fig3

Figure 3. Different methods of electrode structure optimization^[47-50]. SEM pictures of the nickel electrode: (A1) the surface with 5 μm pores; (A2) the other surface with 100 μm pores; (B) the current-voltage curve of the Ni electrodes. These figures are quoted with permission from Kim et al.^[47]. SEM images of (C1) an array of 20 μm ø Ni film and (C2) an array of 20 μm ø Ni pillars. SEM images of prepared Ni micro-patterned electrodes: (D1) cylindrical with large diameter; and (D2) semispherical structure. These figures are quoted with permission from Paul et al.^[48]; Corresponding in situ optical microscope images: (E1) cylindrical Ni microarray, Ni coverage: 39.9%, contact angle: 89.5°; and (E2) semispherical Ni microarray, Ni coverage: 74.7%, contact angle 112.5°. These figures are quoted with permission from Fujimura et al.^[49]. SEM images of (F1-F4) the electrodeposited nickel foil and determined the PTFE coverage. (G1-G4) side and (H1-H4) top views of oxygen bubbles corresponding to PTFE coverage in alkaline water splitting experiments performed with porous electrodes. These figures are quoted with permission from Iwata et al.^[50]. PTFE: Polytetrafluoroethylene.