A review of the microporous layer in proton exchange membrane fuel cells: Materials and structural designs based on water transport mechanism

Proton exchange membrane fuel cells (PEMFCs) have exhibited great potential as future electrochemical devices to power a wide scope of applications. Despite recent rapid progress in optimizing the individual component such as catalyst and membrane, efficient water management has been relatively underexplored. Improper water loading raises various issues including material degradation and local reactant starvation, which accordingly compromises the long-term durability of the cell. Introducing the microporous layer (MPL) to the gas diffusion layer (GDL) has been demonstrated as an effective strategy to resolve these issues by promoting smooth gas and water transport. Here, we summarize recent progress on the materials and structural designs of MPL, as well as investigations involving the correlated water transport behaviors. Influence of the key parameters of MPL including pore size, porosity, thickness, hydrophobicity and hydrophilicity, and surface morphology are thoroughly discussed from both mechanistic and performance-driven perspectives. We also highlight the employment of advanced fabrication and characterization techniques, which afford important insights into the prevention of water flooding and membrane dehydration. We hope the efforts presented here can guide rational material design and exquisite structure engineering of MPL, which will set the stage for future research in this area and beyond.