Anisotropic membrane with high proton conductivity sustaining upon dehydration.

In fuel cells and electrolyzers, suboptimal proton conductivity and its dramatic drop at low humidity remain major drawbacks in proton exchange membranes (PEMs), including current benchmark Nafion. Sustained through-plane (TP) alignment of nanochannels was proposed as a remedy but proved challenging. We report an anisotropic composite PEM, mimicking the water-conductive composite structure of bamboo that meets this challenge. Micro- and nanoscale alignment of conductive pathways is achieved by in-plane thermal compression of a mat composed of co-electrospun Nafion and poly(vinylidene fluoride) (PVDF) nanofibers stabilizing the alignment. This translates to pronounced TP-enhanced proton conductivity, twice that of pure Nafion at high humidity, 13 times larger at low humidity, and 10 times larger water diffusivity. This remarkable improvement is elucidated by molecular dynamics simulations, which indicate that stronger nanochannels alignment upon dehydration compensates for reduced water content. The presented approach paves the way to overcoming the major drawbacks of ionomers and advancing the development of next-generation membranes for energy applications.