Strong Facet Effects on Interfacial Charge Transfer Revealed through the Examination of Photocatalytic Activities of Various Cu2O–ZnO Heterostructures

Confirming the photocatalytic inactivity of Cu 2 O nanocubes through the formation of Au‐decorated–Cu 2 O heterostructures, spiky ZnO nanostructures are grown on Cu 2 O cubes, octahedra, and rhombic dodecahedra to demonstrate that charge transfer across semiconductor heterojunctions is also strongly facet dependent. Unintended CuO formation in the growth of ZnO on perfect Cu 2 O cubes makes them slightly active toward methyl orange photodegradation. Under optimal ZnO growth conditions without CuO presence, Cu 2 O cubes remain inactive, while rhombic dodecahedra show an enhanced photocatalytic activity due to better charge transfer according to normal Cu 2 O–ZnO band alignment. Surprisingly, photocatalytically active Cu 2 O octahedra become inactive after ZnO deposition. An extensive interfacial microscopic examination reveals preferential formation of the ZnO (101) planes on the {111} surfaces of Cu 2 O octahedra, while different ZnO lattice planes are observed to deposit on Cu 2 O cubes and rhombic dodecahedra. The photocatalytic inactivity of ZnO‐decorated Cu 2 O octahedra is explained in terms of an unfavorable band alignment arising from an unusual degree of band bending for the ZnO {101} face relative to the band energy of the Cu 2 O {111} surface. The efficiency of charge transfer across semiconductor heterojunctions strongly depends on the band edge energies of the contacting planes.