Photocatalytic CO2 reduction by a Z-scheme mechanism in an aqueous suspension of particulate (CuGa)0.3Zn1.4S2, BiVO4 and a Co complex operating dual-functionally as an electron mediator and as a cocatalyst

Abstract

A visible-light-driven Z-scheme photocatalytic CO2 reduction reaction (CO2RR) to produce CO was demonstrated using an aqueous particulate dispersion containing two bare semiconductors, (CuGa)0.3Zn1.4S2 for CO2RR and BiVO4 for water oxidation. The semiconductors were mixed with a water-soluble cobalt tris(dimethylbipyridine) complex. The CO selectivity was 98% (against H2), and the rate of CO generation was 1–2 orders of magnitude higher than those of previously-reported aqueous suspension photocatalytic systems. O2 was continuously evolved, and isotope tracer analyses confirmed that CO2 was the carbon source for CO. Experimental studies and calculations suggest that the Co complex acts dual-functionally in synergy with (CuGa)0.3Zn1.4S2 and BiVO4: it behaves as an efficient ionic electron mediator, and also acts as a new active CO2RR cocatalyst after a structural change by accepting photoexcited electrons from (CuGa)0.3Zn1.4S2. This simple method, operating in a self-optimizing manner in solution, has great potential to help achieve sustainable, highly active artificial photosynthetic systems.