High-power radiatively cooled thermoelectric generator for diurnal waste heat harvesting

Governed by the second law of thermodynamics, waste heat generation is inevitable and has been a major source of energy loss and environmental concern in human society. Harvesting waste heat into useful energy has thus become a paramount priority, but has remained challenging with efficiency and cost constraints. Thermoelectric generators (TEGs), which convert heat into electricity whenever there is a temperature difference, play a crucial role in waste heat harvesting. However, sustaining the temperature difference for uninterrupted and high-power density electricity generation is a major challenge in TEGs to achieve practical applications due to the thermal equilibrium. Here, we demonstrate a diurnal waste heat harvester by integrating a high-power radiative cooling film as the cool end of TEGs to enable a large and continuous temperature difference. Significant voltage increase from 30.0 mV to 65.7 mV was achieved, leading to a dramatic power density enhancement of 4.8 times from 35.2 mW m − 2 to 168.6 mW m − 2 . In an open zone, an ultra-high power density of 2.76 W m − 2 was achieved at a heat source temperature of 80 °C, exceeding the performance of state-of-the-art radiatively cooled TEGs. More importantly, a portable and foldable thermal energy harvesting prototype composed of 24 TEGs arranged in an array has been constructed. When attached to a hot object (e.g. a car engine hood), it can output 5 V to charge personal electronics (e.g. a cellphone), making it a promising practical device for harvesting waste heat in a wide range of outdoor applications.