Effect of anion functional groups on the conductivity and performance of anion exchange polymer membrane fuel cells

Abstract

A study of the effect of anion functional group on the conductivity and performance of alkaline anion exchange membrane fuel cells (AAEMFCs) is reported.Membranes and ionomer were characterised in terms of ionic conductivity and separate anode, cathode and cell performances. TMA functionalised (LDPE-co-VBC) or PVBC offered the highest conductivity amongst the various selections of amine/sulphide-based functional groups with conductivities values up to 0.25 (in plane) and 0.043Scm−1 (through plane). Sulphide-based groups showed lower stability with temperature in comparison to amine-based groups. The increase in length of the chain in the aryl group attached to the nitrogen or sulphur led to lower conductivity. The high OH− conductivity in membranes functionalised with TMA is reflected by its low activation energy of 12kJmol−1; close to the reported value for H+ conductivity in Nafion.The ionomer functional groups affected oxygen permeability, the activation energy and the exchange current density for oxygen reduction. TMA functionalised ionomer provided an improved medium for the oxygen reduction reaction with exchange current density some 300 times higher than that with DMS. Anode flooding appeared to severely restrict cell performance and was determined by the type of functional group used for the ionomer. TMA functionalized electrodes showed superior cell performance with a current density of 0.722Acm−2 at 0.6V and a peak power density of 478mWcm−2.