Author: Zhefei Pan (Chongqing University) - Ammonia as a hydrogen carrier has become more arresting recently, primarily because of its zero-carbon emission and cost-effectiveness in production, storage, and transportation [1]. Directly feeding ammonia to fuel cells can produce electricity whenever and wherever needed [2]. Since ammonia fuel solution itself creates an alkaline environment, an anion exchange membrane, which conducts hydroxide ions, is typically employed to build ammonia fuel cells [3]. As a key component, the membrane plays a very important role in the ion conduction and electrode reactions [4]. Hence, it is critically important to investigate and understand its physicochemical characteristics [5]. In this work, we have built an ammonia fuel cell with an anion exchange membrane. Five commercial anion exchange membranes were characterized in the aspects of ionic conductivity and ammonia crossover rates and their influences on the performance of the ammonia fuel cell were comparatively examined. It is found that both a high conductivity and low ammonia crossover rate of the anion exchange membrane contribute to a higher cell performance. Additionally, a mathematical model incorporating the mass transport, electrochemical reaction, and ammonia crossover occurring in the ammonia fuel cell has been constructed. The model exhibited good agreement with the experiment results. It suggests that a major cause of the voltage loss in the ammonia fuel cell is the anode polarization. Also, it is displayed that the cell performance improves by increasing the reactant concentration because of the increased mass transfer rate of reactants and decreased activation loss of the electrochemical reaction.
