Electrochemical Reduction of CO2 to CO in Membrane Electrode Assembly (MEA) Setup

Abstract

The global concern of the increasing levels of CO2 is growing quickly in the recent years. Therefore, a lot of research is currently underway with respect to closing the carbon cycle. The electrochemical reduction of CO2 is a promising technology that could help utilize the CO2 as a feedstock to produce chemicals and fuels, while storing the excess energy generated from renewable energy sources in chemical bonds. Due to its simplicity and economic feasibility, the conversion of CO2 to CO has a high potential in the industrial market. Membrane Electrode Assembly (MEA) is an interesting electrochemical reactor configuration to produce CO on industrial scale due to the low ohmic losses and reduced risk of catalyst poisoning. Optimizing the catalyst and operating conditions are key steps towards the commercialization of the process. This research focuses on understanding the influence of different process parameters on the CO selectivity while analyzing the performance challenges. Multiple inlet flow rates of CO2 were tested at different current densities to evaluate its impact on the faradaic efficiency. The experiments were performed using KOH-exchange MEA cell with gas diffusion electrodes and Sustainion membrane. Since the product of interest is CO, Ag-based catalyst layer was sputtered on the gas diffusion electrode. The cathodic products were identified and quantified using gas chromatograph. The experimental results have shown that increasing current density resulted in lower CO selectivity, while the inlet flow rate did not have a significant effect. It was also shown that the cell could not achieve higher than 200mA/cm2 due to the accumulation of salts blocking the gas flow channel.
On top of that, a simple 2D model was developed in COMSOL Multiphysics to understand the mass transport and concentration distribution in the gas flow channel. The model was not able to simulate the complexities of the electrochemical process and represented an ideal plug flow reactor. It is understood that the incorporation of reaction kinetics and current distribution is necessary to replicate the real scenario.