Polyethylene-based radiation grafted anion-exchange membranes for alkaline fuel cells

Abstract

Vinyl benzyl chloride was grafted onto ultra-high molecular weight polyethylene powder (UHMWPE) by radiation grafting. The grafted powder was subsequently fabricated into membrane by melt pressing. The effect of absorbed radiation dose on the degree of grafting (DG) is discussed. The melt-flow properties of PVBC grafted PE with low degree of grafting was conducive to forming homogeneous pore-free membranes, which was confirmed by scanning electron microscopic analysis. The grafted polyethylene membranes were post functionalized with trimethylamine, followed by alkalization to obtain anion-exchange membranes (AEMs). The structures of the resulting AEMs were characterized by Fourier transform infrared spectroscopy, which showed that the grafted membranes were successfully functionalized. The properties of the AEMs, including ion exchange capacity, water uptake, in-plane swelling, methanol uptake, methanol permeability and hydroxide ion conductivity were investigated. The AEMs showed reasonably good chemical stability, as evidenced by the ion exchange capacity being maintained for a long duration, even in highly alkaline conditions. The membranes exhibited a maximum ionic conductivity of 47.5mScm−1 at 90°C (30mScm−1 at 60°C). Methanol permeability was found to be in the order of 10−8cm2s−1, which is considerably lower than that of Nafion®. The membranes have useful properties consistent with anion exchange membranes suitable for alkaline fuel cells.