Sn(IV) Glyphosine Phosphonates as Precursor of Fast Proton Conductors based on SnP2O7

Abstract

Metal phosphonates (MPs) combine good chemical and thermal stability alongside tuneable properties, which provide appealing features for electrochemical applications [1-2]. They exhibit not only remarkable proton conductivity properties but also can be potential precursors of electrolytes. useable in intermediate-temperature fuel cells (ITFCs), operating at 100 - 250 ºC [3].

In this work, we present the synthesis and characterization of a novel family of amorphous tin(IV) glyphosine-based phosphonates, Sn1-xMx[(O3PCH2)2-N-CH2CH2COOH)]1-x[(O3PCH2)2-NH-CH2CH2COOH]x n(H₂O) (M = Mg2+, Al3+; x < 0.3). Upon pyrolysis at 750 °C in air, these compounds were converted to the corresponding tin(IV) pyrophosphates and their proton conductivity properties measured. In comparison with the as-synthesized materials, that exhibited proton conductivities up to ~7·10⁻⁴ S/cm (90 °C and 95% RH), the resulting SnP2O7 derivatives showed values up to 1.3·10⁻² S/cm at the same conditions, with Ea < 0.12 eV characteristic of a water-mediated Grotthuss proton transfer mechanism (Figure 1). On the basis of solid-state 31P MAS-NMR studies, the proton conduction of these materials was found to be consistent with the formation of a core of crystalline tin(IV) pyrophosphate surrounded by an amorphous acidic phosphate-containing layer. Current efforts are focused on evaluating the performance of these materials in the range of 100 – 250 ºC and variable water vapor pressure.

References [1] J. Jia, S. Bao, G.K.H. Shimizu, L. Zheng, Coord. Chem. Rev. 534 (2025) 216558. [2] Á. Vílchez-Cózar, R.M.P. Colodrero, M. Bazaga-García, D. Marrero-López, S.M. El-Refaei, P.A. Russo, N. Pinna, P. Olivera-Pastor, A. Cabeza, Appl. Catal. B 337 (2023), 122963 [3] Z. Wang, J. Zhang, S. Lu, Y. Xiang, Z. Shao, S.P. Jiang, Adv. Sustainable Syst. 7 (2023) 2200432.