Sulfonated Low-Cost Ionomers as Acidic Cross-Linkers for High-Temperature PBIOO Membranes

Abstract

The low-cost polymers poly(styrene) and poly(α-methylstyrene) have been sulfonated in a first step. Then both sulfonated ionomers have been blended with PBIOO® (30 wt% sulfonated ionomer, 70 wt% PBIOO), the sulfonated ionomer serving as acidic cross-linker which enhances the PBIOO stability. Both membrane types were treated with Fentons Reagent to investigate their oxidative stability. Of particular interest was whether the poly(α-methylstyrene) ionomer was more stable against radical attack. It was indeed found that the PBIOO-sulfonated poly(α-methylstyrene) blend membrane showed less weight loss during and after Fenton Test than the respective poly(styrene sulfonic acid) PBIOO-containing membrane. The macromolecules are partially degrading by radical attack to the main chain of the sulfonated poly(α-methylstyrene) polymers but still remain in the blend membrane matrix due to acid-base interactions. Since the PBIOO/sulfonated poly(α-methylstyrene) blend membranes conserved their integrity even after Fentons Test they can be regarded as interesting low-cost high-T fuel cell membranes.

Monomers, Polymers and Cross-Linked Membranes for Membrane Fuel Cells and Electrolysis

“…For achievement of proton conduction these membranes have to be doped with phosphoric acid in excess since phosphoric acid shows a significant proton self-conductivity (21). It has been demonstrated in previous experiments that pure PBIOO can dissolve in an excess of phosphoric acid at elevated temperatures of >100°C, while PBIOO blend membranes with sulfonated polymers do not dissolve under these conditions which makes their application to intermediate-T fuel cells favourable (22). Those PBI-excess blend membranes which are displayed in Table 1 have been tested in terms of radical stability by immersion in Fenton´s Reagent for up to 120 h (8).…”