Boosting Efficiency and Stability of CuBi2O4 Photocathodes Achieved through Template Engineering and FeOOH Modification

Abstract

The ternary oxide CuBi2O4 is a promising photocathode material for solar water splitting due to its appropriate bandgap and positive photocurrent onset potential. However, its performance is severely constrained by poor charge transport and the formation of a porous structure during high-temperature annealing. To overcome these limitations, we introduce a dual-function template engineering strategy using a flower-like Cu2O seed layer with a uniform (111) crystal orientation as a substrate for high-quality CuBi2O4 synthesis. This seed layer not only guides the growth of a high-crystallinity film but also serves as a bottom-up Cu source during annealing, effectively suppressing pore formation. To further enhance surface kinetics, a uniform FeOOH cocatalyst layer was galvanostatically deposited. Under H2O2-assisted conditions, the FeOOH/CuBi2O4 photocathode delivers a nearly threefold enhancement in photocurrent, together with a high onset potential approaching 1.2 V versus the reversible hydrogen electrode (RHE). In addition, it achieves an incident photon-to-current conversion efficiency (IPCE) of approximately 30% at 400 nm under 0.6 VRHE bias. Crucially, the FeOOH/CuBi2O4 photocathode maintains a photocurrent of ~4 mA cm-2 at 0.6 VRHE under 455 nm LED illumination for 12 hours without degradation. This work demonstrates a scalable fabrication paradigm that resolves the critical morphological and stability bottlenecks of CuBi2O4, paving a pathway for robust and efficient ternary oxide photocathodes in solar-to-energy conversion.