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The proton‐exchange membrane is a crucial component of proton‐exchange membrane fuel cells (PEMFCs), and its mass transfer plays a vital role in the performance and energy conversion efficiency of fuel cells. In this article, the fundamental structure and working principle of PEMFCs, as well as the microstructure of the membrane, are introduced. The mass‐transfer mechanism of the membranes is systematically sorted out from the model of mass transfer and the corresponding simulation method, and the mass transfer is quantitatively calculated from the macroscopic perspective. Additionally, methods to improve the mass‐transfer efficiency from both internal and external aspects are discussed. In conclusion, in this article, mass transfer in PEMFCs is comprehensively discussed and a valuable reference is offered for future research and development in this field. [ABSTRACT FROM AUTHOR]

Herein, Fe 3 O 4 @MnO 2 @Ni-Co/C composites derived from PBAs were successfully fabricated. Firstly, Ni-Co Prussian blue analogues (Ni-Co PBAs) were used as precursors to derive a carbon layer on their surface by annealing treatment and subsequently translated into MnO 2 @Ni-Co/C nanocubes after hydrothermal reactions. Fe 3 O 4 @MnO 2 @Ni-Co/C composites were finally obtained after depositing Fe 3 O 4 nanoparticles through the annealing process. Their electromagnetic wave (EMW) absorption performance apparently enhanced, thanks to the excellent impedance matching and strong attenuation derived from the synergy between the dielectric loss and the magnetic loss. In particular, the minimum reflection loss (RL min ) of Fe 3 O 4 @MnO 2 @Ni-Co/C reached -41.2 dB with a thickness of 4.0 mm and the effective absorption bandwidth (EAB) reached 7.1 GHz with a thickness of 2.0 mm. Therefore, the results could be significant for synthesizing EMW absorbers with excellent performance, a broad bandwidth, strong absorption, thin thickness and light weight.