Tröger's base reinforced poly(oxindole biphenylene) membranes for high-temperature proton exchange membrane fuel cells with superior dimensional stability and durability

PIB reinforcement dramatically suppresses severe swelling of pure TB at high temperatures. • Intermolecular N H···N hydrogen bonds ensure good compatibility and structural integrity of the blend. • The PIB/TB-2/8 membrane achieves a proton conductivity of 102 mS cm −1 at 180 °C. • Superior durability with low voltage decay is achieved at 160 °C for 900 h and at 200 °C for 800 h. The development of high-temperature proton exchange membranes based on Tröger's base (TB) is constrained by severe dimensional instability and fuel barrier deterioration caused by high phosphoric acid (PA) doping levels. To overcome these limitations, we introduce a physical blending strategy using poly(oxindole biphenylene) (PIB), a highly stable ether-free aromatic polymer. Theoretical calculations and experimental analyses confirm excellent compatibility between PIB and TB, with intermolecular hydrogen bonding contributing to membrane integrity. The optimized PIB/TB-2/8 membrane exhibits outstanding oxidative stability, retaining 80% of its mass after more than 500 h of Fenton's test. Despite a lower PA uptake, the membrane maintains exceptional dimensional stability at temperatures ranging from 160 °C to 200 °C and achieves a proton conductivity of 102 mS cm −1 at 180 °C under anhydrous conditions. In single-cell tests, the blend membrane delivers a peak power density of 432.5 mW cm −2 at 160 °C and demonstrates superior fuel barrier performance over pure TB, as evidenced by a lower hydrogen permeation current density and a stable open-circuit voltage during accelerated stress cycling. Notably, the hydrogen permeation current density is also substantially lower than those of previously reported HT-PEMs, further confirming the exceptional fuel-barrier capability of the blend. More importantly, the PIB/TB-2/8-based single cell operates steadily for 900 h at 160 °C with a voltage decay rate of 98.8 μV h −1 , and for over 800 h at 200 °C with a decay rate of 75 μV h −1 . The work provides a practical blending solution that simultaneously improves dimensional stability, durability, and fuel barrier performance without compromising proton conductivity, marking a key advancement for the practical application of durable high-temperature proton exchange membrane fuel cells. PIB/TB blending via hydrogen bonding achieves high conductivity, excellent stability, and exceptional durability for HT-PEMFCs. Download: Download high-res image (188KB) Download: Download full-size image