Colossal liquid-state barocaloric Effect

Abstract Vapor-compression refrigeration, though ubiquitous, relies on gaseous refrigerants with substantial climate footprints. Solid-state caloric (SSC) cooling offers a green alternative, yet its performance is constrained by field hysteresis and parasitic losses from secondary‑fluid heat exchange. Here we demonstrate the liquid-state barocaloric effect in molecular liquids, achieving isothermal entropy changes of 230 J·kg -1 K -1 and adiabatic temperature changes of 32 K. Without requiring a liquid-solid transition, the liquid-state BC effect is robust over a temperature span exceeding 100 K. Together with the colossal entropy change, this leads to a relative cooling power three times that of SSC materials. Crucially, the liquid serves simultaneously as refrigerant, heat-transfer medium, and pressure-transmitting fluid, eliminating interfacial thermal resistance and enabling a Carnot-like cycle with a coefficient of performance far surpassing that of SSC systems. Molecular dynamics simulations and quasi-elastic neutron scattering reveal that the colossal thermal response originates from pressure-suppressed translational and rotational molecular motions, primarily governed by molecular polarity and intermolecular interactions. Our work establishes liquid-state barocaloric cooling as a sustainable paradigm that circumvents the longstanding efficiency bottlenecks of SSC refrigeration.