Metal organic framework–derived, N–C–SO₃H/COOH–incorporated, phenolphthalein-based propyl sulfonated poly(arylene ether) composite membranes for proton exchange membranes in fuel cells

The proton exchange membrane (PEM) is a critical component of fuel cells, but balancing mechanical stability while maintaining high proton conductivity remains a challenge. Organizing functional groups to improve interactions has become a popular pursuit in recent years. Capitalizing on these advances, we prepared phenolphthalein-based propyl sulfonated poly(arylene ether) containing a sulfonated aliphatic side-chain (SPAEPP) polymer and incorporated metal organic framework–derived SO₃H- and -COOH–functionalized nitrogen-doped porous carbon (N–C–SO₃H/COOH). SPAEPP, along with composite membrane containing N–C–SO₃H/COOH at various weight percentages demonstrated improved mechanical and electrochemical activities. Continuous hydrophilic-hydrophobic polymer networks typically expedite the proton transformation of the composite's PEM, allowing proton conductivity to reach 145 mS cm⁻¹ at 90 °C and a relative humidity of 100 %, which is twice that of pristine SPAEPP. The SPAEPP/N–C–SO₃H/COOH composite membrane achieved a power density of 0.57 W cm⁻², outperforming SPAEPP and commercial Nafion 212. The optimized SPAEPP/N–C–SO₃H/COOH membrane demonstrated long-term durability with minimal loss of power over 120 h of continuous operation and no degradation of catalyst-membrane morphology. The efficient proton-conduction ability and admirable power performance of the SPAEPP/N–C–SO₃H/COOH membrane suggests a potential use for metal organic framework derivatives and phenolphthalein-based polymers as efficient PEMs in fuel cells as part of a sustainable energy portfolio.