Scaling up electrochemical CO 2 reduction to formate through comparative reactor analysis

Abstract

Electrochemical CO 2 reduction to formate using Sn and Bi catalysts was stepwise scaled up and evaluated, enabling the identification of optimal configurations and performance metrics for potential industrial deployment. This study presents scalable reactor designs at a lab-scale pilot level for the electrochemical CO 2 reduction reaction (eCO 2 RR) 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 cm 2 single electrode, 300 cm 2 stack (3 electrodes of 100 cm 2 ) and 400 cm 2 single electrode were evaluated for eCO 2 RR at 100 mA cm −2 at two different laboratories (UFZ and VITO). The 100 cm 2 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 cm 2 GDEs, hence stacked 300 cm 2 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 cm 2 (average r HCOO − and CE of 35 mM h −1 and 73%, respectively). The Bi-GDE in the similar setup of 400 cm 2 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 eCO 2 RR, the 400 cm 2 Sn-GDE setup demonstrated strong potential for long-term eCO 2 RR 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 eCO 2 RR platforms.