Recent Advances of the Confinement Effects Boosting Electrochemical CO2 Reduction

Powered by clean and renewable energy, electrocatalytic CO2 reduction reaction (CO2 RR) to chemical feedstocks is an effective way to mitigate the greenhouse effect and artificially close the carbon cycle. However, the performance of electrocatalytic CO2 RR was impeded by the strong thermodynamic stability of CO2 molecules and the high susceptibility to hydrogen evolution reaction (HER) in aqueous phase systems. Moreover, the numerous reaction intermediates formed at very near potentials lead to poor selectivity of reaction products, further preventing the industrialization of CO2 RR. Catalysis in confined space can enrich the reaction intermediates to improve their coverage at the active site, increase local pH to inhibit HER, and accelerate the mass transfer rate of reactants/products and subsequently facilitate CO2 RR performance. Therefore, we summarize the research progress on the application of the confinement effects in the direction of CO2 RR in theoretical and experimental directions. We first analyzed the mechanism of the confinement effect. Subsequently, the confinement effect was discussed in various forms, which can be characterized as an abnormal catalytic phenomenon due to the relative limitation of the reaction region. In specific, based on the physical structure of the catalyst, the confinement effect was divided in four categories: pore structure confinement, cavity structure confinement, active center confinement, and other confinement methods. Based on these discussions, we also have summarized the prospects and challenges in this field. This review aims to stimulate greater interests for the development of more efficient confined strategy for CO2 RR in the future.