New proton conducting membranes with high retention of protic ionic liquids

Abstract

New proton conducting membranes, exhibiting a high proton conductivity (10(-2) S cm(-1), without humidification at 160 degrees C), based on the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate (BMIm-BF(4)) were investigated. The incorporation of a similar initial IL loading was found to reduce the proton conductivity loss of a sulfonated polydiacetylene based membrane, i.e. SPDA70-IL70 by 19.2% and IL-based Nafion by 64.6%; additionally, the SPDA70-IL70 was able to maintain a proton conductivity of more than 10(-3) S cm(-1) after centrifugation. The introduction of both a cross-linked structure and a high degree of sulfonation into the polymer matrix, resulted in significant improvements to the membranes' thermal properties, the dispersion of ionic domains, and the retention of IL-together with a reduction of proton conductivity loss. The membranes, which have a high degree of sulfonation with thermally cross-linkable diacetylene in the polymer's main chain, avoid the drawback of poor miscibility commonly associated with sulfonated polymers and cross-linking agents. When the composite membrane was used in a H(2)/O(2) fuel cell without humidification at 100 degrees C, a power density > 250 mA cm(-2) was achieved together with a maximum current denisty of 122 mW cm(-2).