From biomass to high performance solar-thermal and electric-thermal energy conversion and storage materials

We demonstrate that lightweight, highly electrically conductive, and three-dimensional (3D) carbon aerogels (CAs) can be produced via a hydrothermal carbonization and post pyrolysis process using various melons as raw materials. This two-step process is a totally green synthetic method with cheap and ubiquitous biomass as the only raw material. These black-colored, highly electrically conductive and 3D structured CAs are ideal materials for energy conversion and storage. Paraffin wax was impregnated into the CA scaffold by vacuum infusion. The obtained CA-wax composites show excellent form-stable phase change behavior, with a high melting enthalpy of 115.2 J g(-1). The CA-wax composites exhibit very high solar radiation absorption over the whole UV-vis-NIR range, and 96% of light can be absorbed by the phase-change composite and stored as thermal energy. With an electrical conductivity of 3.4 S m(-1), the CA-wax composite can be triggered by low electric potential to perform energy storage and release, with an estimated electric-heat conversion efficiency of 71.4%. Furthermore, the CA-wax composites have excellent thermal stability with stable melting-freezing enthalpy and excellent reversibility. With a combination of low-cost biomass as the raw materials, a green preparation process, low density, and excellent electrical conductivity, the 3D CAs are believed to have promising potential applications in many energy-related devices.