Accepted Manuscript Investigation of electrochemical capacitance of 18k nanoporous current collector incorporated MnO2 V.S. Prabhin, K. Jeyasubramanian, I. Jeyaseeli Rashmi, G.S. Hikku, Pandiyarasan Veluswamy, Byung Jin Cho PII: S0254-0584(18)30721-1 DOI: 10.1016/j.matchemphys.2018.08.056 Reference: MAC 20899 To appear in: Materials Chemistry and Physics Received Date: 29 July 2017 Revised Date: 24 March 2018 Accepted Date: 20 August 2018 Please cite this article as: V.S. Prabhin, K. Jeyasubramanian, I. Jeyaseeli Rashmi, G.S. Hikku, P. Veluswamy, B.J. Cho, Investigation of electrochemical capacitance of 18k nanoporous current collector incorporated MnO2, Materials Chemistry and Physics (2018), doi: 10.1016/j.matchemphys.2018.08.056. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. ACCEPTED MANUSCRIPT Investigation of Electrochemical capacitance of 18k nanoporous current collector incorporated MnO2 V.S. Prabhina, K. Jeyasubramanianb,*, I. Jeyaseeli Rashmic, G.S. Hikkud, Pandiyarasan Veluswamye, & Byung Jin Choe Department of Electronics and Communication, VV College of Engineering, RI PT a Tisaiyanvilai, India. *,b Centre for Nano Science and Technology, Department of Mechanical Engineering, Mepco Schlenk Engineering College, Sivakasi, India. Department of Electronics and Communication, Kamaraj College of Engineering and SC c Technology, Virudhunagar, India. d Department of Electronics and Communication, PSN College of Engineering and Department of Electrical Engineering, KAIST, 291 Daehak-ro, Yuseong-gu, Daejeon EP TE D 34141, Republic of Korea AC C e M AN U Technology, Tirunelveli, India. ACCEPTED MANUSCRIPT Investigation of Electrochemical capacitance of 18k nanoporous current collector incorporated MnO2 RI PT Abstract: This paper deals with the fabrication of super capacitor electrode material employing a facile etching process followed by electrodeposition. Nanoporous gold current collector has been fabricated by chemically dealloying commercially available 18k gold having a composition of 74 % Au and 24 % Cu and 2 % Ag, with dilute HNO3 solution. Electrochemically deposited SC MnO2 over the prepared porous Au electrode exhibits a very high specific capacitance value of 1 M AN U 670 Fg-1 which is about 1.65 times greater than of MnO2 coated unetched Au electrode (407 Fg). Etched and unetched MnO2 coated electrode materials are characterized using XRD, FESEM with EDAX and AFM. Electrochemical characterization of the obtained hybrid material is evaluated by running several cyclic voltagramms using electrochemical workstation. In contrast to the MnO2 coated unetched Au hybrid electrode system, nanoporous Au-MnO2 electrode TE D displays higher phase angle (79º) and lower time constant (2 ms) derived from the bode plot suggesting a better capacitance electrode. The high specific capacitances offered with good charge/discharge rates at a potential window of 0 to 0.8 V, in the scan rate of 100 mV/s for 1000 EP cycles, exhibiting high-energy storage density of 32.56 wh/kg and 53.6 wh/kg and power density AC C of 366 w/kg and 603 w/kg for un-etched and etched electrodes respectively. Keywords: Electrochemical deposition, supercapacitor electrode, nanoporous thin gold foil, etching. 1 ACCEPTED MANUSCRIPT 1. Introduction Electrochemical supercapacitor is one of the prominent alternative power storing devices that mainly stores the charges by electrostatic charging (Helmholtz double layer) or reverse RI PT faradic reactions . Recently, it has attracted the attention of researchers since they connect the energy and power density gap between batteries and capacitors . In the supercapacitor electrode fabrication, the selection of electrode material and current collector plays a major role. SC Current collector is normally chosen from precious metals like gold since it possesses excellent chemical stability and very high conductivity . Compared to the usage of smooth electrode, M AN U porous electrodes are widely used in consideration of storage capacity, reaction rates and transport of mass and charge. The pores found in the electrode not only increase the surface area but also accommodate more active material that are used and display high specific capacitance values. Such predominant characteristics of supercapacitor electrode pores are achieved by many TE D routes. Especially, if the pore size is too small (<1 nm), the removal of solvated molecules is difficult, whereas if the pore size increases beyond the mesoporous range (>50 nm), the capacitance value gets decreased owing to the reduction in the surface area . So, care should EP be taken in controlling the mesoporous range (10-50 nm), otherwise the efficiency might be less. So far, different kinds of active materials are being used along with electrodes. Selection AC C of these materials is based on some specific characteristics like toxic level, availability, stability, etc. Among them carbon-based materials like activated carbon, CNT, graphene oxides, graphene, etc. are most popular, and a few of them have significant porosity and facilitate more charge storing properties [5-11]. Using hierarchically porous polymer scaffolds and carbon monoliths, high-voltage aqueous supercapacitors were fabricated which works in the potential window of 2.4V . Composite films produced using graphene-CNT, graphene-polymer combinations and 2 ACCEPTED MANUSCRIPT edge enriched graphene quantum dots have displayed higher specific capacitances [13, 14]. Doping of metal oxides (CuO2, TiO2) into sulphonated polyaniline (SPAN) enhances the electrochemical capacitance values [15-19]. The reduced crumbled graphene is used as electrode RI PT material displays higher energy density [20-23]. Conducting polymer-based electrodes are preferred in medium power applications . While compared with the other electrode materials, polymer-based materials exhibit reduced lifecycles. Besides, some pervoskite materials are also SC used in the fabrication of supercapacitor electrode material . Furthermore, among the transition metal oxide, MnO2 nanoparticles are used as a dielectric material owing to its high M AN U capacitance, easy synthesis procedure, availability, nontoxic nature and stability [26-30]. Apart from the use of nanoporous dielectric materials used in the supercapacitor electrodes, researchers have developed pores on the electrode by employing various synthetic strategies. Recently, Xing Lang et al. achieved nanolevel pores on the alloy of Ag65Au35 by dipping into a 70 % HNO3 TE D solution , and they report about the capacitance of 601Fg-1. Laleh Enayati Ahangar et al prepared the nanoporous gold electrode from small pieces of recordable compact disk (CD) made of gold. The protective layer of the CD is etched using nitric acid. Eventually, pores are . EP developed on nanometer range which helps in improving the efficiency of the resultant system AC C Instead of using porous Au substrate Jeyasubramanian et al. reported the usage of needle- shaped Cu collector with fractals having large space that is able to accommodate more charges. Subsequent coating of nano MnO2 through electrodeposition displays a very high capacitance of 486 Fg-1 . It is clear from all these facts that higher specific capacitance can be achieved by the usage of nanoporous current collector followed by coating nano-shaped MnO2 particles through electrodeposition. The novelty of this work is the fabrication of nanoporous Au substrate 3 ACCEPTED MANUSCRIPT from the commercially available 18k gold foil of thickness around 1.0 mm employing nitric acid as etchant. Role of porosity generated on the gold substrate is compared with the electrode surface not having any pores towards the charge storing property of the electrodes. Further, the RI PT electrochemically obtained manganese oxide results in transformation of MnO2 to Mn3O4 and Mn2O3 which limits the use of this electrode at high temperatures . Since the 18k gold is an alloy of Au, Cu and Ag, during the etching with nitric acid, the Cu and the Ag atoms present on SC the substrate reacts spontaneously with nitric acid and depart from Au foil leaving nanopores. Electrochemically deposited MnO2 over the porous Au substrate exhibits a very high capacitance M AN U in contrast to the MnO2 coated unetched Au substrate. 2. Materials and Methods Sodium sulphate (Na2SO4 ≥ 99% purity), Manganese acetate (Mn(CH3COO)2, 99.9 % pure, have been purchased from E Merck, India and the thin film of 18 karat gold (74 % gold and TE D 24 % Cu and 2 % Ag) substrate with 1mm thickness was purchased from the market, India. 2.1 Synthesis of nanoporous Au substrate In this study, nanoporous gold electrode is prepared using 18k gold (74 % Au and 26 % EP Cu) in the form of thin electrode as electrode material. The gold film is thoroughly cleaned using acetone and then dipped in 70 % HNO3 for 2 h making the Au electrode porous. On soaking in AC C nitric acid, the copper atom is found on the alloy getting leached into the acid medium leaving a porous nature. Such a porous structure is one of the prerequisites for electrode material. A facile method adopted here provides the porosity that can be tuned to any degree depending on the time in which it is being soaked. 2.2 Electrochemical deposition of MnO2 4 ACCEPTED MANUSCRIPT The uniform electrodeposition of MnO2 as active material for capacitor application is employed using Electrochemical workstation (CHI660C, US) in a standard three electrode cell. It consists of nanoporous gold substrate as a working electrode, Ag/AgCl as a reference electrode RI PT and Pt wire as a counter electrode. Electrochemical deposition of MnO2 have been carried out with various precursors like manganese acetate, manganese sulphate, manganese nitrate etc., of which manganese acetate claimed to be a premium source because of its high deposition rate at SC lower potentials. The electrochemical reaction of manganese oxide formation from an aqueous solution of Mn2+ is given below , M AN U Mn2+ + 2H2O → MnO2 + 4H+ + 2e− The pre-treated porous electrode is dipped in the 100 ml electrolyte bath solution containing 0.1M (CH3COO)2 Mn.4H2O and 0.1M NaOH with other two electrodes. Under bulk electrolysis mode and at an operating voltage of 0.5 V, the electrodepositing process was done TE D for 300 sec. After electrodeposition of MnO2 the coated electrode was removed, washed with water and air dried for 24 h. The quantity of MnO2 deposited on the electrode surface was found out by weighing equal to 0.0002 g. The same procedure is adopted to coat MnO2 particles over EP un-etched Au film too. 3. Results and discussion AC C 3.1 XRD analysis of MnO2 deposition Fig. 1a-b represents the XRD patterns of MnO2 coated over unetched (Fig. 1a) and etched (Fig. 1b) 18k gold foil using the precursor’s manganese acetate and sodium hydroxide employing electrochemical deposition technique. From the obtained diffraction peaks, the prepared samples show tetragonal phase structure with body centered lattice of α-MnO2 (JCPDS No. 72-1982). The diffraction peaks at 2θ = 38.3°, and 69.3° correspond to the miller indices (121) and (451) 5 ACCEPTED MANUSCRIPT respectively. The obtained product exhibits single phase crystal with sharp peaks indicating the crystalline nature of the α-MnO2 . Compared to the unetched substrate, the α-MnO2 coated over etched substrate shows lesser crystalline nature. This fact may be attributed to the blending RI PT of α-MnO2 into the pores of etched gold foil. However, the less crystalline nature is beneficial to enhance the electrochemical performance of the fabricated super-capacitor. The amorphous nature of the oxide layer will provide stress-free insertion and expelling of electrons between the SC electrode and the electrolyte. Therefore, the overall performance of the electrode is improved. Since the α-MnO2 is evenly coated over the 18k gold substrate, the diffraction peaks of Au and EP TE D M AN U Cu are backed out. Fig. 1 (a) XRD pattern of MnO2 nanoparticles coated on unetched and (b) etched gold substrate (c) XPS survey of MnO2 nanoparticles coated over etched Au substrate AC C The chemical composition of MnO2 nanoparticles deposited over Au substrate is displayed in Fig. 1c. To determine the correct valence of Mn in MnO2, the O 1s spectrum is evaluated. XPS spectrum also depicts three peaks at 529.7 eV, 531.5 eV and 532.7 eV contributes anhydrous manganese oxide (Mn-O-Mn), hydrated manganese oxides (Mn-O-H) and water molecules (H-O-H) respectively . 6 ACCEPTED MANUSCRIPT AC C EP TE D M AN U SC RI PT 3.2 EDX scan spectra and Elemental mapping 7 ACCEPTED MANUSCRIPT Fig. 2 EDX-analysis of the electrode (a) un-etched Au substrate (b) un-etched Au substrate after coating with MnO2 nanoparticles (c) etched Au substrate (d) etched Au substrate after deposition of MnO2 and (e-h) maps depicting the distribution of O, Mn and Au elements. RI PT The elemental composition of the as-prepared etched electrode was analysed using elemental Mapping and the results are established in Fig. 2e-h. The Fig. 2f&h reveals that the elements oxygen and manganese are evenly distributed over the substrate. Fig. 2h depicts the SC mapping of etched Au substrate. Here there is no evidence of Cu, however there is some trace amount of Cu found in EDX spectrum. M AN U EDX spectrum reveals about the presence of various elements present in the substrate before and after coating the electro active MnO2 by electrodeposition process. The presence of the constituent elements found in the electrode is analyzed using Energy dispersive X-ray spectroscopy. Fig. 2a is the EDX spectrum of 18k gold specimen recorded before etching. Since TE D the commercially available 18k gold is the alloy of Au, Ag and Cu, it shows characteristic peak for Au as a major peak and Cu as less intense peak. Apart from the two peaks, it also shows peaks for Ag and Oxygen. Oxygen peak may be originated from the oxide of copper and Ag is EP found along with commercial gold. The EDX spectrum of unetched Au substrate after coating with MnO2 nanoparticles is shown in Fig. 2b. The EDX micro analysis indicates that Mn and O AC C peaks deposited using electrochemical deposition. Fig. 2c is the EDX of Au electrode after etching with nitric acid. From this it is evident that the less intense peak that has originated from Cu atom is attributable to its dissolution in acid. However, 100% etching of Cu is not noticed owing to the thickness of Au foil (1 mm), the complete etching has not taken place. Fig. 2d is the EDX spectrum of nanoporous Au electrode coated with MnO2 particles. This spectrum revealed 8 ACCEPTED MANUSCRIPT about the presence of Mn and O peaks originated from MnO2 particles, found apart from Au and Cu atoms. EP TE D M AN U SC RI PT 3.3 FESEM analysis Fig. 3 Micrograph of Au specimen (a) before etching, (b) after etching with HNO3, (c) FESEM AC C image of gold/MnO2 hybrid structure on unetched gold substrate, (d) FESEM image of gold/MnO2 hybrid structure on etched gold substrate Fig. 3a-d represents the Field Emission Scanning Electron Microscope image recorded through ZEISS (Germany) at an applied voltage of 20 kV with the magnification of 81000X, 58000X, 50000X and 300000X respectively. Fig. 3a is the FESEM image of the unetched Au substrate which appears like platelets of Au. Fig. 3b is the FESEM image of the etched gold substrate obtained after immersing in nitric acid. The image clearly reveals the porous nature of 9 ACCEPTED MANUSCRIPT substrate having pore size of about 25 nm that arises due to the removal of Cu from 18k Gold. These facts are more advantageous for supercapacitor electrode material since the porosity effects of the electrode facilitate the electrochemical faradic transfer rates. RI PT Fig. 3c is the FESEM image of MnO2 coated Au substrate in an unetched electrode. It can be seen from the figure that it gives the appearance of a needle-shaped MnO2 of size around 15 nm. FESEM image of MnO2 deposited over porous Au electrode is depicted in Fig. 3d. The size SC of MnO2 particles is found in the range of 20 nm. Apart from the larger surface area of the electrode, the higher specific capacitance is also determined by other parameters like pore size M AN U distribution and the pore shape which influence the transportation of ions in the electrolyte . The image clearly reveals that the nanopores formed after etching by HNO3 are filled with spherical-shaped MnO2 nanocrystal of size 25 nm. 3.4 Topography studies by AFM TE D AFM images of unetched, etched and MnO2 coated specimens are recorded using XE70 scanning probe microscope, South Korea. Fig. 4a&b represents the AFM image of Au substrate imaged in such a way that the AFM tip is made to scan the interface of coated and uncoated EP regions of MnO2 deposited Au electrode (unetched and etched). The bottom portion of Fig. 4a&b is the line profile analysis drawn using the software provided by XE70 AFM. The horizontal line AC C drawn across the images ensured about the thickness of MnO2 nanoparticles coated over the Au substrate. A horizontal line at 0-1.25 µm is drawn that travels in the uncoated region (0-1.25 µm) and then rises to 50 nm indicating that the thickness of the MnO2 film formed is about 50 nm. The line profile analysis shown in Fig. 4b corresponds to the Au substrate etched with nitric acid. The MnO2 particles deposited over it is about 15 nm. It is also measured through the line profile analysis. In Fig. 4b, at 1.5 µm, the line shoots up to a higher level (0 nm to 1.5 nm) indicating 10 ACCEPTED MANUSCRIPT almost the thickness of 15 nm of MnO2 coated over porous Au substrate. It is interesting to find that with the same coating process and time, the thickness of the MnO2 coated over unetched Au substrate is about 30 nm whereas on the etched Au substrate it is only of 15 nm. This may be due RI PT to the porous nature of the etched current collector used in which the pores of the electrode are filled by the MnO2 owing to the decrease in the coating thickness to around 15 nm. Fig. 4d&f is the canny edge image of 3-D AFM image obtained after performing image SC processing technique. Edge detection is one of the mathematical method through which it is possible to identify a digital image where the discontinuity originates or exists. Canny edge M AN U detector with MATLAB is one of the popular multi-stage edge detection algorithms which is used to compute sharp gradient and applications seeking edge location of particular objects. The first and the second gradient derivatives of all pixels found in the image are used to find the edges of the image and are plotted [37, 38]. Fig. 4f is the canny edge image of Fig. 4e. It clearly TE D displays more gradient peaks located throughout the entire surfaces of coated and uncoated regions than Fig. 4d which is the canny edge image of Fig. 4c. Fig 4g&h depicts the topography of unetched and etched Au substrates after the MnO2 is deposited over it. MnO2 particles over EP unetched and etched Au substrate are uniformly deposited with a size of 20 nm and 25 nm respectively. Coating thin MnO2 film in a close proximity to the current collector circumvented AC C the poor conductivity of MnO2 (10-5–10- 6 S cm-1) and reduced solid state transport of insertion cations . 11 AC C EP TE D M AN U SC RI PT ACCEPTED MANUSCRIPT Fig. 4 (a,b) AFM line profile analysis, and (c,e) 3-D top view topography of coated and uncoated regions of unetched and etched substrate respectively, (d,f) Canny Edge detected image of c and e, (g,h) AFM topography image of MnO2 coated over unetched and etched substrates 3.5 Electrochemical Analysis Fig. 5c&d represents the corresponding linear voltage versus time graph for charging and discharging at the current densities of 0.3 mA, 0.4 mA and 0.5 mA for unetched and etched 12 ACCEPTED MANUSCRIPT electrodes. The shape of the curve is an equilateral triangle because of the presence of pseudocapacitance characteristics and good reversibility during the charge/discharge processes. It is clear from the charge-discharge graph that there exists an IR drop or potential drop at the RI PT beginning of the discharging curve. As seen from the charge-discharge profile, it is evident that the charging and discharge time increases as the current density is decreased. Generally, the IR drop is resulted from electrolyte resistance, charge transfer resistance of the material and SC contact between the electrode and electrolyte . The greater charging and discharging time for etched Au electrode suggests greater loading of MnO2 in the open pores of the porous M AN U electrode. A specific capacitance of 360 F/g and 580 F/g is obtained from the galvanostatic charge discharge curve for unetched and etched Au electrode using the following equation, = (1) ∗ where I is the discharge current (mA), and M is the mass of the material coated and the TE D slope taken from charge-discharge curve. Comparison of specific capacitance values obtained in this work with data available in literature is given in Table 1. Table 1 Comparison of specific capacitance. CFF/MnO2 AC C Cu/MnO2 Morphology EP Electrode material Capacitance References Coral like -1 467 Fg  Nano-needles over copper 486 Fg-1  170 mAg-1  f-FWNT/r-CGO Disordered structure r-GO/r-GONM Mesh pattern 291/418 Fg-1  Flat/Nanoporous MnO2 Needle/Porous 407/670 Fg-1 Present work 13 AC C EP TE D M AN U SC RI PT ACCEPTED MANUSCRIPT Fig. 5 (a&b) Cyclic voltammetry (current density vs potential) at various scan rates between 5 mV and 100 mV, (c&d) charge-discharge cycles between 0.5 mA to 0.3 mA, (e) specific capacitance vs. scan rates, (f) specific capacitance vs. current densities, (g&h) Electrochemical cycling stability after 1000 cycles in 2 M NaOH electrolyte at a scan rate of 100 mVs-1 for MnO2 deposited over unetched and etched electrodes respectively 14 ACCEPTED MANUSCRIPT Fig. 5e outlines the specific capacitance calculated for unetched and etched Au electrodes for different scan rates. The falling slope in the specific capacitance with the increase in the = / / / RI PT scan rate is described by Randles - Sevcik equation . (2) where k is the constant which is equal to 2.72*105, n is the number of moles of electrons transferred per mole of dielectric species, A is the area of the electrode in cm2, D is the potential in V/s. M AN U 3.6 Electrochemical Impedance Analysis SC diffusion coefficient in cm2 /s, H is the solution concentration in mole/L, and f is the scan The Nyquist plots for the prepared electrodes at a frequency range of 1 Hz to 100 kHz in 1 M Na2SO4 aqueous solution are shown in Fig. 6a. Fig. 6b represents the magnified portion of the nyquist plots at higher frequencies in which the full semicircle is not noticed. This may be TE D attributed to the reason that the full semicircle region further falls on the high frequency than 100 kHz which could not be traced by the device. The studies by Shuang Wang et al.  discuss that the highly porous geometrics lead to high frequency semicircle. The Nyquist plots obtained EP for etched electrode display a vertical slope with a close ideal capacitive behavior whereas the unetched electrode does not shows a prominent vertical line which may be due to the leakage AC C problem. Corresponding resistance of 16 Ω and 31 Ω were obtained by extrapolating the vertical portion of the plot to the real impedance of etched and unetched electrodes, while a transition time constant semicircle and the ion transport resistance are observed in the regime of 14 Ω and 25 Ω at a frequency of 2.1 kHz and 1 kHz for etched and unetched electrodes respectively. Fig. 6c&d depicts the equivalent circuit parameters of the unetched and etched Au electrodes. Here, the resistance R1 is more related to the response of the electrode considering the geometry of pores and conductivity of the electrode, whereas the resistance R2 is more related to 15 ACCEPTED MANUSCRIPT the electrolyte property. For a good dynamic capacitor, the difference between R1 and R2 must be minimum . The difference between R1 and R2 is 3.61 Ω and 1.99 Ω for unetched and etched Au electrodes respectively. Thus the electrode having pore displays more dynamic character in AC C EP TE D M AN U SC RI PT the typical frequency range. 16 ACCEPTED MANUSCRIPT Fig. 6 Electrochemical impedance analysis (a) Nyquist plots of unetched and etched sample, (b) Zoomed Nyquist plot at higher frequencies, (c&d) Equivalent circuit for unetched and etched electrodes, (e&f) Bode plots for unetched and etched electrodes RI PT In the equivalent circuit shown in the Fig. 6c&d, there is more than one number of series RC elements in parallel with each other which is possibly the case for overlapping time constants. The overlapping time constants may originate due to the different charge SC accumulation modes such as deep traps, surface roughness, inhomogeneous doping and nonuniform potential distribution . M AN U Fig. 6e&f is the bode plot of the fabricated unetched and etched Au electrodes. The phase angle and time constant extracted from the bode plots are 55º and 4 ms for unetched Au electrode and 79º and 2 ms for etched Au electrode. The high phase angle of 80º and low time constant advocate better supercapacitive phenomenon of the porous electrode . TE D The fabricated electrode exhibits good electrochemical performance with an energy density of 32.56 wh/kg and 53.6 wh/kg and power density of 366 w/kg and 603 w/kg for = 1 8 = (3) (4) AC C EP unetched and etched electrodes calculated from the following equations [49, 50]. where Cs is the specific capacitance calculated by cyclic voltammetry, V is the voltage window, and t is the time taken to complete one sweep cycle. Conclusion In summary, the hybrid supercapacitor electrode with non-porous and porous Au current collector is successfully demonstrated. The nano-porous Au substrate developed by chemical etching process behaves as a double layer capacitor eventually providing good ionic 17 ACCEPTED MANUSCRIPT conductivity to augment the pseudocapacitive properties of MnO2 crystal. The higher specific capacitance of 670 Fg-1, high phase angle of 800 and low time constant of 2 ms for etched Au electrode advocates the good performance of porous electrode. The fabricated electrodes also RI PT fulfill high energy density without sacrificing the power density and cycle stability. This high performance electrode put forward confidence in the fabrication of supercapacitors using AC C EP TE D M AN U SC various metal-metal oxides which is needed for high power applications. 18 ACCEPTED MANUSCRIPT References AC C EP TE D M AN U SC RI PT  I.S. Ike, I. Sigalas, S. Iyuke, K.I. Ozoemena, An overview of mathematical modeling of electrochemical supercapacitors/ultracapacitors, J. Power Sources, 273 (2015) 264-277.  J. 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Kuang, Curly graphene nanosheets modified by nanoneedle-like manganese oxide for electrochemical capacitors, RSC Advances, 5 (2015) 88950-88957.  G.K. Veerasubramani, K. Krishnamoorthy, P. Pazhamalai, S.J. Kim, Enhanced electrochemical performances of graphene based solid-state flexible cable type supercapacitor using redox mediated polymer gel electrolyte, Carbon, 105 (2016) 638-648.  K. Krishnamoorthy, G.K. Veerasubramani, S. Radhakrishnan, S.J. Kim, Supercapacitive properties of hydrothermally synthesized sphere like MoS 2 nanostructures, Materials Research Bulletin, 50 (2014) 499-502. 21 ACCEPTED MANUSCRIPT Investigation of Electrochemical capacitance of 18k nanoporous current collector incorporated MnO2 Highlights: MnO2 is incorporated into porous and flat 18k Au substrates by bulk electrolysis. RI PT The MnO2 depositions are characterized using XRD, XPS, FESEM, EDX mapping and AFM. Electrochemical analysis shows the high specific capacitance of the porous electrode. SC The impedance analysis suggests the superior characteristics of porous electrode. AC C EP TE D M AN U The prepared electrodes prove to be good candidate for high power applications.