Liquid-Gas Dual-Phase Water Energy Harvesting via Lotus Leaf-Inspired Janus Surfaces

Harvesting energy from dispersed water sources (e.g., rain, atmospheric moisture) offers a promising route for powering distributed low-power electronics. However, most existing water-enabled electric generators exploit only a single phase of water, overlooking their coexistence and causing inefficient utilization of the hydrological cycle energy. Here, inspired by the Janus wetting properties of lotus leaves, we present a liquid-gas dual-phase water energy harvester capable of simultaneously harvesting energy from liquid-phase and gas-phase water. This dual-function device features a hydrophobic top surface that converts the kinetic energy of water droplets into pulsed electricity, and a hydrophilic bottom surface embedded with ionic hydrogels that absorb moisture and convert moisture-induced ion-concentration gradients and electrochemical potentials into continuous electricity. With a maximum power density of 78.91 µW cm^-2, a 36 cm × 28 cm array can generate a continuous voltage of 8.2 V and a current of 5.6 mA, and additional transient voltage pulses up to 150 V and pulsed currents of 0.3 mA are superimposed under rainfall at 16.5 mm min^-1, sufficient to power a road lamp and mobile phones in real time. The coplanar-electrode design ensures favorable scalability, making it a promising solution for off-grid IoT deployments across water-rich remote or outdoor environments.