Electrochemical/Photoelectrochemical Water Splitting on Self-Limiting Electrodeposited Iron-Group Mutual Alloys

Abstract

Scalable energy conversion/storage by water splitting is significantly hindered by the slow kinetics of oxygen evolution reaction (OER). Implementation of electrochemical catalysts with low cost and high turn-over efficiency, or application of a photoanode in photoelectrochemical (PEC) cell using a semiconductor with proper protection layer are two possible solutions. Herein, two binary Iron-group alloy films (Ni-Co and Ni-Fe) and one ternary Iron-group alloy film (Ni-Co-Fe) under self-limiting deposition condition are investigated and continuous ultrathin films with various composition are generated. The self-limiting deposition, corroborated by XPS depth profile, is caused by the precipitation of hydroxide/oxyhydroxide species under high local pH, enabled by the privation of pH buffer species. Each binary and ternary Iron-group mutual alloy films exhibits improved water oxidation kinetics compared to pure i or Co film. In particular, an overpotential of 0.314 V at 10 mA cm−2 and a Tafel slope of 34.7 mV dec−1 are obtained on the Ni-Fe-Co film. The Iron-group mutual alloy deposited GaAs is further investigated for photoelectrochemical water oxidation. The stability towards photocorrosion under the light in an aqueous solution containing K3Fe(CN)6/K4Fe(CN)6 is significantly improved by electrodepositing the mutual alloy films while the optimum stability property is found on the ternary alloy film.