CUHK Researchers Establish a Universal Standardized Method for Output Capability Assessment of Nanogenerators Laying the Foundation for Nanogenerator Technology Development

Nanogenerator is a type of new technology that converts thermal and mechanical energy as produced by small-scale physical change into electricity. Its presence secures a stable and sustainable source of electricity that powers a wide range of small electronic devices equipped with a variety of features. A research team led by Prof. ZI Yunlong, Assistant Professor in the Department of Mechanical and Automation Engineering at The Chinese University of Hong Kong (CUHK), has recently developed a universal standardized method for evaluating the output capacity of nanogenerators. Compared with the conventional one, the new method can reflect the practical output capacity of the nanogenerator more accurately. This research will set an important foundation for the practical application and commercialisation of nanogenerators as an emerging energy harvesting technology. This research was published recently in the prestigious scientific journal Nature Communications (

A nanogenerator has three typical approaches: piezoelectric, triboelectric, and pyroelectric nanogenerators. Triboelectric nanogenerators (TENG), which harvest energy from triboelectric effect, can provide high energy output and high energy conversion efficiency. They have caught a lot of attention because they can acquire electricity by rubbing commonly-used materials such as clothes fabric and papers. However, the unique capacitive output characteristics of the nanogenerator make the traditional characterisation method not applicable. To solve this problem, the Figure-of-Merit (FOM) defined by a maximized energy output cycle has become a standard for quantitative evaluation of output performance. However, the development of TENG is still hindered since the current FOM definition does not consider the breakdown effect, and the corresponding standardized performance assessment and well-standardized experimental evaluation methods have not been developed yet, limiting the wide application of this FOM as the evaluation standard.

Prof. Zi and his team members have discovered that a specific measuring circuit can solve the most difficult part, which is measuring the breakdown limit. Based on the designed process flow, the breakdown areas of contact separation (CS) mode and contact freestanding (CFT) mode TENG were determined and the results were consistent with the theoretical calculations. The team redefined FOM based on the experimentally measured maximized effective energy output to reflect the actual output capacity of the TENG. The team also applied this method to a piezoelectric nanogenerator based on polyvinylidene fluoride (PVDF) thin film, further proving the wide applicability of the method. This study provides a standardized method for evaluating output capacity, which is advantageous due to the standardized process flow for experimental operation and considerations of the breakdown effect. It can be widely applied to various types of nanogenerators and will make an important contribution to the standardized application and commercialisation of the nanogenerator technology.

About Prof. Zi Yunlong

Prof. Zi joined the CUHK since 2017. He has been working on the development of the emerging energy harvesting technology of nanogenerators, especially TENG, with a series of independent research achievements and several awards. This project was funded by the Innovation and Technology Fund of the Innovation and Technology Commission of the Hong Kong SAR, Shun Hing Institute of Advanced Engineering and CUHK.

Prof. Zi (5th left) and his research team.

Air breakdown of arc which can be seen in CS mode.

An introduction to evaluation methods. (a) Energy conversion of TENG system; V-Q diagram of , where "+" is the non-breakdown area and "-" is the breakdown area. (c) circuit diagram of the measurement method; (d) flow chart of standardized measurement methods.