Highly active nickel oxide water oxidation catalysts deposited from molecular complexes

Nickel oxide (NiOₓ) water oxidation catalysts with high catalytic activity have been electrodeposited from [Ni(en)₃]Cl₂ (en = 1,2-diaminoethane, NiOₓ-en) in a 0.10 M borate buffer (NaBi) solution (pH = 9.2). Electrolysis experiments at a fixed applied potential of 1.1 V (vs. Ag/AgCl) established that the NiOₓ-en films sustain a stable current of 1.8 mA cm⁻² for extended periods, compared with 1.2 mA cm⁻² for films derived from [Ni(OH₂)₆](NO₃)₂ and [Ni(NH₃)₆]Cl₂ when tested in a 0.60 M NaBi buffer. XAS studies indicate that the γ-NiOOH phase is formed in each case whereas SEM studies revealed significant differences in film morphology. The NiOₓ-en films were found to be more homogenous and to have a higher electroactive surface area, as determined from capacitance measurements. The results highlight the influence that the choice of molecular precursor can have on the activity and robustness of electrodeposited NiOₓ water oxidation catalysts