Catalyst layer (CL) is the major component of proton exchange membrane fuel cells (PEMFCs) and routinely fabricated by a catalyst ink-based processing method. Such conventional CLs typically confront low activity, unaffordable Pt loading, and severe mass transport issues due to the thick and disordered structure, hampering the widespread commercial application of PEMFCs. Engineering of nanostructured CLs with low/ultralow Pt loading, ordered and/or ultrathin CLs, provides a highly promising pathway for overcoming these limitations. For the practical application of the nanostructured CLs in PEMFCs, this review comprehensively summarizes and comments on the important research and development of nanostructured CLs over recent years, involving ordered electronic conductor-based CLs, ordered ionomer-based CLs, and ultrathin CLs. The reviewed processes include (i) analyzing the motivation and necessity to design and fabricate nanostructured CLs based on the structure and mass transport process of conventional CLs, (ii) scrutinizing structure and composition, preparation methods, advantages, as well as some feasible strategies for the remaining challenges of various nanostructured CLs in detail, (iii) the progress of single cell activity and durability of the nanostructured CLs. Finally, some perspectives on remaining challenges and future development of the nanostructured CLs are presented to guide the exploitation for the next-generation of advanced CLs of PEMFCs. © 2025 Elsevier B.V.
