Amorphous Cobalt–Iron Hydroxide Nanosheet Electrocatalyst for Efficient Electrochemical and Photo-Electrochemical Oxygen Evolution

Finding efficient electrocatalysts for oxygen evolution reaction (OER) that can be effectively integrated with semiconductors is significantly challenging for solar-driven photo-electrochemical (PEC) water splitting. Herein, amorphous cobalt-iron hydroxide (CoFe-H) nanosheets are synthesized by facile electrodeposition as an efficient catalyst for both electrochemical and PEC water oxidation. As a result of the high electrochemically active surface area and the amorphous nature, the optimized amorphous CoFe-H nanosheets exhibit superior OER catalytic activity in alkaline environment with a small overpotential (280 mV) to achieve significant oxygen evolution (j = 10 mA cm(-2)) and a low Tafel slope (28 mV dec(-1)). Furthermore, CoFe-H nanosheets are simply integrated with BiVO4 semiconductor to construct CoFe- H/BiVO4 photoanodes that exhibit a significantly enhanced photocurrent density of 2.48 mA cm(-2) (at 1.23 V vs reversible hydrogen electrode (RHE)) and a much lower onset potential of 0.23 V (vs RHE) for PEC-OER. Careful electrochemical and optical studies reveal that the improved OER kinetics and high-quality interface at the CoFe-H/BiVO4 junction, as well as the excellent optical transparency of CoFe. H nanosheets, contribute to the high PEC performance. This study establishes amorphous CoFe. H nanosheets as a highly competitive candidate for electrochemical and PEC water oxidation and provides general guidelines for designing efficient PEC systems.