A wiping-type semiconductor-liquid generator utilizing water-bearing solid materials and hydrated biological tissues

The charge generation due to the interaction between solids and liquids is an important branch for microenergy collection. This work presents a wiping-type semiconductor-liquid generator, which provides an ultrahigh transferred charge density of 186 mC m⁻². Underwater Kelvin probe force microscopy reveals that different aggregation states of water molecules on the surface of both metals and silicon result in different interfacial dipole moments and surface fields, which greatly change the output voltage of the device. The generator has a free-standing working mode with no wire-connection to the movable liquid, and the utilization of water-bearing solid materials constrains the liquid in a more controllable state, which can enhance the robustness and the scope of application of the device. Accordingly, it can be used to harvest energy from the frictional motion of hydrated biological tissues, including both tongue licking and eyelid blinking. A smart contact lens is also fabricated and an average current density of 0.05 A m⁻² is obtained from the eyelids of rabbits. This work expands the application fields of solid-liquid generators and the physical analysis of underwater surface potential can also elucidate various electronics processes happening on the liquid-semiconductor interface.