Single-Electron Activation of CO2 on Graphene-Supported ZnO Nanoclusters: Effects of Doping in the Support

Use of solar energy to convert the greenhouse gas CO2 into useful chemicals or fuels could not only reduce the accumulation of CO2 in the atmosphere but also provide a solution to sustainable energy development. There has been much interest in understanding the mechanistic role of graphene when added to semiconductor nanostructures to reduce CO2 because of the observation of enhanced photo-catalytic activities in recent experiments. In this work, we investigate the adsorption and single-electron activation of CO2 on ZnO nanoclusters with and without a modified graphene support using a first-principles approach, with a special focus on the effect of the support. The formation of the CO2- anion is identified under simulated photoexcitation conditions and is energetically more favorable than for previously studied oxide photocatalysts. The calculated results suggest that single-heteroatom doping in graphene has a significant impact on the catalytic activity of ZnO. The electronic coupling between the support and the semiconductor cluster plays a critical role in the activation of CO2 on the supported ZnO cluster. n-type doping helps to retain the photoexcited electron on ZnO and facilitates CO2 reduction on ZnO, whereas p-type doping enhances charge transfer from the photoexcited ZnO to graphene and would be useful for reductions occurring on graphene.