Thermal-Treated α-Bi 2 O 3 Electrocatalyst for Efficient CO 2 Electroreduction toward Formate

The electrochemical CO2 reduction reaction (CO2RR) provides a renewable avenue to convert CO2 to value-added fuels and chemicals. Bismuth (Bi)-based electrocatalysts are known as promising candidates for CO2RR to formate (HCOO-), yet their performance is frequently limited by structural reconstruction during operation, resulting in reduced activity and selectivity. This work describes a thermal treatment approach to tuning the catalytic chemistry of α-Bi2O3 for CO2RR. A thermally optimized Bi-400 electrocatalyst achieves a high Faradaic efficiency of 93.0% for HCOO- at -0.95 V vs RHE, along with good stability over 70 h. Through detailed structural and mechanistic studies, it is revealed that the preserved Bi-O motifs in Bi-400 facilitate CO2 activation and modulate the binding energy of the *OCHO intermediate, thereby enhancing both activity and selectivity toward HCOO- production. This study would provide an in-depth understanding of the selective formation of HCOO- products on Bi-based electrocatalysts in CO2RR.