All-biomass-based beeswax/copper-loaded reed-derived porous carbon composite phase change materials for efficient solar photothermal conversion and thermal storage.

To address the utilization bottleneck caused by the intermittency of solar radiation and the mismatch between energy supply and demand, and to realize the high-value utilization of agricultural and forestry biomass wastes, this study prepared biomass porous carbon (BPC) using reed straw as the raw material. Copper nanoparticles (Cu NPs) were uniformly loaded on the surface of the carbon skeleton to obtain a composite support, and beeswax (BW) was further impregnated via the vacuum impregnation method to fabricate a novel biomass-based composite phase change energy storage material (CPCMs). The results show that the as-prepared composite phase change material exhibits excellent shape stability and outstanding comprehensive performance. Its thermal conductivity reaches 0.88 W·m-1·K-1, which is 3.52 times that of pure beeswax. After 200 thermal cycles, the latent heat retention rate remains as high as 99%. The photothermal conversion efficiency reaches 92%, demonstrating favorable solar energy absorption capacity. This study provides theoretical and technical support for the development of biomass-based high-efficiency photothermal PCMs, and is of great significance for promoting the high-value utilization of agricultural and forestry wastes as well as the advancement of solar thermal storage technology.