Poly-Hydroxyethylidene-1,1-Diphosphonic Acid (Phedp) As A Highly Effective Water -Retentive And Proton -Conductive Material For Low -Humidity Proton Exchange Membranes

To improve the proton conductivity and fuel cell performance of a perfluorosulfonic acid (PFSA) membrane under low-humidity conditions, a series of poly-hydroxyethylidene-1,1-diphosphonic acid (PHEDP) materials are designed and synthesized through a self-polycondensation reaction. Self-humidifying proton exchange membranes are fabricated by combining PHEDP with commercial PFSA resin, then optimized by using various amounts of PHEDP. The experimental results show that the PHEDP/PFSA composite membrane provides a proton conductivity of up to 28.2 mS cm−1 at 30% RH and up to 13.6 mS cm−1 at 10% RH, which are respectively 5.6 and 13.6 times higher than a pristine PFSA membrane, and 4.5 and 6.8 times higher than a commercial Gore 740 membrane. In addition, the PHEDP/PFSA composite membrane exhibits superior fuel cell performance and low ohmic resistance under low relative humidity. The results show that the PHEDP/PFSA composite membrane's superior performance arises from its ability to absorb and retain more water in the membrane, enhance water transport from cathode to anode, and form new proton transport channels, indicating that the PHEDP/PFSA composite membrane has great potential for application in low relative humidity.