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

ABSTRACT 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.