Hydrogenation of Graphene by Reaction at High Pressure and High Temperature

Abstract

The chemical reaction between hydrogen and purely sp(2)-bonded graphene to form graphene's purely sp(3)-bonded analogue, graphane, potentially allows the synthesis of a much wider variety of novel two-dimensional materials by opening a pathway to the application of conventional chemistry methods in graphene. Graphene is currently hydrogenated by exposure to atomic hydrogen in a vacuum, but these methods have not yielded a complete conversion of graphene to graphane, even with graphene exposed to hydrogen on both sides of the lattice. By heating graphene in molecular hydrogen under compression to modest high pressure in a diamond anvil cell (2.6-5.0 GPa), we are able to react graphene with hydrogen and propose a method whereby fully hydrogenated graphane may be synthesized for the first time.

Near‐Stoichiometric Bulk Graphane from Halogenated Graphenes (X = Cl/Br/I) by the Birch Reduction for High Density Energy Storage

“…The hydrogen evolution process was further confirmed by Raman spectroscopy, by observation of characteristic changes in the Raman signals on increasing temperature up to 700 °C . This experiment was performed for the HG‐I graphene with the highest hydrogen concentration.…”

“…Key diagnostic features comprise the D (disorder) band at 1350 cm −1 arising from sp 3 ‐hybridized carbons, and the G (graphitic) band at ≈1580 cm −1 due to sp 2 graphitic regions . Specifically, after successful hydrogenation, monolayer hydrogenated graphene exhibits a sharp increase in its D band intensity, while highly hydrogenated graphenes in bulk quantities are known to show a large fluorescence background . Hence, as illustrated in Figure b, the Raman spectrum of HG‐Cl is observed with a narrow G band and a wide D band, and the average ratio of integrated D/G peak intensities is 2.4, suggesting extensive conversion of sp 2 ‐hybridized carbons to sp 3 as a result of hydrogenation.…”

“…Raman spectroscopy was subsequently employed to investigate the fundamental changes in structure and as a validation method to confirm hydrogenation . Key diagnostic features comprise the D (disorder) band at 1350 cm −1 arising from sp 3 ‐hybridized carbons, and the G (graphitic) band at ≈1580 cm −1 due to sp 2 graphitic regions .…”

“…Since then, additional strategies to produce hydrogenated graphenes were developed and can be categorized based on gaseous or liquid‐phase hydrogenation. Gaseous hydrogenation is typically achieved either at high applied pressure and temperature or under a hydrogen plasma . More recently in 2015, Smith et al proposed a method where fully hydrogenated graphane might be accessible using heat and compression in a diamond anvil cell, although no exact quantification of the hydrogen content was given.…”

“…Gaseous hydrogenation is typically achieved either at high applied pressure and temperature or under a hydrogen plasma . More recently in 2015, Smith et al proposed a method where fully hydrogenated graphane might be accessible using heat and compression in a diamond anvil cell, although no exact quantification of the hydrogen content was given. In comparison, liquid‐phase hydrogenation is performed via the esteemed Birch reduction, as first shown by Rao and co‐workers on few‐layer graphene in 2011 .…”