Spatial porosity design of Fe-N-C catalysts for high power density PEM fuel cells and detection of water saturation of the catalyst layer by a microwave method

The porous structure is essential for non-precious metal catalysts (NPMCs) to achieve high utilization of active sites and efficient mass transfer in proton exchange membrane fuel cells (PEMFCs). Here, submicron Fe-N-C catalyst particles with three representative types of micropore/mesopore distributions are prepared to investigate the effects of the spatial porosity of the catalyst on fuel cell performance. A microwave detection method is used to monitor the water saturation in the catalyst layer. The structure of the mesoporous surface/microporous core is demonstrated to be the optimal spatial porosity, and the related Fe-N-C catalyst achieves a high PEMFC power density of 1.08 W cm⁻² under only 1.5 bar H₂-O₂. By comparison with fully microporous and fully mesoporous particles, it is found that the mesoporous surface has advantages in improving the number, accessibility, and utilization of active sites, while the microporous core enables the catalyst to avoid the core flooding that occurs in fully mesoporous particles. This study identifies the optimal porosity of NPMCs and proposed a microwave detection method to analyze the water saturation in the electrodes.