Continuous electricity generation from solar heat and darkness

The need to power off-grid electronics such as Internet-of-Things (IoT) sensors has stimulated extensive research on energy conversion from the environment into electricity. However, it is challenging to provide sustainable electricity at night when photovoltaic systems no longer operate. In this work, we demonstrate a low-cost continuous electricity generator to convert the diurnal temperature variation to electricity via a charging-free thermally regenerative electrochemical cycle (TREC) with the assistance of graphene as a bifunctional solar absorber and radiative cooler. This TREC system with lithium ferrocyanide and lithium iron phosphate can achieve a thermoelectric efficiency of 19.91% relative to Carnot efficiency, almost five times the highest efficiency of reported charging-free TRECs. The maximum power density also exceeds ten times the best reported charging-free TRECs. The experimental rooftop demonstration shows its practical capability for self-power supply at both daytime and night with greatly enhanced power density compared with other thermoelectric generators at night.