Novel composite proton-exchange membrane based on silica-anchored sulfonic acid (SASA)

A new approach to the synthesis of a low-cost proton-exchange composite membrane (C-PEM) based on PVDF and silica with surface-anchored sulfonic acid (SASA) groups, is presented for the first time. SASA membranes of different compositions have been prepared and characterized with the use of SEM, DSC, TGA, BET and electrochemical techniques. The room-temperature conductivity of SASA-based C-PEMs, is in the range of 2.0-50 mS cm−1. The equivalent weight of two SASA powders, SASA3(A) and SASA4(A) are 1600 and 2500 g equiv.−1 respectively. The typical pore size as measured by BET is about 4 nm. The membrane is thermally stable up to 250 °C. Direct methanol fuel cells (DMFCs) have been assembled with some of the membranes. Preliminary tests show that the cell resistance with a non-optimized membrane is in the range of 3 Ω cm−2, therefore the maximum cell power density achieved so far does not exceed 32 mW cm−2 at 70 °C. The crossover-current density for a 100 μm-thick membrane DMFC measured in 1 M methanol at 80 °C is 110 mA cm−2.