Size- and facet-dependent photoelectrochemical properties of Cu2O crystals

Abstract

For size- and facet-dependent photoelectrochemical (PEC) activity comparison, Cu₂O cubes with average sizes of 58, 213, and 441 nm, octahedra, rhombic dodecahedra, and cuboctahedra were synthesized. The crystals exhibit clear optical size and facet dependence. However, a mixture of large and small cubes produces a homogenous solution color. Under front-side illumination with particles deposited on an indium tin oxide (ITO) glass electrode, cubes show the best photon-to-current efficiency. Unexpectedly, octahedra have the lowest charge transfer resistance, but exhibit very weak photosensitivity. The stacked rhombic dodecahedra yield a weak PEC performance from hindered hole transport, but photocurrent is greatly enhanced with back-side illumination. Cuboctahedra exposing {100} and {111} faces have intermediate PEC responses. Under back-side illumination, photocurrents also increase greatly for 213 and 441 nm cubes. The PEC performance of Cu₂O crystals exhibits high correlation to the exposed faces, but band diagrams constructed from Mott–Schottky measurements do not agree with the PEC activity order. A shorter path for hole transport from Cu₂O to ITO electrode is critical to PEC performance.