Surface engineering of commercial activated carbon for improving the charge storability of electrochemical capacitors / Sunil Vaishak

Faculty of Industrial Sciences and Technology

Thesis (Master of Science) -- Universiti Malaysia Pahang – 2023

Supercapacitors based on activated carbon are the representatives of sustainable devices among electrochemical energy storage devices because of their renewable electrode materials, eco-friendliness, longer life cycle and superior charge-discharge rate capabilities. However, to expand their commercial value, their current energy densities should be made comparable with the market leading Lithium-ion batteries. One of the approaches to increase the energy density is by maximizing the number of pores to incorporate more ions. A majority of the research on supercapacitors demonstrated excellent laboratory-scale results through improving porosity, where the mass loading of such electrodes has a staggering difference from the industrial standards. These factors predominantly suppressed the initiatives to lift the biomass-derived carbon-based electrodes into the commercial picture. To address this issue, the present thesis focuses on expanding the electrochemical properties of commercial activated carbon derived from palm kernel shells by engineering its porosity in an eco-friendly and cost-effective manner. Herein, we employ the nitric acid refluxing method for the activation purpose, which, unlike the conventional routes, not only limits the usage of harsh chemicals, but also enables recyclability. We have optimized the performance of the electrode materials by refluxing the activated carbon for various acid to precursor ratios and refluxing duration. The electrochemical performances of the resulting materials were examined in a three-electrode system configuration in 1 M sodium sulphate electrolyte. The specific capacitance of the optimum sample was increased ~110% following a significant reduction in Warburg impedance. To understand the physicochemical alterations introduced upon refluxing, the as-synthesized carbon samples were characterized using X-ray Diffraction, Fourier Transform Infrared Spectroscopy, Scanning ElectronMicroscopy, Energy Dispersive Spectroscopy, and gas adsorption measurements. With~75% increment, a highest surface area of ~722 m2·g-1 was recorded for the 72 hoursrefluxed sample, which aligns with the increased electrochemical performance incorresponding electrodes. Further, supercapacitor devices were fabricated using thisoptimized sample by varying the mass loading (~3, ~6, ~9, ~12, and ~14 mg·cm2), andthe electrochemical properties were studied. All the fabricated devices achieved apotential window of 1.8 V in 1 M sodium sulphate. The highest mass loaded (~14 mg·cm-2)device fabricated using the prepared material has delivered a maximum arealcapacitance of ~494 mF·cm-2, an energy density of ~13 mWh·cm-3, and a maximumpower density of ~2189 mW·cm-3. The current research thereby demonstrates anenvironmentally friendly and economic approach for engineering the porosity ofcommercial activated carbon to enhance the charge storability for practical applications.