Unraveling the effect of anions (molybdate and carbonate) on reconstruction of BiOX catalysts for electrocatalytic CO2 to formate

[Display omitted] •Bi2O2CO3 was synthesized through the ion-exchange of Bi2MoO6 with CO32−.•Bi2MoO6 proceed rapidly reduction while the Bi2O2CO3 structure remained intact in electrolysis.•The anion affect the reconstruction by influencing the Bi-O bonding energy.•The higher electronegativity C than Bi enhances electron transfer from Bi to O in Bi-O-C bond.•Bi3+ in Bi2O2CO3 is more catalytically active for *OCHO formation than the metallic Bi. The catalytic performance of Bi2MoO6 and Bi2O2CO3, synthesized through the ion-exchange of Bi2MoO6 with CO32–, was investigated to discern the influence of anions on the electrochemical CO2 reduction reactions (ECO2RR) activity. In-situ Raman measurements uncovered that the reconstruction of Bi2MoO6 proceeded rapidly reduction to metallic Bi after reduction onset, marked by a short-lived transition state, while the Bi2O2CO3 structure remained intact. The anion effects on the reconstruction were attributed to their influence on Bi-O bonding energy, with the Bi-O bond in Bi-O-C being stronger due to higher electronegativity of carbon than Bi, which enhances electron transfer from Bi to O; conversely, the similarity in electronegativity between Mo and Bi weakened the Bi-O bond. This thesis is also applicable for predicting the reconstruction of Bi2WO6 and BiOI samples through electrolysis. The catalytic activity was correlated with the structural changes. Bi2O2CO3 demonstrated a peak formate selectivity of 93.4 % at a current density of 36.2 mA cm−2 at −1.0 V versus the reversible hydrogen electrode (RHE). Additionally, a high FEformate of over 90 % with a jformate of 554.8 mA cm−2 was obtained in the flow cell. At a comparable potential of −1.0 V versus RHE, Bi2MoO6 showed a formate Faradaic efficiencies of 67.4 % at a current density of 26.1 mA cm−2. DFT calculations revealed that the retention of Bi3+ in Bi2O2CO3 is more catalytically active for *OCHO formation than the metallic Bi produced from Bi2MoO6. This suggests that anions in BiOX can modulate ECO2RR performance by governing the reconstruction of pre-catalysts. This study provides a pathway for the rational design of electrocatalysts for liquid fuel synthesis.