Dr. Qiwei Hu

Dr. Qiwei Hu

Research Area A

Institute of Physical Chemistry
University of Freiburg


Project description
The triboelectric effect describes the following phenomenon: when two dissimilar contacting materials move in opposite directions, the difference in their electron-affinities causes charges to separate. However, for insulators, it is unclear whether electrons, ions or material fragments transfer during contact. In my research, I utilize Atomic Force Microscopy (AFM) with Kelvin Probe method to analyze the topography and surface potential of triboelectric interfaces before and after contacting. This approach will provide a better understanding of the relation between surface properties and triboelectric behavior.

Project outcomes
Functional materials are important for various applications in industries and our daily lives, such as adapting to different environments and harvesting energy. Atomic force microscope (AFM) is a powerful tool for revealing the structure of designed functional interfaces and other properties such as the surface potential. In this work, we used AFM imaging to examine the structures of various functional interfaces used in catalysis and solution filtration. Additionally, we investigated the triboelectric effect for energy harvesting using Kelvin Probe Force Microscopy (KPFM) and AFM-based force spectroscopy.

In the first project, we studied enzymes called hydrogenases, which can catalyze the reversible oxidation of hydrogen gas. These enzymes were attached to a specific surface and AFM imaging was used to measure their thickness. We found that the enzymes formed a single layer on the surface.

In our second project, we investigated the stability of porous membranes made of a specific type of block copolymer under different conditions using AFM. We discovered that treating the membranes with ultraviolet light for cross-linking improved their stability, making them more resistant to water and ethanol. We also confirmed the presence of nanopores in another type of polymer film. These pores were not affected by the ozonolysis treatment.

To understand the triboelectric effect, we established an AFM-based methodology called triboelectrification assay at the micro-scale (TEAMS). This method allowed us to study the physical origin of the triboelectric effect. We used KPFM to detect surface potentials and force spectroscopy to contact different materials at the micro-scale. We found that the separation of the contact and the humidity of the atmosphere had big effects on the charge generation. In addition, a noble type of organic compounds, redox active molecules, could enhance the triboelectric effect, making them promising for use in triboelectric nanogenerators. We believe that the TEAMS methodology can provide us valuable insights into a molecular understanding of the triboelectric effect.

Prof. Dr. Thorsten Hugel

Publications in livMatS