Eco-friendly synthesis of chemically cross-linked chitosan/cellulose nanocrystal/CMK-3 aerogel based shape-stable phase change material with enhanced energy conversion and storage.

Phase change materials (PCMs) have attracted numerous attention owing to their high energy storage density, cost-effective and operationally simple, however, the "solid-liquid" leakage and limited solar absorbance seriously hinder their widespread applications. Herein, an innovative chitosan/cellulose nanocrystal/CMK-3 (CS/CNC/CMK-3) aerogel based shape-stable PCM (SSPCM) was successfully synthesized, in which chemically cross-linked CS and CNC acted as three-dimensional supporting skeleton, CMK-3 endowed solar-to-thermal energy conversion ability and the impregnating polyethylene glycol (PEG) acted as the latent heat storage unit. The as-synthesized CS/CNC/CMK-3 aerogel/PEG (CCCA/PEG) showed ultrahigh melting/crystallization enthalpy of 178.5/171.1 J g and excellent shape stability. The PEG was effectively embedded into the hierarchical porous architecture and the composite PCM could preserve its original shape without any leakage even compressed above the melting point of PEG. Meanwhile, the CCCA/PEG exhibited robust thermal reliability with an ultralow enthalpy fading rate of 0.030 ± 0.012 % per cycle over 100 thermal cycles. Intriguingly, the introduction of CMK-3 also significantly improved the solar-to-thermal energy conversion performance of CCCA/PEG, and a high solar-to-thermal conversion efficiency of 93.1 % could be realized. This work provided a potential strategy to design and synthesize high-performance sustainable SSPCM, which showed tremendous potential in the practical solar energy harvesting, conversion and storage applications.