Electrocatalytic Interconversions of CO₂ and Formate on a Versatile Iron-Thiolate Platform

Exploring bidirectional CO2/HCO2- catalysis holds significant potential in constructing integrated (photo)electrochemical formate fuel cells for energy storage and applications. Herein, we report selective CO2/HCO2- electrochemical interconversion by exploiting the flexible coordination modes and rich redox properties of a versatile iron-thiolate platform, Cp*Fe(II)L (L = 1,2-Ph2PC6H4S-). Upon oxidation, this iron complex undergoes formate binding to generate a diferric formate complex, [(L-)(2)Fe(III)(mu-HCO2)Fe(III)](+), which exhibits remarkable electrocatalytic performance for the HCO2--to-CO2 transformation with a maximum turnover frequency (TOFmax) similar to 10(3) s(-1) and a Faraday efficiency (FE) similar to 92(+/- 4)%. Conversely, this iron system also allows for reduction at -1.85 V (vs Fc(+/0)) and exhibits an impressive FE similar to 93 (+/- 3)% for the CO2-to-HCO2- conversion. Mechanism studies revealed that the HCO2--to-CO2 electrocatalysis passes through dicationic [(L-2)Fe-center dot(III)(mu-HCO2)Fe(III)](2+) generated by unconventional oxidation of the diferric formate species taking place at ligand L, while the CO2-to-HCO2- reduction involves a critical intermediate of [Fe(II)-H](-) that was independently synthesized and structurally characterized.