The directional and long-range droplet transportation is of great importance in microfluidic systems. However, it usually requires external energy input. Here we designed a wettability gradient surface that can drive droplet motion by structural topography. The surface has a wettability gradient range of over 150° from superhydrophobic to hydrophilic, which was achieved by etching silicon nanopillars and adjusting the area of hydrophilic silicon dioxide plane. We conducted force analysis to further reveal the mechanism for droplet self-propulsion, and found that the nanostructures are critical to providing a large driving force and small resistance force. Theoretical calculation has been used to analyze the maximal self-propulsion displacement on different gradient surfaces with different volumes of droplets. On this basis, we designed several surfaces with arbitrary paths, which achieved directional and long-range transportation of droplet. These results clarify a driving mechanism for droplet self-propulsion on wettability gradient surfaces, and open up new opportunities for long-range and directional droplet transportation in microfluidic system.

Harvesting energy from natural water evaporation has been proposed as a promising alternative to supply power for self‐powered and low‐power devices and systems, owing to its spontaneous, ubiquitous, and sustainability. Herein, an approach is presented for harvesting water‐evaporation‐induced electricity based on liquid–solid triboelectric nanogenerators (LS‐TENGs), which has various advantages of easy preparation, substrate needless, and robustness. This developed harvester with porous Al₂O₃ ceramic sheet can generate a continuous and stable direct current of ≈0.3 µA and voltage of ≈0.7 V by optimizing the sheet physical dimensions and ambient parameters such as relative humidity, temperature, wind velocity, and ion concentration. The output power also can be improved significantly by series or parallel connection the harvesters, which has superior electrical compatibility and environmental suitability. The development of the water‐evaporation‐induced electricity harvesting shows many application prospects including power supply for digital calculator and charging capacitor. This research provides an in‐depth experimental study on water‐evaporation‐induced electricity harvesting based on LS‐TENGs and an efficient approach to supply electricity for low‐power devices.