Advances in p-type CuBi₂O₄ based photocathodes for photoelectrochemical water splitting: achievements, challenges and strategies for improvements

Copper bismuth oxide (CuBi₂O₄) is a p-type semiconductor with a tetragonal Kusachiite structure, making it a promising material for visible-light-driven photoelectrochemical (PEC) water splitting as a photocathode for hydrogen (H₂) energy production. This is due to its suitable optical band gap (1.5–1.8 eV) and favourable photocurrent onset potential (>1 V vs. RHE). However, there are limited literature reviews specifically focused on the PEC performance of CuBi₂O₄ photocathode. This gap exists partly because photocathodes made from CuBi₂O₄ and its heterostructures have yet to achieve high photoconversion efficiencies, and the factors limiting these efficiencies remain under investigation. In this review, we provide a comprehensive overview of the electronic structure and optical properties of CuBi₂O₄, along with its synthesis strategies. We explore methods to enhance its PEC performance by examining the effects of morphology, doping, and heterostructure construction. In conclusion, we address existing challenges, research gaps, and future outlooks to offer insights for the design and enhancement of highly effective CuBi₂O₄ photocathodes for PEC water splitting, with a particular emphasis on H₂ production.