Fabrication of High Performance Carbon Nanostructured based Electrodes for Supercapacitor Applications
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2021-06
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Supercapacitors are the promising next-generation energy storage devices that bridge the gap between traditional capacitors and batteries, but still require their electrode material to be further developed. Here, this thesis aims at the development of novel, simple, scalable, and efficient techniques for fabrication of advanced electrode materials suitable for flexible planar supercapacitors (PSCs). Direct writing technique offers a way to pattern interdigitated electrodes precisely without using masks or cleanroom operations, thus giving the flexibility to produce supercapacitors in various sizes and architectures at low cost. The miniaturization of the electrodes to microscale results in enhanced charge storage capacity and rate capability in addition it promotes on chip integration of SCs. A CO2 Laser machine is used as a direct writing technique.
In the first study, a CO2 Laser system is used for concurrent in-situ doping, reduction, and patterning of graphene oxide-based films supported on flexible polyethylene terephthalate (PET) substrate. Three different devices are fabricated using the proposed approach, Laser reduced graphene oxide (LrGO), nitrogen-doped Laser reduced graphene oxide (N-LrGO), and sulfur-nitrogen co-doped Laser reduced graphene oxide (SN-LrGO) PSCs. Structural and elemental characterizations are performed to prove the successful integration of nitrogen and sulfur atoms into the graphene framework with high contents up to 3.71 at% N and 1.82 at% S, and at a low density of structural defects. Electrochemical performance of the devices is tested. An areal capacitance as high as 13.8 mF cm-2 at 10 mV s-1 and a maximum power density of 151.7 mW cm-3 at an energy density of 0.152 mWh cm-3 is achieved by SN-LrGO PSC composed of 10 interdigitated fingers with an excellent retention rate. Furthermore, higher operating voltage window and current ratings were easily achieved via series and parallel combinations of SN-LrGO PSCs directly on the same substrate. This manifests the versatility of the proposed approach for producing flexible and high-performance graphene-based electrochemical storage devices.
In the second study, a CO2 Laser system is used to carbonize fine coating of polyaniline supported on polyurethane (PU) nanofibers to produce high quality graphitic carbon. Controlling pore size distribution and structure in conventional carbonization method is challenging. Laser carbonization allow precise control over the distribution of pore size to be in the range of mesoporous(< 50 nm) by tuning Laser parameters . At first, PU is electrospun into fine nanofibers. The electrospinning conditions are tuned to control porosity and the radius of the nanofibers.