Study On Nitrogen - Containing Carbon Nanofibrous Membrane Electrode For Supercapacitor

In this paper, the polymer fiber paper was prepared from melamine formaldehyde resin (MF) solution and polyvinyl alcohol (PVA) solution mixture by the electrospinning method. After carbonizing the polymer fiber paper, the nitrogen-enriched carbon fiber paper was obtained which is flexible and freestanding. The electrode can be directly made from the nitrogen-enriched carbon fiber paper without any binders, and be capable of directly assembling the supercapacitor. The materials were characterized by SEM, XPS, TG, nitrogen adsorption/desorption and other methods. The electrochemical properties of materials and supercapacitors were studied by the cyclic voltammetry test, galvanostatic charge/discharge test and impedance measurement.The effects of the electrospinning process on the specific capacitance of the nitrogen-enriched carbon fiber paper were discussed by the orthogonal experiment. The Result shows that the nitrogen-enriched carbon fiber paper possesses 3D network structure in which fibers are connected each other and the average diameter of nitrogen-enriched carbon fibers is about 200nm-500nm. The optimal electrospinning condition is the volume ratio of MF and PVA solution of 3:1, the elctrospinning distance of 25cm, the flow rate of 0.8 mL/h, voltage of 25kV. The specific capacitance of the electrode material prepared by the optimal condition is 152F/g, measured at the scanning rate of 0.001 V/s by cyclic voltammetry. With the increase of the MF content in the electorspinning solution, the nitrogen content of nitrogen-enriched carbon fiber paper increases. Based on the optimal electrospinning condition, the influences of the carbonization temperature on the performance of samples were studied. Results show that with the increase of the carbonization temperature, the nitrogen content of nitrogen-enriched carbon fiber paper decreases from 7.02 at.% to 1.81 at.%, and the graphitized carbon content increases which is beneficial for the improvement of the conductivity. The specific capacitance of nitrogen-enriched carbon fiber paper obtained by the optimal carbonization condition of 700 ℃ is 192F/g. Because nitrogen-enriched carbon fiber paper has better conductivity and more nitrogen atoms with the pseudocapacitance than the nitrogen-enriched carbon powder, it has better specific capacitance. At the same time, the nitrogen-enriched carbon fiber paper and its supercapacitor exhibit good electrochemical properties and stability.The effects of the magnesium citrate content and carbonization temperature on the porous nitrogen-enriched carbon fiber paper were investigated. With the increase of magnesium citrate content, the fiber diameter and specific capacitance increases. With the increase of carbonization temperature, the nitrogen content of nitrogen-enriched carbon fiber paper decreases and the graphitized carbon content increases which is beneficial for the improvement of the conductivity. The porous nitrogen-enriched carbon fiber paper has more specific surface areas, more mesoporous content and better specific capacitance compare with the nitrogen-enriched carbon fiber paper. The specific capacitance of the porous nitrogen-enriched carbon fiber paper, prepared by the optimal condition of the carbonization condition of 700℃ and the magnesium citrateis content of 5%, is 208.3F/g, measured at the scanning rate of 0.001V/s by cyclic voltammetry. Its supercapacitor could achieve the specific capacitance of 32.82F/g at the current density of 5mA/cm2 and the retention ratio of specific capacitance is 91% after 10000 cycles. The porous nitrogen-enriched carbon fiber paper is a kind of good electrode material.