Bis(dialkylammonium)-based hybrid organic–inorganic ionic materials as solid–solid phase change materials

The application of phase change materials (PCMs) in thermal energy storage (TES) systems is often restricted by challenges such as volume expansion, phase segregation, stability issues and potential leakage, particularly prominent in conventional solid–liquid PCMs. In response to these limitations, solid–solid PCMs have emerged as a promising alternative, garnering increasing attention. While both organic and inorganic solid–solid PCMs have been extensively studied, hybrid organic/inorganic materials represent a distinct class of solid–solid PCMs that have recently garnered significant interest due to their inherent properties such as high thermal stability, non-flammability or long cycle life. Organic-inorganic layered perovskites are emerging as potential good solid–solid PCMs as they present energetic solid–solid transitions and high thermal stability. In this work we propose the synthesis and thorough thermal characterization and cyclability of a series of new hybrid organic–inorganic ionic materials based on n-dialkylamines of different lengths (C8, C10, C12 and C18) with general formula of the type 2[(CnH2n+1)2NH2][MX4], using three different tetrachlorometalates anions ([FeCl4]2-, [MnCl4]2- and [CuCl4]2-). Among the new ionic materials prepared six of them have shown solid–solid transition enthalpies higher than 100 J/g. In particular, the 3 bearing the secondary n-dioctadecylamines as cations have shown unprecedent solid–solid transitions enthalpies ca. 90 °C, for this kind of ionic materials of 167.5 J/g, 157.7 J/g and 146.9 J/g for [DODA]2[MnCl4], [DODA]2[CuCl4] and [DODA]2[FeCl4] respectively. In addition, the latter ionic materials have undergone reliability tests showing excellent performance up to 500 heating/cooling cycles.