## 1 Introduction  
Supercapacitors and batteries are two popular types of energy storage being stimulated for development to meet the demand for portable electronics and electric vehicles. Researchers aim for higher power and energy density, that depend significantly on the materials used in these devices [1; 2; 3; 4]. As a versatile method, electrospinning has been actively used to produce one-dimensional (1D) nanomaterials such as polymers, inorganic materials and sp\({}^{2}\) carbon with diameters ranging from nanometers to several micrometers [5; 6; 7; 8]. In particular, 1D nanomaterials formed using electrospinning have a larger specific surface area and aspect ratio and more pore interconnections than those manufactured using other processes, making them suitable for energy storage and as conversion materials [9; 10]. In addition, the electrospinning method is environmentally friendly and offers a simple principle of operation as well as production flexibility and cost reduction [11]. Among the electrospinning 1D materials, carbon nanofibers are not only easily manufactured in large quantities, but are also widely used as supercapacitor electrode materials due to their physical adsorption/desorption operation mechanism [12; 13; 14]. Many polymers are used as precursors for synthesizing carbon nanofibers using electrospinning, such as polyimide, cellulose, polyacrylamide(PAN), etc. Among them, PAN is the most commonly used precursor because of its high carbon yield and excellent compatibility with electrospinning systems [15; 16; 17]. Porous carbon nanofibers not only efficiently transport electrons in the longitudinal direction, but also enable the smooth transport of ions due to their high surface-to-volume ratio with the electrolyte [18; 19; 20]. Therefore, research on the production of porous carbon nanofibers is actively conducted in order to maximize the energy storage capacity of carbon nanofibers [21; 22]. The most commonly used method is to induce a chemical reaction using a strong acid or a strong base aqueous solution with carbon nanofibers derived from PAN in order to prepare surface-modified activated carbon nanofibers [23; 24]. Recently, an attempt has been made to prepare and form porous carbon nanofibers using electrospinning from a mixed solution of a carbon precursor (e.g., PAN) and a pore-forming polymer (poly(methyl methacrylate) (PMMA) and poly(styrene) (PS)) [25; 26; 27; 28]. [PERSON]'s group prepared composite porous carbon nanofibers to which MnO\({}_{2}\) nano-hairs were attached by means of chemical oxidation and applied as a supercapacitor electrode material [29]. However, most of the processes that attempt to activate carbon fibers not only fail to control the amount and type of functional groups introduced using solution-based methods but also have the disadvantage of discharging harmful substances into the environment. The plasma method is a widely used process of modifying the surface of a substrate using high-energy plasma gas [30; 31; 32]. Recently, research has been attempted that prepares activated carbon by exposing a high-energy plasma gas to carbon materials [33; 34]. Specifically, the goal is to develop a carbon material with micropores and structural defects due to introducing functional groups by inducing a reaction between chemically unreactive sp\({}^{2}\) carbon and high-energy plasma gas [35; 36]. [PERSON]'s group improved the storage capacity of a supercapacitor electrode by activating biochar using a plasma process [37]. However, so far, research on the activation of carbon materials using the plasma method has not reached the stage of precise control of the activation and reaction degree of nanostructures. In this work, we fabricated activated multiporous carbon nanofibers using modified electrospinning and vacuum plasma processes and applied them as supercapacitor electrode materials with excellent energy storage performance.