Published July 26, 2022 | Version v1
Journal article Open

CO2 Conversion at High Current Densities: Stabilization of Bi(III) Containing Electrocatalysts under CO2 Gas Flow Conditions

  • 1. Department of Chemistry, Biochemistry and Pharmaceutical Science, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland
  • 2. Department of Physical Chemistry, Eötvös Loránd University, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary
  • 3. European Synchrotron Radiation Facility (ESRF), 71 Avenue des Martyrs, 38000, Grenoble, France

Description

Herein, we demonstrate the superior performance of novel bismuth subcarbonate ((BiO)2CO3) film catalysts for formate production using a fluidic CO2-fed electrolyzer device. The subcarbonate catalyst readily forms in situ from a CO2-absorbing Bi2O3 precursor material during the CO2 reduction reaction (CO2RR). In 1 mol dm–3 KOH electrolyte solution, a maximum Faradaic efficiency of FEformate = 97.4% (corresponding partial current density of formate formation: PCDformate = –111.6 mA cm–2) was achieved at a comparably low applied electrolysis potential of –0.8 V versus the reversible hydrogen electrode (RHE). Even higher values of PCDformate = –441.2 mA cm–2 (FEformate = 62%) were observed at more cathodic potential, –2.5 V vs. RHE. As the alkalinity of the liquid electrolyte is further increased (e.g., by using 5 mol dm–3 KOH solution), the performance of formate production is boosted beyond PCDformate values of –1 A cm–2. Combined X-ray diffraction and Raman spectroscopic investigations demonstrate an extraordinarily high stability of Bi(III) cations in the catalytically active subcarbonate catalyst phase down to cathode potentials of –1.5 V vs. RHE. This stabilization effect can clearly be attributed to the high abundance of gaseous CO2 under the operating conditions of the gas-fed electrolyzer. In the absence of any CO2 supply, however, the reductive Bi(III)®Bi(0) transition already occurs at much milder conditions of –0.3 V vs. RHE, as evidenced by in situ Raman spectroscopy in CO2-free 1 mol dm–3 KOH electrolyte solution. Advanced X-ray diffraction computed tomography (XRD-CT) technique was applied to gain deeper insights into the spatial distribution of the metallic and carbonate phases comprising the active composite catalyst layer (CL) during the CO2RR.

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Funding

NCCR Catalysis (phase I) 51NF40_180544
Swiss National Science Foundation