A Conical Nanogenerator Consisted of Multi-Walled Carbon Nanotubes

The shift to an industrial ecosystem that operates with abundant water and sunlight on the earth is essential to the sustainability of mankind. One effort to do this is to produce freshwater utilizing solar energy, called solar steam generation. Here, we develop a dual-function ecosystem of the 3-dimensional conical structure consisted of multi-walled carbon nanotubes (MWNTs), which utilizes the solar energy to produce the fresh water from any pollutated water or saline water at the massive production rate and to generate the high electric power of hundreds mW·m -2 using evaporation-enhanced capillary water stream of the structure under ambient daylight conditions. Since this cone-shaped fluidic nanogenerator (CFN) acquires all energy required from the environment, it will find immediate applications in providing electricity and freshwater for living and system maintenance in water-abundant isolated locations such as islands or wetlands. The CFN of MWNTs has advantages in solar steam generation because it can be more exposed to the environment due to its high surface curvature and because it can be thermally isolated from the cold water by the inside air-pocket. A single CFN of which vertical projection area is 0.64 cm 2 can show high water evaporation rate of 1.6 kg·m -2 ·h at 20 °C. Multilayers of functionalized MWNTs can have advantages in fluidic nanogenerator which can harvest large electric power with high open-circuit voltage (V oc ) and current density (J sc ) by the double layer interaction of MWNTs with ions flowing in the evaporation-induced capillary water stream. The CFN of MWNTs can produce strong electric power due to the capillary water stream induced by the solar steam under 1 sun irradiation (1 kW·m -2 ) and the single CFN produces electric powers of 120.7 mW·m -2 (V oc : 0.5V, J sc : 0.12 mA·cm -2 ) at the saline water and of 505.69 mW·m -2 (V oc :0.64 V, J sc : 0.59 mA·cm -2 ) at the 0.6 M KCl aqueous solution.