Electrocatalytic CO2 reduction to formate/formic acid represents a practical and economically viable route for CO2 conversion, among which Sn- and Bi-based materials are regarded as promising electrocatalysts. This thesis explores the structure–performance relationship of Sn- and Bi-based catalysts for electrochemical CO2 reduction reaction (CO2RR) to formate, focusing on two effective optimization strategies: mesostructural engineering and heterometal doping. Sn- and Bi-based catalysts are attractive candidates due to their high selectivity for formate, low cost, and environmental compatibility.

In the first study, mesoporous SnO2 enriched with oxygen vacancies shows enhanced CO2RR performance compared with bulk SnO2 and improved durability. Mechanistic studies reveal that the mesostructure enhances CO2 adsorption, facilitates charge transfer, stabilizes the *OCHO intermediate, and lowers the reaction energy barrier. Moreover, the mesoporous framework promotes the formation and stabilization of oxygen vacancies, maintaining the Sn oxidation state and catalyst stability.

In the second study, Sn-doped BiOCl (the ratio of Sn is 2-10 at. %) nanoplates synthesized via a sol–gel method act as precatalysts that rapidly reconstruct into Sn-modified metallic Bi during the CO2RR. Among the samples investigated, the catalyst with a Sn doping ratio of ~5% achieves a Faradaic efficiency of 87.7% at −1.0 V vs. RHE, considerably outperforming pristine BiOCl. Structural and spectroscopic analyses show that Sn incorporation stabilizes the *OCHO intermediate, facilitates interfacial water dissociation, and promotes the formation of active Bi 003 planes, clarifying the dynamic evolution of active sites.

Overall, this thesis demonstrates that rational control of mesostructure, defect chemistry, and dopant-induced reconstruction can synergistically enhance both activity and stability in Sn- and Bi-based CO2RR catalysts. These insights provide practical guidelines for designing efficient and durable formate-selective electrocatalysts.