Promoting photogenerated charge separation and transfer in a CuBi2O4 photocathode for improved photoelectrochemical performance

Abstract

Copper bismuthate (CuBi₂O₄) is a fascinating photocathode material for photoelectrochemical (PEC) water-splitting due to its high theoretical photocurrent density and large internal photovoltage. However, its PEC performance is hindered by insufficient light absorption, fast charge carrier recombination, sluggish interfacial charge transfer kinetics, and challenges in achieving uniform photocathode fabrication. Herein, a simple and surfactant-assisted sol–gel method is adopted to fabricate a homogeneous CuBi₂O₄ photocathode for improved PEC performance. A small amount of Pluronic P123, a triblock copolymer surfactant, was incorporated into the CuBi₂O₄ precursor sol to enhance film homogeneity and modulate the particle size during the sol–gel synthesis process. The experimental results reveal that the addition of the surfactant facilitates uniform deposition of the CuBi₂O₄ photocathode and significantly reduces its average particle size from 252 nm to 98 nm. This reduction in particle size results in approximately 2 times higher photocurrent density (−3.8 mA cm⁻² compared to −2.0 mA cm⁻²) at 0.2 V versus reversible hydrogen electrode (RHE) in 0.1 M Na₂SO₄ electrolyte with an electron scavenger. The enhanced PEC performance originates from the improved charge separation (30.5% at 0.2 V vs. RHE) and transfer efficiencies (30.1 V vs. RHE) of the surfactant-modulated photocathode. This work provides a straightforward way of fabricating robust, efficient, and large-area CBO photocathodes for PEC application.