0.5% Graphene Slashed 38.8 °C Supercooling in Plastic Crystals

Plastic crystals are promising for thermal management due to their reversible order-disorder phase transitions, but they often face challenges with significant supercooling caused by high energy barriers. We address this challenge by incorporating 0.5 wt % graphene into tris(hydroxymethyl)aminomethane (Tris), resulting in a 38.8 °C supercooling inhibition while boosting enthalpy by 20.8%. The pivotal role of graphene induces "rotational entropy pinning", achieving a 40.3% reduction in entropy alongside a simultaneous enthalpy increase. This effect is rooted in directional rotation confinement and cooperative hydrogen-bond lattice reconstruction. Employing synchrotron XRD, femtosecond IR spectroscopy, and MD simulations, we capture structural transformations from femtosecond molecular vibrations to macroscopic lattice reorganization. This advancement circumvents the classical trade-off between nucleation efficiency and energy storage capacity, extending its universality to plastic crystalline systems and even solid-liquid phase-change architectures. These insights propose an interface-confined rotational dynamics model, heralding a leap in designing ultralow-hysteresis, high-energy-density materials. This dual role of graphene as both a nucleation promoter and molecular ordering template, validated in other plastic crystal systems, provides a universal strategy to suppress supercooling while enhancing energy storage, which advances plastic crystals toward efficient solid-state thermal regulation.