Aerosol Assisted Chemical Vapor Deposition of Cobalt-based Co-Catalysts on Bismuth Vanadate-based Photoelectrodes for Solar Water Splitting Systems

Abstract Cobalt phosphate (CoPi) is a widely used oxygen evolution reaction (OER) catalyst in photoelectrochemical (PEC) water splitting systems. Traditionally, CoPi is fabricated via photo-assisted electrodeposition (PED) from a cobalt-containing electrolyte solution, a method that is limited in scalability. In this study, we demonstrate a novel and scalable route to CoPi, where cobalt oxide (CoOx) is first grown by aerosol-assisted chemical vapor deposition (AACVD) and then surface modified through a dark electrochemical treatment (ET) process. Both fabrication techniques were used to deposit CoPi onto bismuth vanadate (BiVO₄) photoanodes synthesised by AACVD. CoPi-decorated BiVO₄ fabricated via AACVD + ET demonstrated superior charge separation efficiency, stability over four hours of chronoamperometry, and photoelectrochemical performance, achieving an improved half-cell solar-to-hydrogen (HC-STH) efficiency of 1.16% at 1.23 V vs RHE compared to CoPi-decorated BiVO₄ fabricated by PED, which exhibited an HC-STH efficiency of 0.60%. These promising results highlight the potential of AACVD, conducted under atmospheric pressure, to enable the future development of both co-catalysts and scalable photoelectrode fabrication for large-area applications.