CO2 transformation to multicarbon products by photocatalysis and electrocatalysis

The excessively high atmospheric CO2 concentration is associated with rapidly evolving industrial, commercial, and residential uses of fossil fuels, which has caused global warming and climate crisis. Photocatalytic or electrocatalytic reduction of CO2 into value-added hydrocarbon fuels has provided a promising and sustainable solution to addressing these issues simultaneously. Multicarbon products (C2+) with higher energy densities are generally desirable in fueling transportation and other industries. However, the low selectivity and subsequently a higher cost toward these C2+ products have severely limited their larger scale production. Here, we review the strategies of controlling the C2+ product selectivity during the photocatalytic and electrocatalytic CO2 reduction reaction (CRR) processes with their catalytic reaction mechanisms. This review starts with the fundamentals on photocatalytic and electrocatalytic CRR, which is followed by discussions about how reaction mechanisms and process pathways affect the C2+ product selectivity and the main strategies to improve both photocatalysis and electrocatalysis systems. Finally, some outlook for future work and challenges in improving the C2+ product selectivity is included.