Cost-effective, environmentally-sustainable and scale-up synthesis of vertically oriented graphenes from waste oil and its supercapacitor applications

Vertically oriented graphenes (VGs) have attracted tremendous attention in a variety of energy storage-related applications. However, the high cost of preparing VGs significantly hinders their practical applications. Herein we introduce the Ar-plasma-enhanced chemical vapor deposition to demonstrate the cost-effective, environmentally-sustainable, and scale-up synthesis of VGs from waste oil. In our system, Ar gas can improve the electron energy and ionization rate of plasma, which breaks down the chemical bonding of waste oil into essential species to etch the amorphous carbon, yielding large-area VGs (12 × 3.5 cm 2 ) with highly-oriented structure and superior growth efficiency beyond VGs from hydrocarbon precursors. In the supercapacitor applications, the VG-based electrode exhibits significantly enhanced capacitance (~4 times that from conventional hydrocarbon gases) and efficient AC (alternating current) filtering capability RC (resistor-capacitor) (time constant of of 163 μs at 120 Hz), which is obviously superior to the non-oriented counterpart. Besides, MnO 2 /VGs composite electrode is prepared to deliver a maximum energy density of ~33.2 Wh/kg at 1.0 kW/kg and a power density of 10.2 kW/kg at 22.9 Wh/kg. In the end, the economic analysis suggests that the total cost of VGs can be reduced by ~32%. This work provides an environment-friendly and low-cost avenue for preparing VGs for advanced energy storage applications.