Synthesis of nitrogen-doped carbon micro-structure material and its nickel oxide hybrid composite for energy storage property

Abstract

Recently, due to increase of demand for various electronic devices and improvement of life style in developing country causes drastic increase of world energy consumption. Fossil fuel is the major energy source that can sustain present energy consumption demand, but it is necessary to find other energy source because of limited reserve of fossil fuel, as well as environmental pollution and global warming by emission of carbon dioxide. To solve these problems, research for developing alternative energy from various renewa-ble sources and energy storage system that can supply the energy consistently has been performed, but it is necessary to develop new material because ordinary material are not enough competitive to price and energy productivity of fossil fuel. Nanoscale material has very different property from its original bulk property due to its size and unique structure. Due to its remarkable property, it is researched for various application includ-ing energy harvesting and energy storage. Among them, carbon-based nanomaterial are researched by many research group due to its diversity of electronic and mechanical property by changing bonding state and di-mensional structure like fullerene(0D), carbon nanotube(1D), and graphene(2D), even they are consist of only one atom. There are many studies for solving energy problem by using these property, but still need to im-prove the performance for replacing fossil fuel. We have developed a hard template-free synthesis of nickel oxide encapsulated hollow porous nitrogen-rich carbon spheres with multiporosity for high-performance pseudocapacitors having extremely robust cycles, where the pores inside the shell result from the removal of surfactants during the nozzle spray pyrolysis process without any hard templates while the thickness of the shell has been controlled by the amount of nickel atoms. In addition, the heat treatment of spheres generates micropores in the shell of spheres, thus leading to the higher surface area by about 30 times to store redox ions than that of the as-synthesized spheres. Moreover, it resulted in the mesopores capable of enhancing the diffusivity of redox ions. Indeed, these were found to enhance the accessibility of redox ions to nickel metal sites for surface Faradaic reactions, thus giving an ~250% enhancement in capacitance, in addition to 100% capacitance retention over 50 000 cycles at a high current density. Moreover, we provided experimental evidence that assembling the capsulated nickel oxide into a full asymmetric capacitor can be employed as practical posi-tive electrodes in an asymmetric full cell with excellent performance in terms of both energy and power den-sities with robust cycle life. We have synthesized nitrogen-contained carbon aerogel by using Melamine-Resolcinol-Formaldehyde resin, and evaluated its supercapacitor property via nitrogen contents and carbonization tem-perature. Carbonization process doesn’t affect mesopore structure at any temperature, but it influence mi-cropore structure and thus increase specific surface area. As opposed to temperature, nitrogen doping change the mesopore distribution unpredictably, but it does not change micropore distribution. Capacitance of the aerogels show different tendency with nitrogen doping level. Carbon aerogel shows decreased capacitance as carbonization temperature increased without nitrogen, but capacitance of nitrogen-doped carbon aerogels have slightly increased at higher temperature. Also, higher content of nitrogen shows lowest capacitance be-cause of higher probability of linkage between melamine-melamine resin.