Insights into the carbonate effect on water oxidation over metal oxide photocatalysts/photoanodes Hitoshi Kusama,* a Masanori Kodera, a Koichi Yamashita b and Kazuhiro Sayama a a Global Zero Emission Research Center (GZR), National Institute of Advanced Industrial Science and Technology (AIST), AIST Tsukuba West, 16-1 Onogawa, Tsukuba, Ibaraki 305-8569, Japan b Element Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University, Nishikyo-ku, Kyoto 615-8245, Japan Supplementary information Table S1 Summary of the effect of carbonate on a photocatalyst and (photo)anode using TiO2 and BiVO4 Semiconductor TiO2 BiVO4 Photocatalytic activity for water splitting into H2 and O2 Yes No a Improvement of photocurrent Yes Yes H2O2 production on photoanode Yes b Yes H2O2 production on anode in the dark Yes Yes a BiVO4 photocatalyst cannot evolve H2 because of the positive conduction band. b Data in this work. 1 Electronic Supplementary Material (ESI) for Physical Chemistry Chemical Physics. This journal is © the Owner Societies 2022