Unique Features of the Photocatalytic Reduction of H₂O and CO₂ by New Catalysts Based on the Analogues of CdS, Cd₄P₂X₃ (X = Cl, Br, I)

Photochemical reduction of H 2 O and CO 2 has been investigated with a new family of catalysts of the formula Cd 4 P 2 X 3 (X= Cl, Br, I), obtained by the complete aliovalent substitution of the sulfide ions in CdS by P and X (Cl, Br, I). Unlike CdS, the Cd 4 P 2 X 3 compounds exhibit hydrogen evolution and CO 2 reduction from water even in the absence of a sacrificial agent or a cocatalyst. Use of Ni x P y as the cocatalyst, enhances hydrogen evolution, reaching 3870 (apparent quantum yield (AQY) = 4.11) and 9258 (AQY = 9.83) μmol h –1 g –1, respectively, under artificial and natural (sunlight) irradiation, in the case of Cd 4 P 2 Br 3 /Ni x P y . Electrochemical and spectroscopic studies have been employed to understand the photocatalytic activity of this family of compounds. Unlike most of the semiconductor-based photocatalysts, Cd 4 P 2 X 3 catalysts reduce CO 2 to CO and CH 4 in the absence of sacrificial-agent or cocatalyst using water as the electron source. CO, CH 4, and H 2 have been obtained with these catalysts under artificial as well as sun-light irradiation. First-principles, calculations have been carried out to understand the electronic structure and catalytic features of these new catalysts.