Power generation from self-adsorption and evaporation in Janus hydrovoltaics

Adsorption and evaporation is widely available in nature that attracts increasing interests in environmental energy harvesting. Here, we propose self-adsorption and evaporation Janus generator to induce the continuous electricity (ambient humidity of 30 ∼ 85 %), solving the issue of continuous water supply and effective water gradient. The hydrophilic region modified with Calcium chloride (CaCl₂) solution forms self-adsorption functional layer to achieve continuous water supply and the hydrophobic region forms evaporation functional layer. The Janus structure creates a distinct wet/dry interface to maintain effect water gradient. At wetting region, the more positive ions are attracted to carbon surface ascribed to electric double layer (EDL) effect. Through adsorption and evaporation cycles, it generates continuous water flow and ions migration that induces significant potential difference between wetting and drying regions. A centimetre-sized device can generate a continuous voltage of 0.67 V when exposing to the environment. The proposed self-adsorption and evaporation Janus generator provides new insight in environmental energy harvesting, showing great potential in wearable electronic device.