A review on nano-micro structure design of fuel cells for efficient heat and mass transport

Proton Exchange Membrane Fuel Cells (PEMFCs) are a cornerstone technology for the emerging hydrogen economy, yet their performance and durability are fundamentally dictated by the intricate interplay of heat and mass transport within the Membrane Electrode Assembly (MEA). Pervasive challenges such as water flooding, membrane dehydration, and local hot spots are direct consequences of mismanaged water, gas, and thermal gradients in the cell's porous microstructures. Therefore, mastering these transport phenomena through rational microstructural design and engineering of the MEA is the most critical approach to breaking current performance barriers. This review charts the recent progress in microstructure engineering aimed at optimizing these transport processes. Our focus is on two critical functional layers. In the Gas Diffusion Layer (GDL), we discuss strategies that create synergistic pathways for reactant delivery and water removal by engineering graded porosity and controlled wettability. In the Catalyst Layer (CL), we explore beyond conventional ionomer optimization to highlight a paradigm shift: the transition from disordered electrodes to highly ordered architectures like nanowire and nanotube arrays. These structures dramatically lower mass transport resistance by providing low-tortuosity, direct pathways, thereby significantly boosting the ultimate power density of the cell. Understanding the underlying structure-property correlations is key. We touch upon the advanced tools enabling this, from in-situ visualization techniques like X-ray CT and neutron imaging to multi-scale simulations that offer mechanistic insights and guide future design. However, significant hurdles remain, chiefly the scalable and cost-effective manufacturing of advanced structures with proven long-term durability. We conclude with a forward-looking perspective, identifying Additive Manufacturing (3D printing), machine learning-driven design, and bio-inspired concepts as powerful catalysts that will accelerate the development of next-generation, high-performance, and durable fuel cells. Ultimately, this review serves as a comprehensive and forward-looking guide for the research community.