Cobalt　selenide　has　been　developed　as　an　effective　cocatalyst　to　decorate　visible　light　photocatalysts,　including　WO3,　BiVO4　and　g-C3N4,　establishing　intense　surface　contact　with　substrates　for　the　photocatalytic　water　oxidation　reaction.　Compared　with　CoOx　and　CoSx,　CoSe2　is　superior　for　improving　the　photocatalytic　water　oxidation　activity　due　to　the　lower　anionic　electronegativity,　which　leads　to　dense　adhesion　and　enables　fast　interfacial　charge　transfer　for　the　water　oxidation　reaction.