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. Amorphous cobalt–iron hydroxide (CoFeH) nanosheets and BiVO4 are effectively integrated, constructing a catalyst/BiVO4 structure for achieving efficient photo‐electrochemical (PEC) water oxidation. Benefiting from the properties of CoFeH and the rational design of electrocatalyst/semiconductor architecture, CoFeH/BiVO4 photoanodes exhibit an enhanced photocurrent density and a low onset potential for PEC water oxidation.