fig4

Figure 4. (A) Schematic representation of DEMS detection of the isotope O₂; (B) Ni-FeNi₃/Ni_0.5-bFe_0.5-yMo_1.5O_x as the DEMS signal of the ¹⁸O isotope labeled product under electrocatalyst (Copyright 2024, John Wiley and Sons^[81]); (C) OER behavior of Ru-UiO-67-bpydc in different solutions (with and without isotopic substitution and TMA⁺); (D) DEMS tests for ¹⁸O¹⁶O and ¹⁸O¹⁸O signals were performed on ¹⁸O-labeled Ru-UiO-67-bpydc catalysts in 0.5 M H₂SO₄ and H₂¹⁶O (Copyright 2023, Elsevier^[72]); ¹⁸O isotopically labeled IrO_x/Y₂O₃-EC (E) and IrO_x/Y₂O₃-EC (F) for DEMS testing (Copyright 2023, John Wiley and Sons^[82]); Mass spectral cyclic voltametric curves of ¹⁶O¹⁸O-labeled MoNiFe (oxy)hydroxide (G) and ¹⁸O₂-labeled MoNiFe (oxy)hydroxide (H) (Copyright 2022, Springer Nature^[74]); The O₂ product of GB-RuO₂ labelled on the ¹⁸O surface was analyzed by in situ Raman spectroscopy (I) and DEMS signal analysis (J) (Copyright 2024, John Wiley and Sons^[93]); (K) ¹⁸O labeled RuIrCaO_x and RuIrO_x electrocatalysts producing ¹⁶O¹⁸O (m/z = 34) signals in O₂ DEMS measurements (Copyright 2020, John Wiley and Sons ^[94]); (L) DEMS signals (³⁶O₂, ³⁴O₂ and ³²O₂) of Rh-RuO₂/G electrocatalysts in aqueous H₂¹⁸O sulphuric acid solution (Copyright 2023, Springer Nature^[95]). OER: Oxygen generation reaction; DEMS: Differential electrochemical mass spectrometry.