Performance characteristics of a direct ammonia fuel cell with an anion exchange membrane

Abstract

In this work, a direct ammonia fuel cell, which consists of an anion exchange membrane and commercially available PtRu/C and Pd/C catalysts at the anode and cathode, respectively, is developed. Experimental results demonstrate that the direct ammonia fuel cell exhibits a peak power density of 20.7 mW cm-2and an open-circuit voltage of 0.67 V at 95 °C when fed with 3.0 M ammonia and 3.0 M KOH. Besides, the durability test results reveal that the developed direct ammonia fuel cell can maintain stable operation for more than 25 h. In addition, the effects of operating parameters, such as the concentrations of ammonia and KOH, flow rates of anolyte and oxygen, and operating temperatures on the cell performance, are experimentally examined. A higher KOH concentration is observed to increase the cell voltage by enhancing the kinetics of ammonia oxidation, which is facilitated by the higher concentration of OH-in the catalyst layer. However, increasing the KOH concentration leads to higher internal resistance in the cell as a result of the increased viscosity of the anolyte. Besides, the analysis of results suggests that a moderate flow rate of both anolyte and gaseous oxygen can also enhance the cell performance by reducing ammonia crossover and preventing membrane dehydration, respectively. Moreover, increasing the operating temperature of the cell also promotes the kinetics of the electrochemical reactions at the catalyst layers, which is also associated with an enhanced mass transfer within the electrodes. In summary, a direct ammonia fuel cell, using an anion exchange membrane, with relatively high performance has been developed. The study provides insights into the performance-enhancing strategies, via operating conditions, toward the further development of the cell.