Atomic-Level Reactive Sites for Semiconductor-Based Photocatalytic CO2 Reduction

Photocatalytic CO2 reduction is an effective means to generate renewable energy. It involves redox reactions, reduction of CO2 and oxidation of water, that leads to the production of solar fuel. Significant research effort has therefore been made to develop inexpensive and practically sustainable semiconductor-based photocatalysts. The exploration of atomic-level active sites on the surface of semiconductors can result in an improved understanding of the mechanism of CO2 photoreduction. This can be applied to the design and synthesis of efficient photocatalysts. In this review, atomic-level reactive sites are classified into four types: vacancies, single atoms, surface functional groups, and frustrated Lewis pairs (FLPs). These different photocatalytic reactive sites are shown to have varied affinity to reactants, intermediates, and products. This changes pathways for CO2 reduction and significantly impacts catalytic activity and selectivity. The design of a photocatalyst from an atomic-level perspective can therefore be used to maximize atomic utilization efficiency and lead to a high selectivity. The prospects for fabrication of effective photocatalysts based on an in-depth understanding are highlighted.