# Electrospinning-Based Carbon Nanofibers for Energy and Sensor Applications
## 1 Introduction  
The sp\({}^{2}\) carbon structure is often used in research due to its excellent electrical and mechanical properties. Among them, carbon nanofibers (CNFs) are the most popular materials because they can be mass-produced with a simple manufacturing process and have excellent chemical stability. In addition, the electrical and mechanical properties of CNFs can be adjusted by varying the heat-treatment temperature. This means that heat treatment at a very high temperature of up to 2500 \({}^{\circ}\)C may be required to induce the high crystallinity of sp\({}^{2}\) carbon and maximize the electrical properties, but amorphous CNFs can be obtained even at a low temperature of below 800 \({}^{\circ}\)C [1; 2; 3; 4; 5; 6; 7; 8; 9; 10]. Also, by modifying the type of precursor molecule, which is converted to carbon during the heating process, components other than carbon can be easily introduced into the structure, thus changing the chemical properties [11; 12; 13]. The most common method used to prepare CNFs is the vapor-deposition method, in which a mixture of hydrocarbon molecules (such as methane and ethylene) having a small molecular weight grows carbon by reacting with a metal catalyst. By using this method, CNFs with uniform performance can be obtained. In addition, the performance of CNFs can be diversified by using different mixtures of various hydrocarbon molecules and metal catalysts [14; 15; 16]. However, this method has a disadvantage in that it is difficult to obtain a large number of CNFs inexpensively. The other method is to reshape the carbon precursor polymer (such as polyacrylamide(PAN) and polyvinyl alcohol (PVA)) by using a spinning method such as melt-spinning, wet-spinning, and electrospinning [17]. The advantage of the spinning methods is that they can easily produce large amounts of carbon fiber both on a laboratory and industrial scale. Among them, the electrospinning method, which generates uniform polymer nanofibers from polymer solutions using electromagnetic force, has been widely used [18]. The prepared polymer nanofibers were changed into sp\({}^{2}\) carbon material after a carbonization process to generate CNFs. Recently, research has been activelyconducted to improve the electrical and chemical performance of CNFs by introducing metal and metal-oxide components into the carbon and changing the structure of CNFs using an electrospinninging method [19; 20]. In particular, a carbon nanostructure with a maximized surface area was prepared by introducing pores and multi-channel structures to CNFs [21]. CNFs are widely used as sensor-electrode materials because they not only have a high surface-to-volume ratio but also enable rapid electron transfer due to their one-dimensional structure [22]. In particular, using a simple functional group introduction process, molecules that can easily detect the analyte can be introduced onto the surface, which can be applied as a sensor electrode material [23; 24]. In addition, CNFs are also widely used as an energy storage material because metal and metal oxides can be easily incorporated into CNFs and micropores can be formed [25; 26]. Recently, active attempts have been made to manufacture CNFs with a maximized surface area using a simple chemical treatment method and they are applied in a variety of energy storage systems [27; 28; 29]. The aim of this paper is to present various CNFs synthesized based on the electrospinninging method and introduce them to applications in sensors and as energy storage materials. First, various types of polymer carbon precursors used in electrospinning are introduced and their modification into a carbon structure is described. After that, various types of electrospinninging methods are suggested, and the structural deformation of CNFs generated by these methods is mentioned. Common electrospinninging can produce a large number of uniform polymer fibers that act as the precursor for carbon.