Electrocatalytic Interconversions of CO 2 and Formate on a Versatile Iron-Thiolate Platform.

Exploring bidirectional CO 2 /HCO 2 - catalysis holds significant potential in constructing integrated (photo)electrochemical formate fuel cells for energy storage and applications. Herein, we report selective CO 2 /HCO 2 - 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-Ph 2 PC 6 H 4 S - ). Upon oxidation, this iron complex undergoes formate binding to generate a diferric formate complex, [(L - ) 2 Fe(III)(μ-HCO 2 )Fe(III)] + , which exhibits remarkable electrocatalytic performance for the HCO 2 - -to-CO 2 transformation with a maximum turnover frequency (TOF max ) ∼10 3 s -1 and a Faraday efficiency (FE) ∼92(±4)%. Conversely, this iron system also allows for reduction at -1.85 V (vs Fc +/0 ) and exhibits an impressive FE ∼93 (±3)% for the CO 2 -to-HCO 2 - conversion. Mechanism studies revealed that the HCO 2 - -to-CO 2 electrocatalysis passes through dicationic [(L 2 ) -• Fe(III)(μ-HCO 2 )Fe(III)] 2+ generated by unconventional oxidation of the diferric formate species taking place at ligand L, while the CO 2 -to-HCO 2 - reduction involves a critical intermediate of [Fe(II)-H] - that was independently synthesized and structurally characterized.