Microwave plasma-based high temperature dehydrogenation of hydrocarbons and alcohols as a single route to highly efficient gas phase synthesis of freestanding graphene

Abstract

Understanding underlying processes behind the simple and easily scalable graphene synthesis methods enables their large-scale deployment in the emerging energy storage and printable device applications. Microwave plasma decomposition of organic precursors forms a high-temperature environment, above 3000 K, where the process of catalyst-free dehydrogenation and consequent formation of C2 molecules leads to nucleation and growth of high-quality few-layer graphene (FLG). In this work, we show experimental evidence that a high-temperature environment with a gas mixture of H2 and acetylene, C2H2, leads to a transition from amorphous to highly crystalline material proving the suggested dehydrogenation mechanism. The overall conversion efficiency of carbon to FLG reached up to 47%, three times as much as for methane or ethanol, and increased with increasing microwave power (i.e. with the size of the high-temperature zone) and hydrocarbon flow rate. The yield decreased with decreasing C:H ratio while the best quality FLG (low D/G–0.5 and high 2D/G–1.5 Raman band ratio) was achieved for C:H ratio of 1:3. The structures contained less than 1 at% of oxygen. No additional hydrogen was necessary for the synthesis of FLG from higher alcohols having the same stoichiometry, 1-propanol and isopropanol, but the yield was lower, 15%, and dependent on the atom arrangement of the precursor. The prepared FLG nanopowder was analyzed by scanning electron microscopy, Raman, x-ray photoelectron spectroscopy, and thermogravimetry. Microwave plasma was monitored by optical emission spectroscopy.

The application of plasma technology for the preparation of supercapacitor electrode materials

“…4b) to obtain carbon materials with different structures in a mixture of Ar-CH 4 -H 2 and adjusted the graphene phase purity and phase quality by adjusting the C/H ratio, showing that the increase in H 2 content significantly improved graphene purity and quality. Jasek et al 119 used an atmospheric pressure microwave plasma torch to form a high temperature environment of 3000 K to decompose simple hydrocarbons to form high quality few-layer graphene without the use of a catalyst. The research mentioned above demonstrates that direct graphene preparation using plasma technology has made progress and that this technique can produce graphene materials efficiently and greenly.…”

Superhydrophobic Graphene-Like Nanocarbon Film Formation on Arbitrary Surfaces through MgO Nanoparticle Catalysis: Advanced Coatings for Energy Storage and Nanocomposites

“…Recently, plasma-based synthesis of carbon nanomaterials has gained attention because it is energy-efficient, controllable, cost-efficient, easy to implement, and versatile and requires only one step or a few steps while still being environmentally friendly. Cold plasmas generate reactive radicals, charged species, and various reactive oxygen and nitrogen species as well as electromagnetic fields, light emissions, and thermal radiation. , The interaction of plasmas with a sample surface leads to unique physiochemical transformations such as a weakening of the existing bonds, catalysis of reactions leading to the formation of new compounds, surface etching and functionalization, and changes of the physical properties of the sample. − Microwave plasma has been used in the synthesis of graphene using hydrocarbons and alcohol precursors in high-temperature/pressure environments, − and nitrogen-doped graphene has been produced using a magnetically rotating arc-discharge plasma . So far, most of the reported studies of graphene synthesis using plasma technology have used high-temperature/pressure or vacuum environments.…”