Anion exchange membrane (AEM) fuel cells (FC) offer the advantage of having high power densities at operating temperatures of ca. 80 °C, along with the possibility of extending catalyst development beyond the platinum group metals at the cathode. For AEMFCs to become feasible, work is required on the development and scaling of the hydroxide-conducting AEMs. Radiation grafted (RG) AEMs are prepared using high energy radiation which promotes the grafting of comonomers onto a commercial precursor film. This project aims to reduce the variation observed in the synthesis of RG-AEMs, with a particular focus on the impact of precursor film crystallinity.

Density measurements showed that the crystallinity variation across 10 m rolls of commercially supplied high density polyethylene (HDPE) varied significantly (up to 17 % variation); this variation impacted the resulting RG-AEM properties including ion exchange capacity, conductivity and water uptake. When the precursor film had a degree of crystallinity of greater than 81 %, a threshold effect was observed where the variation in the resultant RG-AEM properties was reduced (improved consistency).

A thermal treatment method was developed which increased HDPE film crystallinity above 81 % with larger crystalline domains observed (measured using a rapid Raman mapping method specifically developed to visualise crystallinity at the μm spatial resolution). The distribution of crystalline lamellae sizes and orientations also increased (DSC, SEM, AFM data). The treated HDPE resulted in RG-AEMs with improved performance. The proportion of bulk water within the RG-AEM increased from 58 to 66 % on HDPE treatment, which led to improved conductivities and improved water management in a fuel cell environment. The optimised RG-AEMs achieved a AEMFC performance of 2.7 A cm-2 at 0.7 V compared to 2.1 A cm-2 for the benchmark, untreated, RG-AEM.