Preparation and evaluation of the metal-carbon-based composite phase change materials based on deep eutectic solvents with high photo-thermal conversion efficiency for building energy saving

Efficient solar energy conversion and storage represent a promising strategy for addressing global energy scarcity. This study developed a deep eutectic solvent-based metal-carbon composite phase change material (DES-CPCM), characterized by its straightforward synthesis and superior performance, for efficient solar energy storage. A deep eutectic solvent (DES) served as the carbon source to broaden the spectral absorption range and enhance thermal conductivity. Metal oxides with high thermal conductivity and strong absorbance are employed as metal precursors. Using a template-free, one-pot method, a porous metal-carbon matrix is fabricated, which exhibited high mechanical strength, excellent reproducibility, and pore sizes larger than the molecular dimensions of the PCM. This porous matrix is then utilized to encapsulate the PCM, with structural modifications implemented to reinforce its directional heat-transfer capability. The results indicate that the CPCMs achieve a light absorption rate exceeding 90% in the visible spectrum, a phase change enthalpy of up to 317.03 J/g, and a photothermal conversion efficiency as high as 97.73%. Both the specific heat capacity and thermal conductivity of the composites are significantly improved, with the latter reaching a maximum value of 20.9 W/(m·K). There has an opportunity for the application of high-efficiency photothermal phase change materials in building energy conservation.