# Enhancing Hydration Stability and Proton Transport in Nafion/SiO2 Membranes for Medium- to High-Temperature PEMFCs

## TL;DR

This paper improves the performance of fuel cell membranes at high temperatures by adding SiO2, enhancing water retention and proton conductivity.

## Contribution

The study introduces a sol–gel-assisted method to fabricate Nafion/SiO2 membranes with optimized hydration and proton transport.

## Key findings

- SiO2 incorporation enhances hydration stability and suppresses polymer crystallinity.
- Nafion/SiO2-3 membrane achieves 61.9 mS·cm−1 conductivity at 120 °C and 50% RH.
- Single-cell tests show 11.2% higher open-circuit voltage and 8.9% higher power density compared to Nafion.

## Abstract

Perfluorosulfonic acid (PFSA) membranes suffer from severe conductivity decay caused by dehydration at elevated temperatures, hindering their application in medium- to high-temperature proton exchange membrane fuel cells (MHT-PEMFCs). To address this, Nafion/SiO2 composite membranes with systematically varied filler contents were fabricated via a sol–gel-assisted casting strategy to enhance hydration stability and proton transport. Spectroscopic and microscopic analyses reveal a homogeneous nanoscale dispersion of SiO2 within the Nafion matrix, along with strong interfacial hydrogen bonding between SiO2 and sulfonic acid groups. These interactions effectively suppress polymer crystallinity and stabilize hydrated ionic domains. Thermogravimetric analysis confirms markedly improved water retention in the composite membranes at intermediate temperatures. Proton conductivity measurements at 50% relative humidity (RH) identify the Nafion/SiO2-3 membrane as exhibiting optimal transport behavior, delivering the highest conductivity of 61.9 mS·cm−1 at 120 °C and significantly improved conductivity retention compared to Nafion 117. Furthermore, single-cell tests under MHT-PEMFC conditions (120 °C, 50% RH) demonstrate the practical efficacy of these membrane-level enhancements, with the Nafion/SiO2-3 membrane exhibiting an open-circuit voltage and peak power density 11.2% and 8.9% higher, respectively, than those of pristine Nafion under identical MEA fabrication and operating conditions. This study elucidates a clear structure–property–transport relationship in SiO2-reinforced PFSA membranes, demonstrating that controlled inorganic incorporation is a robust strategy for extending the operational temperature window of PFSA-based proton exchange membranes toward device-level applications.