These images show a graphene flake before (a), and two minutes (b) and eight minutes (c) after being exposed to a solution of lithium and liquid ammonia (Birch-type reaction). This causes the graphene to become gradually hydrogenated, starting at the edges. (Reprinted with permission from Zhang X. et al., JACS, Copyright 2016 American Chemical Society).Adding hydrogen to graphene could lead to it replacing silicon as the semiconductor of choice in computer chips. Researchers at the Center for Multidimensional Carbon Materials (CMCM), within the Institute for Basic Science (IBS) in South Korea, have recently gained further insight into this chemical reaction. Reported in a paper in the Journal of the American Chemical Society, their findings extend the knowledge of the fundamental chemistry of graphene and could bring scientists closer to realizing new graphene-based materials.
Understanding how graphene chemically reacts with a variety of chemicals will increase its utility. Graphene is such an excellent electrical conductor that it cannot be directly used as an alternative to silicon in semiconductor electronics because it does not have a bandgap: its electrons can move without having to climb an energy barrier. Adding hydrogen to graphene opens up a bandgap, potentially allowing it to serve as a semiconductor in new devices.
While other reports describe adding hydrogen to bulk materials, a process known as hydrogenation, this study focused on the hydrogenation of graphene made up of just a single or a few atomic layers. IBS scientists used a reaction based on lithium dissolved in ammonia, known as the ‘Birch-type reaction’, to add hydrogen to graphene through the formation of carbon-hydrogen bonds.
The research team discovered that hydrogenation proceeds rapidly over the entire surface of single-layer graphene, but proceeds slowly and from the edges in graphene that is a few layers’ thick. They also showed that defects or edges are required for the reaction to take place under the conditions used, because pristine graphene with its edges covered in gold did not undergo hydrogenation.
Using bilayer and trilayer graphene, IBS scientists discovered that the reagents can pass between the layers and hydrogenate each layer equally well. Finally, they found that the hydrogenation significantly changed the optical and electric properties of the graphene.
"A primary goal of our center is to undertake fundamental studies about reactions involving carbon materials," said corresponding author Rodney Ruoff, CMCM director and distinguished professor at the Ulsan National Institute of Science and Technology (UNIST) in South Korea. "By building a deep understanding of the chemistry of single-layer graphene and a few-layer graphene, I am confident that many new applications of chemically-functionalized graphenes could be possible, in electronics, photonics, optoelectronics, sensors, composites and other areas."
This story is adapted from material from the Institute for Basic Science, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.