Designer diffusion media microstructures enhance polymer electrolyte fuel cell performance

Gas diffusion media are essential components in polymer electrolyte membrane fuel cells and a broad range of electrochemical technologies, enabling efficient mass transport of gas and liquid, electronic and thermal conductivity, and structural integrity under compression. Conventional diffusion media, typically made from carbon fiber substrates with microporous layers, have been extensively post-treated to enhance performance; however, these approaches offer limited control over three-dimensional microstructure, particularly for advanced architectures with bimodal or gradient porosity - which can facilitate multiphase gas and liquid mass transport - and often rely on complex, multi-step processes. These limitations underscore the need for scalable, cost-effective fabrication methods capable of producing much broader geometrical features. Here, we introduce a scalable, bottom-up fabrication method based on non-solvent induced phase separation (NIPS) to produce carbon-based diffusion media with finely tunable microstructures. By systematically varying processing parameters, we generate thin, mechanically robust diffusion media with tailored in-plane and through-plane porosity, including isoporous and bimodal structures. Using microscopy, porosimetry, and electrochemical diagnostics, we correlate microstructural features with single-cell fuel cell performance, revealing their impact on water management and gas transport. We further demonstrate post-treatment strategies to enhance mass transport properties and benchmark the cost and scalability of NIPS fabrication against conventional carbon fiber-based diffusion media via techno-economic analysis. Our findings highlight the potential of NIPS as a versatile and industrially relevant pathway for next-generation diffusion media, offering new design freedoms to optimize fuel cell performance and reduce system-level costs.