Nanogenerators with capacitor structures based on piezoelectricity, pyroelectricity, triboelectricity and electrostatic induction have been extensively investigated. Although the electron flow on electrodes is well understood, the maximum efficiency-dependent structure design is not clearly known. In this paper, a clear understanding of triboelectric generators with capacitor structures is presented by the investigation of polydimethylsiloxane-based composite film nanogenerators, indicating that the generator, in fact, acts as both an energy storage and output device. Maximum energy storage and output depend on the maximum charge density on the dielectric polymer surface, which is determined by the capacitance of the device. The effective thickness of polydimethylsiloxane can be greatly reduced by mixing a suitable amount of conductive nanoparticles into the polymer, through which the charge density on the polymer surface can be greatly increased. This finding can be applied to all the triboelectric nanogenerators with capacitor structures, and it provides an important guide to the structural design for nanogenerators. It is demonstrated that graphite particles with sizes of 20-40 nm and 3.0% mass mixed into the polydimethylsiloxane can reduce 34.68% of the effective thickness of the dielectric film and increase the surface charges by 111.27% on the dielectric film. The output power density of the triboelectric nanogenerator with the composite polydimethylsiloxane film is 3.7 W m(-2), which is 2.6 times as much as that of the pure polydimethylsiloxane film.

We report a novel pseudocapacitor based on KCu 7 S 4 nanowires. To improve the electrochemical performance of the KCu 7 S 4 capacitor, we changed the structure of the KCu 7 S 4 nanowire electrode by coating Mn particles (Mn/KCu 7 S 4 ). The preferable capacitance is shown by the Mn/KCu 7 S 4 hybrid capacitor, which displays large specific capacitance (1620 F g À1 ) at a scan rate of 1 mV s À1 , high energy density, good cyclic stability and three supercapacitor units in series light 400 light-emitting diodes (LEDs) for 2 min. The much-increased capacity, rate capability, and cycling stability may be attributed to the Mn/KCu 7 S 4 hybrid structure, which enhances ionic and electronic transport through the electrode system.

Design of hybrid nanogenerator that can simultaneously light up 99 commercial blue LEDs connected in series. Additionally, by placing a hand on the nanogenerator the maximum peak current could reach 115 μA.

Three C/KCu7S4 hybrid supercapacitors units in series can light one light-emitting diode for 3.5 min; the hybrid supercapacitors can deliver the largest specific capacitance of 352 F g−1 at the scan rate of 10 mV s−1, the maximum power density of 994.8 kW kg−1, the highest energy density of 26.2 W h kg−1 and cycling stability (86% capacity retention after 2000 cycles).

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