Ternary Facet Junction Engineered Cu ₂ O Photocathode for Efficient Urea Synthesis via CO ₂ and NO ₃ ^– Co-reduction

Facet junction engineering offers an effective strategy to manipulate charge separation in photoelectrocatalysis (PEC), yet its role in CO 2 and NO 3 – co-reduction toward urea synthesis remains unexplored. Herein, ternary facet junction polyhedral Cu 2 O photocathodes exposing {100}, {110}, and {111} facets were synthesized via a pH-controlled precipitation strategy. Density functional theory (DFT) calculations and selective photodeposition experiments reveal that the coexistence of anisotropic facets generates internal electric fields across the junctions, enabling directional charge carrier migration and suppressing charge recombination. Consequently, ternary facet Cu 2 O delivers markedly enhanced PEC urea synthesis performance compared with those of single and binary facet junction samples. In situ infrared spectroscopy and control experiments identify key C–N coupling intermediates, elucidating the mechanism by which facet junction regulated charge dynamics promote CO 2 /NO 3 – co-reduction. This work uncovers a previously unrecognized function of facet junctions in PEC urea synthesis and provides a general design strategy for efficient photocathodes toward sustainable carbon–nitrogen conversion.