Selective electroreduction of CO2 to formate by a heterogenized Ir complex using H2O as an electron/hydrogen source

Abstract

A newly synthesized tetradentate PNNP-coordinated iridium (Ir) complex, Mes-IrPPh2, immobilized on a carbon material, was found to be a superior catalyst for CO₂ electrochemical reduction reaction (CO₂ERR) to give formate, (HCOO⁻), allowing an operation near the theoretical potential (−0.18 V vs. RHE, pH = 7.3) in water. The combined [Mes-IrPPh2] electrode furnished HCOO⁻ with a current density of greater than 2.2 to 7.7 mA cm⁻² over −0.27 to −0.47 V vs. RHE, providing faradaic efficiencies (FE) of >90%. The outstanding robustness of the electrode attained continuous production of HCOO⁻ up to 12.5 mmol with 2.86 μmol of Mes-IrPPh2 at −0.27 V vs. RHE over 168 h. Furthermore, solar-driven electrochemical CO₂ reduction to HCOO⁻ was also carried out in water with a Ni/Fe–Ni foam anode as a water oxidation catalyst and a silicon photovoltaic cell to achieve a solar-to-formate conversion efficiency (η_STF) of 13.7%.