Challenges and prospects in the selective photoreduction of CO2 to C1 and C2 products with nanostructured materials: a review

Solar fuel generation through CO2 hydrogenation is the ultimate strategy to produce sustainable energy sources and alleviate global warming. The photocatalytic CO2 conversion process resembles natural photosynthesis, which regulates the ecological systems of the earth. Currently, most of the work in this field has been focused on boosting efficiency rather than controlling the distribution of products. The structural architecture of the semiconductor photocatalyst, CO2 photoreduction process, product analysis, and elucidating the CO2 photoreduction mechanism are the key features of the photoreduction of CO2 to generate C1 and C2 based hydrocarbon fuels. The selectivity of C1 and C2 products during the photocatalytic CO2 reduction have been ameliorated by suitable photocatalyst design, co-catalyst, defect states, and the impacts of the surface polarisation state, etc. Monitoring product selectivity allows the establishment of an appropriate strategy to generate a more reduced state of a hydrocarbon, such as CH4 or higher carbon (C2) products. This article concentrates on studies that demonstrate the production of C1 and C2 products during CO2 photoreduction using H2O or H2 as an electron and proton source. Finally, it highlights unresolved difficulties in achieving high selectivity and photoconversion efficiency of CO2 in C1 and C2 products over various nanostructured materials.