Modeling and simulation of microfluidic electrolytic cells for CO2 electro-reduction to formic acid: The influence of a Bi-Sn catalyst and ionic liquid electrolyte on cell performance

The concentration of CO2 in the atmosphere has recently exceeded 420 ppm and continues to rise, mainly because of the combustion of fossil fuels, contributing significantly to climate change. CO2 capture, utilization and storage has become recognized as a critical approach to reducing energy and industrial emissions. CO2 utilization through the electrochemical reduction route is a novel alternative to CO2 storage. Microfluidic electrolytic cells for CO2 electro-reduction have recently gained traction due to reduced reactor fouling and flooding rates. However, there is still limited understanding of mass transport, electrochemical interactions, and simultaneous optimization of microfluidic cell performance metrics, such as current density, Faradaic efficiency, and CO2 conversion. This study employed COMSOL Multiphysics 5.3a to develop a steady-state numerical 2D model of microfluidic cell for electroreduction of CO2 to HCOOH and compared the optimized performance of 2 electrolytes. Specifically, this work examined the influence of [EMIM][BF4] (1-ethyl-3-methyl imidazolium tetra-fluoroborate) and [EMIM][CF3COOCH3] (1-ethyl-3-methylimidazolium tri-fluoroacetate) ionic liquid electrolytes on current density, Faradaic efficiency, and CO2 conversion. The analysis showed that a 0.9:0.1 Bi-Sn catalyst weight ratio exhibited the highest CO2 consumption per pass in the cathode gas channel. The model achieved a peak HCOOH current density of 183.8 mA cm−2, Faradaic efficiency of 87% (average of 66%), and CO2 conversion of 31.96% at −4 V compared to a standard hydrogen electrode in a microfluidic cell. Furthermore, parametric studies were conducted to determine the best input parameter for cell optimization.