1, Peking University, Beijing, , China
The phase change materials (PCMs) provide state-of-the-art thermal energy storage capability and offer enormous potential for the development of sustainable energy infrastructure. However, the widespread utilization of PCMs in real life applications is often limited by the intrinsic material problems including shape instability, structural rigidity, low conductivity as well as the lack of multi-charging modes. Therefore, the functionalization of PCMs in order to overcome the aforementioned issues has remained an elusive goal. In current study, we developed nano-pore confined solid-solid phase change composites (PCCs) by infiltrating polyurethane into the pores of carbon nanotube sponge (CNTS). Our fabricated composite structure is dual form-stable, flexible, highly conductive and more importantly can store thermal energy by mean of low voltage as well as sunlight irradiation, which overcomes the intermittency of input energy source. To the best of our knowledge, we achieved the highest energy conversion efficiencies (94 %) for both electro and photo to thermal energy storage among all functionalized PCMs. This high-energy storage efficiency is attributed to the excellent energy conversion/transfer performance of aligned carbon nanotubes (CNTs) network, which remains unaffected over 100 cycles owing to the solid-state phase transition of confined PCM. Moreover, the alignment of CNTs results in anisotropy in thermal transport, which has potential in harvesting/transferring energy in favorable direction. Furthermore, our devised composite with 90 wt% of PCM presents energy storage density 132 J g-1 which is close to solid-liquid PCCs and highest among all the solid-solid PCCs. The combination of multiple features is realized in one single structure, which sets our work apart from previously reported PCCs. Therefore, the presented study will provide breakthrough towards the development of real life applicable PCCs for thermal energy applications.