Electrosynthesis, activation, and applications of nickel-iron oxyhydroxide in (photo-)electrochemical water splitting at near neutral condition

We present the anodic pulse-current electrosynthesis, structural characterization, and OER electrocatalytic properties of the pristine and anodically-pretreated nickel-iron oxyhydroxide borate thin films (Fe:Ni–Bi). In the electrosynthesis of Fe:Ni–Bi, OER kinetics was found to have great influence not only on the current efficiency for film deposition, but also on the surface morphology and crystal structure of the synthesized Fe:Ni–Bi. In addition, the Tafel analyses indicate that incorporating iron modified the OER mechanism and promoted the OER activity. Moreover, both the applied turnover (current) and electrolyte pH used in the anodic pretreatment of Fe:Ni–Bi have great influences on the OER activity of the pretreated Fe:Ni–Bi; the applied turnover rate decides the applied oxidative level and thus affects the extent of phase transformation of β-NiOOH to γ-NiOOH, whereas the solution pH for anodic pretreatment affects the electrochemically effective surface area. Finally, the developed electrosynthetic approach can effectively translate the high OER activity of Fe:Ni–Bi from a flat FTO substrate to a porous BiVO₄ photoanode, facilitating the interfacial hole transfer and improving photostability of BiVO₄.