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

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 hours refluxed 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 a real capacitance of ~494 mF·cm-2, an energy density of ~13 mWh·cm-3, and a maximum power density of ~2189 mW·cm-3. The current research thereby demonstrates an environmentally friendly and economic approach for engineering the porosity of commercial activated carbon to enhance the charge storability for practical applications

Hybrid Nanocomposite Metal Oxide Materials for Supercapacitor Application

Transition metal oxides qualify themselves as promising electrode material for supercapacitor applications by virtue of its large values of capacitance and energy density, facilitated by reversible faradaic redox reactions at the electrode-electrolyte interface. However, poor conductivity, lower surface area and lower power density curb their deployment in practical applications. Towards this end, establishing a synergistic effect among the transition metal oxides has been recognized as a feasible way to overcome the limitations of individual metal oxide components without compromising its pseudocapacitance. These hybrid metal oxide composite electrodes can achieve better electrical conductivity and enhance the flow of electrolytic ions into the active part of the electrode material, thereby utilizing the full potential of the device. This chapter intends to present a decent update on the synthesis methods, structural properties and electrochemical performances of various hybrid nanocomposite transition metal oxide materials for supercapacitor application

Characterization of supercapacitive charge storage device using electrochemical impedance spectroscopy

In combination with an analogous circuit pattern, the electrochemical impedance (EIS) spectra aids in examining the physical origin of the different electrical components involved in the device. In this research, to illustrate the various physical processes taking place in energy-storing electrodes, the EIS spectra in the entire frequency area is divided into specific electrical elements such as resistors and capacitors with the help of Z view software and determined origin of their charge storage properties. The EIS spectra of activated carbon (AC) – TiO2 or MnO2 composites containing TiO2 in the range 5 – 20 wt% and nominal composition of MnO2 (5 wt% MnO2) are analyzed using the equivalent circuit fitting technique and the corresponding electrode parameters and performances are correlated

Pfibrolizer: A new paradigm for large scale electrospinning from lessons learnt from Malaysian kitchen

Electrospinning is a fiber production method, in which a liquid droplet is electrified to generate a jet, followed by stretching and elongation to generate fibers. Electrospinning setup mainly consists of 3 parts, a spinneret, high voltage source and a collector. The currently available electrospinning spinneret in markets has several drawbacks which limits its efficiency. Inspired from the Malaysian kitchen, we have designed a simple electrospinning spinneret head which is beneficial for large scale nanofiber production. This design also allows the user to easily modify the spinneret according to the requirements of morphology and number of fibers

Tailoring the charge storability of commercial activated carbon through surface treatment

Sustainability concerns in the electrochemical charge storage realm revitalized research on the electrochemical capacitors (ECs), or synonymously, supercapacitors (SCs), because of the renewability of their electrode materials and environmental benignity thereby, longer life cycle to improve materials circularity, and their inherent superior rate charging/discharging than batteries. As SCs store energy via the reversible adsorption of electrolyte ions on the electrode pores, maximizing the number of pores to accommodate the ions is the most desired way to improve the charge storability. In this regard, we report herewith a simple and facile approach for engineering the porosity of commercial activated carbon by refluxing it in nitric acid as a function of time; the BET surface area of the 72 h refluxed samples increased by 75 %. Charge storage properties of the modified electrodes are evaluated in a three-electrode system configuration in 1 M Na2SO4 electrolyte; a 75 % increase in the surface area led to an increase in specific capacitance over 110 % following a significant reduction in Warburg impedance. Besides, symmetric SC full cells were fabricated by varying the electrode mass between 3 and 14 mg·cm−2 in five steps. All the fabricated devices achieved a potential window of 1.8 V in 1 M Na2SO4. The highest mass loaded (∼14 mg·cm−2) device fabricated using the prepared material has delivered a maximum capacitance of ∼990 mF, the maximum areal capacitance of ∼494 mF·cm−2, an energy density of ∼13 mWh·cm−3, and a maximum power density of ∼2189 mW·cm−3. The device also maintained ∼97 % retention in capacitance with a remarkable coulombic efficiency of ∼97 % after 5000 cycles. The performance of the device is comparable with the commercial SCs used for low voltage DC hold-up applications such as embedded microprocessor systems. The procedure developed herewith supports easy recycling and reusing of the activation agent, and thereby reduces the release of toxic chemicals into the environment