Invited Paper PS+2D-ThM4
Plasma Processes of Graphene and Related 2d Materials for Energy Applications

Thursday, October 22, 2015, 9:00 am, Room 210A

Plasma-assisted direct-growth of arrayed graphene and related hybrids will be presented. The main advantages of this type of nanostructures include high conductivity, high surface area and corrosion resistance, making them excellent candidates as electrocatalytic supports or electrodes for electrochemical (EC) energy applications, including fuel cells, supercapacitors and solar fuels. We will demonstrate the fabrication of integrated energy devices in an on-chip manner. Since the carrier transfer rate of electrode plays a crucial role in determining the energy-conversion performance, special emphases will be placed on the control of interfaces. Vertically aligned and edge-oriented graphene arrays were first synthesized by microwave plasma-enhanced chemical vapor deposition. Subsequent chemical doping can also be done in the same plasma reactor via either in-situ or ex-situ manners. Interestingly, for nitrogen doping in graphene, plasma process resulted in selective bond configuration. When applied as an EC electrode, the arrayed graphene exhibits nearly reversible redox characteristics. By varying the process parameters, samples can be produced with controllable compressive or tensile strains, which in term show strong effects on the resultant catalytic properties.

The hierarchical graphene nanowalls can be directly grown on a variety of substrates, including Si wafers, carbon cloth as well as flexible and ultralight carbon nanofibers. The latter substrate makes such electrode an ideal portable platform having high gravimetric, areal, and volumetric electrochemical characterizations. For instance, the carbon nanofibers supported graphene-based supercapacitors exhibit excellent specific capacitance of 352.53 F/g (220.33 mF/cm²) at a specific current of 13.33 A/g, which is among the highest reported to date. Meanwhile, 99 % of Coulomb efficiency and 98 % of the initial capacitance after 10,000 charge-discharge cycles were maintained. Finally, efficient and simple routes to further attach other heterogeneous nanostructures onto graphene nanowalls have also been developed. Cyclic voltammeter studies for electro-oxidation of methanol show a high ratio of forward anodic peak current to reverse peak current, suggesting an efficient oxidation of methanol to CO₂ on the graphene-based electrode. Our approach offers a promising route toward wafer-scale fabrication of graphene not only for fundamental research but also opens up various potential applications in sensing, catalysis, as well as energy storage and production.