Unraveling the selectivity puzzle of H2 evolution over CO2 photoreduction using ZnS nanocatalysts with phase junction

Abstract

Catalytic reduction of CO2 is usually accompanied by competitive H2 evolution. However, the selectivity between CO2 reduction and H2 evolution is not completely understood hitherto. Here ZnS is chosen as the model catalyst to study this and are prepared by hydrothermal treatment of ZnS(en)0.5 precursor. ZnS nanoparticles exhibit high production yield of solar fuels due to the formation of internal Sphalerite-Wurtzite phase junction within a single particle. The predominant product of H2 can reach a yield as high as 31.5 mmol/g-cat after 4-h reaction, meanwhile with a high CO yield of 279.3 μmol/g-cat. The mechanism is proposed from both dynamic (adsorption/desorption of reactants/products) and thermodynamic (redox potential, change in Gibbs free energy of key intermediates) point of view. This work not only provides useful information on the reaction selectivity between CO2 reduction and H2 evolution, but also pave a way to adjust the yield of a specific product upon photocatalysis.