Novel synthesis of highly porous spinel cobaltite

Novel synthesis of highly porous spinel cobaltite ( NiCo 2 O 4 ) electrode material for supercapacitor applications A. Nirmalesh Naveen and S. Selladurai Citation: AIP Conference Proceedings 1591, 246 (2014); doi: 10.1063/1.4872560 View online: http://dx.doi.org/10.1063/1.4872560 View Table of Contents: http://scitation.aip.org/content/aip/proceeding/aipcp/1591?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Sonochemically precipitated spinel Co 3 O 4 and NiCo 2 O 4 nanostructures as an electrode materials for supercapacitor AIP Conf. Proc. 1512, 1216 (2013); 10.1063/1.4791488 Determination of Crystal Changes on Sodium Cobaltite ( NaCo 2 O 4 ) by Reitveld Analysis as a Suitability Function in Thermoelectric Materials AIP Conf. Proc. 1217, 83 (2010); 10.1063/1.3377894 Magnetic frustration in the spinel compounds Ge Ni 2 O 4 and Ge Co 2 O 4 J. Appl. Phys. 97, 10A512 (2005); 10.1063/1.1863113 Porous nanotubes of Co 3 O 4 : Synthesis, characterization, and magnetic properties Appl. Phys. Lett. 85, 2080 (2004); 10.1063/1.1789577 Synthesis and magnetic properties of CoFe 2 O 4 spinel ferrite nanoparticles doped with lanthanide ions Appl. Phys. Lett. 78, 3651 (2001); 10.1063/1.1377621

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Novel Synthesis of Highly Porous Spinel Cobaltite (NiCo2O4) Electrode Material for Supercapacitor Applications A. Nirmalesh Naveen1,* and S. Selladurai1 1

Ionics Laboratory, Department of Physics, Anna University, Chennai-600025, India *Email: [email protected]

Abstract. High performing porous nickel cobaltite (NiCo2O4) nanomaterial is prepared using novel cost effective auto combustion technique. Physical characterization reveals the formation of nickel rich spinel cobaltitie with average crystallite size of 17 nm. Electrochemical evaluation of the sample is carried using cyclic voltammetry (CV), chronopotentiometry (CP) and AC impedance techniques. The Pseudocapacitive nature of the material is observed from CV and CP studies exhibiting a high specific capacitance of 772 Fg-1 at a current density of 1 Ag-1. The low resistive behavior of the material is seen from the impedance spectra, projecting nickel cobaltite as promising material for supercapcitor applications. Keywords: Nickel cobaltite, Auto combustion, Supercapacitors and Cyclic Voltammetry. PACS: 82.47.Uv, 82.45.-h, 88.40.fh, 88.85.jp.

nickel cobaltite (NiCo2O4) has been investigated as the high performing electrode material for supercapacitor application owing to its high electrical conductivity and better electrochemical activity than binary Nickel oxide (NiO) and Cobalt oxide (Co3O4). Previously, there are several reports on the synthesis of nickel cobaltite and its electrochemical evaluation. For example Lu et. al have prepared high performing nickel cobaltite using epoxide assisted sol-gel method, surfactant assisted solution method has been used [1], nanorods and ultrathin nanosheets of NiCo2O4 on carbon nano fiber was obtained by Genqiang and Xiang [2] and self-assembled porous NiCo2O4 on Ni foam using hydrothermal method was reported by Liu et.al [3]. Here for the first time we are reporting the synthesis of highly porous nickel cobaltite using auto combustion (or solution combustion) technique. It is a very rapid and cost effective synthesis process where the product is obtained in 4 to 5 h. For large scale mass production of nanomaterials auto combustion proves to be an efficient method. It is well known that highly porous nanomaterials with large specific area are obtained by gases evolved during the combustion process, which are most desirable for supercapacitor applications.

INTRODUCTION Efficient energy storage devices are recently the center of attraction among the researchers. Electrochemical devices like battery, capacitors, fuel cells etc. play an important role in energy storage. Supercapacitors are highly attractive for their high power density, faster charge/discharge process, and longer lifespan, and hold great potential as power sources for applications requiring fast bursts of energy or as backup power sources in electric vehicles. Flexible and size reduced electronic devices are possible with the help of flexible solid state supercapcitors, which will gain much scope in the future market. Unfortunately, commercial availability of supercapacitors is hindered by the heavy cost of high performing electrode materials. Materials for supercapacitor can be broadly classified into three categories 1) Carbon materials 2) Transition metal oxides and 3) Conducting polymers. Among these transition metal oxides like RuO2 have exhibited ideal superior performance but its applicability is limited by the high cost and toxicity of the material. Undoubtedly nanostructured transition metal oxides are capable of delivering the required enhanced capacitive performance. Characteristics like high surface area, shorter ion diffusion pathways and fast electron transport made transition metal oxides a promising material for capacitive applications. Recently ternary

Solid State Physics AIP Conf. Proc. 1591, 246-248 (2014); doi: 10.1063/1.4872560 © 2014 AIP Publishing LLC 978-0-7354-1225-5/$30.00

246 This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to IP: 14.139.161.3 On: Sat, 03 May 2014 07:21:12

size estimated from the equation was 17 nm. Hence the solution combustion method proves to be a viable method for the preparation of small size nanoparticles.

MATERIAL SYNTHESIS All the chemicals were used without further purification. In this typical procedure 20 ml of 0.125 M of Ni(NO3)2 and 0.25 M of Co(NO3)2 (1:2 molar ratio) was stirred together to form a homogeneous solution. To this mixturee 10 ml of nitric acid was added. 2.8 g of citric acid (fuel) was added to the above solution. Sol-gel gel was obtained by heating under stirred condition which was later transferred to the hot plate for the initiation of auto combustion process. Porous productt obtained was calcined at 400 ̊ C for 4 h.

Electrochemical Evaluation The capacitive behavior of the material was examined qualitatively using the cyclic Voltammetry technique.. CV recorded in 1 M KOH electrolyte is shown in figure 2. The CV curve of the material deviates from the ideal rectangular shape observed for electric double layer capacitance (EDLC), hence the major type of charge storage mechanism is pseudocapacitive in nature. Fig. 1 (a) shows the CV curve of the sample recorded orded at 5 mV scan rate between -0.2 – 0.55 potential window. Large potential window means high energy density of the material. A distinct pair of redox peaks was observed corresponding to the oxidation and reduction reaction along with regions where there is a constant response of specific current with the change of scanning potential. The CV curve shows two distinguishable regions, electric double layer region and redox reaction area. Hence the total capacitance is the sum of electric double layer capacitance Cdl and pseudocapacitance Cp. Evidently a large contribution to total capacitance comes from pseudocapacitance visible from the large integrated area under the redox region in voltammogram. The electrochemical reaction of nickel cobaltite here obeys the he reaction mechanism reported previously for mesoporous NiCo2O4 [6].

Structure and Phase Analysis Powder X-ray ray diffraction (PXRD) studies were carried for the structure and phase determination of the prepared compound. Figure 1 shows the PXRD pattern of nickel cobaltite calcined at 400 ̊ C for 4 h. Characteristic peaks of the nickel cobaltite were identified by comparing the XRD pattern with JCPDS data and major peaks were indexed. All the peaks corresponds to face centered cubic NiCo2O4 with a space group of Fd3m (JCPDS card no. 73-1702) 7 [4, 5]. A small peak at 51.6 ̊ indicates the presence of trace amount of nickel in the prepared material. material Less crystalline nature of the material calcined at 400 ̊ C can be seen from the figure.

FIGURE 1. Powder X-ray ray diffraction pattern of nickel cobaltite calcined at 400 C ̊ for 4 h.

FIGURE 2.. CV curve recorded at 5 mVs-1 scan rate in 1 M aqueous KOH OH electrolyte (a), CV recorded for 5, 10, 20 & 25 mVs-1 scan rates.

The average crystallite size of the material was calculated from the PXRD data using Debye-Scherrer Debye equation.

d=

0 .9 ∗ λ β ∗ cos θ

Cathodic sweeps of CV curves are not completely symmetric to their corresponding anodic sweeps, which denotes some irreversibility in faradaic process. Asymmetric CV curve depicts the rate kinetics of the redox reactions were quasi reversible. Factors like polarization during faradaic redox reaction for

(1)

Where, λ -X-ray wavelength, β -full width at half maximum, and θ- diffraction angle. Average crystallite


pseudocapacitors and ohmic resistance due to electrolyte diffusion into the porous electrode kinetically limits the reversibility for the positive and negative sweeps [7]. CV shape changes on increasing the scan rate. At low scan rates all the active species spec of the electrode material was fully utilized, whereas diffusion of ions to the innermost sites was hindered at high scan rates. Porous nature of the material felicitates rapid insertion/exertion of electrolyte electrol ions during redox reaction. The he current density de versus the square root of scan rate wass linear revealing the electrochemical reaction to be a diffusion controlled process.

region reveals the small ion diffusion resistance offered by the porous cobaltite nanomaterial.

FIGURE 4.. Complex plane impedance plots (Nyquist plot) of nickel cobaltite between 1 Hz - 105 Hz.

CONCLUSION Nickel cobaltite nanoparticles of 17 nm were synthesized using novel auto combustion technique. Electrochemical characterizations like CV, CP and impedance spectra reveal the superior pseudocapacitve behavior of the material. Porous cobaltite cobalti material exhibits a maximum specific capacitance of 772 Fg-1 at 1 Ag-1 current density. Low resistive nickel cobaltite is a promising electrode material for supercapacitor applications.

FIGURE 3. (a) Galvanostatic charge-discharge discharge curve of the material at 1 Ag-1 (b) for different current densities in 1 M KOH.

Galvanostatic charge discharge study (Chronopotentiometry) is a complimentary technique to CV. The charge - discharge profile of the material at a constant current is determined from this technique. The Pseudocapacitive behavior of the electrode material can be seen from the non-linear non chargedischarge curve (figure 3),, which is in good agreement with the CV studies. The specific capacitance of the nickel cobaltite was calculated from the equation

SC =

I ∗ ∆t m ∗ ∆V

ACKNOWLEDGMENTS Authors would like to appreciate the financial assistance stance provided by Anna University by providing Anna Centenary Research Fellowship (ACRF) for A. Nirmalesh Naveen (Lr.No.CR/ACRF/2013/37).

REFERENCES (2) 1. Genqiang Zhang and Xiong Wen (David) Lou, Adv. Mater. 25, 976–979 (2013). 1. Genqiang Zhang & Xiong Wen (David) Lou, Lou SCIENTIFIC REPORTS 3, 1470 (2013). 2. X.Y. Liu, Y.Q. Zhang, X.H. Xia, S.J. Shi, Y. Lu, X.L. Wang, C.D. Gu, J.P. Tu, Journal of Power Sources 239, 157-163 (2013). 4. Jun Liu, Chunping ping Liu, Yanling Wan, Wei Liu, Zengsheng M, Shaomin Ji, Jinbing Wang, Yichun Zhou, Peter Hodgsonb and Yuncang Li, Cryst Engg. Comm. 15, 1578–1585 (2013). 5. Rakkiyasamy Manimekalai,, Kalimuthu Kalpanadevi and Rangasamy Sinduja, Res. J. Chem. Sci. Sci (3), 76-78 (2013). 6. Rui Ding, Li Qi & Hongyu Wang, Wang J Solid State Electrochem 16, 3621–3633 (2012). (2012) 7. Sumanta Kumar Meher, P. Justin and G. Ranga Rao Nanoscale 3, 683–692 (2011). ).

Where, I – Current, Δt - discharge time, m – mass of the electrode material (0.3 mg) and ΔV – Potential difference (0.5 V). Nickel cobaltite exhibits a maximum specific capacitance of 772, 697, 600 6 and 300 Fg-1 at a current density of 1, 2, 5 and 10 A g-1 respectively. High specific capacitance is due to the porous nature of the material this is higher than previously reported values for porous nickel cobaltite and binary nickel cobalt oxide [6]. Nyquist plot obtained from the AC impedance technique summarizes the electron and ion transport properties in the electrode material. In figure 4 absence a of semicircle at high frequency region indicates the low contact and interfacial resistance of the material. Nearly linear line parallel to Y-axis axis at low frequency
