Near-room-temperature waste heat recovery through radiative cooling for both daytime and nighttime power generation

Abstract

With the rapid growth in global energy consumption, the recovery of waste heat is becoming an important issue. Nevertheless, the recovery of near-room-temperature waste heat remains challenging because the slight temperature difference with the surroundings leads to extremely low thermoelectric power generation. In this study, we combined a daytime radiative cooling (DRC) technology with a thermoelectric generator (TEG) to efficiently recover near-room-temperature waste heat. We investigated the effects of the thermal radiation and thermal conduction properties of DRC materials on near-room-temperature waste heat recovery (WHR). We designed a hierarchical micro–nano h-BN/ZnO composite (MNHZC) that possessed an outstanding daytime radiative cooling ability and moderate thermal conductivity. With this hierarchical h-BN/ZnO composite, we achieved record-high levels of thermoelectric power generation of 225.3 and 412.3 mW m⁻² during the daytime and nighttime, respectively, with enhancements in thermoelectric power of 1030 and 190%, respectively. The attractive power generation ability of the MNHZC/TEG system suggests its great potential in low-grade waste heat recovery and environmental energy harvesting by consistently generating power in both the daytime and nighttime.