Synergistic Coherent Interface and Geometric Field Engineering in a Cu ₂ O@Cu ₃ N Photocathode for High-Efficiency and Stable CO ₂ -to-CO Conversion

The development of efficient and stable cuprous-oxide-based photocathodes for CO 2 reduction is hindered by the intrinsic trade-off between rapid photocorrosion and inefficient charge separation. Herein, we construct a Cu 2 O@Cu 3 N heterojunction photocathode featuring a unique hierarchical architecture, which integrates atomic-scale coherent interfaces (N–Cu–O bonds) with microscale geometric field enhancement from abundant nanoscale tips at pore vertices. This rational integration is designed to simultaneously improve charge transport and favor reactant accumulation at the active sites. As a result, the optimized electrode achieves a CO Faradaic efficiency of 96% at a mild potential, maintains >90% selectivity across a broad voltage window, and operates stably for over 3 h. This work demonstrates that co-designing atomic-scale interfaces and microscale morphology is a powerful pathway to high-performance solar fuel generation.