Proceedings Article | 24 April 2020
KEYWORDS: Standards development, Energy conversion efficiency, Control systems, Video, Ferroelectric polymers, Nanotechnology
As a new type of energy harvester that is based on the Maxwell’s displacement current, the unique capacitive model of nanogenerators makes traditional characterization methods unsuitable for unveiling the output capability. Among different nanogenerators, triboelectric nanogenerator (TENG) has been intensively studied due to its high output and high energy conversion efficiency, with area power density reaching 500 W/m2 and the total energy conversion efficiency of up to 85%. However, it should be noticed that with traditional approaches, only a small portion of the maximized energy per cycle (Em) of TENG can be outputted, which cannot reflect its real output capability. To address this issue, the figure-of-merits have been developed. However, the current version of figure-of-merits has limitations in applications, without considering the breakdown effect that seriously affects the effective maximized energy output. Meanwhile, the method to evaluate output capability of nanogenerators is missing. Here, a standardized method is proposed for evaluating the output performance of TENG, which can correctly measure the output capability with the breakdown effect considered. To develop such kind of universal standardized method, we have developed the process flow of the measurement on the maximized effective energy output Eem per cycle. The trickiest part is how to measure the breakdown limits, which can be solved through the measurement circuit developed. The measurement circuit is composed of a TENG as the high voltage source, a targeted device and several electric meters to control the surface charge density and quantitively measure the breakdown point. The targeted device will be powered by the high voltage source TENG and then be triggered to the breakdown condition with typical output characteristic. Through this method, we firstly show the measurement results of breakdown points in the Q-V curves which illustrate sudden changes in both charge and voltage, where the slope before the breakdown point is the measured capacitances at a certain displacement of TENG, and the first inflection point of the Q-V curve is the threshold breakdown point of the device. Based on this, V-Q plots with breakdown points of contact separation and contact freestanding-triboelectric-layer modes TENG are derived through experiments to demonstrate this method, which are consistent with that calculated by Paschen’s law. During the experiments, visible sparks were generated and recorded by video, showing the existence of breakdown. The maximized effective energy output Eem are calculated based on the measured results. And then the standardized evaluation of a PVDF film-based PENG is conducted to further demonstrate the broad applicability of this method. The FOM was revised based on Eem, and calculated for each nanogenerator to enable the comparison across different mechanisms and structures since the former definition of FOM did not consider the breakdown effect, limitating its wide application. This study proposes a standardized method for evaluating the effective output capability of nanogenerators, which is crucial for standardized evaluation and applications of nanogenerator technology.
