Preparation Of Polyaspartic Acid-based Nitrogen-doped Carbon And Their Electrochemical Performance For Supercapacitor

Supercapacitors, a unique class of electrical energy storage devices, have attracted increasing attention around the world in recent years owing to their ultrafast charge-discharge rate, high power capa-bility, low maintenance, and long cycle life. The electrode material tremendously affects the electrochemical properties of the supercapacitor. So looking for high-performance materials as electrode materials for supercapacitors has been a research hotspot. Carbon materials are regarded as the most promising electrode materials for electrical energy storage devices. It has reported that nitrogen doping seems to be the most promising method for enhancing the capacity, surface wettability and electronic conductivity of the carbon materials. Therefore, it is attractive and inspiring to find an easy method and a new precursor that is environmental friendly, cheap and high nitrogen content. Biopolymer polyaspartic acid(PASP) is a common polyamino acid, which is environmental friendly, low cost and high nitrogen content. We did not find report about that it as a carbon precursor to the preparation of nitrogen doped carbon materials.In this paper, biopolymer polyaspartic acid is used as raw material to prepare nitrogen-doped carbon. A nitrogen doped carbon is prepared by direct carbonization, and the effect of temperature for the structure of carbon is investigated. A porous activated carbon is preparation by using ZnCl2 as activating agent, and the effect of amount of activating agent for the materials is investigated. The combination of Ca(OH)2 and NH4 Cl are used as activator and nitrogen source to prepare novel crumpled nitrogen-doped porous carbon(N-PASP) which has ultrahigh nitrogen content(13.8%). The morphology, structure and electrochemical properties of all the materials are characterized in detail. The main research contents and results are as follows:1. A nitrogen doped carbon is prepared by direct carbonization using biopolymer polyaspartic acid(PASP) as raw material and the temperature that can affect the morphology, structure and the nitrogen content is investigated. When the temperature increased from 500 to 800 oC, the BET surface area increases from 255 to 1865m2 g-1, for PASP700 and PASP800 samples, the SBET value increased up to 420.0% and 731.4%, the vtotal values increased up to 381.3% and 725.0% in contrast to that of the PASP500 sample, while the nitrogen content decreases from 8.51%(PASP500) to 3.83%(PASP800) by element content analysis. The PASP700 sample exhibits high specific capacitance 166.1 F g-1 at current density of 1 A g-1, good cycling stability with 97% specific capacitance remains after 5000 cycles.2. Polyaspartic acid-based nitrogen-doping porous carbons(N-APCs) have been prepared by one-step activation and carbonization of polyaspartic acid at 700 oC in N2 atmosphere. The morphologies and structures of the N-APCs deeply depend on the additive amount of activating agent. The activated carbon synthesized at 2:1 ratio of ZnCl2 and polyaspartic acid has shown the best performance with specific capacitance of 265 F g-1 at 0.5 A g-1 current density. The N-APC2 showed very high capacitance retention(93%) even after 5000 cycles.3. Using polyaspartic acid(PASP) as carbon precursor, the combination of calcium hydroxide and ammonium chloride as an activator and nitrogen source, by facile one-step method, a novel nitrogen-doped porous carbon with abundant wrinkled porous structure and ultrahigh nitrogen content(13.8%) has been made. The N-PASP800 exhibits high specific capacitance, as high as 231 F g-1 at a current density of 0.5 A g-1 and 170.2 F g-1 even at a high current density of 20 A g-1. It exhibits perfect cycling stability with 99% specific capacitance remains after 5000 cycles.