbyite-type lanthanide metal sesquioxides in metallic Ni toward HER[77]. The Yb2O3 could provide abundant active sites and optimize the free energies of water dissociation and hydrogen adsorption. Therefore, the screened Ni/Yb2O3 electrocatalyst exhibited excellent HER performance (η10= 20 mV) and outstanding durability (360 h at 500 mA cm-2)[77]. The interphasic synergy with charge redistribution in monometallic structures was also reported to successfully tune the adsorption-desorption strength of intermediate species (H/OH) in HER processes. Electronic structure analysis showed that a lot of Ni d band electrons at the Fermi level could accelerate the charge transfer from Ni(OH)2 to Ni-N/Ni-C. Accordingly, the prepared Ni(OH)2@Ni-N/Ni-C heterostructured electrocatalyst displayed decent HER activity with an overpotential of 113 mV at
Moreover, metal-organic polymers, particularly conjugated variants, have become increasingly important in the field of electrocatalysis due to their customizable composition, varying metal oxidation states, abundant active sites, and impressive conductivity. These polymers can be prepared under relatively mild conditions. By fine-tuning metal active sites and strategically using functionalized ligands, it is possible to precisely design active sites and foster strong interactions between ligands and metal sites. Therefore, polymers can also be utilized to modify the internal interface of electrocatalyst. For example, Liu et al. prepared a self-supported bimetallic Mo-Ni-C3N3S3 CP (Mo-NT@NF), featured by robust metal-ligand interactions and varying H2O adsorption energy[89]. A range of Mo-NT@NF samples were prepared using a simple solvothermal method, and their multivalent metal states and performance towards HER were systematically assessed. The theoretical calculations and experiments revealed that the strong adsorption of the Mo5+ site of water molecules weakens the O-H bond, in conjunction with efficient proton transfer by the proton relay N and S, leading to a highly effective HER catalysis on the site[89]. Zhang et al. presented a simple and cost-effective approach to fabricate ultrasmall Ni/NiOx heterostructures coated with carbon nano-onions (CNOs) through a single-step thermal decomposition of ultra-thin 2D Ni-based CPs (CPs)[90]. The rapid low-temperature graphitization of CPs is crucial for enhancing the performance and scalability of the catalysts prepared. By confining the process within low-temperature graphitization conditions, the ultrasmall size of the Ni/NiOx heterojunction (< 5 nm) is guaranteed, leading to a significant increase in interfacial areas and a concurrent rise in active site density. Given the favorable electronic configuration of Ni3+ for OHad adsorption, the ultrasmall NiOx phase enhances the intrinsic catalytic activity for water decomposition. The low-temperature graphitization process also allows CNOs to maintain abundant hydrophilic functional groups, facilitating efficient mass transfer[90].
For multi-component heterostructured electrocatalysts, decoupling the different elementary steps on various active components has been shown to improve the overall reaction kinetics. Moreover, regulating the charge transfer behavior between diverse components can also reduce the reaction energy barrier or tune intermediate adsorption behaviors, which is an effective strategy to enhance the catalytic performance.
Electrocatalyst/electrolyte interface
In addition to the intrinsic activity of the electrocatalyst, the mass transport between the electrocatalyst and electrolyte interface is also very important for the overall reaction performance. Especially in the high current density condition, a great many of bubbles would be generated on the electrode surface, which will hinder the contact between the electrolyte and electrode, bringing about a decline in catalytic performance. Through the interfacial wettability engineering of the electrode surface and the rational design of electrical double layer (EDL) structure, the mass/electron transfer between reactive species and active sites can be well promoted to improve the HER performances.
Wettability
The wettability of electrocatalysts can significantly affect the catalytic activity under high current density conditions. The most distinctive difference between low (< 100 mA/cm2) and high current HER processes is the population of generated gas bubbles during the reaction. If gas bubbles cannot timely detach from the electrode surface, the small air bubbles would coalesce into larger ones as they minimize their surface energy. The large air bubble coverage on electrodes would create an insulator barrier between electrolyte and catalysts, resulting in shrunken effective surface area and high cross-interface ionic resistance with deteriorated HER catalytic performance. Moreover, the attached gas bubbles will continue to grow until the increased buoyancy overcomes the adhesion force between the bubble and catalyst, leading to the induced inner stress at the bubble/catalyst interface which could potentially trigger severe structural damage with compromised catalytic activity. Therefore, engineering the (electrocatalyst/electrolyte) interfacial hydrophilicity and aerophobicity can provide a fast mass and charge transfer pathway to improve the electrocatalytic activity.
Kim et al. fabricated a series of morphology-controlled metallic Ni electrocatalysts to systematically investigate the effect of wettability on hydrogen bubble release behaviors [Figure 7A][91]. The wettability (hydrophilicity or aerophobicity) of the catalyst surface is closely related to its porousness. The optimal superaerophobic Ni electrocatalyst exhibited the best HER performance with the highest porosity of approximately 52% among the Ni catalysts. It is observed that the unique superaerophobic surface structure of the metallic Ni electrocatalyst combined with the effective mass transport can accelerate the detachment of H2 bubbles, substantially improving catalytic performance[91]. As shown in Figure 7B-M, Xu et al. first prepared 3D-printed Ni electrodes, modified with active materials of MoNi4 and NiFe LDH, which exhibited superior electrocatalytic HER performance[92]. The special porous structure of 3D Ni electrodes allows fast bubble generation and release, providing generous active sites. The MoNi4@3D Ni electrode only required an overpotential of 104 mV at 500 mA cm-2[92]. Fujimura et al. employed Ni microarray electrodes prepared by photolithography and electrodeposition; the correlation between HER efficiency and surface wettability was explored[93]. Furthermore, in-situ video surveillance of the electrode surface during the HER process clearly demonstrated that the size of generated air bubbles increased as the wettability of the electrode surface decreased. The larger bubbles will increase the ohmic loss and block the active sites on the electrode surface[93]. Shang et al. fabricated a HER electrocatalyst (Ni/NiMoN) constructed by NiMoN nanowire arrays modified by metallic Ni nanoparticles on a copper foam[94]. Theoretical analysis indicated that the Ni nanoparticles can accelerate H2O dissociation rate, boosting the feed of protons in the neutral media. Simultaneously, hydrogen bubbles can quickly leave the electrocatalytic surface to refresh the catalytic active sites because the dense nanowire arrays endow the electrode surface with superaerophobic properties. Therefore, the Ni/NiMoN electrode demonstrated excellent HER activity (η10= 33 mV) in a neutral media[94]. Li et al. designed superhydrophilic Ni-based multi-component array (Ni NCNA) catalyst on NF, which only needed -47 mV to achieve 10 mA cm-2. The water contact angle analysis displayed that it took only 0.2 s for the water droplet to completely spread on the electrode surface. Owing to its superhydrophilic properties, the Ni NCNA catalyst can operate stably under high current conditions[95]. A typical graphite electrode surface can be transformed into a superhydrophilic structure after Ni-Sb alloy modification using a one-step electrodeposition method. Benefiting from its superhydrophilic surface property, the optimized Ni-Sb alloy electrode achieved superior HER electrocatalytic performance[96]. Moreover, Yu et al. prepared a Ni-Mo-based catalyst with superhydrophilic and aerophilic surfaces. Owing to its high intrinsic activity and porous structure, the Ni-Mo-based catalyst presented remarkable HER activity in all-pH media[97]. Therefore, the appropriate modulation of surface wettability, specifically, minimizing the size of gas bubbles at detachment, would be beneficial to alleviate the inner stress and facilitate the rapid release of the generated air bubbles from the electrode surface, enabling enhanced high current density HER performance.
Figure 7. (A) Schematic illustrations of the H2 bubble-release behavior of different Ni catalysts. (B) Contact angles on 3DP Ni and (C) NF. (D) Bubble adhesive force measurements of 3DP Ni and (E) NF. (F-I) Digital images of bubble release from 3DP Ni and (J-M) NF structures. This figure is quoted with permission from Kim et al.[91] and Xu et al.[92].
Electrical double layer
The EDL is where the electrochemical reaction takes place. The inner/outer Helmholtz plane (IHP/OHP) and the diffuse layer together form the EDL [Figure 8][98]. IHP is crucial for an electrochemical reaction, which contains various reaction-involving molecules and ions. For alkaline HER, the main species are H2O, adsorbed Had and OHad/OH- from water dissociation, and H2 and specific cations from the electrolyte solution. The transfer impedance of reactive species in EDL can increase the overall reaction overpotential and energy loss. Unfortunately, it is very hard to directly monitor the interfacial effect of EDL during alkaline HER due to the lack of effective methods for detecting interfacial species. This is because the structural or compositional changes of EDL could only be studied via in situ/operando technology due to its instantaneous property changes with the applied electric field, and the thickness of EDL is only around
Figure 8. Simplistic view of EDL for alkaline HER. Red: O; Blue: H. This figure is quoted with permission from Jiang et al.[98].
For example, Zhang et al. employed interfacial chemistry engineering to tune the adsorption free energy of H2O dissociation and H simultaneously[99]. The hybrid Ni0.2Mo0.8N microrod arrays supported on NF were decorated with Ni nanoparticles. Theoretical analysis suggested that the Ni0.2Mo0.8N and Ni acted as adsorption active sites for hydrogen and hydroxyl, respectively, synergistically promoting alkaline HER. The resulting Ni0.2Mo0.8N/Ni electrocatalyst exhibited excellent HER electrocatalytic activity (-70 mV at
Figure 9. (A) Schematic diagram of the excellent activity of Ni0.2Mo0.8N/Ni. (B) Schematic representation of the interfacial model for
The additive in electrolyte can also regulate the structure of EDL to improve HER reaction kinetics. For instance, Amaral et al. investigated the impact of incorporating three homemade salicylate ([Sal])-based ionic liquids (ILs) in KOH electrolyte solutions on HER[102]. Electrochemical analysis indicated increased currents and a slight impact on activation energy in the IL-containing electrolytes. Tafel analysis and EIS demonstrate that the Volmer reaction is the rate-limiting step of HER, with a significant reduction in overall impedance observed in the IL-enhanced electrolytes, promoting stable operation. The charge transfer and polarization resistances are notably lowered in the IL-containing solutions, particularly following the addition of [Bmim][Sal], with the influence of the additives diminishing as temperature rises. This research suggested that incorporating small quantities of specific ILs into KOH electrolytes could enhance HER performance in alkaline environments[102]. Then, Amaral et al. also synthesized two bromide-based ILs and studied their impact as additives in alkaline electrolytes for HER[103]. Electrochemical analysis was conducted using Pt electrodes in an 8 M KOH electrolyte without ILs and with the addition of 1 or 2 vol.% of each IL. The inclusion of 2 vol.% of [Beim][Br] resulted in higher current densities. These homemade bromide-based additives influenced the HER kinetics, resulting in slightly elevated Tafel slopes and minor changes in the charge transfer coefficient and exchange current density. Impedance measurements revealed a significant reduction in overall impedance in the presence of the bromide-based ILs in the alkaline electrolytes, with Nyquist plots showing a predominant intermediate frequency relaxation associated with adsorbed hydrogen. The bromide-based ILs demonstrate an improvement in electrolyte properties and enhance the efficiency of alkaline electrolysis[103].
SUMMARY AND OUTLOOK
In conclusion, as HER is an electrochemical process involving a ternary gas-liquid-solid interface, the rational design of multi-interface in electrodes is extremely significant for enhancing alkaline HER performance. Herein, we summarized the recent progress in interface engineering for Ni-based HER electrocatalysts, including substrate/electrocatalyst interface, internal heterointerface of electrocatalyst, and electrocatalyst/electrolyte interface. The latest advancements of interface engineering on Ni-based catalysts discussed in the review have been summarized in Table 1. The polymer binders can retard the electron transfer across the substrate/electrocatalytic interface (from the conductive substrate to the active site), so the method of in situ grown catalytic active materials on conductive substrates or directly preparing freestanding electrodes has been proposed to solve this problem. The intrinsic catalytic activity of electrocatalyst is closely related to its electronic structure, which can be rationally tuned by engineering its internal heterointerface. For example, the electron distribution at the interface can be well regulated by introducing defects or heterostructures, thus optimizing the adsorption and desorption behavior of key intermediate species to improve the catalytic performance. Moreover, the mass transfer at an electrocatalyst/electrolyte interface is particularly important under high current conditions in HER process. By adjusting the wettability of the catalyst surface and the EDL structure, the mass transport efficiency can be greatly improved. Although great progress and achievements have been made in advanced HER electrocatalysts by multi-interface engineering, several key issues remain to be addressed.
Summary of Ni-based catalysts for alkaline hydrogen evolution reaction
| Catalysts | Substrate | Electrolyte | Current density (mA cm-2) | Overpotential (mV) | Ref. |
| MoO2-Ni NWs | Ni foam | 1 M KOH | 10 | 58.4 | [42] |
| Ni4Co1Fe4-P | Ni foam | 1 M KOH | 20 | 61 | [43] |
| Ni-Cu-P@Ni-Cu | Ni foam | 1 M KOH | 10 | 70 | [44] |
| Ru@Ni-MOF | Ni foam | 1 M KOH | 10 | 22 | [45] |
| Ni NTAs/NF | Ni foam | 1 M KOH | 10 | 101 | [46] |
| MoO2/Ni@NF | Ni foam | 1 M KOH | 10 | 50.5 | [47] |
| Ni-WOx@NF | Ni foam | 1 M KOH | 10 | 45.7 | [48] |
| W-NT@NF | Ni foam | 1 M KOH | 10 | 88 | [49] |
| Ni/TiO2 | Ni foam | 1 M KOH | 10 | 46 | [50] |
| NiFeCoSx@FeNi3 | FeNi3 foam | 1 M KOH | 10 | 88 | [51] |
| Ni-Co alloy | 1 M KOH | 10 | 54 | [52] | |
| Cu2S@Ni | Cu foam | 1M NaOH | 500 | 200 | [53] |
| W2C-Ni/CC | Carbon cloth | 1 M KOH | 10 | 37 | [54] |
| NiO/Ni@CC | Carbon cloth | 1 M KOH | 10 | 40 | [55] |
| Ni-Ni3C/CC | Carbon cloth | 1 M KOH | 10 | 98 | [56] |
| Ni/V2O3 | Carbon cloth | 1 M KOH | 10 | 44 | [57] |
| Ni/NiO-CNTs | 1 M KOH | 10 | 98 | [59] | |
| C-20Ni-Pd | 1 M KOH | 10 | 590 | [60] | |
| Ni/CeO2@N-CNFs | 1 M KOH | 10 | 100 | [61] | |
| Fe@Ni NFs | 1 M KOH | 10 | 55 | [62] | |
| Ni0.95Cu0.05DSS | 1 M KOH | 100 | 179 | [63] | |
| Ni-Ni3P@NPC/rGO | 1 M KOH | 20 | 200 | [64] | |
| Vs-Ni3S2/NF | Ni foam | 1 M KOH | 10 | 88 | [65] |
| Ni/NiFeMoOx/NF | Ni foam | 1 M KOH | 10 | 22 | [66] |
| Ni/MoO2-x/NF | Ni foam | 1 M KOH | 10 | 27 | [67] |
| Ni-MoSe2 | Carbon cloth | 0.1 M KOH | 10 | 98 | [68] |
| Co0.9Ni0.1Se | 1 M KOH | 10 | 185.7 | [69] | |
| Ni/NiO-400 | Carbon cloth | 1 M KOH | 10 | 41 | [70] |
| P-V-NiFe LDH NSA | Ni foam | 1 M KOH | 10 | 19 | [71] |
| Mo-NiO/Ni | 1 M KOH | 10 | 50 | [72] | |
| SGNCs | 1 M KOH | 10 | 27 | [73] | |
| NiFe@Pt | 0.1 M KOH | 10 | 70 | [74] | |
| Ni/NiFe-LDO | Ni foam | 1 M KOH | 10 | 29 | [75] |
| Ni-Fe NP | Carbon fiber paper | 1 M KOH | 10 | 46 | [76] |
| Ni/Yb2O3 | 1 M KOH | 10 | 81 | [77] | |
| Ni(OH)2@Ni-N/Ni-C | Ni foam | 1 M KOH | 10 | 60 | [78] |
| Ir@Ni-NDC | 1 M KOH | 10 | 19 | [79] | |
| Co-Ni-P/MoS2 | 1 M KOH | 10 | 116 | [80] | |
| Ni/Ni(OH)2 | 1 M KOH | 10 | 77 | [81] | |
| Ni-Ni(OH)2/NF | Ni foam | 1 M KOH | 10 | 72 | [82] |
| Cu2O@NWNH | Cu foam | 1M PBS | 10 | 39 | [83] |
| Ni/MoO2@NF-E | Ni foam | 1 M KOH | 10 | 19 | [84] |
| Ni-MoN | Cu foam | 1 M KOH | 100 | 61 | [85] |
| Ni-NiO/Ti3C2Tx | 1 M KOH | 10 | 72 | [86] | |
| Ni-CeF3-VN | Ni foam | 1 M KOH | 10 | 33 | [87] |
| NiS-Ni2P/Ni/NF | Ni foam | 1 M KOH | 10 | 53 | [88] |
| Ni-80 | Ni film | 1 M KOH | 10 | 135 | [91] |
| MoNi4-MoO2 | 3DP Ni | 1 M KOH | 500 | 104 | [92] |
| Ni microdots | Cu film | 1 M KOH | 50 | 476 | [93] |
| Ni NCNAs | Ni foam | 1 M KOH | 10 | 47 | [95] |
| Ni-Sb alloy | Graphite | 1 M KOH | 10 | 158 | [96] |
| Pt/Ni-Mo-N-O | Ni foam | 1 M KOH | 100 | 40.6 | [97] |
| Ni0.2Mo0.8N/Ni | Ni foam | 1 M KOH | 100 | 40 | [99] |
| NA-Ru3Ni/C | 1 M KOH | 1000 | 168 | [100] |
(1) The interfacial compatibility between the conductive substrate and catalytic materials can largely determine their binding strength, thus proving crucial for the overall stability of the electrode, especially for the high current density working conditions in alkaline medium. The generation, coalescence, and detachment of large amounts of gas bubbles could induce great stretch pressure at the interface, which would not only result in decreased effective surface area and high ionic diffusion resistance but also bring fatal damage to the electrode structures. Therefore, delicate interface construction aiming to minimize the bubble size while maximizing their transport/release should be given more attention, which has not been fully investigated.
(2) It is well established that defects or heterogeneous interfaces can lead to charge redistribution at the interface, which can achieve rational regulation of the adsorption/desorption characteristics of key reaction intermediates. As an important intrinsic determinant, the intrinsic electronic structure and interactions with intermediates can also determine the electrocatalyst by influencing the intrinsic conductivity and reaction energy barrier. For alkaline water splitting, OHad has an important role in both cathodic (HER) and anodic (OER) reactions. It had been pointed out that the adsorption behavior of OHad is deeply intertwined with OER activity, which is associated with the bonding strength of the active site and oxygen. The crystal field theory provides theoretical guidance for the design of OER electrocatalyst. In octahedral symmetry, the d-orbital and ligand electrons repel each other, causing the d-orbital energy levels to split into high-energy orbitals eg and low-energy orbitals t2g. The occupancy of eg orbitals in the design of OER catalysts has been widely used as a descriptor of bonding strength between the active site and oxygen. Transition metal ions with eg orbital occupancy approaching 1 generally have better OER intrinsic activity. Active atoms with high occupancy (eg > 1) will be too weakly bonded to oxygen, while low occupancy (eg < 1) will be too strongly bonded to oxygen. Based on the above understanding, for the design of internal heterointerface of electrocatalyst towards alkaline HER, the adsorption strength of OHad can also be tuned by adjusting the eg orbital occupancy of the active site so as to promote water dissociation or alleviate the poison effect of OHad. Moreover, understanding its intrinsic mechanism is mostly based on the oversimplified theoretical calculations and lack of effective in-situ characterization. Therefore, the effect of the internal heterointerface of electrocatalyst is worthy of further study.
(3) At present, few researches focus on mass transfer at gas-liquid-solid interface, namely, electrocatalyst/electrolyte interface. In fact, for the industrial water electrolyzer, the mass transfer capacity of the electrocatalyst under high current conditions is particularly important, which can be improved by engineering wettability and EDL of the electrocatalyst. Nevertheless, the reaction mechanism and its physical structure at the electrocatalyst/electrolyte interface need more in-depth study, which depends on more accurate in situ characterization techniques.
In fact, when optimizing the substrate/electrocatalyst interface, constraints imposed by the substrate characteristics often limit the use of milder methods for in situ growth of active species on the conductive surface. To enhance the intrinsic activity of electrocatalysts, commonly employed methods, such as high-temperature treatments or mechanical ball milling, are utilized to introduce defect sites at the internal interface of electrocatalysts. However, this approach is in conflict with the mild reaction conditions required for optimizing the catalyst-substrate interface, posing challenges to achieving both objectives simultaneously. Furthermore, optimizing the electrocatalyst/electrolyte interface through control of wettability or EDL is predominantly achieved by modulating the surface morphology of the electrocatalyst. However, this process necessitates changes in reaction conditions, making it challenging to simultaneously meet the growth requirements of active species and precisely introduce defect sites, thereby imposing higher demands on material synthesis methods.
Although optimizing three interfaces simultaneously poses certain challenges through conventional experimental methods, the integration of advanced material synthesis techniques can partially mitigate this issue. For example, after growing active species on a conductive substrate using conventional hydrothermal synthesis, plasma etching can introduce vacancy-like defect sites on the electrocatalyst surface. Additionally, techniques such as magnetron sputtering or atomic layer deposition can be combined to precisely fabricate heterostructures on the electrocatalyst surface to enhance the intrinsic catalytic activity. These methods differ from conventional approaches in their ability to circumvent the need for harsh reaction conditions and stringent substrate requirements, thereby enabling simultaneous optimization of all three interfaces alongside traditional preparation techniques.
In summary, the multi-interface design for the electrocatalyst is crucial to the HER electrocatalyst performance, including activity and stability. When designing efficient HER electrocatalysts, it is imperative to consider the synergistical modulation of these three key interfaces simultaneously.
DECLARATIONS
Authors’ contributions
Proposed the topic of this review: Wang C
Wrote the manuscript: Zhang X, Guo Y, Wang C
Reviewed the manuscript: Wang C
Availability of data and materials
Not applicable.
Financial support and sponsorship
This research was supported by the Natural Science Foundation of Shanxi Province (202103021224440), Shanxi Scholarship Council of China and Youth Innovation Promotion Association CAS (2020180).
Conflicts of interest
All authors declared that there are no conflicts of interest.
Ethical approval and consent to participate
Not applicable.
Consent for publication
Not applicable.
Copyright
© The Author(s) 2024.
REFERENCES
1. He Q, Zhou Y, Shou H, et al. Synergic reaction kinetics over adjacent ruthenium sites for superb hydrogen generation in alkaline media. Adv Mater 2022;34:e2110604.
2. Fan K, Tsang YH, Huang H. Theoretical evidence of self-intercalated 2D materials for battery and electrocatalytic applications. Energy Mater 2023;3:300047.
3. Tian X, Li X, Yang T, et al. Porous worm-like NiMoO4 coaxially decorated electrospun carbon nanofiber as binder-free electrodes for high performance supercapacitors and lithium-ion batteries. Appl Surf Sci 2018;434:49-56.
4. Cao X, Zhang L, Huang K, Zhang B, Wu J, Huang Y. Strained carbon steel as a highly efficient catalyst for seawater electrolysis. Energy Mater 2022;2:200010.
5. Tian X, Yang T, Song Y, et al. Symmetric supercapacitor operating at 1.5 V with combination of nanosheet-based NiMoO4 microspheres and redox additive electrolyte. J Energy Stor 2022;47:103960.
6. Xu HG, Zhang XY, Ding Y, et al. Rational design of hydrogen evolution reaction electrocatalysts for commercial alkaline water electrolysis. Small Struct 2023;4:2200404.
7. Zhu B, Zou R, Xu Q. Metal-organic framework based catalysts for hydrogen evolution. Adv Energy Mater 2018;8:1801193.
8. Yan D, Mebrahtu C, Wang S, Palkovits R. Innovative electrochemical strategies for hydrogen production: from electricity input to electricity output. Angew Chem Int Ed 2023;62:e202214333.
9. Li J, Xia Z, Xue Q, et al. Insights into the interfacial lewis acid-base pairs in CeO2 -loaded CoS2 electrocatalysts for alkaline hydrogen evolution. Small 2021;17:e2103018.
10. Chen Z, Gong W, Wang J, et al. Metallic W/WO2 solid-acid catalyst boosts hydrogen evolution reaction in alkaline electrolyte. Nat Commun 2023;14:5363.
11. Jin J, Yin J, Liu H, et al. Atomic sulfur filling oxygen vacancies optimizes H absorption and boosts the hydrogen evolution reaction in alkaline media. Angew Chem Int Ed 2021;60:14117-23.
12. Liu Y, Feng Q, Liu W, et al. Boosting interfacial charge transfer for alkaline hydrogen evolution via rational interior Se modification. Nano Energy 2021;81:105641.
13. Zhang JZ, Zhang Z, Zhang HB, et al. Prussian-blue-analogue-derived ultrathin Co2P-Fe2P nanosheets for universal-pH overall water splitting. Nano Lett 2023;23:8331-8.
14. Li Y, Xu T, Huang Q, et al. C60 fullerenol to stabilize and activate Ru nanoparticles for highly efficient hydrogen evolution reaction in alkaline media. ACS Catal 2023;13:7597-605.
15. Zhao X, Li X, Xiao D, et al. Isolated Pd atom anchoring endows cobalt diselenides with regulated water-reduction kinetics for alkaline hydrogen evolution. Appl Catal B Environ 2021;295:120280.
16. Wu J, Fan J, Zhao X, et al. Atomically dispersed MoOx on rhodium metallene boosts electrocatalyzed alkaline hydrogen evolution. Angew Chem Int Ed 2022;61:e202207512.
17. Men YN, Tan Y, Li P, et al. Tailoring the 3D-orbital electron filling degree of metal center to boost alkaline hydrogen evolution electrocatalysis. Appl Catal B Environ 2021;284:119718.
18. Jiang Y, Leng J, Zhang S, et al. Modulating water splitting kinetics via charge transfer and interfacial hydrogen spillover effect for robust hydrogen evolution catalysis in alkaline media. Adv Sci 2023;10:e2302358.
19. Yang W, Li M, Zhang B, et al. Interfacial microenvironment modulation boosts efficient hydrogen evolution reaction in neutral and alkaline. Adv Funct Mater 2023;33:2304852.
20. Wan C, Zhang Z, Dong J, et al. Amorphous nickel hydroxide shell tailors local chemical environment on platinum surface for alkaline hydrogen evolution reaction. Nat Mater 2023;22:1022-9.
21. Zhang R, Li Y, Zhou X, et al. Single-atomic platinum on fullerene C60 surfaces for accelerated alkaline hydrogen evolution. Nat Commun 2023;14:2460.
22. Alsabban MM, Eswaran MK, Peramaiah K, et al. Unusual activity of rationally designed cobalt phosphide/oxide heterostructure composite for hydrogen production in alkaline medium. ACS Nano 2022;16:3906-16.
23. Yi L, Ji Y, Shao P, et al. Scalable synthesis of tungsten disulfide nanosheets for alkali-acid electrocatalytic sulfion recycling and H2 generation. Angew Chem Int Ed 2021;60:21550-7.
24. Wang X, Long G, Liu B, et al. Rationally modulating the functions of Ni3Sn2-NiSnOx nanocomposite electrocatalysts towards enhanced hydrogen evolution reaction. Angew Chem Int Ed 2023;62:e202301562.
25. Li Z, Yu C, Wen Y, et al. Mesoporous hollow Cu-Ni alloy nanocage from core-shell Cu@Ni nanocube for efficient hydrogen evolution reaction. ACS Catal 2019;9:5084-95.
26. Song J, Jin YQ, Zhang L, et al. Phase-separated Mo-Ni alloy for hydrogen oxidation and evolution reactions with high activity and enhanced stability. Adv Energy Mater 2021;11:2003511.
27. Wang M, Yang H, Shi J, et al. Alloying nickel with molybdenum significantly accelerates alkaline hydrogen electrocatalysis. Angew Chem Int Ed 2021;60:5771-7.
28. Lu W, Li X, Wei F, et al. In-situ transformed Ni, S-codoped CoO from amorphous Co-Ni sulfide as an efficient electrocatalyst for hydrogen evolution in alkaline media. ACS Sustain Chem Eng 2019;7:12501-9.
29. Xu H, Fei B, Cai G, et al. Boronization-induced ultrathin 2D nanosheets with abundant crystalline - amorphous phase boundary supported on nickel foam toward efficient water splitting. Adv Energy Mater 2020;10:1902714.
30. Chen N, Du Y, Zhang G, Lu W, Cao F. Amorphous nickel sulfoselenide for efficient electrochemical urea-assisted hydrogen production in alkaline media. Nano Energy 2021;81:105605.
31. Su J, Wang Q, Fang M, et al. Metastable hexagonal-phase nickel with ultralow Pt content for an efficient alkaline/seawater hydrogen evolution reaction. ACS Appl Mater Interfaces 2023;15:51160-9.
32. Pang QQ, Bai X, Du X, Zhang S, Liu ZY, Yue XZ. Facet modulation of nickel-ruthenium nanocrystals for efficient electrocatalytic hydrogen evolution. J Colloid Interface Sci 2023;633:275-83.
33. Nguyen DN, Phu TKC, Kim J, et al. Interfacial strain-modulated nanospherical Ni2P by heteronuclei-mediated growth on Ti3C2Tx MXene for efficient hydrogen evolution. Small 2022;18:e2204797.
34. Li Y, Min K, Han B, Lee LYS. Ni nanoparticles on active (001) facet-exposed rutile TiO2 nanopyramid arrays for efficient hydrogen evolution. Appl Catal B Environ 2021;282:119548.
35. Su H, Tang Y, Shen H, et al. Insights into antiperovskite Ni3In1-xCuxN multi-crystalline nanoplates and bulk cubic particles as efficient electrocatalysts on hydrogen evolution reaction. Small 2022;18:e2105906.
36. Liu J, Wang J, Fo Y, et al. Engineering of unique Ni-Ru nano-twins for highly active and robust bifunctional hydrogen oxidation and hydrogen evolution electrocatalysis. Chem Eng J 2023;454:139959.
37. Lu J, Chen S, Zhuo Y, Mao X, Liu D, Wang Z. Greatly boosting seawater hydrogen evolution by surface amorphization and morphology engineering on MoO2/Ni3(PO4)2. Adv Funct Mater 2023;33:2308191.
38. Lyu C, Cao C, Cheng J, et al. Interfacial electronic structure modulation of Ni2P/Ni5P4 heterostructure nanosheets for enhanced pH-universal hydrogen evolution reaction performance. Chem Eng J 2023;464:142538.
39. Xu Q, Zhang J, Zhang H, et al. Atomic heterointerface engineering overcomes the activity limitation of electrocatalysts and promises highly-efficient alkaline water splitting. Energy Environ Sci 2021;14:5228-59.
40. Wei J, Zhou M, Long A, et al. Heterostructured electrocatalysts for hydrogen evolution reaction under alkaline conditions. Nanomicro Lett 2018;10:75.
41. Huang C, Zhou J, Duan D, et al. Roles of heteroatoms in electrocatalysts for alkaline water splitting: a review focusing on the reaction mechanism. Chin J Catal 2022;43:2091-110.
42. Liu X, Ni K, Niu C, et al. Upraising the O 2p orbital by integrating Ni with MoO2 for accelerating hydrogen evolution kinetics. ACS Catal 2019;9:2275-85.
43. Chang J, Wang W, Wu D, et al. Self-supported amorphous phosphide catalytic electrodes for electrochemical hydrogen production coupling with methanol upgrading. J Colloid Interface Sci 2023;648:259-69.
44. Darband GB, Lotfi N, Aliabadi A, Hyun S, Shanmugam S. Hydrazine-assisted electrochemical hydrogen production by efficient and self-supported electrodeposited Ni-Cu-P@Ni-Cu nano-micro dendrite catalyst. Electrochim Acta 2021;382:138335.
45. Deng L, Hu F, Ma M, et al. Electronic modulation caused by interfacial Ni-O-M (M=Ru, Ir, Pd) bonding for accelerating hydrogen evolution kinetics. Angew Chem Int Ed 2021;60:22276-82.
46. Li D, Hao G, Guo W, Liu G, Li J, Zhao Q. Highly efficient Ni nanotube arrays and Ni nanotube arrays coupled with NiFe layered-double-hydroxide electrocatalysts for overall water splitting. J Power Sources 2020;448:227434.
47. Liang W, Dong P, Le Z, et al. Electron density modulation of MoO2/Ni to produce superior hydrogen evolution and oxidation activities. ACS Appl Mater Interfaces 2021;13:39470-9.
48. Liang W, Zhou M, Lin X, et al. Nickel-doped tungsten oxide promotes stable and efficient hydrogen evolution in seawater. Appl Catal B Environ 2023;325:122397.
49. Liu M, Zou W, Qiu S, Su N, Cong J, Hou L. Active site tailoring of Ni-based coordination polymers for high-efficiency dual-functional HER and UOR catalysis. Adv Funct Mater 2024;34:2310155.
50. Zhou P, Wang S, Zhai G, et al. Host dependent electrocatalytic hydrogen evolution of Ni/TiO2 composites. J Mater Chem A 2021;9:6325-34.
51. Shen J, Li Q, Zhang W, et al. Spherical Co3S4 grown directly on Ni-Fe sulfides as a porous nanoplate array on FeNi3 foam: a highly efficient and durable bifunctional catalyst for overall water splitting. J Mater Chem A 2022;10:5442-51.
52. Wang J, Shao H, Ren S, Hu A, Li M. Fabrication of porous Ni-Co catalytic electrode with high performance in hydrogen evolution reaction. Appl Surf Sci 2021;539:148045.
53. Zhang B, Xu W, Liu S, et al. Enhanced interface interaction in Cu2S@Ni core-shell nanorod arrays as hydrogen evolution reaction electrode for alkaline seawater electrolysis. J Power Sources 2021;506:230235.
54. Yang B, Fu HC, Chen XH, et al. Nanoarchitectonics for synergistic action coupling of Ni nanoparticles with W2C nanowires for highly efficient alkaline hydrogen production. Appl Surf Sci 2023;630:157460.
55. Chen H, Ge D, Chen J, et al. In situ surface reconstruction synthesis of a nickel oxide/nickel heterostructural film for efficient hydrogen evolution reaction. Chem Commun 2020;56:10529-32.
56. Wang P, Qin R, Ji P, et al. Synergistic coupling of Ni nanoparticles with Ni3C nanosheets for highly efficient overall water splitting. Small 2020;16:e2001642.
57. Zhou P, Lv X, Gao Y, et al. Enhanced electrocatalytic HER performance of non-noble metal nickel by introduction of divanadium trioxide. Electrochim Acta 2019;320:134535.
58. Sun J, Zhu M, Fan M, et al. Mo2C-Ni modified carbon microfibers as an effective electrocatalyst for hydrogen evolution reaction in acidic solution. J Colloid Interface Sci 2019;543:300-6.
59. Yang L, Zhao X, Yang R, et al. In-situ growth of carbon nanotubes on Ni/NiO nanofibers as efficient hydrogen evolution reaction catalysts in alkaline media. Appl Surface Sci 2019;491:294-300.
60. Barhoum A, El-Maghrabi HH, Iatsunskyi I, et al. Atomic layer deposition of Pd nanoparticles on self-supported carbon-Ni/NiO-Pd nanofiber electrodes for electrochemical hydrogen and oxygen evolution reactions. J Colloid Interface Sci 2020;569:286-97.
61. Li T, Yin J, Sun D, et al. Manipulation of mott-schottky Ni/CeO2 heterojunctions into N-doped carbon nanofibers for high-efficiency electrochemical water splitting. Small 2022;18:e2106592.
62. Tao J, Zhang Y, Wang S, et al. Activating three-dimensional networks of Fe@Ni nanofibers via fast surface modification for efficient overall water splitting. ACS Appl Mater Interfaces 2019;11:18342-8.
63. Zhang X, Wang J, Wang J, Wang J, Wang C, Lu C. Freestanding surface disordered NiCu solid solution as ultrastable high current density hydrogen evolution reaction electrode. J Phys Chem Lett 2021;12:11135-42.
64. Li G, Wang J, Yu J, et al. Ni-Ni3P nanoparticles embedded into N, P-doped carbon on 3D graphene frameworks via in situ phosphatization of saccharomycetes with multifunctional electrodes for electrocatalytic hydrogen production and anodic degradation. Appl Catal B Environ 2020;261:118147.
65. Jia D, Han L, Li Y, et al. Optimizing electron density of nickel sulfide electrocatalysts through sulfur vacancy engineering for alkaline hydrogen evolution. J Mater Chem A 2020;8:18207-14.
66. Li YK, Zhang G, Lu WT, Cao FF. Amorphous Ni-Fe-Mo suboxides coupled with Ni network as porous nanoplate array on nickel foam: a highly efficient and durable bifunctional electrode for overall water splitting. Adv Sci 2020;7:1902034.
67. Liang W, Zhou M, Li X, et al. Oxygen-vacancy-rich MoO2 supported nickel as electrocatalysts to promote alkaline hydrogen evolution and oxidation reactions. Chem Eng J 2023;464:142671.
68. Mao B, Sun P, Jiang Y, et al. Identifying the transfer kinetics of adsorbed hydroxyl as a descriptor of alkaline hydrogen evolution reaction. Angew Chem Int Ed 2020;59:15232-7.
69. Zhong W, Wang Z, Gao N, et al. Coupled vacancy pairs in Ni-doped CoSe for improved electrocatalytic hydrogen production through topochemical deintercalation. Angew Chem Int Ed 2020;59:22743-8.
70. Jiao Y, Hong W, Li P, Wang L, Chen G. Metal-organic framework derived Ni/NiO micro-particles with subtle lattice distortions for high-performance electrocatalyst and supercapacitor. Appl Catal B Environ 2019;244:732-9.
71. Tang Y, Liu Q, Dong L, Wu HB, Yu X. Activating the hydrogen evolution and overall water splitting performance of NiFe LDH by cation doping and plasma reduction. Appl Catal B Environ 2020;266:118627.
72. Huang J, Han J, Wu T, et al. Boosting hydrogen transfer during volmer reaction at oxides/metal nanocomposites for efficient alkaline hydrogen evolution. ACS Energy Lett 2019;4:3002-10.
73. Gu Y, Xi B, Wei R, Fu Q, Qain Y, Xiong S. Sponge assembled by graphene nanocages with double active sites to accelerate alkaline HER kinetics. Nano Lett 2020;20:8375-83.
74. Xue S, Haid RW, Kluge RM, et al. Enhancing the hydrogen evolution reaction activity of platinum electrodes in alkaline media using nickel-iron clusters. Angew Chem Int Ed 2020;59:10934-8.
75. Tian Y, Huang A, Wang Z, et al. Two-dimensional hetero-nanostructured electrocatalyst of Ni/NiFe-layered double oxide for highly efficient hydrogen evolution reaction in alkaline medium. Chem Eng J 2021;426:131827.
76. Suryanto BHR, Wang Y, Hocking RK, Adamson W, Zhao C. Overall electrochemical splitting of water at the heterogeneous interface of nickel and iron oxide. Nat Commun 2019;10:5599.
77. Sun H, Yan Z, Tian C, et al. Bixbyite-type Ln2O3 as promoters of metallic Ni for alkaline electrocatalytic hydrogen evolution. Nat Commun 2022;13:3857.
78. Dastafkan K, Shen X, Hocking RK, Meyer Q, Zhao C. Monometallic interphasic synergy via nano-hetero-interfacing for hydrogen evolution in alkaline electrolytes. Nat Commun 2023;14:547.
79. Yang J, Shen Y, Sun Y, Xian J, Long Y, Li G. Ir nanoparticles anchored on metal-organic frameworks for efficient overall water splitting under pH-universal conditions. Angew Chem Int Ed 2023;62:e202302220.
80. Bao J, Zhou Y, Zhang Y, et al. Engineering water splitting sites in three-dimensional flower-like Co-Ni-P/MoS2 heterostructural hybrid spheres for accelerating electrocatalytic oxygen and hydrogen evolution. J Mater Chem A 2020;8:22181-90.
81. Dai L, Chen ZN, Li L, Yin P, Liu Z, Zhang H. Ultrathin Ni(0)-embedded Ni(OH)2 heterostructured nanosheets with enhanced electrochemical overall water splitting. Adv Mater 2020;32:e1906915.
82. Zhong W, Li W, Yang C, et al. Interfacial electron rearrangement: Ni activated Ni(OH)2 for efficient hydrogen evolution. J Energy Chem 2021;61:236-42.
83. Tang Y, Dong L, Wu HB, Yu X. Tungstate-modulated Ni/Ni(OH)2 interface for efficient hydrogen evolution reaction in neutral media. J Mater Chem A 2021;9:1456-62.
84. Li J, Zhang Q, Zhang J, et al. Optimizing electronic structure of porous Ni/MoO2 heterostructure to boost alkaline hydrogen evolution reaction. J Colloid Interface Sci 2022;627:862-71.
85. Wu L, Zhang F, Song S, et al. Efficient alkaline water/seawater hydrogen evolution by a nanorod-nanoparticle-structured Ni-MoN catalyst with fast water-dissociation kinetics. Adv Mater 2022;34:e2201774.
86. Zhang B, Du Z, Sun R, et al. Tremella-like Ni-NiO with O-vacancy heterostructure nanosheets grown in situ on MXenes for highly efficient hydrogen and oxygen evolution. ACS Appl Mater Interfaces 2022;14:47529-41.
87. Zhou P, Tao L, Tao S, et al. Construction of nickel-based dual heterointerfaces towards accelerated alkaline hydrogen evolution via boosting multi-step elementary reaction. Adv Funct Mater 2021;31:2104827.
88. Liu M, Sun Z, Zhang C, et al. Multi-interfacial engineering of a coil-like NiS-Ni2P/Ni hybrid to efficiently boost electrocatalytic hydrogen generation in alkaline and neutral electrolyte. J Mater Chem A 2022;10:13410-7.
89. Liu M, Zou W, Cong J, Su N, Qiu S, Hou L. Identifying and unveiling the role of multivalent metal states for bidirectional UOR and HER over Ni, Mo-trithiocyanuric based coordination polymer. Small 2023;19:e2302698.
90. Zhang J, Cui F, Ma Q, Cui T. Ni3+-rich Ni/NiOx@C nanocapsules below 4 nm constructed by low-temperature graphitization of self-assembled few-layer coordination polymers toward efficient alkaline hydrogen evolution electrocatalysis. Small 2024:e2311057.
91. Kim J, Jung SM, Lee N, Kim KS, Kim YT, Kim JK. Efficient alkaline hydrogen evolution reaction using superaerophobic Ni nanoarrays with accelerated H2 bubble release. Adv Mater 2023;35:e2305844.
92. Xu X, Fu G, Wang Y, et al. Highly efficient all-3D-printed electrolyzer toward ultrastable water electrolysis. Nano Lett 2023;23:629-36.
93. Fujimura T, Hikima W, Fukunaka Y, Homma T. Analysis of the effect of surface wettability on hydrogen evolution reaction in water electrolysis using micro-patterned electrodes. Electrochem Commun 2019;101:43-6.
94. Shang L, Zhao Y, Kong X, et al. Underwater superaerophobic Ni nanoparticle-decorated nickel-molybdenum nitride nanowire arrays for hydrogen evolution in neutral media. Nano Energy 2020;78:105375.
95. Li Y, Li J, Qian Q, et al. Superhydrophilic Ni-based multicomponent nanorod-confined-nanoflake array electrode achieves waste-battery-driven hydrogen evolution and hydrazine oxidation. Small 2021;17:e2008148.
96. Gugtapeh HS, Rezaei M. Facile electrochemical synthesis of Ni-Sb nanostructure supported on graphite as an affordable bifunctional electrocatalyst for hydrogen and oxygen evolution reactions. J Electroanal Chem 2022;922:116726.
97. Yu W, Chen Z, Fu Y, et al. Superb all-pH hydrogen evolution performances powered by ultralow Pt-decorated hierarchical Ni-Mo porous microcolumns. Adv Funct Mater 2023;33:2210855.
98. Jiang Y, Huang J, Mao B, An T, Wang J, Cao M. Inside solid-liquid interfaces: understanding the influence of the electrical double layer on alkaline hydrogen evolution reaction. Appl Catal B Environ 2021;293:120220.
99. Zhang B, Zhang L, Tan Q, et al. Simultaneous interfacial chemistry and inner helmholtz plane regulation for superior alkaline hydrogen evolution. Energy Environ Sci 2020;13:3007-13.
100. Gao L, Bao F, Tan X, et al. Engineering a local potassium cation concentrated microenvironment toward the ampere-level current density hydrogen evolution reaction. Energy Environ Sci 2023;16:285-94.
101. Tan H, Tang B, Lu Y, et al. Engineering a local acid-like environment in alkaline medium for efficient hydrogen evolution reaction. Nat Commun 2022;13:2024.
102. Amaral L, Minkiewicz J, Šljukić B, et al. Toward tailoring of electrolyte additives for efficient alkaline water electrolysis: salicylate-based ionic liquids. ACS Appl Energy Mater 2018;1:4731-42.
Cite This Article
Export citation file: BibTeX | EndNote | RIS
OAE Style
Zhang X, Guo Y, Wang C. Multi-interface engineering of nickel-based electrocatalysts for alkaline hydrogen evolution reaction. Energy Mater 2024;4:400044. http://dx.doi.org/10.20517/energymater.2023.115
AMA Style
Zhang X, Guo Y, Wang C. Multi-interface engineering of nickel-based electrocatalysts for alkaline hydrogen evolution reaction. Energy Materials. 2024; 4(4): 400044. http://dx.doi.org/10.20517/energymater.2023.115
Chicago/Turabian Style
Xiaoxiang Zhang, Yuxuan Guo, Congwei Wang. 2024. "Multi-interface engineering of nickel-based electrocatalysts for alkaline hydrogen evolution reaction" Energy Materials. 4, no.4: 400044. http://dx.doi.org/10.20517/energymater.2023.115
ACS Style
Zhang, X.; Guo Y.; Wang C. Multi-interface engineering of nickel-based electrocatalysts for alkaline hydrogen evolution reaction. Energy Mater. 2024, 4, 400044. http://dx.doi.org/10.20517/energymater.2023.115
About This Article
Special Issue
Copyright
Data & Comments
Data
0
Comments
Comments must be written in English. Spam, offensive content, impersonation, and private information will not be permitted. If any comment is reported and identified as inappropriate content by OAE staff, the comment will be removed without notice. If you have any queries or need any help, please contact us at support@oaepublish.com.