We further analyzed the cooccurrence between the various devices and the most reported photocatalysts (Figure ). Bismuth vanadate and tungsten trioxide have a higher than usual contribution to the photoanodes category, as they are predominantly used for the oxidation of water. Molybdenum disulfide, cupric oxide, cuprous oxide, and cadmium sulfide are the photocatalysts used in photocathodes for the reduction of water to produce hydrogen, whereas nickel monoxide is co-catalyst used to enhance the hydrogen production.