New amphiphilic semi-interpenetrating networks based on polysulfone for anion-exchange membrane fuel cells with improved alkaline and mechanical stabilities

As considerable advance has recently been made in enhancing the conductivity of anion-exchange membranes, durability has become the critical requirement in the development of fuel cells. Such properties often develop at the expense of the other. In this work, new amphiphilic semi-interpenetrating networks composed of free polysulfone and crosslinked polysulfone are synthesized for the first time. The same nature of both polymers makes them highly compatible. The free polymer provides the hydrophobic component, whereas the crosslinked polysulfone, functionalized with trimethylammonium, 1-methylimidazolium, or 1,2-dimethylimidazolium groups, is responsible for the ionic conductivity. The compatibility between both components in the blend, improves the mechanical properties, while unaffecting the transport properties. Thus, the obtained membranes exceed the mechanical behaviour of commercial materials, even in conditions of extreme humidity and temperature. The tensile strength of these synthesized membranes can reach to relatively high values, and when compared to the commercial PSU, the difference in tensile strength can be noted to be as low as 10%. Moreover, the tensile strength and the ductility values of the crosslinked PSU are higher than those obtained with non-crosslinked PSU. Furthermore, the membranes presented in this work show a great alkaline stability (e.g. semi-interpenetrating network containing 1,2-dimethylimidazolium maintains 87% of the ionic conductivity after 14 days of treatment). Thus, these membranes provide an improvement in the durability limiting factors, in comparison to functionalized polysulfones, fulfilling the requirements to be used as electrolytes in anion-exchange membrane fuel cells.