Characterizations of the PTR. (A) The photograph (left) and cross-sectional schematic (right) of a PTR, which is mainly composed of the hierarchical Cu foam with paraffin and CAB-hBN hybrid film. The thermally conductive silicone grease and Cu film are utilized for thermal integration. (B) Schematics of the microcosmic designs of the hierarchical Cu foam. (C) Phase change point and enthalpy of the paraffin with different numbers of carbon atoms. Large enthalpy of over 220 kJ kg⁻¹ with customized phase change temperature ensures efficient and broad ranges of heat/cold energy storage. The inset is an example that shows the molecular structure of hexadecane with sixteen carbon atoms. (D) Schematic illustration of the CAB-hBN hybrid film. (E) Optical spectra of the hierarchical Cu foam and CAB-hBN hybrid film. The solar spectrum, atmosphere transmission spectrum, and black-body radiation at 288 K to 308 K are presented for reference. (F) Temperature curves show the opposite temperature responses of the hierarchical Cu foam and CAB-hBN hybrid film of the PTR. (G) Temperature profiles depict that adjustable heating temperatures from 19 to 31°C are realized via changing the chain length of paraffin.