CO2 flow electrolysis – limiting impact of heat and gas evolution in the electrolyte gap on current density

Abstract

Research in CO₂ electro-reduction with the aim of providing green chemical feedstock (e.g., CO) has been driven towards optimization of individual components such as CO₂-reducing gas diffusion electrodes (GDEs) to achieve stable electrolysis processes. Moving forward, investigation into the performance of electrodes at a cell- and system-level is needed to identify key operational parameters that enhance electrode efficiency. In this study, we characterize self-regulated steady-states within an electrolytic cell. Additionally, we explore the circumstances under which the current density passing through the cell becomes self-limiting. GDE-relevant system parameters and their impact on the overall electrode durability during electrolysis at high current densities up to −1.2 A cm⁻² were analyzed on an intermediate time scale. Integration of inline sensors to the electrolysis test setup enabled close monitoring of changes in the electrolyte temperature and electrolyte pH, as well as the detection of pressure changes around the cathode. In the presented study, the GDE did not appear to be the bottleneck to achieving high current density CO₂-electrolysis. Instead, electrolyte heating and gas evolution within the electrolyte gap limited the maximum current densities that could be applied to a GDE flow cell. Our results suggest that electrode performance (selectivity, durability) can sometimes be underestimated when electrolysis cells and their periphery are not optimally suited for operation with GDEs yet, thus preventing performance windows from being reached.