Photocatalytic CO(2) Reduction Using Water as an Electron Donor under Visible Light Irradiation by Z-Scheme and Photoelectrochemical Systems over (CuGa)(0.5)ZnS(2) in the Presence of Basic Additives

[Image: see text] We demonstrated photocatalytic CO(2) reduction using water as an electron donor under visible light irradiation by a Z-scheme photocatalyst and a photoelectrochemical cell using bare (CuGa)(0.5)ZnS(2) prepared by a flux method as a CO(2)-reducing photocatalyst. The Z-scheme system employing the bare (CuGa)(0.5)ZnS(2) photocatalyst and RGO-(CoO(x)/BiVO(4)) as an O(2)-evolving photocatalyst produced CO of a CO(2) reduction product accompanied by H(2) and O(2) in a simple suspension system without any additives under visible light irradiation and 1 atm of CO(2). When a basic salt (i.e., NaHCO(3), NaOH, etc.) was added into the reactant solution (H(2)O + CO(2)), the CO formation rate and the CO selectivity increased. The same effect of the basic salt was observed for sacrificial CO(2) reduction using SO(3)(2–) as an electron donor over the bare (CuGa)(0.5)ZnS(2) photocatalyst. The selectivity for the CO formation of the Z-schematic CO(2) reduction reached 10–20% in the presence of the basic salt even in an aqueous solution and without loading any cocatalysts on the (CuGa)(0.5)ZnS(2) metal sulfide photocatalyst. It is notable that CO was obtained accompanied by reasonable O(2) evolution, indicating that water was an electron donor for the CO(2) reduction. Moreover, the present Z-scheme system also showed activity for solar CO(2) reduction using water as an electron donor. The bare (CuGa)(0.5)ZnS(2) powder loaded on an FTO glass was also used as a photocathode for CO(2) reduction under visible light irradiation. CO and H(2) were obtained on the photocathode with 20% and 80% Faradaic efficiencies at 0.1 V vs RHE, respectively.