Highly active nickel oxide water oxidation catalysts deposited from molecular complexes

Abstract

Nickel oxide (NiO_x) water oxidation catalysts with high catalytic activity have been electrodeposited from [Ni(en)₃]Cl₂ (en = 1,2-diaminoethane, NiO_x-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 NiO_x-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 NiO_x-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 NiO_x water oxidation catalysts.