Radiation grafted membranes for superior anion exchange polymer membrane fuel cells performance

A study of radiation grafted polymers on the conductivity and performance of alkaline anion exchange membrane fuel cells (AAEMFCs) is reported. The aminated poly (LDPE-g-VBC), poly (HDPE-g-VBC) and poly (ETFE-g-VBC) membranes were produced by the using the radiation grafting technique. Differences in grafting behaviour are observed between the studied materials caused by differences in the base polymer film properties as molar mass, crystallinity, orientation or grafting technique used. In plane conductivities increased with Degree of Grafting DOG. At a DoG of 68% the LDPE-g-VBC membrane achieved an in-plane ionic conductivity between 0.18 and 0.32 S cm(-1) in the temperature range 20-80 degrees C. Measured through plane conductivities were lower than that of the in plane ones for all studied membranes. Membranes with the highest degree of swelling showed the highest through plane conductivity of 0.07-0.11 S cm(-1). The membrane specific resistance (per MEA cm(2)) of most of the produced membranes was in the range of 0.09-0.18 Omega cm(2). While membrane conductivity and hence IR loss is a crucial factor in fuel cell performance, membrane water permeability is a similarly crucial key for optimised water transport to the cathode. The main source of performance loss of AAEMFCs is believed to be restricted mass transport of water to the cathode reaction sites. The highly humidified anode stream along with large amount of water produced at the anode at high current densities could lead to flooding if water is not removed quickly to the cathode via the membrane (back diffusion) where it is consumed. High peak power densities were obtained, at a high potential of 500 mV, the highest reported yet in the literature for AAEMFCs of 823 mW cm(-2) at 60 degrees C, 718 mW cm(-2) at 50 degrees C and 648 mW cm(-2) at 20 degrees C under oxygen (atm). Peak power densities with air were also high; 424, 451 and 471 mW cm(-2) at cell potential of 0.6 V at 40, 50 and 60 degrees C, respectively. These values are similar to the maximum power density reported for proton exchange membrane fuel cells using Nafion at 80 degrees C with oxygen using the same catalyst loading. This highlights the major importance of radiation grafted membranes for AAEMFCs. The advantage of AAEMFCs over PEMFC is clearly demonstrated with enhanced ORR kinetics and superior performance and power output. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.