Magnetic Field-Induced Through-Plane Alignment of the Proton Highway in a Proton Exchange Membrane

J Hyun and G Doo and S Yuk and DH Lee and DW Lee and S Choi and J Kwen and H Kang and R Tenne and SG Lee and HT Kim, ACS APPLIED ENERGY MATERIALS, 3, 4619-4628 (2020).

DOI: 10.1021/acsaem.0c00289

Proton exchange membranes with high through-plane proton conductivity are a critical component of high-performance fuel cells, electrolyzers, and batteries. However, isotropically distributed proton-conducting channel structures of current membranes present a limitation. Herein, a proton exchange membrane with straight proton-conducting channels aligned in the thickness direction is fabricated, achieved by magnetic field-induced alignment of proton-conductive, paramagnetic, and one- dimensional (1D) tungsten disulfide nanotubes (pms-WS2) distributed in a perfluorinated sulfonic acid (Nafion) membrane. The pms-WS2 nanotubes feature straight WS2 nanotubes as a core, a polystyrenesulfonate (PSS) skin layer, and surface-decorated Fe3O4 nanoparticles. A molecular dynamics simulation suggests that straight proton-conducting channels are constructed at the interface of Nafion/pms-WS2 due to densely populated sulfonic acids. Spectroscopic investigation and magnetization measurements verify the through-plane alignment of pms-WS2 under a weak through-plane magnetic field (0.035 T) during the removal of solvent from the membrane cast. Compared with a recast Nafion membrane with the same thickness, the through-plane aligned composite membrane exhibits 69% higher proton conductivity and 51% higher power performance in a proton exchange membrane fuel cell, demonstrating its efficacy. The through-plane alignment of a proton-conductive inorganic 1D material promises improved power performance of advanced electrochemical devices.

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