Research into graphene-based electrodes is performed throughout both academia and industry. Researchers are always looking for new ways to increase the efficiency and properties of graphene-based electrodes.
A team of Researchers from China have now developed a graphene/activated carbon electrode coated in manganese dioxide (MnO2) microspheres for use in flexible solid-state supercapacitors.
Developments into new graphene-based electrodes for batteries and supercapacitors has exponentially increased in recent years. From pure graphene electrodes, to graphene coated electrodes, coated graphene electrodes and composite graphene electrodes, the field has become significant.
Activated carbon was the first and most widely used electrode for a long time before it became unfavorable in lieu of graphite, and subsequently graphene. New carbonaceous electrodes are appearing all time and small advancements are always being made, regardless of the carbon allotrope used.
There is a large pressure from industry to produce new electrodes with high efficiencies and excellent (or novel) properties due to the demands of new and next-generation technologies.
The Researchers from China have now fabricated high capacitance urchin type MnO2 microspheres onto a composite electrode film composed of both graphene and activated carbon, for use as a supercapacitance material.
The Researchers fabricated the electrode through a two-step binder-free self-assembly method using a facile vacuum filtration process.
Graphene oxide sheets were created using a modified Hummers’ method and the activated carbon was created using a series of wet chemical and carbonization techniques from waste fibreboard materials.
The activated carbon particles were then dispersed amongst the graphene sheets using ultrasonic methods to create flexible films, followed by the deposition of MnO2 microspheres in a controllable and tuneable manner using an electro-deposition process.
The supercapacitor device itself was fabricated by taking two pieces of the electrode film, placing them in parallel, incorporating a polyvinyl acetate (PVA) gel electrolyte, packing the device with a nickel foam and subjecting the components to high pressures to bind them all together.
The interspersion of the activated carbon particles helped to facilitate and efficient electrolyte ion transport and the deposition of MnO2 microspheres, which was controlled by a simple adjustment in the reaction times.
The Researchers characterized the electrodes using a combination of scanning electron microscopy (SEM, JEOL JSM-7001F), transmission electron microscopy (TEM, JEM-1010), field emission scanning electron microscopy (FESEM, SU8010). X-ray diffraction (XRD, Bruker D8), Raman spectroscopy (LabRAM HR Evolution) and X-ray photoelectron spectroscopy (XPS, Axis Ultra DLD).
The team also employed a CHI 660D electrochemical workstation with a three-electrode system to simultaneously measure cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), impedance spectroscopy (EIS) and cycling stability of the electrodes and the supercapacitance devices
The synergistic effects between the graphene sheets, activated carbon and MnO2 microspheres led to an electrode with excellent mechanical properties and electrochemical performance. The morphology of the MnO2 microspheres, which was determined through the tuneable deposition process, was found to affect the electrochemical performance of the electrodes.
The electrodes produced with an MnO2 deposition time of 1200 seconds were found to produce the most efficient and promising electrodes.
The composite electrodes were found to exhibit a maximum specific capacitance of 1231 mF cm-2 and a current density of 0.5 mA cm-2. The symmetrical supercapacitance device was found to possess a high mechanical flexibility. It retained 88.6% of their original capacitance after 500 bends, a high cycling stability with 82.8% of its original capacitance being retained after 10000 cycles, a maximum energy density of 0.27 mWh cm-3 and a maximum power density of 0.02 Wcm-3.
In addition to exhibiting excellent properties, the electrochemical performance was found to be stable overall and hasn’t fallen prey to common problems associated with new high energy electrodes, where an enhanced electrochemical performance is found but often at the expense of the device’s stability.
Overall, the Researchers have demonstrated an efficient and stable graphene-based electrode and supercapacitance device. Whether the research makes it past academia and into the commercial sector remains to be seen, but it does offer itself as a potential electrode material for flexible energy storage devices and wearable/flexible electronic device applications.
“High-performance MnO2-deposited graphene/activated carbon film electrodes for flexible solid-state supercapacitor”- Xu L., Scientific Reports, 2017, DOI:10.1038/s41598-017-11267-0