Impact of the SG phase morphology on the performances and durability of hybrid polymer membranes for fuel cell applications

Abstract

International audienceProton-Exchange Membrane Fuel Cells (PEMFC) has emerged as a promising emission-free energy conversion device. However, the ionomer membrane at the heart of the device fails to deliver durable performance (to be achieved: 8000h for transportation, 50000h for stationary) at high temperature (100-150°C vs 80°C for std. Nafion) and low relative humidity (30%RH). The aim of our work is to improve existing membranes (better chemical and thermomechanical stabilities, better conductivities) by Sol-Gel (SG) hybridization. SG precursors are selected to diffuse through commercial membranes and introduce stabilizing organo-functional groups offering either a sacrificial stabilization (consumed over time) or a redox stabilization (regenerable) by degrading oxidizing agents produced during Fuel Cell operation. As the morphology (size, interaction/dispersion, connectivity) and localization (polar/apolar regions) of the SG phase inside the host matrix are parameters expected to be crucial for properties (H+ conductivity, water uptake), durability (H2O2-accelerated aging tests to assess the effectiveness of the reactive SG phase) and performances (FC operation) of the hybrid membranes, we explored their morphology at all relevant length scales. In this purpose, we use a combination of direct space (AFM/SEM/TEM) and reciprocal space (contrast variation SANS/SAXS) techniques (dimensional scale covered: from a hundred to a few nanometers) with regard to the chemistry of the SG Precursors (SGPs) (stabilization group, number of hydrolysable functions), yielding a variety of morphology (mass fractal structure vs. dispersed spherical aggregates vs. interconnected ones). H2O2-accelerated aging tests and preliminary fuel cell tests show promising operability of the hybrid membranes and the potential of the SG phase to inhibit the chemical ageing of sPEEK. With this work, we are confident to reach a predictive approach of the key parameters governing the final properties