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This article reviews photocatalysis for water splitting by various kinds of metal oxides and nitrides such as ferroelectric metal oxides, different kinds of titanates with d0 (Ti4+) electronic configuration as a core metal ion, and various typical metal oxides with d10 (In3+, Ga3+, Ge4+, Sn4+, Sb5+) configuration, and d10 (Ga3+) metal nitride, together with d10s2 (Pb2+) and d0f0 (Ce4+) metal oxides. Ferroelectric metal oxides with single domain structure showed anomalous photovoltaic effects that controlled the behavior of photoexcited electrons. Various metal oxides involving ionic alkaline metal/alkaline earth metal ions showed good correlation between photocatalytic activity and the distortion of octahedral XO6/tetrahedral XO4 (X = core metal ion). When the metal oxides involved covalent metal ions such as Zn2+ and Pb2+, the activity was invoked even in distortion-free structures: this is due to strong electronic effects that affect the band structure. The activity of d10 metal oxides and nitrides is associated with conduction bands of hybridized sp orbitals with large dispersion that are able to generate photoexcited electrons with large mobility. A feature of the photocatalytically active metal oxides and nitrides discovered so far, which is their closed shell electronic structures is discussed.
Yasunobu Inoue (Thu,) studied this question.