Highly anion conductive, alkyl-chain-grafted copolymers as anion exchange membranes for operable alkaline H2/O2 fuel cells

Abstract

In order to obtain anion exchange membranes (AEMs) with well-defined micro-phase separation and high ionic conductivity for operable alkaline H₂/O₂ fuel cells, we designed and prepared a series of alkyl-chain-grafted poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) AEMs containing side-chain-type quaternary ammonium (QA) groups via Cu(I)-catalyzed “click chemistry”. It has been demonstrated that a small amount of (10 mol%) grafted alkyl chains induced well-defined micro-phase separation of the obtained AEMs as confirmed by small-angle X-ray scattering (SAXS). Thus, the highest conductivity was observed for grafted PPO AEMs with an alkyl chain length of 16 carbon atoms (C-16). The side-chain-type QA groups gave the excellent alkaline stability of AEMs according to the change in hydroxide conductivity after alkaline stability testing. These quaternized, grafted copolymers were employed as membranes for alkaline H₂/O₂ fuel cells. The results suggested that the C-16 alkyl-chain-grafted membrane had a better initial performance due to its high hydroxide conductivity in spite of its lower IEC value or water uptake. In contrast, the corresponding comb-shaped copolymers having C-16 alkyl chains failed to serve as anion exchange membranes for practical fuel cells.