Understanding the Fundamental Drivers for Performance Losses in Operating AEMFCS in the Presence of CO2

Abstract

Anion exchange membrane fuel cells (AEMFCs) have recently received significant attention as a future high efficiency, environmentally energy conversion device. This attention is due to the potential advantages that AEMFCs can offer compared the much more common, and commercialized, proton exchange membrane fuel cells (PEMFCs) – most notably lower cost. However, there are several remaining roadblocks for the AEMFC technology to be widely adopted, such as: i) the stability of the anion exchange membranes (AEMs) and anion exchange ionomer (AEIs); ii) the development of highly active low-platinum group metal (PGM) for non-PGM catalysts; iii) the discovery of water management strategies to prevent from electrodes flooding or drying out; and iv) reducing the negative effect of CO2 on the AEMFC performance. In an AEMFC operating on ambient air, CO2 reacts with the OH- anions created from the oxygen reduction reaction at the cathode, forming HCO3- and CO3 2-. These carbonates are transported from the cathode to the anode during operation. The presence of carbonate anions has multiple impacts on the operating AEMFC; carbonates decrease the conductivity and water uptake of AEM, introduce additional charge transfer resistance at the hydrogen oxidation anode and change the anode pH (resulting in a thermodynamic decrease in the cell operating voltage). In total, the CO2-related overpotential can be up to 400 mV, which is unacceptable from a practical perspective. Unfortunately, to date, only very few (especially experimental) studies have focused on quantifying the effect of CO2 on AEMFC performance. This poster will present an extensive array of experiments that deconvolutes the fundamental electrochemical mechanism for carbonate “poisoning” in AEMFCs. We also investigate the dynamics of CO2 uptake and removal and dynamics in these systems – with a particular focus on the impact of CO2 concentration in the reacting gas, temperature, AEM thickness and AEM chemistry. Finally, strategies to reduce the CO2 related overpotential below 100 mV will be shown.