Improving Faradaic Efficiency for Conversion of Bicarbonate to Formate Using Indium–Bismuth Alloy Electrocatalysts

Abstract

The bicarbonate reduction reaction (BRR) is a promising approach for valorizing captured CO2. However, intense competition from hydrogen evolution reaction (HER) activity generally limits BRR’s intrinsic selectivity to form products such as formate on bismuth catalysts. Herein, to boost BRR Faradaic efficiency (FE) to formate, we successfully developed metallic indium–bismuth alloy catalysts that increase the thermodynamic limiting potential for HER (lowering HER activity) and decrease the thermodynamic limiting potential for BRR to formate (raising BRR activity), which we characterized via combined theoretical and experimental approaches. Specifically, our density functional theory calculations reveal that introducing indium into metallic bismuth weakens *H binding and lowers the reaction energy for *OCHO intermediate formation. In addition, through experimental rotating disk electrode measurements, we determined that thermodynamic factors primarily govern improvements in BRR performance at low indium concentrations. Consequently, this state-of-the-art composition offers improved intrinsic BRR selectivity over bismuth across a large current density window, and we observe a FEformate of 83.5% ± 1.1% at 60 mA·cm–2 and 60.8 ± 0.6% at 400 mA·cm–2. Moreover, we also combine experimental and theoretical approaches to systematically characterize HER and BRR activity changes in the relevant catalyst phases, determining the distinct roles of indium in metallic bismuth, bismuth oxide, and bismuth subcarbonate. Specifically, indium suppresses HER in the metallic bismuth phase while facilitating HER in the subcarbonate phase, which shows the significance of phase engineering in the design of BRR electrocatalysts.