Researchers reveal effects of defects on the electron emission property of graphene electrodes

Researchers reveal effects of defects on the electron emission property of graphene electrodes

Schematic representation of a thermionic energy converter. Photo credit: Zhao Ming

After studying the effects of irradiation defects on the work function of graphene electrodes in thermionic energy converters (TECs), a research team found that creating defects in graphene through irradiation would increase the work function and decrease the electron emission capacity. This leads to reduced output power and conversion efficiency of TECs.

The research team, led by Prof. Yu Jie and associate Prof. Jiang Zhizhong from the Hefei Institute of Physical Science, Chinese Academy of Sciences, published their findings in Applied Surface Science.

Graphene has tremendous application potential as an electrode coating material for TECs of microreactor, which can significantly improve the electron emission ability of the electrode.

Electrode materials are exposed to irradiation by high-energy particles during the use of TECs. Previous studies have shown that the types of defects induced in graphene by irradiation are mainly Stone-Wales defects, doping defects, and carbon vacancies. The occurrence of defects affects the adsorption properties of alkali and alkaline earth metals on the graphene surface in the electrode gap, and then changes the electron emission properties of the graphene coating.

In this study, researchers analyzed the internal mechanism of influence of defects on the properties of graphene. They studied the adsorption and migration behavior of alkali and alkaline earth metals on the surface of defective graphene at the atomic level by using the DFT calculations.

Researchers reveal effects of defects on the electron emission property of graphene electrodes

Migration behavior of alkali and alkaline earth metal atoms on pristine and oxygenated defective graphene surfaces. Photo credit: Zhao Ming

“The defect sites act as traps to trap metallic adatoms,” explained Zhao Ming, a member of the team. “Metal diffusion near the Stone-Wales defect and the carbon vacancy defect has been severely hampered. The metal migration barrier on the graphene surface doped with boron (B) or oxygen (O) also increased slightly.”

And in particular, it turned out that the work function of graphene with Stone-Wales defect, carbon vacancy defect and dopants was significantly increased, which was mainly due to the decrease in the probability of dipole formation and the increase in the cohesion energy of the metal.

These fundamental findings provide theoretical guidelines for the application of graphene-coated materials in TECs.

More information:
Ming Zhao et al, Basic principle study on adsorption and migration of alkali and alkaline earth metals (Rb, Cs and Ba) on graphene, Applied Surface Science (2022). DOI: 10.1016/j.apsusc.2022.155505

Provided by the Chinese Academy of Sciences

Quote: Researchers Reveal Effects of Defects on Electron Emission Property of Graphene Electrodes (2022, November 23), Retrieved November 23, 2022 from https://phys.org/news/2022-11-reveal-effects-defects-electron-emission. html

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