Visible photocatalytic hydrogen production from CH3OH over CuO/WO3: The effect of electron transfer behavior of the adsorbed CH3OH

Tungsten oxide (WO3) and copper oxide (CuO)/WO3 samples were prepared, and their photocatalytic performance towards the reforming of CH3OH to hydrogen was compared under visible light irradiation at ambient temperature. CuO/WO3 had an approximately 64 times higher hydrogen production activity than bare WO3. CH3OH accepted electrons from WO3 but provided electrons to CuO/WO3 thin films, indicating that the hydrogen production from CH3OH was related to electron transfer during CH3OH adsorption. The characterization results showed that Cu exists in a mixed-valence state in CuO/WO3, which activated the lattice oxygen of WO3 to form the corresponding interfacial oxygen vacancies (VOs). The oxygen atom of CH3OH was fixed at VOs sites, which facilitated the cleavage of the OH bond. Cu2+ sites favored the cleavage of the CH bond in CH3OH because VOs fixed the oxygen atom. Then, the production of hydrogen via these two processes was accompanied by the transfer of electrons from CH3OH to Cu2+ sites at the interface. This was followed by hydrogen production after accepting photogenerated electrons from WO3. The reason for the low catalytic activity of the WO3 support was that it contained no VOs nor Cu2+ sites to oxidize CH3OH to produce more protons. This study provides an approach to improve catalysts used for the photocatalytic reformation of methanol.