High-Current-Density Electrosynthesis of Formate from Captured Co2 Solution by Mof-Derived Bismuth Nanosheets

Abstract

Greenhouse gas emissions present a significant challenge to humanity, and utilizing renewable electricity to convert emitted CO2 into value-added products offers a promising solution; however, traditional CO2 capture and regeneration processes remain energy-intensive, restricting the overall system efficiency and decarbonization efficacy. In this study, an advanced direct reduction of captured CO2 with large current densities for formate electrosynthesis was demonstrated without the need for CO2 regeneration or compression. MOF-based bismuth with 2D nanosheet structure (DRM-BiNS) was successfully synthesized as a new family of catalytic materials with large surface area and interconnected porosity for direction reduction of captured CO2. By seamlessly combining experimentation and simulation, insights into structure-parameter-performance relation were acquired in flow cell setting, including critical membrane-electrode distance, cell orientation, and pumping flow rate. Important flow-cell components, such as catholyte volume, electrode substrate, membrane choice, and ionomer type, were also carefully examined to enhance the cell performance.  In sharp contrast to prior studies limited to current densities below 20 mA/cm² in bicarbonate-based captured CO2 solutions, this work demonstrates a remarkable current density of 300 mA/cm² with an FE to formate comparable to the case with gas-fed CO2 reduction. Moreover, the process sustained an FE above 50% at a high current density of 500 mA/cm². The DRM-BiNS catalyst exhibited outstanding selectivity, activity, and stability, significantly outperforming oxide-derived bismuth nanosheets (OD-BiNS) in captured CO2 reduction. These findings offer critical insights into the development of sustainable and scalable CO2 utilization technologies.

Keywords: Captured CO2 reduction, MOF-derived Bismuth, Nanosheet catalysts, high current density, Flow cell