# Orientation Control of Perfluorosulfonic Acid Films via Addition of 1,2,4-Triazole during Casting

## TL;DR

Adding 1,2,4-triazole during casting controls the structure of PFSA films, improving proton conductivity in specific directions for better fuel cell performance.

## Contribution

A novel method to control ion-cluster orientation in PFSA films using 1,2,4-triazole during casting is introduced.

## Key findings

- Proton conductivity was higher along the film surface and lower through the film thickness.
- Anisotropic ion-cluster structures formed due to phase separation and bonding with 1,2,4-triazole.
- Surface segregation of fluorine contributed to the observed structural anisotropy.

## Abstract

Perfluorosulfonic acid (PFSA) polymers are used as electrolyte membranes in polymer electrolyte fuel cells. To investigate the effect on proton conductivity through structural orientation control, we added 1,2,4-triazole to PFSA films during casting to impart anisotropy to the ion-cluster structure of the films. The proton conductivities of the films were found to be high in the film-surface direction and low in the film-thickness direction. Structural analysis using small-angle X-ray scattering suggested that the anisotropy in proton conductivity was due to anisotropy in the ion-cluster structure, which in turn was attributed to the formation of a phase-separated structure via strong bonding between sulfonic acid groups and 1,2,4-triazole during cast film formation and the surface segregation of fluorine. We expect the findings of this study to aid in the fabrication of PFSA films with controlled ion clusters.