Techniques for surface charge measurements and exploring contact electrification

Contact electrification (CE) is one of the most important physical phenomena within a realm of surface science, with a history spanning over 2600 years. Although numerous experiments have been conducted to detect CE, and theories regarding electron, ion, and material transfer have been proposed, the mechanism of CE remains a subject of ongoing debate and continues to intrigue scientists. A key issue in the CE studies is to accurately measure the charge transfer in various situations. The development of charge transfer measurements has consistently led to a deeper understanding of CE. In this review, we explore the field of CE, focusing on methods for measuring charge transfer. Introducing six experimental methods from macroscopic to microscopic and first-principle calculation for CE studies aims to promote their proper use and inspire the design of new methods. Moreover, we point out the shortcomings of the present research approach and provide a perspective on future methodological developments.