A water vapor-driven PNG is compose

A water vapor-driven PNG is composed of a piece of pyroelectric polymer film as the nanogenerator part, with hotwater vapor and air flow as the energy source, and anexternal circuit for energy collection and storage(Figure 1a). Water vapor would condense to form a lot oftiny water droplets (a few hundred micron in diameter) onthe surface of the PNG, and release heat to heat up thePNG. When air flow passes by, the local humidity around thePNG would decrease. These tiny water droplets wouldquickly evaporate and absorb heat to cool down the PNG.Hot water vapor is commonly available in industry and in ourdaily life. For example, a cup of hot coffee can providesufficient hot water vapor for the water vapor-driven PNG,as shown in Figure 1b.