Synthesis of nanostructured β -Ni(OH)₂ by electrochemical dissolution–precipitation and its application as a water oxidation catalyst

A straightforward electrochemical dissolution–precipitation approach has been developed to synthesize nanostructured β -Ni(OH)₂ powders (particle size 10–100 nm, specific surface area ∼100 m² g⁻¹) from Ni metal anodes. The approach differs from existing electrochemical synthesis methods in that it predominantly results in bulk precipitation of nanoparticles, without significant film growth on either of the electrodes. Heat treatment of the as-synthesized β -Ni(OH)₂ afforded NiO with mostly preserved nanostructure and very high specific surface area (≤100 m² g⁻¹, depending on calcination temperature). The as-synthesized β -Ni(OH)₂ was found to be an excellent catalyst for the oxygen evolution reaction (OER) in the technologically important water electrolysis process, apparently contradicting recent reports that the α polymorph is required for such high activity. With catalyst loadings <0.1 mg cm⁻², OER current densities of 10 mA cm⁻² were sustained at overpotentials as low as 340 mV, with Tafel slopes of only ∼38 mV/decade. The catalyst was highly stable in alkaline media over the course of electrolysis experiments lasting for several hours. This performance surpasses that of many previously reported earth-abundant OER catalysts and is comparable to that obtained with state-of-the-art RuO₂ and IrO₂ catalysts. (paper)