Scaling up electrochemical CO2 reduction to formate through comparative reactor analysis

Abstract

This study presents scalable reactor designs at a lab-scale pilot level for the electrochemical CO₂ reduction reaction (eCO₂RR) to formate, utilizing formate-selective catalysts such as tin (Sn) and bismuth (Bi) at the electrodes in different sizes. Furthermore, it evaluates multiple scaled-up reactor configurations, providing critical insights into their performance, efficiency, and potential for industrial deployment. Electrochemical cells comprising VITO CORE® gas diffusion electrodes (GDEs) of 100 cm² single electrode, 300 cm² stack (3 electrodes of 100 cm²) and 400 cm² single electrode were evaluated for eCO₂RR at 100 mA cm⁻² at two different laboratories (UFZ and VITO). The 100 cm² Sn-GDEs showed an average formate production rate (r_HCOO⁻) and coulombic efficiency (CE) of 29 mM h⁻¹ and 80%, respectively. However, stacking three 100 cm² GDEs, hence stacked 300 cm² Sn-GDEs, showed lower performance (average r_HCOO⁻ and CE of 19 mM h⁻¹ and 50%, respectively), with a variation among the replicates. Operational efficiency and stability were regained by further scaling up using a single Sn-GDE to 400 cm² (average r_HCOO⁻ and CE of 35 mM h⁻¹ and 73%, respectively). The Bi-GDE in the similar setup of 400 cm² showed lower performance (average r_HCOO⁻ and CE of 23 mM h⁻¹ and 63%, respectively), which we related to electrode structural degradation as revealed by SEM-EDX analyses. With its notable durability, stable performance, and relatively low overpotential for eCO₂RR, the 400 cm² Sn-GDE setup demonstrated strong potential for long-term eCO₂RR to formate. The corresponding power consumptions at the largest scale for formate production using both Sn- and Bi-GDEs were determined to be 190.8 and 501.8 Wh mol⁻¹, respectively. This situates the technology at the upper boundary of laboratory-scale and the early stages of pilot-scale operation. Although the system has not yet achieved kilowatt-level performance, the results underscore a promising and scalable approach toward the development of industrially relevant eCO₂RR platforms.

Keywords: eCO₂RR; Scale up; Formate; Gas diffusion electrodes; Flow cells; Stacked reactors.