Electrocatalytic Performance And Pseudo-Capacitive Characteristics Of Modified Graphite Electrode And PAN-based Carbon Fiber Electrode

Faced with the global energy crisis and environmental pollution, all governments pay much attention to the development and utilization of key technology related with energy. Clean renewable energy is widely developed to reduce the traditional fuel, and the energy storage becomes an important factor With the application of solar, wind and other new sources of energy, the investigation on the new, high efficiency, long life and low cost of energy storage technology seems particularly important.In this paper, the graphite and PAN-based carbon fiber electrode were modified using recurrent galvanic pulses technique and the activated carbon electrodes with high performance were prepared therefore. Furthermore, the surface structure and properties of both activated carbon electrodes were evaluated by scanning electron microscope (SEM), X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), thermogravimetry and X-ray photoelectron spectroscopy (XPS). The capacitive and electrocatalytic performance of both activated carbon electrodes was tested by electrochemical measurements such as constant current charge-discharge, cyclic voltammogram (CV), etc. In this paper, the results were obtained as following:(1) After modification, the surface of both carbon materials presented crystallization with different degree and more defects appeared. The number of active sites corresponding to the oxygen-containing functional groups (hydroxyl, carbonyl and carboxyl groups, etc.) significantly increased; however, the species and amount of oxygen-containing functional groups were different for both carbon materials, more hydroxyl groups were obtained on PAN-based carbon fiber electrode and more carboxyl and carbonyl groups were obtained on graphite electrode.(2) The MGE(modified graphite electrode) had high electrocatalytic activity and good reversible characteristics for the redox reaction of Fe3+/Fe2+because of a large quantity of oxygen-containing functional groups on the MGE surface. The apparent area-specific capacitance of the MGE in2.0mol·L-1H2SO4solution containing0.5mol·L-1Fe3+and0.5mol·L-1Fe2+reached2.157F·cm-2, which was almost double that in2.0mol·L-1H2SO4without Fe3+/Fe2+. Meanwhile, increasing the concentration of iron ions increased the capacitance of the MGE. The addition of Fe3+/Fe2+made the charge-discharge curves more symmetric and change more slowly, which increases the charge-discharge time, and effectively improves the capacitive energy storage and high power performance for an electrochemical capacitor (EC).(3) By comparison of the electrochemical performance for Ti4+/Ti3+, Fe3+/Fe2+, V5+/V4+, these results can be obtained:after modification, good pseudocapacitance characteristics appeared on graphite electrode and PAN-based carbon fiber electrode, but their electrocatalytic performance is different. MGE had better electrocatalytic performance and the modified PAN-based carbon fiber electrode showed some side effects related with nitrogen. By XPS, different oxygen functional groups had different catalytic effects for these redox cation couples. Hydroxyl groups showed better catalytic activity at more negative redox potential, carbonyl groups were better at the middle of redox potential, and carboxyl groups were better at more positive redox potential.