Towards efficient sorption-based heat harvesting via hierarchical pore structures tailored by novel salt–porous composites

Sorption-based thermochemical energy storage presents a sustainable strategy for harvesting low-grade heat from ambient moisture. Salt-porous matrix composites are key materials for this application; however, their performance is often limited by low water uptake and slow sorption kinetics due to single type of pores (e.g., micropores or macropores). In this study, we explore the impact of pore structures on the sorption behaviour and heat storage capacity of such composites. A bimetallic ZIF-derived carbon matrix (C-BMZIF), integrated with LiCl to form LiCl@C-BMZIF, was tailored with multiple pore types to illustrate the structure-performance relationship. Experimental results indicate that the composite with hierarchical pore structure exhibited a good water sorption capacity of 0.527 g/g, a rapid sorption rate of 0.041 s −1 , and heat storage capacity of 1390 kJ/kg. LiCl@C-ZIF-8 and LiCl@CAZIF, similar composites with single type pores of micropores or small mesopores, showed much lower water sorption capacity and kinetics, which confirms the critical role of hierarchical porous structure in enhancing sorption performance. GCMC simulations further revealed that hierarchical pore size distribution in the composites promotes superior sorption characteristics on composites and confirmed enhanced sorption effects of impregnated salts to the matrix. Combing experimental and computational studies, our research highlights the critical role of hierarchical pores in enhancing sorption-based heat harvesting and provides insights for design the next-generation sorption materials. • Hierarchical porous carbon derived from BMZIF enhances thermochemical heat storage. • LiCl@C-BMZIF shows 0.527 g/g uptake and 0.041 s −1 rate at 60 % RH. • Heat storage capacity reaches 1390 kJ/kg at 60 %RH with high stability. • GCMC simulations confirm the pore size distribution boosts water adsorption.