Capillary front broadening for water-evaporation-induced electricity of one kilovolt

Water evaporation through nanoporous materials, such as carbon black films, can induce electricity at the volt level, but how to boost the output remains a challenge. Herein, we revealed that the gas-liquid-solid three phase region in the nanoporous film dominates the induced electricity across two terminals and can be efficiently broadened via gravity dragging and evaporation thinning of a preformed water film. This strategy readily enhanced the evaporation-induced voltage by one order to 5 V in an 8 mm × 10 mm device consisting of semiconducting bismuth oxyhalide nanoplates, compared to that in conventional devices with the bottom end immersing in water. Water evaporation from the three-phase region and the induced capillary flow were found to contribute to the induced electricity. In addition, the strategy enabled facile device integration, which was inaccessible for conventional devices due to electrical shorting by bulk water. An unprecedented voltage output over one kilovolt was achieved and successfully drove gas ionization at atmospheric pressure. Our results shed light on a reliable approach to advance hydrovoltaic technology with respect to harvesting energy from water evaporation.