Tunable green syngas generation from CO and HO with sunlight as the only energy input.

The carbon-neutral synthesis of syngas from CO and HO 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 with HO into syngas using core/shell Au@CrO 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 CrO are synergetic in deforming the linear CO molecule to a bent state with an O-C-O angle of 116.5°, thus significantly reducing the energy barrier of CORR compared with that over a single component of Au or CrO. Hydrogen evolution reaction was promoted by the same cocatalyst simultaneously. By combining the cooperative catalytic properties of Au@CrO with the distinguished optoelectronic virtues of the multistacked InGaN NW semiconductor, the developed photocatalyst demonstrated high syngas activity of 1.08 mol/g/h with widely tunable H/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/h, and isotopic testing confirmed that syngas originated from CORR. The solar-to-syngas energy efficiency approached 0.89% during overall CO reduction coupled with water splitting. The work paves a way for carbon-neutral synthesis of syngas with the sole inputs of CO, HO, and solar light.