# Aerosol assisted chemical vapor deposition of cobalt-based co-catalysts on bismuth vanadate-based photoelectrodes for solar water splitting systems

## TL;DR

A new scalable method to make cobalt-based catalysts for solar water splitting improves efficiency and stability.

## Contribution

A novel and scalable AACVD-based fabrication route for CoPi co-catalysts on BiVO4 photoanodes is demonstrated.

## Key findings

- AACVD-fabricated CoPi on BiVO4 achieved a 1.16% half-cell solar-to-hydrogen efficiency.
- The method showed 84% charge separation efficiency and retained ~90% performance after four hours.
- This approach outperforms traditional electrodeposition in scalability and performance.

## 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 vapour 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.

The growing demand for clean energy has led to increased interest in solar-driven water splitting. This study explores the use of bismuth vanadate (BiVO4) photoanodes, enhanced with cobalt phosphate (CoPi) co-catalysts, to improve photoelectrochemical (PEC) water splitting efficiency. Researchers used aerosol-assisted chemical vapour deposition (AACVD) to deposit CoOx, which was then converted to CoPi through electrochemical treatment. This method was compared to traditional photoelectrodeposition (PED). Results showed that AACVD-fabricated CoPi on BiVO4 achieved a sixfold increase in photocurrent density compared to bare BiVO4, with a significant improvement in charge separation efficiency. The AACVD method also demonstrated superior stability, maintaining over 90% of its initial photocurrent after four hours of operation. This scalable and cost-effective approach holds promise for commercial PEC applications, with future work needed to explore long-term stability and scalability. "This summary was initially drafted using artificial intelligence, then revised and fact-checked by the author."

In this study, we demonstrate a novel and scalable route to CoPi, where cobalt oxide (CoOx) is first grown by aerosol-assisted chemical vapour deposition (AACVD) and then surface modified through a dark electrochemical treatment (ET) process. CoPi was grown onto bismuth vanadate (BiVO4) photoanodes, also synthesised by AACVD. CoPi-decorated BiVO4 demonstrated high charge separation efficiency (84%), stability over four hours of chronoamperometry (~90% of initial performance retained), and photoelectrochemical performance, achieving a half-cell solar-to-hydrogen (HC-STH) efficiency of 1.16% at 1.23 V vs RHE. Overall, our study demonstrates the viability of the AACVD technique to produce scalable photoanodes for solar water splitting applications.