Metal tri-phosphonates containing aliphatic tertiary amines for medium-temperature proton conduction

New medium-temperature proton conductors (MATMP) were synthesized from amino trimethylene phosphonic acid (ATMP) and metal ions (Fe²⁺, Ce⁴⁺ and Zr⁴⁺) with varying molar ratios. The high content of phosphonic acid groups of ATMP endowed MATMP with good ion exchange capacity (IEC, 0.58～3.45 meq·g^?1) and proton conductivity. The aliphatic tertiary amine in ATMP improved proton conduction via ionic and hydrogen bonds. The proton conductivity of FeATMP(1:2) reached 0.124, 0.079 and 0.038 S cm^?1 at 100%, 50% and 0 RH at 180 °C, respectively. MATMP exhibited good thermal and oxidative stability, demonstrating promising applications in fuel cell technology.