Photocatalyst-mediated water splitting driven by sunlight has created tremendous interest as a scalable, cost-effective technique for producing hydrogen. Semiconductors with small bandgaps can be exploited to develop highly efficient solar-powered photocatalytic water splitting systems. As the Se 4p orbitals create shallower valence bands than O 2p and S 3p orbitals, the transition metal selenide semiconductors have smaller bandgaps than equivalent metal (oxy) sulphides. In addition to having a low bandgap, these materials have also been widely studied in the field of solar energy conversion, including photovoltaics and photoelectrochemical cells. As most selenides’ valence band maxima are more negative than the water oxidation potential and preferentially the selenides easily oxidize themselves when exposed to light (photocorrosion). Therefore, their involvement in photocatalytic water splitting has not been understood as successful. So far, the selenide-based semiconductors have only been applied to the hydrogen evolution process in the presence of sacrificial reagents. Using selenides as hydrogen evolution photocatalysts to build a Z-scheme process with other oxygen evolution photocatalysts is one method of applying them for overall water splitting, but how to effectively consume photogenerated holes from the selenides before their self-oxidization remains a key issue.