Cu 2 O/CeO 2 Photo-electrochemical Water Splitting: A Nanocomposite with an Efficient Interfacial Transmission Path under the Co-action of a p-n Heterojunction and Micro-mesocrystals.

Cu 2 O is an ideal p-type material for photo-electrochemical (PEC) hydrogen evolution, although serious electron-hole recombination and photocorrosion restrict its further improvement for PEC activity. In this work, CeO 2 nanoparticles (NPs) self-assemble on the surface of Cu 2 O octahedra, thus successfully forming a Cu 2 O/CeO 2 structure in which p-n heterojunctions and micro-mesocrystals (m-MCs) work together. The optimum Cu 2 O/CeO 2 composite, without the use of any cocatalyst, exhibits a fivefold higher photocurrent density (4.63 mA cm -2 at 0 V vs. the reversible hydrogen electrode) than that of Cu 2 O octahedra, which is better than most Cu 2 O-based photocathodes without cocatalyst and even comparable with advanced Cu 2 O-based photocathodes. The hydrogen production of the optimal Cu 2 O/CeO 2 (Faradaic efficiency of ∼100 %) is 17.5 times higher than that of pure Cu 2 O octahedra, and the photocurrent shows almost no decay under the 12 h stability test. The delicately designed Cu 2 O/CeO 2 structure in this work provides reference and inspiration for the design of cathodes materials.