Monitoring ammonia and water transport through anion exchange membranes in direct ammonia fuel cells

Abstract

Anion exchange membrane direct ammonia fuel cells (AEM-DAFCs) can generate clean electricity with zero carbon emissions. However, their performance are hindered by severe ammonia crossover, which causes a mixed potential at the cathode, thereby reducing the cell voltage. Meanwhile, the produced intermediates, such as Nads species, adsorb onto catalyst, causing poisoning and thus impeding the oxygen reduction reaction (ORR). Another key issue for AEM-DAFCs is to maintain an appropriate water content at the cathode, which is crucial for promoting ORR and avoiding water flooding. In this work, an in-situ observation method is developed to quantitatively characterize the rates of ammonia and water crossover. Besides, a half-cell configuration is designed and developed to evaluate the cathode potential drop caused by ammonia crossover. The effects of operating conditions (such as ammonia concentration and cell temperature) and membrane electrode assembly (MEA) design parameters (such as membrane thickness and cathode wettability) on behaviors of ammonia and water crossover are thoroughly examined. The findings show that ammonia crossover can be substantially reduced by using a low-concentration ammonia solution or a thicker membrane. Moreover, this study offers guidance on developing fuel and water management strategies to enhance the performance of AEM-DAFCs.