“…In the photocatalytic water oxidation system, apart from semiconductors coupled with cobalt oxide, there are still some cobalt based photocatalysts can play dual roles, which they act as both light absorption centers and water oxidation sites without any photosensitizer or cocatalyst [163][164][165]. For example, Wang et al [163] investigated the photocatalytic water oxidation differences of the same Co@Co3O4 core-shell catalyst under [Ru(bpy)3] 2+ /S2O8 2− /light and S2O8 2− /light systems. In [Ru(bpy)3] 2+ /S2O8 2− /light system, both the catalyst and photosensitizer played important roles in OER, while the catalyst had bifunctional roles in S2O8 2− /light system: light absorb center and active catalytic site.…”