Solar thermal energy conversion and storage within phase change materials (PCMs) can overcome solar radiation intermittency to enable continuous operation of many heating-related processes. However, the energy-harvesting performance of current storage systems is always limited by low efficiencies in either solar thermal energy conversion or thermal transport within PCMs. Although PCM-based nanocomposites can address one or both of these issues, achieving high-performance composites with simultaneously enhanced photothermal performance and thermal transport capacity remains challenging. Here, we demonstrate that dual-functional aligned and interconnected graphite nanoplatelet networks (AIGNNs) yield the synergistic enhancement of interfacial photothermal conversion and thermal transport within PCMs to accelerate the solar thermal energy harvesting and storage. The AIGNNs include the naked part as the three-dimensional optical absorber and the incorporated part as thermally conductive pathways within PCMs. First, a phase change composite composed of the AIGNNs and the solid-solid PCM of polyhydric alcohol is synthesized using a facile three-step method, and shows 400% thermal conductivity enhancement for per 1 wt % graphite loading compared to pristine PCMs. After the elaborate surface treatment, a small part of the graphite networks is in situ exposed as the 3D optical absorber to boost the surface full-spectrum sunlight absorptivity up to 95%. This dual function design takes full advantage of the integrated AIGNNs in terms of both photothermal conversion and thermal transport capacities, superior to the traditional coating-enhanced photothermal conversion. This work offers a promising route to accelerating solar thermal energy harvesting and storage within PCMs.
Keywords: expanded graphite; phase change material; solar thermal energy conversion; thermal conductivity; thermal energy storage; vertically aligned graphite network.