为了改善M-N-C阴极催化层“水淹”和物质传输效率低的问题, 通过对催化层中全氟磺酸离聚物侧链上亲水性磺酸根的可控热解, 在催化剂活性位点原位调控亲疏水平衡, 优化催化层中质子、水和氧传输效率, 构建高效三相反应界面, 提升膜电极的输出性能与稳定性. 结果表明通过调节热处理温度和时间, 可以有效控制催化层离聚物侧链上磺酸根的热解程度. 以离聚物和Fe-N-C催化剂质量比(I/C)为0.5的催化层作为模型催化层, 在N₂气氛下250 ℃热处理40 min, 全氟磺酸离聚物中磺酸根分解比例为16.3%, 催化层疏水性显著提升, 表面水接触角由113°增加至134°, 同时催化层保持了较高的离子传导能力, 对应的膜电极输出性能最佳, 峰值功率密度达到359.7 mW•cm^－2, 较热处理前膜电极性能提升了38%. 在0.4 V恒压条件下测得热处理后催化层的物质传输电阻为242.48 mΩ•cm², 较热处理前下降了29.8%. 由热处理40 min催化层组装的电池性能衰减缓慢, 可以稳定运行至少100 h. 本研究工作探究了催化层中离聚物部分可控热解对提升M-N-C非贵金属膜电极燃料电池性能和稳定性的可行性.

Non-precious metal M-N-C catalysts have a low density of active sites, which requires increasing the catalyst loading amount per unit area to obtain sufficient active sites to ensure the required apparent output current of the proton exchange membrane fuel cells (PEMFCs). This inevitably increases the thickness of the catalytic layer. On the one hand, a thick catalytic layer increases the resistance to material transfer, and on the other hand, a thick catalytic layer is more prone to causing “flooding” problems, which further worsens the material transfer problem of the catalytic layer. To address the water flooding and material transfer efficiency challenges of Fe-N-C cathode catalytic layers, this study employed controlled pyrolysis of perfluorinated sulfonic acid ionomer side chains with hydrophilic sulfonic acid groups within the catalytic layer. The in-situ modulation of the hydrophilic-hydrophobic balance at the active sites of the catalyst creates an efficient three-phase interface, enabling high ion conductivity and efficient water and oxygen transport within the Fe-N-C catalytic layer. Consequently, the output performance and stability of the membrane electrode are significantly improved. The results demonstrate that the degree of sulfonic acid group pyrolysis within the catalytic layer ionomer can be effectively controlled by adjusting the pyrolysis temperature and duration. Using a catalytic layer with an ionomer to Fe-N-C catalyst mass ratio (I/C) of 0.5 as a model, the perfluorinated sulfonic acid ionomer's sulfonic acid group decomposition rate was 16.3% after 40 minutes of heat treatment at 250 ℃ under a N₂ atmosphere, resulting in an increased hydrophobicity of the catalytic layer surface, as indicated by a surface water contact angle increasing from 113° to 134° while maintaining high ion conductivity. The corresponding membrane electrode exhibited optimal output performance, with a peak power density of 359.7 mW• cm^－2, representing a 38% improvement over the pre-treatment electrode. Additionally, under a constant voltage of 0.4 V, the material transfer resistance of the heat-treated catalytic layer decreased by 29.8% to 242.48 mΩ•cm² compared to the pre-treatment condition. During the 20-hour constant voltage discharge test at 0.4 V, the heat-treated Fe-N-C catalytic layer exhibited higher discharge current density than the untreated membrane electrode. This study demonstrates that partially controlled pyrolysis of catalytic layer ionomer is an effective method for improving the performance and stability of M-N-C non-precious metal catalyst membrane electrode fuel cells.