Reversible Colossal Barocaloric Effects in Hydrogen Bond-Engineered Plastic Crystals: chCl and [ch]2MnCl4

Plastic crystals are a promising class of materials for sustainable cooling technologies due to their large entropy changes during phase transitions. However, practical applications have been hindered by substantial thermal hysteresis and inappropriate phase transition temperatures. Here, we suggest that modulation of the hydrogen bond network, achieved through molecular structural variation, may provide a viable approach to tuning these properties. Through the substitution of [Cl]- with [MnCl4]2- in ionic plastic crystal, chCl [ch denotes choline], we achieve a striking 2-fold enhancement in reversible barocaloric performance and an over 500% increase in refrigeration capacity under small applied pressures (0.1 GPa). This modification reduces thermal hysteresis by more than 68% while also lowering the phase transition temperature by 19.5%. Our results suggest that the modulation of the hydrogen bond network in choline-based ionic plastic crystals can effectively tune the phase transition behavior, providing new insights into the relationship between intermolecular interactions and barocaloric performance. These findings highlight a potential pathway for exploring materials toward efficient and sustainable cooling applications.