Synthesis and characterisation of TiP2O7 derived from Ti(IV) aminotris(methylenephosphonate) as proton conductor for intermediate temperature fuel cells

Abstract

Metal phosphonates, built up of phosphonate linkers bonded to metal ions, have garnered significant attention due to their hybrid organic-inorganic frameworks and properties as proton-conducting materials, which make them promising candidates for proton exchange membranes in fuel cells (PEMFCs). Specifically, tetravalent metal pyrophosphates are attractive for fuel cells working in intermediate temperatures (ITFCs), between 100 and 300 ºC. In this study, we present the synthesis and characterization of a new titanium(IV) aminotris(methylenephosphonate), Ti[(HO₃PCH₂)(O₃PCH₂)NH(CH₂PO₃)]·2H₂O (Ti- ATMP), which, upon calcination at 600 °C in air, leads to the formation of crystalline TiP₂O₇ (Ti-ATMP@600). Proton conductivities, measured at 90 °C and 95% relative humidity (RH), were 1.6·10⁻³ S·cm⁻¹, for Ti-ATMP, and 2.3 × 10-³ S·cm⁻¹, for Ti- ATMP@600, respectively. The activation energy values (E < 0.3 eV) indicate a a Grotthuss proton transfer mechanism for both materials. Currently, Ti-ATMP@600 compound is being tested as electrolyte in ITFCs at operating conditions.