Elsevier

Electrochimica Acta

Volume 225, 20 January 2017, Pages 493-502
Electrochimica Acta

Synthesis and Characterizations of Electroless Oil Palm Shell Based-Activated Carbon/Nickel Oxide Nanocomposite Electrodes for Supercapacitor Applications

https://doi.org/10.1016/j.electacta.2016.12.101Get rights and content

Abstract

Activated carbon (AC) prepared by two-stage microwave-induced physical activation of oil palm shell have been coated using electroless plating technique to form nanocomposite material. The composite materials were calcinated at different temperature of 300, 400 and 500 °C for one hour. The nanocomposite materials were evaluated as potential electrodes for supercapacitors. Using the composite electrodes in a two-electrode symmetrical capacitor, the properties of the composite electrodes were investigated by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS). Results from electrochemical measurements show that the nanocomposite electrodes exhibit superior capacitive performance compared with the AC electrode. The specific capacitance have been found to increase by 85–205% with respect to the AC electrode. In addition, the specific capacitance as well as the energy density were found to reduce with the increment of the calcination temperature. The composite electrode calcinated at 300 °C offers the maximum enhancement of 205% in both specific capacitance and energy density.

Introduction

Supercapacitors – also known as electrochemical capacitors or ultracapacitors – are rechargeable energy storage devices that convert chemical energy into electrical energy by means of electrochemical reactions and store the energy as charge on the electrode surface or sub-surface layer. The storage of charge on the electrode surface affords the supercapacitors the opportunity to provide high power due to the relative ease with which they release energy from electrode surface unlike batteries that store energy in bulk material. In addition, supercapacitors possess excellent cycling ability because the charging-discharging occurred on the electrode surface and does not induced drastic structural changes upon electroactive materials. Therefore, supercapacitors which are currently lying between electrochemical batteries and conventional capacitors are seeing as a promising replacement for batteries especially in the areas of load levelling and electrical energy storage devices, and also for applications that required maximum power, long cycle life, operational stability, fast charge-discharge time, low level of heating, appropriate dimension/weight and low cost [1], [2], [3].

Electrode material being one of the major factors that determine supercapacitors’ performance has continued to attract a lot of research interests. There are three types of electrode materials namely, carbon-based materials, transition metal oxides and conducting polymers; however, their usage falls into two categories. While carbon-based materials such as activated carbon [4], [5], carbon black [6], carbon nanotubes [7], glassy carbon, carbon aerogel [8], and graphene [9] are used as electrode materials in electrochemical double-layer capacitor, transition metals such as RuO2 [10], MnO2 [11], NiO [12], [13], ZnO [14] and TiO2 [15] or conducting polymers such as polyaniline [16], polythiophene [17] and polypyrrole [18] are used for pseudocapacitors. And recently, transition metal phosphide and molybdenum chalcogenides (MoS2) have been investigated due to their low cost [19], [20]. Each of these electroactive materials that are commonly use as electrode has merits and demerits whichare uniquely associated with them and which govern their application in supercapacitors as enumerated below.

  • a

    Carbon-based materials: Provide high power density due to high surface area and have long cycle life but small specific capacitance which are mainly double layer capacitance

  • b

    Metal oxides/hydroxides: Have wide potential window and combined pseudocapacitance with double layer capacitance but have poor cycle life and relatively small surface area.

  • c

    Conducting polymers: Have good conductivity, high capacitance, low cost and ease of fabrication but have poor cycle life and relatively low mechanical stability [21].

The combination of these disparate capacitive materials to form a composite electroactive material constitutes an important approach to the development, control and optimization of the structure and properties of the electrode material to augment their performance for supercapacitors. For example, supercapacitors with high specific capacitance and rate capability could be obtained when asmall amount of transition metal oxide is uniformly dispersed on the high surface area, porous and conductive carbon materials [22], [23]. The properties of composite electrodes are dependent on the individual components and the morphology and interfacial characteristics of the composites. In the last decade, there has been an increase in research interest towards the development of composite electrode materials. As a result, researchers have come up with all kind of composite materials such as activated carbon mixed with either metal oxides or conducting polymers, metal oxides mixed with conducting polymers, graphene mixed with metal oxides or conducting polymers andcarbon nanotube with metal oxides or conducting polymers. Material selection, surface area, particle size, synthesis method, fabrication process parameters and electrical conductivity are some of the factors to be considered during design and fabrication of composite electrode materials [21].

Many researchers have used different experimental techniques to synthesize composite electrode materials.Among these experimental techniques wet impregnation and electrodeposition are the most widely used synthesis methods, however, good control of morphology and particle size are lacking in wet impregnation while in electrodeposition additional electricity and electrodes are needed. Recently, electroless deposition is gaining more interest among researchers as an effective synthesis method of depositing metal nanoparticles [14], [24] due to its low cost, simple process, ability to produce deposit with uniform thickness on surfaces with complex shapes and geometrics, high reproducibility and simple equipment requirement [24], [25]. However, the effect of electroless deposited nickel oxide particles on the surface of the AC and their influence on the power and energy capacity of the supercapacitor has not been investigated. Furthermore, there is no reported work on the application of oil palm shell based-activated carbon and its composites as electrodes for supercapacitors, to our knowledge.

In this study, oil palm shell based-activated carbon/nickel oxide nanocomposites have been organized using electroless deposition method. Three samples were prepared and heat treated at different temperature in other to study the effect of heat treatment temperature on the supercapacitive performance and compared with respect to AC electrode. The activated carbon electrodes were prepared using a two-stage microwave induced physical activation. Activated carbon from biomass is most widely used as supercapacitor electrodes because of large surface area due to high surface porosity, controlled pore structure, good electrical conductivity, good thermal and chemical stability, ease of processability, low framework density, compatibility in nanocomposite materials, ready abundance and relatively low cost [26], [27], [28].

Section snippets

Preparation of activated carbon

Oil palm shells (OPS), which are wastes obtained from local palm oil mill located in the Johor State of Malaysia, was used as precursor for preparing microporous activated carbons. The OPS was washed with distilled water and dried. The OPS was then ground and sieved to obtain average particle size of 2 mm. A two-step microwave-induced physical (CO2) activation was used to prepare the activated carbon (AC). First, OPS was carbonized in a modified domestic microwave (1 kW, 2.45 GHz) attached with

Structural analysis and morphological characteristics

Pore structure characterization of the OPSAC was carried out using the standard Nitrogen adsorption procedure. Fig. 1(a) depicts the N2 adsorption/desorption isotherm of the OPSAC. Based on IUPAC classification, the isotherm belong to Type I. From Fig. 1(a) it can be seen that at relatively low P/Po (up to 0.2), there is high adsorption as a result of enhanced adsorbent-adsorbate interaction which indicates that the OPSAC is predominantly microporous. In addition, there is an increment in the

Conclusion

Oil palm shell-based activated carbon (OPSAC) electrodes for supercapacitor applications were prepared by two-stage microwave-induced physical activation. The OPSAC electrode with surface area of 574.37 m2/g was modified by electroless deposition of nickel oxide (NiO) nanoparticle on the surface of the electrode to form a composite electrode. The nanocomposite electrodes were calcinated at 300, 400 and 500 °C for 1 hour. Two-electrode symmetrical supercapacitor cells containing 1 M H2SO4

Acknowledgement

Financial supports from the Ministry of Higher Education (MOE), Malaysia and UTM through the Research University GrantsVot Nos 4F600 and 10H23 are gracefully acknowledged. Abubakar Tafawa Balewa University, Bauchi and TetFund, Nigeria are also acknowledged for the intervention program.

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