Acid doped branched poly(biphenyl pyridine) membranes for high temperature proton exchange membrane fuel cells and vanadium redox flow batteries

Both high temperature proton exchange membrane fuel cell (HT-PEMFC) and vanadium redox flow battery (VRFB) are represented as two advanced energy conversion and energy storage devices. They have a same core component of the separator membrane, which still faces several intractable scientific and industrial issues. For HT-PEMFC, the increase in conductivity is normally as the expense of mechanical strength; while for VRFB, the improvement in proton transport always brings in serious vanadium ion crossover. Meanwhile, the membrane also should possess an excellent chemical stability towards the attack by radicals or high valence vanadium ions. The above questions can be well solved by the preparation of triphenylbenzene (TPB) branched poly(biphenyl-4-acetylpyridine) membranes (x%TPB-PBAP), which are synthesized by one-step Friedel-Crafts polymerization. Amounts of alkaline pyridine groups equip x%TPB-PBAP membranes with good phosphoric acid and sulfonic acid absorption capability, resulting in high proton conductivity in both HT-PEMFC and VRFB. Meanwhile, the construction of the branched structure, i.e. a kind of covalently crosslinked network, can improve the mechanical strength and chemical stability. Consequently, the 1.5 %TPB-PBAP membrane displays large potential in both HT-PEMFC and VRFB. A single H₂-O₂ cell based on the 1.5 %TPB-PBAP/263 %PA membrane shows a peak power density of 1010 mW cm⁻² at 180 °C without any back pressure. Meanwhile, the VRFB based on above membrane also depicts better battery efficiencies and cycle durability than that with Nafion 212.