Synergistic Surface and Interface Engineering of Porous CuBi ₂ O ₄ Photocathode for Efficient Solar Water Splitting

Abstract The development of highly efficient and durable photocathode materials represents a critical pathway toward the large‐scale implementation of photoelectrochemical (PEC) technology for sustainable hydrogen production. Herein, the high‐performance porous CuBi ₂ O ₄ (p‐CBO) integrated photocathodes for solar water splitting via a synergistic surface and interface engineering strategy are rationally designed. The construction of CuO/CBO heterojunction and NiO hole‐transport interfaces synergistically enhances the PEC performance of p‐CBO by almost four times. After surface platinization, the integrated photocathode exhibits a record‐high photocurrent density of 3.50 mA cm ⁻² at 0.4 V _RHE with a maximum applied bias photon‐to‐current efficiency of 1.60%. Importantly, its photostability and durability can be further improved by an ultrafine Pt/RuO ₂ dual co‐catalyst. The experimental and theoretical results suggest the enhanced PEC performances mainly ascribed to increased light absorption, promoted interfacial charge transfer and bulk charge separation, accelerated surface reaction kinetics and reduced electron accumulation. By coupling the optimized photocathode with an oxygen‐deficient TiO _2‐x nanocomposite photoanode, a solar‐to‐hydrogen efficiency of 0.31% is achieved with excellent operational stability, establishing a leading performer among CBO‐based tandem configurations for unassisted solar overall water splitting. This work demonstrates the key roles of surface and interface engineering in designing high‐performance photoelectrodes for solar hydrogen production.