Porous matrix derived from steel slag for shape-stabilized phase change materials based on NaNO3

Recycled steel slag enables high-performance C-PCMs for thermal energy storage; • A novel hierarchical skeleton achieves 69 wt% NaNO 3 loading, improved by 130%; • The prepared C-PCMs show superior heat storage density, up to 637 J/g (100–400 °C); • The prepared C-PCMs exhibit excellent chemical compatibility and cycling stability; • The mechanism of high heat storage density of prepared C-PCMs is revealed. Shape-stabilized phase change materials (PCMs) effectively address the issues of leakage and corrosion associated with pure PCMs. This study specifically tackles the low PCMs loading capacity and leakage problems of traditional steel slag skeleton by proposing a hierarchical steel slag ceramic (HSSC) structure to create shape-stabilized PCMs with high energy storage density. The desired effect is achieved through a core-shell structure with varying pore sizes within HSSC, specifically, a “large pore for PCMs storage-small pore for PCMs leakage prevention”. A comprehensive examination of unique structure of HSSC, as well as structural and thermophysical properties of the composite PCMs, is presented. The results indicate that the synergistic effect of foaming agent (SDS) and foam stabilizer (CTAB) is responsible for the high-apparent porosity (76.3%) observed in core structure of HSSC. Further modification with calcium carbonate (CaCO 3 ) and diatomite aids in creating a hierarchical structure within HSSC, characterized by a range of larger pores from 50 to 300 μm and smaller ones from 5 to 50 μm. The integration of a finely porous shell layer into HSSC significantly enhances its loading capacity for NaNO 3 salt. Specifically, NaNO 3 /C5D5-B3 exhibited the highest PCM loading ratio of 69 wt%, the largest latent heat of 117.4 J/g, and a relatively high heat storage density of 637 J/g (100–400 °C), a compressive strength of 9.94 MPa, along with a good cycling stability. This research presents a novel approach to the effective utilization of industrial solid waste and establishes a theoretical foundation for the development of superior composite PCMs.