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.