Converting plastic waste into carbon nanotubes as electrode materials for supercapacitors application

Abstract

There has been an increase in global demand for renewable energies due to the depletion and detrimental environmental impact of the traditional non renewable energy sources such as fossil fuels. Along with this, there is also an increase in demand for storage technologies to store renewable energy for non-immediate use. On the other hand, plastic pollution has always been a significant global environmental issue as most of the plastic products are non-degradable by nature and poses harmful risk to both human and the environment. This study evaluates the performance of in-house synthesized multi-wall carbon nanotubes from plastic as electrode materials for supercapacitor applications. Few walls carbon nanotubes (FWCNTs), multi-wall carbon nanotubes (MWCNTs) are being produced from plastic feed stock. The MWCNTs then undergo functionalisation with insertion of oxygen functional group using thermal method to produce functionalized multi-wall carbon nanotubes (FMWCNTs). These synthesized materials are characterized using Nitrogen Isotherm Adsorption Brunauer-Emmett-Teller (BET) surface area analysis, Raman Spectroscopy, X-Ray Photoelectron (XPS) analysis and Field Emission Scanning Electron Microscope (FESEM) and X-Ray Diffraction (XRD). Their performance on supercapacitor is also assessed using galvanostatic charge discharge analyser (GCD). The study found that MWCNTs have better capacitive performance than typical carbon-based electrode commercial supercapacitor. FMWCNTs have slightly higher specific energy and specific capacitance at ~10 mAh/g and 16.4 mWh/g respectively than MWCNTs with specific energy and specific capacitance at 9.97 mAh/g and 16.07 mWh/g). This can be attributed to higher specific surface area of FMWCNTs to provide more active site for the reaction as well as the oxygen functionalization to promote better charge transfer. However, the energy efficiency of FMWCNTs is lower at 81.84% than MWCNTs (87.27%) which can be attributed to the higher voltage drop for FMWCNTs during charge discharge study due to higher internal resistance of FMWCNTs. It is recommended to confirm the internal resistance using electrochemical impedance spectroscopy (EIS) for future study. A total of 2000 cycles are carried out on each sample and the results show stable cyclability with negligible capacity fading after 2000 cycles. Hence this project concludes that converting plastic waste to MWCNTs as electrode materials for supercapacitor are highly feasible to replace the electrode in typical commercial carbon-based electrode supercapacitor. This will also result in a win-win situation where waste plastic is being recycled to produce better performing electrode for supercapacitor, which is one of the answers to tackle the world energy crisis, climate change and plastic pollution.