Abstract: Ion-exchange membrane fuel cells (IEMFCs) and ion-exchange membrane water electrolyzers (IEMWEs) have become the focus of research in the field of clean energy conversion. However, the problem of membrane and electrode species transport is still a bottleneck for their industrialization. Biological behavior in nature provides valuable insights into the design of energy conversion devices. The phenomenon in which fish groups achieve efficient passage through orderly arrangement reveals the unique advantage of aligned transport structures in increasing the transport efficiency of species. This evolutionary law from disorder to order is reflected in energy devices as the oriented design of membrane electrode assemblies (MEAs). Conventional MEAs suffer from inefficient mass transport, catalyst agglomeration, and insufficient ion conductivity, which are rooted in transport disorder caused by isotropic channels. Novel uniaxial transport structures construct a directly connected path for ion conduction, gas diffusion, and water transport through-plane to the overall alignment of the MEAs, and this design significantly reduces the internal resistance and increases the energy density and conversion efficiency. Starting with ion-exchange membranes, this review describes the importance of overall alignment from membranes to electrodes for ion, gas, and water transport and systematically compares the differences in transport mechanisms among isotropic, anisotropic, and through-plane aligned structures. The synthesis methods and fabrication techniques for achieving these aligned transport architectures are summarized, and their structural stability and device stability are evaluated. The prospects for the industrialization of uniaxially oriented MEAs are envisioned, and possible solutions to existing challenges are proposed.

Key words: Aligned structure, Uniaxial transport, Membrane electrode assembly, Ion-exchange membrane, Fuel cell, Water electrolyzer