Nanotechnology: Applications of Carbon Nanotubes in Electrical Engineering

Invention Journal of Research Technology in Engineering & Management (IJRTEM) ISSN: 2455-3689 www.ijrtem.com Volume 3 Issue 4 ǁ May –June 2019 ǁ PP 08-13

Nanotechnology: Applications of Carbon Nanotubes in Electrical Engineering Matthew N. O. Sadiku1, Yogita P. Akhare2 1

(Department of Electrical and Computer Engineering, Prairie View A&M University, Prairie View Texas, USA) 2 (Department of Electrical and Computer Engineering, Prairie View A&M University, Prairie View Texas, USA)

ABSTRACT : Nanotechnology is a rapidly advancing technology which has the potential to revolutionize the world by providing a variety of products and services at an ultra-small scale. The main objective of this paper is to find out the most important applications of carbon nanotubes (CNT) in electrical engineering. It addresses the uniqueness of nanotubes that makes them better than their competitors for specific applications. It also discusses the types, electrical properties and several examples of the already existing commercial uses of nanotubes and then point out feasible nanotube applications in electrical engineering. This paper distinguishes between the various kinds of nanotubes in play today, ranging from multiwall nanotubes having different degrees of perfection to the near-perfect molecular single-wall nanotubes. The last decade of research in this field points to several possible applications for these materials; electronic devices and interconnects, field emission devices, electrochemical devices, such as supercapacitors and batteries, nanoscale sensors, electromechanical actuators.

KEYWORDS: Nanotechnology, Carbon nanotubes, Supercapacitors, Nanoscale.

I. INTRODUCTION The United States Department of Energy’s prediction is that the world’s energy consumption will increase by 20% in the next 10 years. Hence it is necessary to develop efficient energy storage system to reach the worlds future energy targets [1]. To deal with these energy challenges faced by the human being in the 21st century, novel technologies will be the solution for clean, safe, and sustainable energy future. Nanotechnology plays significant role in the energy storage or transportation process starting from the primary energy sources to the end user [2]. Nanotechnology adopt the materials whose structures have attributes on the nanoscale i.e. 10 -9 meter. Undoubtedly this size is very small as compared to the objects around us, yet it is not distinctly small on an atomic scale which is of the order of 10-10meter [3]. Carbon nanotube (CNT) based materials are achieving prominent recognition as an advanced material for renewable energy conversion and storage. The most optimistic research in the applications of CNT’s towards energy conversion and storage is highlighted [4]. There are many features of Carbon nanotubes which makes it different from traditional materials [5]. CNT’s superior and uniquely chemical, optical, physical, mechanical and electronic properties make it useful in a variety of applications in nanotechnology such as engineering, medicine and material science [6],[7]. Novel design of transmission wires proposed consists of carbon-nanostructure (CNS) epoxy composites in a multilayered form to empower multifunctional capabilities [8]. It will be possible to construct carbon nanotube fibers exceeding both the electrical and mechanical performance of conductive metals currently used in electrical engineering [9].

Carbon nanotubes are used as an electrode material for the electrochemical capacitors, often called as supercapacitor or ultracapacitor which is used as an energy device since the mid 70’s. Single walled (SW) or multi walled (MW) carbon nanotubes possess a high electrical conductivity and prominent mechanical and thermal stability which are worthwhile characteristics of high-power capacitor [10]. Use of CNT’s as a capacitor electrode material resulted in a 90% reduction in equivalent series resistance (ESR) [11].

II. BACKGROUND To meet the world’s energy future demand, the development of energy efficient system is necessary due to the increasing population and energy cost. The world’s energy consumption data from the period of 1980 to 2030 given by the United States Department of Energy values and Forecast is as shown in Fig. 1. Fig. 2 shows the flowchart of energy production and storage processes. In the first-row different energy sources are shown. The second row contains the energy production processes where nanotechnology has potential key roles grouped by

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Nanotechnology: Applications of Carbon Nanotubes‌ the arrows while the arrows in the last row comprises of energy storage or transportation processes where nanotechnology plays significant role. Nanotechnology positively impact on the efficient usage and sustainability of energy along with the environmental protection. Renewable energies are inefficient for base load power as they are fragmentary and dispersed regarding watts per square meter at any time unless the availability of costeffective energy storage system or large distance power networks [3].

Fig. 1. The United States Department of Energy values and Forecasts for energy Utilization in the period from 1980 to 2030 [1].

Fig. 2. Flow chart of the energy production and storage processes showing contribution of Nanotechnology [2].

III. TYPES OF CARBON NANOTUBES Carbon nanotubes are allotropes of carbon with a cylindrical nanostructure. Nanotubes have been constructed with length-to-diameter ratio of up to 132,000,000:1 which is significantly larger than any other material. These cylindrical carbon molecules have novel properties which make them potentially useful in many applications in nanotechnology, electronics, optics, and other fields of materials science, as well as potential uses in power system. They exhibit extraordinary strength and unique electrical properties and are efficient thermal conductors.

Single-wall carbon nanotube (SWCNT) can be formed by the rolling of a single layer of graphite (graphene layer) into a seamless cylinder. A multiwall carbon nanotube (MWCNT) can similarly be a coaxial assembly of cylinders of SWCNT, like a Russian doll, one within another; the separation between tubes is about equal to that

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Nanotechnology: Applications of Carbon Nanotubes… between the layers in natural graphite. Hence, nanotubes are one dimensional object with a well-defined direction along the nanotube axis that is analogous to the in-plane directions of graphite.

(a) SWCNT

(b) MWCNT

Fig. 3. Types of Carbon Nanotubes

A nanotube's chiral angle, the angle between the axis of its hexagonal pattern and the axis of the tube determines whether the tube is metallic or semiconducting. A grapheme sheet can be rolled more than one way, producing different types of carbon nanotubes. The three main types are armchair, zig-zag, and chiral as shown in Fig. 4.

(a)

(b)

(c)

Fig. 4. Rolling of graphene sheet to make the nanotube: (a) Armchair (b) Zig-Zag (c) Chiral (Asymmetric) The bonding in CNTs is similar, but not identical, to the graphene sheet. A widely used approach to identify the types of SWCNT is by reference to rolling up the graphene sheet. From Figure 4, the key geometric parameter associated with this process is the roll-up vector Ch, which can be expressed as the linear combination of unit vectors (a1 and a2). T denotes the tube axis. Thus, we have Ch = na1 +ma2. It is then possible to associate a integer pair (n, m) with each SWCNT. The relation between n and m defines three categories of CNT: m = 0, ‘Zigzag’, n = m, ‘Armchair’, other, ‘Chiral’. Because of the symmetry and unique electronic structure of graphene, the structure of a nanotube strongly affects its electrical properties. For a given (n, m) nanotube, if n = m, the nanotube is metallic; if n−m is a multiple of 3, then the nanotube is semiconducting with a very small band gap, otherwise the nanotube is a moderate semiconductor.

IV.

PROPERTIES OF CARBON NANOTUBES

Apart from remarkable tensile strength, nanotubes exhibit varying electrical properties (depending on the way the graphite structure spirals around the tube, and other factors, such as doping), and can be superconducting, insulating, semiconducting or conducting. Nanotubes can be either electrically conductive or semi conductive, depending on their helicity, leading to nanoscale wires and electrical components. These one-dimensional fibers exhibit electrical conductivity as high as copper, thermal conductivity as high as diamond, strength 100 times greater than steel at one sixth the weight, and high strain to failure. The different properties of CNT which

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Nanotechnology: Applications of Carbon Nanotubes‌ determined computationally and experimentally, are given in Table 1. CNTs and graphene are the strongest known materials due to the high strength of covalent bonds between adjacent sp2 carbon atoms.

Table 1. Properties of Carbon Nanotubes [4] Sr. No. 1 2 3 4 5 6 7

Property Young’s modulus [TPa] Tensile Strength [GPa] Electrical conductivity [S/m] Thermal conductivity [W/m.K] Charge mobility [cm2/V. s] Thermal stability in air [ °C] Surface area [m2/g]

Computational Calculation 1.5 to 5.0 300 1x107 80 -9500 1.2 x 105 750 50-1315

Experimental measurements 2.8 to 3.6 150 6.6 x103 3500 1 x 103 420 619.1

V. APPLICATIONS OF CARBON NANOTUBES Conventional carbon materials have been utilized either as the electrode materials themselves or the conductive filler for the active materials in various electrochemical energy-storage systems due to their good chemical stability and high electrical conductivity. Hence, it is natural that carbon nanotubes have been adopted as the preferred alternative electrode material because they have unique electrical and electronic properties, a wide electrochemical-stability window, and a highly accessible surface area. Regarding energy generation and storage, nanotubes show great promise in supercapacitors, solar cells and fuel cells; and energy applications could become the largest applications domain in the bulk application of nanotubes. For energy storage devices other than batteries, supercapacitors have been extensively and actively investigated because they are able to store and deliver energy rapidly and efficiently for a longer life cycle via a simple charge separation process. In addition, their wide range of power capability makes it possible to hybridize them with other energy-storage devices, such as batteries and fuel cells [4],[5].

Solar Cells: Carbon Nanotubes could Make Efficient Solar Cells. Using a carbon nanotube in place of traditional silicon, researchers have created the basic elements of a solar cell that hopefully will lead to much more efficient ways of converting light to electricity than now used in calculators and on rooftops. In Fig. 5, electrons and holes areas where electrons used to be before becoming excited release their excess energy to efficiently create more electron-hole pairs when light is emitted on the device. The researchers fabricated, tested and measured a simple solar cell called a photodiode, formed from an individual carbon nanotube. They describe how device converts light to electricity in an extremely efficient process that multiplies the amount of electrical current that flows. This process could prove its important for next generation high efficiency solar cells [6],[7].

Fig. 5. Carbon nanotube-based photodiode

Fig. 6. Carbon nanotubes wrapped in TNA

Power Transmission Line Materials: Since world demand for power increases, the burden on our electricity infrastructure grows. A major challenge is to develop new transmission line materials that are of lighter weight and lower loss than copper. Individual carbon nanotube fibers have an electrical conductivity like or better than copper at only one-sixth the weight and with negligible eddy current loss. This high conductivity derives from the highly efficient transmission of electrons down the individual tubes acting as quantum wave guides in one direction, and the efficient resonant quantum tunneling of the electrons from tube to tube as the current passes down the fiber.

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Nanotechnology: Applications of Carbon Nanotubes‌ Several researchers have demonstrated that one single wall carbon nanotube can carry currents up to 20 microamperes. With an assumed 5% efficiency of conduction from nanotube to nanotube along the length of the fiber and a carbon nanotube packing density of 1014 per square centimeter, a carbon nanotube fiber bundle could carry currents of 100 milli amperes per square centimeter which is 100 times the current carrying capacity of the best low temperature superconductors. Recent production of single-wall nanotubes typically results in fibers that are less than 100 micrometers in length and have widely varying electrical conduction properties [8].

Wires and cables industries: The wire and cable industry are moving from using halogen flame retardants to halogen-free flame-retardant materials. Use of zero-halogen flame retardant materials have challenges such as drop in mechanical properties of cable sleeves from high flame-retardant filler content, die drooling and cable flame test. Modern cable industries offer a simple, effective solution made of carbon nanotubes for all cable constructions. A thin 150Îź coating will act as the most efficient flame barrier and will ensure that the cable remains operational for an extended period [9].

Electrode material for Supercapacitor: The performance of supercapacitors depends intimately on the structure properties of the electrode materials. In order to utilize the merits of supercapacitors, a hybrid electrode has been widely adopted. Carbon materials can supply a good charge transfer path for moving the generated electrical energy in composite electrodes, the nanostructured carbon is one of the core electrode materials for high performance supercapacitors. Among various nanocarbon-based materials, CNT has superior electrical conductivity, as well as large specific surface area which can dramatically boost the supercapacitance of the carbon composites [10].

Discharging of powerful waves of electricity: For the past twenty years scientists are focusing their energies on carbon nanotubes, graphene sheets and buckey balls. They find these three most promising for clean and green energy research. It has been observed that as the moving pulses of heat pass through the carbon nanotubes, electrons also travel along. This movement of electrons is responsible for generation of electric current [11].

Carbon nanotubes with a layer of reactive fuel TNA (cyclotrimethylene trinitramine) as shown in Fig. 6, can generate heat by decomposing. This fuel was then ignited by a laser beam or high voltage spark at the one end of the nanotube. This ignition resulted in fast moving thermal waves. When this thermal wave enters carbon nanotube, its velocity increases thousand times than the fuel itself. When heat waves contact the thermal coating, they produce a temperature of 3,000 kelvins. This ring of heat runs to the length of the tube 10,000 times faster than the normal spread of this chemical reaction. The unusual occurrence is that electrons also travel with the heat inside the tube as shown in Fig. 7.

Fig. 7. Heat transfer along the length of the CNT

VI. CONCLUSION AND FUTURE SCOPE The most important applications of Carbon nanotubes (CNT) along with its different types and properties have been discussed. Although many applications may take significant investments of time and money to develop to reach commercial viability, there are plenty of applications today in which CNT add significant benefits to existing products with relatively low implementation costs. The next decade will be the decade of nanotechnology thus requiring research in nanotechnology. Carbon nanotubes and their products will have an influential role to play.

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Nanotechnology: Applications of Carbon Nanotubes…

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