Replacing a battery by a nanogenerator with 20 V output.

IC A IO N We have been working on “self-powered nanotechnology” since 2005 with the aim to build self-powered systems that operate independently, sustainably, and wirelessly without the use of a battery. [ 1 , 2 ] One of the great applications for such a self-powered system is that it can be used for driving portable/wearable personal electronics in our daily life. Nanogenerators (NG) are one of the technologies that are developed to harvest irregular mechanical energy with variable frequency and amplitude in our environment by way of the piezoelectric effect. [ 3–12 ] It is designed to have a tolerance for variable environments without relying on the traditional approach of cantilever-based resonators. Irregular mechanical energy can manifest itself in the form of gentle airfl ows, ambient noise, and activity of the human body, such as walking, typing, etc. Such energy forms are abundant in the working environment for personal consumer electronics. In fact, after sustainable development the NG has been demonstrated to power small electronic devices, such as the lighting of a small LCD screen of a calculator [ 13 ] and fl ashing a single LED. [ 7 , 8 ] But the low output current limits the application of the NG to drive commercial consumer electronics, which usually have a higher power consumption and require a power source with a regulated voltage and maintaining a constant current supply. To solve this problem, the optimization of the NG’s performance and in particular the output current is desperately needed. And a convertor is required to obtain a sustainable regulated power source from the stored energy harvested by the NGs. In this work, we have systematically investigated various approaches for improving the intrinsic properties of ZnO in order to achieve a high performance. The NGs’ performance was greatly improved by pretreatment of the ZnO nanowire (NW) arrays in the device with oxygen plasma, annealing in air and surface passivation with certain polymers. The maximum output voltage reached from a single layer of nanowire reached 20 V, and the maximum output current exceeded 6 μ A, in corresponding to a power density of 0.2 W cm − 3 , which is 20 times larger than the former best NG we have achieved. [ 12 ] The NG’s performance is good enough to drive a commercial buck convertor board, and a regulated voltage of 1.8 V with constant current load was achieved to drive an electrical watch for more than 1 minute after the board was charged by the NG with 1000 cycles of deformation. This is the fi rst time that a NG works as a battery part for real commercial consumer electronics.