Harvesting Electricity from Water Evaporation through Micro-Channels of Natural Wood.

When external pressure drives the electrolyte solution in a capillary tube with a charged inner surface, we obtain streaming potential/current. This effect is also manifested when water flows through the micro-channels of a tree, which is driven by capillary pressure and natural evaporation. Thus, by making use of natural evaporation, we took advantage of anisotropic three-dimensional wood structures to fabricate nanogenerators drawing electricity from streaming potential/current. As a result, direct current can be harvested continuously simply through a piece of wood. 300 mV open-circuit voltage and 10 μA short circuit current (ISC) were recorded from a single device, which surpassed the ISC values of most previous works by an order. By series connecting five wood nanogenerators, a calculator can work full functionally as a demonstration for practical application.