CuCoO2/CuMO2 (M = B, Al, Ga, In) delafossite isomorphous heterostructures for photocatalytic overall water splitting: Design strategy from DFT study

Delafossite CuCoO₂, with its half-metal electronic configuration, shows remarkable photocatalytic O₂ evolution activity. While the heterostructure approach enhances H₂ evolution and promotes water splitting, conventional non-isomorphic heterostructures often face interface stress, distortions, and defects, which destabilize interfaces and hinder optimal band alignment. Herein, a systematic Density Functional Theory (DFT) calculation investigation was conducted on CuCoO₂/CuMO₂ (M = B, Al, Ga, In) delafossite isomorphous heterostructures, focusing on the effects of varying M−site. CuCoO₂/CuBO₂ and CuCoO₂/CuInO₂ exhibit stronger interfacial chemical bonding, and the obvious atomic relaxation at the interface of the CuCoO₂/CuBO₂ model accounts for its most negative interfacial binding energy. The density of states demonstrates superior carrier transport efficiency in CuCoO₂/CuInO₂. Meanwhile, the spin polarization phenomenon mainly occurs on the CuCoO₂ side, while the CuMO₂ side remains nearly spin-degenerate. Quantitative analysis of interfacial electric fields elucidates the photocatalytic enhancement mechanisms, with CuCoO₂/CuBO₂ and CuCoO₂/CuAlO₂ forming traditional type-II heterojunctions, while CuCoO₂/CuGaO₂ and CuCoO₂/CuInO₂ exhibit direct Z-scheme charge transfer mechanisms. Notably, M = Al/Ga/In configurations display favorable overpotentials for overall water splitting. Furthermore, optical characterization demonstrates broadened visible/infrared light absorption in isomorphous heterostructures. This study offers theoretical guidance for future experiments and provides principles for designing efficient photocatalysts for water splitting.