Within PEGASUS project a disruptive plasma technology and corresponding laboratory prototype (TRL ~ 3-5) of a versatile microwave plasma-based machine for a gram-scale fabrication of high-quality graphene and derivatives have been developed. Plasma based machine is a versatile, simple to use, provides high level of customization. It enables conversion of cheap carbon-based precursors (ethanol, CH4, etc.) into high-valued, high-quality graphene derivatives with tailored properties. Using the same machine different structures, can be fabricated, such as pure graphene sheets, N-graphene, hybrid nano-materials using graphene as a highly conductive matrix to incorporate metal oxides nanoparticles. The plasma machine provides high level of control and customisation via the application of special protocols, resulting in a controllable level of N-doping, oxygen impurities and sheets size (~300 – 400 nm). The type and level of doping is controlled by the position where N-precursor is injected into plasma environment and by the type of precursor used. Controllable, continuous fabrication of graphene/N-graphene at a gram scale ensuring high-level single layer selectivity (~50 %), high production rate (~30 mg/min) and repeatability while using ethanol, methane, acetonitrile as starting materials has been achieved. The fabricated graphene/N-graphene sheets possess high quality as evidenced by comprehensive physicochemical analyses made (for pure graphene C/O ratio: > 50; sp2% ~ 70%; for N-graphene C/O ratio: > 40; sp2% >60%).
Moreover, a novel method for a single-step, microwave plasma driven controllable assembly of nanocomposites comprising N-graphene sheets decorated with metal oxide nanoparticles at atmospheric pressure that circumvent drawbacks associated with conventional methods was developed. The plasma-based method enables reduction of micron sized metal oxides particles into nanoparticles as well as formation of new phases of metal oxides.
Furthermore, vertically aligned N-graphene structures were fabricated using low-pressure radio frequency inductively coupled cold nitrogen plasma treatment, and a high doping level (~8-12 at %N) was attained. It is also identified that the bonding configurations of the nitrogen groups can be adjusted by varying plasma parameters. Based on the experimental evidences, a nitrogen incorporation mechanism in graphene is established. A fast and facile technique for decorating vertical graphene and vertical carbon structures with metal nanoparticles using plasma sputtering was also elaborated. Exploiting capacitively coupled RF plasma where temperatures go as low as 480°C fast growth (minutes) of vertical graphenes/N-graphenes was achieved for a large variety of substrates. Using a hybrid microwave-DC plasma reactor vertically oriented carbon nanostructures were successfully grown on Ni-foam in a very short time (~ 8 min) at atmospheric pressure conditions as well.
Taking advantage of the exceptional electrical conductivity and extensive electrochemically active surface area of the graphene produced within the project, two supercapacitor demonstrators were developed. Aimed at IoT applications, a graphene-based supercapacitor as well as a smoothing AC-DC converter supercapacitor with the potential to replace tantalum electrolytic capacitors have been developed.
In addition to the above energy storage applications, some of the graphene-based vertical nanostructures produced during the PEGASUS period have been shown to have excellent energy storage properties for battery systems, suggesting the extension of the project to various research areas related to energy.
