Influence of Operating Conditions and Cell Design on the Performance of Low-Temperature Direct Ammonia Fuel Cells

Abstract

This work investigates the effect of operating and cell design parameters on the performance of a low-temperature direct ammonia fuel cell (DAFC), employing an anion exchange membrane (AEM). The effects of temperature, ammonia and KOH concentrations, reactant flow rates, and air humidity are evaluated in a 5 cm2 DAFC. Temperature is identified as the most influential operating condition, with higher values enhancing electrochemical kinetics and membrane conductivity. Increased concentrations of both ammonia and potassium hydroxide solutions also tend to have a beneficial effect. The highest performance is achieved at 5 M NH4OH and 2 M KOH. Variations in feeding solution and air flow rates have a relatively small effect on the performance. At 40 °C, the relative humidity of the air (RHair) has no effect on the DAFC performance. At 60 °C, decreasing RHair from 100% to 75% increases performance, but no further benefit is observed with RHair of 50%. Among the membranes tested, FAS-30 exhibits the best performance, whereas Sustainion X37-50 grade RT performance is limited by high ammonia permeability. Although not directly compared, results indicate that bimetallic PtIr/C catalysts outperform Pt-based catalysts in the anode. Increasing the loading of the Pt and PtIr/C catalysts improves the activity of the electrode. Using PtIr/C electrodes in combination with a FAA-3-PK-130 membrane yields a peak power density of 12.2 mW·cm–2 at 80 °C. This study provides valuable insights into the operation and design of DAFCs, thereby contributing to the limited data currently available on this type of fuel cell.