A durable anion conducting membrane with packed anion-exchange sites and an aromatic backbone for solid-state alkaline fuel cells

Abstract

Contemporary design strategies aimed at developing highly functional anion conducting membranes (ACMs) for solid state alkaline fuel cell (SAFC) applications are often hampered by intrinsic limitations such as less efficiency in controlling swelling, declined alkaline durability, high fuel cross-over and/or poor stability against OH radicals especially for polyelectrolytes composed of aliphatic chains. Hence, it is a challenging task to develop an ACM that satisfies all pre-requisites: high conductivity, alkaline durability, chemical stability and very low fuel cross-over for successful SAFC applications. Here we present the systematic design of a simple molecular architecture based on the benzyl ammonium group and benzene without a hetero atom segment as a promising alkaline durable ACM with high anion conductivity. We have designed a new monomer 1,3,5-tri[p-(N′,N′′-dimethylaminomethyl)phenyl]benzene (TDAMPB) with three tertiary amino groups that generates poly-TDAMPB (PTDAMPB) with three anion-exchange sites per molecule upon in situ cross-linking. This highly cross-linked aromatic polyelectrolyte could generate highly packed anion-exchange sites by polymerization in the pores of a porous substrate and thereby presents an imperative solution for the existing challenges associated with current SAFC membranes. The PTDAMPB membrane performances were compared with an aliphatic poly(vinylbenzyltrimethyl ammonium chloride) (PVBTAC) membrane. The results demonstrate that the PTDAMPB membrane exhibited high OH⁻ ion conductivity similar to PVBTAC membranes, but exceptionally low methanol permeability and low swelling while maintaining good durability against hot alkali, boiling water and oxidative decomposition in contrast to PVBTAC. The functionalities of the PTDAMPB membrane satisfy the anticipated requirements for a viable SAFC, which is difficult to attain simultaneously for a conventional anion-conducting membrane and hence the results of this work address a major unresolved challenge representing an advancement toward successful SAFC applications.