Advances and challenges in porous electrodes of proton exchange membrane fuel cells with enhanced mass transport performance: from ordered structures to integrated structures

ABSTRACT An ultrahigh power density requires proton exchange membrane fuel cells (PEMFCs) to operate stably with a high output voltage at an elevated current density, which enhances the mass transport efficiency of the porous electrodes. Conventional PEMFC electrodes, especially the cathode electrode, suffer from limited catalyst utilization and sluggish mass transport owing to their random pore structure and tortuous transport pathways. Systematic optimizations of the electrode components and structures are well recognized as an effective strategy for addressing the corresponding mass transport limitations and challenges. In this review, recent advancements in improving the mass transport efficiency and PEMFC performance at high current density through the optimization of electrode structure are comprehensively evaluated, specifically focusing on the ordered structures and integration of the gas diffusion layer (GDL) and catalyst layer (CL). The key mechanisms of oxygen transport resistance in the GDL and CL were firstly explored, which provided a theoretical basis for the structural design and fabrication of porous electrodes with enhanced mass transport efficiency. Strategies for enhancing the mass transport efficiency of GDL, including the proposal of gas-liquid separation through wettability gradient design, oxygen distribution uniformity enhancement via ordered pore structure, and controllable nanostructure manipulation through electrospinning techniques, are summarized. Meanwhile, strategies for synergistically boosting oxygen mobility and catalyst utilization in CL are mainly focused on precise manipulations of hierarchical pore structures, ordered array nanostructures, and fiber arrangement architectures. Moreover, an integrated electrode was proposed to enhance the mass transport efficiency by reducing the tortuous transport pathways. For instance, an integrated GDL-free design can reduce oxygen transport resistance by 55% and concentration loss by 88.6%, resulting in a 43% increase in power density at 0.6 V. Finally, the potential advantage of porous electrode with ordered and integrated structure is discussed, and the integration of porous electrode and porous flow field is presented to provide guidance for the further development and commercialization of the next-generation PEMFCs with ultrahigh power density.