Form-stabilized phase change composites based on biochar and n-Eicosane for photo- and electro-thermal conversion and heat storage

To overcome the obstacles of poor thermal conductivity of pure n-Eicosane, a typical single-phase change material, and prevent the melt from leaking during the phase change process, a biochar/n-Eicosane based composite phase change material that possesses high form stabilization, photo- and electric-thermal converting, and enhanced phase change heat transfer was prepared. Firstly, corn straw was selected as the raw material of biomass, and pyrolyzed at higher temperature. Following a KOH etching procedure at 700℃, a biochar support with large surface area and hierarchically interconnected pores were obtained. Then, KBC/n-Eicosane composite phase change materials were prepared by injecting n-Eicosane into biochar skeletons via ethanol melting and vacuum impregnation. The as-prepared composite materials were characterized by SEM, XRD, FTIR and other characterization methods. The thermal stability and heat storage capacity were also tested by TG and DSC. The effect of mass content of n-Eicosane to melting enthalpy and crystallization enthalpy were calculated, and the results reveal that the optimized mass content is mKBC∶mn-Eicosane=1∶2 associated with the melting enthalpy and crystallization enthalpy of 121.3 J·g−1 and 117.6 J·g−1, respectively. Notably, after 100 thermal cycles, the melting enthalpy and crystallization enthalpy have negligible changes, and no clear liquid leaking is observed through all thermal cycles, indicating significant thermal storage ability and cycling stability. In addition, the ability of photo- and electro-thermal conversion and storage of the composite phase charge materials were tested by simulated sunlight irradiating and DC power supply powering. The results display that the KBC/n-Eicosane composite phase materials are capable of converting solar energy or electric energy into thermal energy and storing as latent heat with excellent performance. Thus, the as-prepared KBC/n-Eicosane are not merely a phase charge materials with remarkable properties, but can realize varied energy transformation and storage, showing great potential for use in green and renewable energy conversion and storage. © 2023 Beijing University of Aeronautics and Astronautics (BUAA). All rights reserved.