Low pressure reversibly driving colossal barocaloric effect in two- dimensional vdW alkylammonium halides

YH Gao and DH Wang and FX Hu and QZ Huang and YT Song and SK Yuan and ZY Tian and BJ Wang and ZB Yu and HB Zhou and Y Kan and Y Lin and J Wang and YL Li and Y Liu and YZ Chen and JR Sun and TY Zhao and BG Shen, NATURE COMMUNICATIONS, 15, 1838 (2024).

DOI: 10.1038/s41467-024-46248-1

Plastic crystals as barocaloric materials exhibit the large entropy change rivalling freon, however, the limited pressure-sensitivity and large hysteresis of phase transition hinder the colossal barocaloric effect accomplished reversibly at low pressure. Here we report reversible colossal barocaloric effect at low pressure in two- dimensional van-der-Waals alkylammonium halides. Via introducing long carbon chains in ammonium halide plastic crystals, two-dimensional structure forms in (CH3-(CH2)(n-1))(2)NH2X (X: halogen element) with weak interlayer van-der-Waals force, which dictates interlayer expansion as large as 13% and consequently volume change as much as 12% during phase transition. Such anisotropic expansion provides sufficient space for carbon chains to undergo dramatic conformation disordering, which induces colossal entropy change with large pressure-sensitivity and small hysteresis. The record reversible colossal barocaloric effect with entropy change Delta S-r similar to 400 J kg(-1) K-1 at 0.08 GPa and adiabatic temperature change Delta T-r similar to 11 K at 0.1 GPa highlights the design of novel barocaloric materials by engineering the dimensionality of plastic crystals.

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