Highly Anion Conductive, Alkyl-Chain-Grafted Copolymer as Anion Exchange Membrane for Operable Alkaline H2/O2 Fuel Cell
In order to obtain the anion exchange membranes (AEMs) with well-defined micro-phase separation and high ionic conductivity for operable akaline H2/O2 fuel cell, 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 small amount of (10 mol%) grafted alkyl chains induced well-defined micro-phase separation of obtained AEMs as confirmed by small-angle X-ray scattering (SAXS). Thus, the highest conductivity was observed for grafted PPO AEMs with 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 chain were failed to serve as anion exchange membrane for practical fuel cell.