(A) magnetic field-induced through-plane alignment of proton highway in proton exchange membrane

Abstract

Proton exchange membranes with high through-plane proton conductivity are enormously required for high performance fuel cells, electrolyzers, and batteries. However, isotropically-distributed proton-conducting channel structures of current membranes presents a limitation. Herein, we report a proton exchange membrane with straight proton-conducting channels aligned in thickness direction, achieved by magnetic field-induced alignment of proton-conductive, paramagnetic, one-dimensional tungsten disulfide nanowires (pms-$WS_2$) distributed in a perfluorinated sulfonic acid (Nafion) membrane. The pms-$WS_2$ nanowires feature straight $WS_2$ nanowire as a core, polystyrenesulfonate (PSS) skin layer, and surface-decorated $Fe_3O_4$ nanoparticles. Molecular dynamics simulation suggests that straight proton-conducting channels are constructed at the interface of Nafion/pms-$WS_2$ due to densely populated sulfuronic acids. Spectroscopic investigation and magnetization measurement prove the through-plane alignment of of pms-$WS_2$ under a weak through-plane magnetic field (0.035 T) during the removal of solvent from membrane cast. Compared with a recast Nafion membrane with same thickness, the through-plane aligned composite membrane exhibits 70% higher proton conductivity and 110% higher power performance in proton exchange membrane fuel cell, demonstrating its efficacy. We identify the through-plane alignment of proton-conductive inorganic 1D material promising for improving power performance of advanced electrochemical devices.