Optimization of the Cathode Catalyst Layer for Boosting Direct Ammonia Fuel Cell Performance by Orthogonal Tests

Abstract

The design of the cathode catalyst layer (CCL) for the oxygen reduction reaction is critical to improving the performance of anion-exchange membrane-based direct ammonia fuel cells (AEM-DAFCs) due to the impact of ammonia crossover. Herein, the effects of three factors (cathode catalyst loading, binder type, and binder content) and their corresponding three levels on the CCL have been investigated to achieve optimal cell performance by the orthogonal test for the first time. CCLs are characterized by scanning electron microscopy, mercury intrusion porosimetry, and contact angle measurements, which further verify the reliability of the orthogonal test results. The results show the following order of influence on the cell performance: binder type > binder content > cathode catalyst loading. These factors affect the mass transport and the number of three-phase interfaces in the CCL by changing its thickness, surface morphology, pore structure, and hydrophobicity, thus affecting the cell performance. An AEM-DAFC with a champion peak power density (PPD) of 158.6 mW cm–2 has been achieved under the optimal combination of cathode catalyst loading (2 mg cm–2), binder type (poly(tetrafluoroethylene) (PTFE)), and binder content (15 wt %). This work provides an alternative avenue to improve the performance of AEM-DAFCs using state-of-the-art catalysts and binders through rapid optimization of the CCL structure in the future.