Design , Fabrication and Characterization of a Commercially Prepared Carboxyl Multiwalled Carbon Nanotubes With a Hybrid Polymer Electrolytes

We reported the fabrication of three different supercapacitor cells using a commercially prepared carboxyl multiwalled carbon nanotubes (CPCMWCNTs) as electrode, and hybrid solid polymer electrolytes (HSPE) of different electrical conductivities as separators. The Three cells were then constructed and leveled as cell-A (C90PVdF-HFP10 |H50| C90PVdF-HFP10), cell-B (C90PVdF-HFP10 |H60| C90PVdF-HFP10) and cell-C (C90PVdF-HFP10 |H70| C90PVdF-HFP10). Numbers of analysis, such as FESEM, XRD, TGA and electrochemical analysis were carried out on both the commercial CNT and that of the electrolytes. From the overall results of the electrochemical analysis of cyclic voltammetry (CV), cell-B delivered higher capacitance of 60.10 Fgdoubling that of cell-A, and tripling cell-C. Whereas the charge-discharge (CD) tests carried out in the cells reveals that even at the lower voltage window of 1.5 V, cell-A delivered slightly better than that of B and C with a balanced and good discharge capacitance of 86.06 Fg and higher energy/power densities of 432.22 Jg/8.37 Jgsand less internal resistance. All the cells were able to deliver a modest capacitance at a voltage window of 3V.


Introduction
Experts in the energy and its usage have identified the recognition of energy, pattern of consuming energy (Paul et al., 2012), the role of industry structure and its values as an energy paradigm change of the globe, with many of them, suggesting and developing a new paradigm, which occurred as a result of the complicated problems such as petroleum exhaustion, environmental pollution, greenhouse effect and climate change.They, however, forecasted that, the future energy paradigm will include concepts that diminishing wasteful energy, enriching the lifestyle and not burdening the environment (Iwama et al., 2012).All these, is in order to pave away to the few prominent energy storage devices such as batteries and most importantly "Supercapacitor" which could be one among the most efficiently used sustainable paradigm which also could tackle the current paradigm (Choi et al., 2012;Dubal et al., 2012).Supercapacitors, also known as ultracapacitors (Inagaki et al., 2014a;Hashim & Khiar, 2011;Burke, 2009) or power capacitors, store electrochemical energy by accumulating the charge from electric double layer, which is caused by electrostatic attraction.In this case, the capacity of the supercapacitor is proportional to the electrode surface, i.e., the electrochemically active surface, where, how much ions are attracted, (Gund et al., 2013;Jiang et al., 2013).Electrochemical Double Layer Capacitors (EDLCs) are possible to be fully charged and discharged in seconds.Although their energy density (about 5-10 Whkg -1 ) is lower than in batteries or fuel cells, higher power density (10 Whkg -1 ) can be reached in a short time (Choi et al.,201).The most attractive advantage of EDLCs is a high power capability (Ayad et al., 2011;Domingo-Garcia et al., 2010;Snook et al., 2011;) with the fast charge/discharge rate (Zheng et al., 2012;Choi et al., 2012).Moreover, most of the EDLCs are safer against short circuit than batteries in terms of the possibility of self-ignition.They do not contain any hazardous or toxic materials (Aravinda et al., 2013a;Aravinda et al., 2013b) and have the durability during long CD cycles.
Basically supercapacitors can be represented by two distinct mechanisms describing them: (i) EDLC and (ii) Psuedocapacitor.EDLCs store the charge electrostatically following a reversible adsorption-desorption cycles of electrolyte ions onto active electrode materials.These active materials might not only be electrochemically stable, but also have accessible large surface area and with no any Faradaic reaction at EDLC electrode.The surface storage mechanism allows very fast energy uptake and delivery, and better power performance.However, the physicochemical process and electrode polarization in EDLC are not enough to apply high energy devices.On the other hand, pseudocapacitors, undergoes reversible Faradaic reactions.Chemically modified carbon materials, (Inagaki et al., 2014 b;Inagaki, 2012;Inagaki et al., 2014 c;Inagaki et al., 2014d;Inagaki et al., 2014 e), metal oxide, (Choi et al., 2012;Paul el al., 2012) and conducting polymers (Hsieh et al., 2012;Choi et al., 2012;Paul el al., 2012) are used as electrodes.In case of pseudocapacitors, the stability for charge-discharge (CD) cycling is relatively poor, though, their energy densities are relatively high compared to EDLCs.Furthermore, the response time is longer than EDLCs, because it takes longer time to move electrons during the redox reaction (Choi et al., 2012).Although supercapacitors can be regarded as "still evolving" into the area of ever more energy containing and powerful devices, they have since been able to address the increasing needs of electronic (cell phones, digital cameras, etc. (Probstle et al., 2002), industrial (uninterruptible power supplies, grid conditioning, windmills, cranes, etc.) (Payman et al., 2008;Wu et al., 2012) and in the sectors of transportation/automotive (trains, busses, cars) (Shi et al., 2013;Tran et al., 2013;Wu et al., 2013;Inagaki et al., 2014).Although supercapacitors have higher capacity than batteries and capacitors, it may present disadvantage of high raw material cost and process difficulty.However the application of thin film processes to the fabrication of the supercapacitors might overcome the above disadvantage.As a result, supercapacitors in thin film form (and using solid and flexible electrolyte) (Wang et al., 2013) are gaining increasing interest in the field of lightweight, ultrathin energy management devices for wearable electronics (Dubal et al., 2012).So far most of the current supercapacitors uses liquid electrolyte which could have side effect on the environment in terms of its hazards; the housing of the cell after the sealing of the electrolyte could also be another issue (Wang et al., 2013), the reason why we chose the former method for the cell fabrication.
Recently, number of researchers have diverted their attentions towards the development of advanced electrode materials, which could replace the most commonly used once (such as Activated Carbon (AC)), by mainly using Carbon Nanotubes (CNTs) networks or graphene as flexible electrodes, for high-performance flexible supercapacitors.CNTs, especially MWCNTs have high inherent conductivity, flexibility, chemical and mechanical stability, and larger surface area polarizability (Paul et al., 2012), and can operate within the voltage window of 3 V or more.Furthermore, their predominant exohedral surface favors the quick accumulation and transport of electrolyte ions so as to increase the performance of quick charge and discharge under high currents (Zheng et al., 2012).This will be vindicated in our cell construction and fabrication highlighted in this paper.In order to reduce the toxic effect to the environment and its inhabitants, (Dumortier et al., 2006) functionalized CNTs were selected for this purpose.Functionalized CNTs are said to be stable for long-term storage, are soluble in aqueous solution, have low toxicity, (Capek, 2009), while increasing more reactivity at their surface walls (Prato et al., 2007;Mittal, 2011).Most importantly, when CNTs are functionalized, their pore sizes will be widened up, thereby increasing the chances of ionic penetration at the electrode-electrolyte interface of fabricated supercapacitor (Van Hooijdonk et al., 2013).

Electrolytic Materials
Hybrid Solid Polymer Electrolyte (HSPE) was prepared from a percentage ratio of 70:30, 60:40 and 50:50 wt.% respectively of PVA and H 3 PO 4 with cellulose filter paper immersed into it.The H 3 PO 4 (>85 wt.% in water, molar mass of 98.00 gMol -1 , product, number of 1502-80) was obtained in aqueous form from R & M marketing, Essex, UK brand, while the PVA (molecular weight; 89,000-98,000, 99 + % hydrolyzed) was obtained from Sigma Aldrich.Both H 3 PO 4 and PVA were used as-received without further treatment or purification.An aqueous solution of PVA was then prepared by combining PVA with distilled water in the ratio of 1:10 by volume.This solution is mechanically agitated by magnetic stirring at 60 °C for five hours to thoroughly dissolve the PVA in the distilled water.H 3 PO 4 was then mixed with the PVA aqueous solution in the ratio of 70:30, 60:40 and 50:50 wt.% as mentioned above.After the mixture cools to a room temperature, the resulting homogenous solution of PVA/H 3 PO 4 was cast over a plastic Petri dish.This was after a cellulose filter paper (Whatman brand) was cut into a 6 cm x 5.5 cm and soaked in a segment of the aforementioned solution.The above mixture took roughly four weeks before it dries.After which it can be able to peel off was used as the separator and at the same time as the HSPE. www.ccsen

Electro
The carbo diameter o area of >4 MC8/21/2 product nu mixture of slurry was that, an app was aroun 100 0 C. Af films were weights of was set up (see Figure The surfac Resolution spectra we angles betw and CV w "e-machin instrument The follow

Micros
As mentio wavelengt at 40 kV a

Therm
The therm (N 2 ) flow previous w were (a); C90PVdF-Before beg residue an just 11.07 have very Figure 9 (b losses wer loss of 5.9 that, the in process.were investig re 10 shows 00 mV; 3 V-v ate of 50 mV an of the electrode re using the fo he electrode an 30.1 Fg −1 , 13.5 f the relationsh 2 Fg −1 which co ).It can also b analysis.
C90PVdF-HFP e of 50 mV; 1 1 Fg −1 for scan attributed to th e least, is the can rates of 1,       (3) (4) ge (or Fg −1 es are ell-B, urrent 77.54 wing results for the capacitance; 8.89 Fg −1 , 17.80 Fg −1 and 89.28 Fg −1 respectively at an applied current density of 100, 20 and 10 mA; power/energy densities are 44.70Jg −1 /0.02 Jg −1 s −1 , 89.41 Jg −1 /0.04 Jg −1 s −1 and 448.40 Jg −1 /0.19 Jg −1 s −1 at the said current densities.From the overall results, it can be observed that, the discharged capacitance decreases with the increase in current density, which could be as a result of the low penetration of ions into the inner region of the pores due to fast potential changes.

Conclusion
In this work, we have explored the noble of CPCWMCNT used as an electrode for high performance supercapacitors using HPSE as a separator.Three cells were constructed and leveled as cell-A (C90PVdF-HFP10 |H50| C90PVdF-HFP10), cell-B (C90PVdF-HFP10 |H60| C90PVdF-HFP10) and cell-C (C90PVdF-HFP10 |H70| C90PVdF-HFP10) with changes in the separator.The XRD peaks of the sample electrode C90PVdF-HFP10 appeared in θ= 26° and θ= 43° which might be as a result of the hexagonal structure of ( 002) and ( 101) respectively, which also indicates that the carboxyl multiwalled CNT have high conductivity.Again, a wider diffraction at θ=20.1° which correspond to crystalline peaks of PVDF.TGA traces shows that, the pure CPCWMCNT experience a major loss of just 11.0719 %, which occurred at 611.76 °C leaving a residue of 87.9109 %, which also shows that, the pure MWCNT have very good thermal stability and consequently, good in application for electrochemical devices.This result, even gets better when the active material was added.From the overall results for the electrochemical analysis of the CV, cell-B delivered higher capacitance of 60.10 Fg −1 doubling that of cell-A, and tripling cell-C.Also in CD analysis with much lower voltage window of 1.5 V, cell-A delivered slightly better than B and C with a balanced and better discharge capacitance of 86.06 Fg −1 with higher energy/power densities of 432.22 Jg −1 /8.37 Jg −1 s −1 and lowest in terms of internal resistance. Figure Figure 2

Figure
Figure 14.CD