A new high temperature polymer electrolyte membrane based on tri-functional group grafted polysulfone for fuel cell application

Abstract

One critical issue for the application of high-temperature polymer electrolyte membranes (HT-PEMs) is to obtain good balance between their proton conductivities and mechanical strength. In this work, a novel strategy has been developed to achieve the balance by increasing the number of functional groups in the grafting site of the side chain of polysulfone (PSU). 2,4,6-tri(dimethylaminomethyl)-phenol (TDAP) with three tertiary amine groups was grafted on PSU (TDAP-PSU) to achieve higher phosphoric acid (PA) uptake at a lower grafting degree. Moreover, the bundle of amine groups in one grafting site reduces the volume swelling compared to the single tertiary amine group grafted PSU membrane (DMA-PSU). Thereby, the TDAP-PSU membrane with 75% grafting degree achieves comparable PA uptake with the DMA-PSU membrane with 99% grafting degree, whereas the mechanical strength of former membrane after PA doping is 2.2 times higher than that of the later one after PA doping. Moreover, single cells based on the TDAP-PSU membrane reach the peak power density of 453 mW cm−2 and excellent stability without external humidification. Overall, increasing the number of active groups in the grafting site of the polymer side chain is a promising strategy to deal with the trade-off between the proton conductivity and membrane dimensional stability of HT-PEMs.