Abstract: Developing clean and efficient barocaloric (BC) materials is the prerequisite for advancing the application of BC refrigeration technology. In this paper, the BC behavior of the water-ice phase transition is thoroughly investigated. A reversible isothermal entropy change (∆S_rev) of 949 J kg^-1 K^-1 was achieved under a pressure as large as 205 MPa, arising from the water-ice phase transition. By introducing a nucleating framework constructed of expanded graphite (EG) and silver iodide (AgI), the heterogeneous nucleation capability of water was significantly enhanced. It led to a considerable dramatic reduction in driving pressure (∼86 MPa), but a noticeable rise in ∆S_rev (∼1089 J kg^-1 K^-1). The molecular dynamics simulations indicate that lower pressure has less influence on the translational degrees of freedom of water molecules, resulting in a larger entropy difference between ice and water at 86 MPa. Moreover, the high thermal conductivity of EG accelerates the phase transition process, ensuring high operating frequency and output power when applied in refrigeration devices. The significance of this work extends beyond the investigation of the water-based BC material. More importantly, it offers a novel approach to optimizing the BC performance of liquid-solid phase-change materials by regulating the nucleation kinetics process of the liquid-solid phase transition.

Key words: Water-ice phase transition, Barocaloric effect, Heterogeneous nucleation, Silver iodide, Expanded graphite