Copper‐Nickel Alloy Modified‐Silicon Photoanodes for Photoelectrochemical Water Oxidation and Urea Oxidation

Abstract The development of silicon (Si) photoanodes for photoelectrochemical (PEC) oxidation is highly crucial for the progress of solar‐driven hydrogen production. Apart from the typical water oxidation reaction or oxygen evolution reaction (OER), the urea oxidation reaction (UOR) is gaining more attention due to favorable thermodynamics. In this work, we study Si photoanodes modified with electrodeposited copper‐nickel (CuNi) alloy for OER and UOR. The optimized photoanodes exhibit a low onset potential of 1.15 V vs reversible hydrogen electrode (RHE) and a current density of 6 mA cm⁻² at 1.23 V vs RHE (the thermodynamic potential for water oxidation) for OER. Further, CuNi alloy‐modified photoanodes can drive the UOR at a lower onset potential (1.05 V vs RHE) and generate a higher current density of 31 mA cm⁻² at 1.23 V vs RHE. Importantly, the CuNi alloy can extend the stability for UOR under PEC conditions when compared to a planar Ni film deposited by a vacuum‐based process. This work demonstrates that CuNi alloy can further improve the properties of inhomogeneous metal‐insulator‐semiconductor Si photoanodes which can be efficiently utilized for both OER and UOR.