Tunable green syngas generation from CO 2 and H 2 O with sunlight as the only energy input.

The carbon-neutral synthesis of syngas from CO 2 and H 2 O powered by solar energy holds grand promise for solving critical issues such as global warming and the energy crisis. Here we report photochemical reduction of CO 2 with H 2 O into syngas using core/shell Au@Cr 2 O 3 dual cocatalyst-decorated multistacked InGaN/GaN nanowires (NWs) with sunlight as the only energy input. First-principle density functional theory calculations revealed that Au and Cr 2 O 3 are synergetic in deforming the linear CO 2 molecule to a bent state with an O-C-O angle of 116.5°, thus significantly reducing the energy barrier of CO 2 RR compared with that over a single component of Au or Cr 2 O 3 . Hydrogen evolution reaction was promoted by the same cocatalyst simultaneously. By combining the cooperative catalytic properties of Au@Cr 2 O 3 with the distinguished optoelectronic virtues of the multistacked InGaN NW semiconductor, the developed photocatalyst demonstrated high syngas activity of 1.08 mol/g cat /h with widely tunable H 2 /CO ratios between 1.6 and 9.2 under concentrated solar light illumination. Nearly stoichiometric oxygen was evolved from water splitting at a rate of 0.57 mol/g cat /h, and isotopic testing confirmed that syngas originated from CO 2 RR. The solar-to-syngas energy efficiency approached 0.89% during overall CO 2 reduction coupled with water splitting. The work paves a way for carbon-neutral synthesis of syngas with the sole inputs of CO 2 , H 2 O, and solar light.