| Redox flow battery (RFB) is an efficient and large-scale energy storage device. It has attracted a lot of researchers because of outstanding properties, such as long cycle life, deep discharge, flexible design and simple maintenance. Electrode as the key part of the redox flow battery has important influence on cost and performance; however, the poor electrochemical activity of traditional carbon materials limits the wide application.In this study, graphite electrodes were modified with different cycle number by recurrent galvanic pulse method in 2.0 mol/L HClO4 solution, and their capacitive and eletctrocatalytic performance were tested by cyclic voltammogram (CV) and electrochemical impedance spectroscopy (EIS). The results show that the graphite electrode modified with 5 cycles showed the best specific capacitance (1.29 F/cm2), electrocatalytic activity and reversible characteristics for V(V)/V(IV), V(III)/V(II) and Ti(Ⅳ)/Ti(Ⅲ).Electrocatalytic performance of graphite electrode modified with 5 cycles toward V(V)/V(IV), V(Ⅲ)/V(Ⅱ) and Ti(IV)/Ti(III) in H2SO4 solution was compared with that of unmodified graphite eletrode. Its peak currents significantly increase, and the peak potential differences reduce. A synergetic mechanism between redox reactions of surface oxygen-containing groups dependent on potential with those of V(V)/V(IV), V(Ⅲ)/V(Ⅱ) and Ti(IV)/Ti(III) was proposed. Carboxyl and carbonyl groups have synergetic effect on V (V)/V (IV) at more positive redox potential, whereas hydroxyl and carbonyl groups have synergetic effect on V (Ⅲ)/V (Ⅱ) and Ti (Ⅳ)/Ti (Ⅲ) at more negative redox potential.Finally, a V/Ti redox flow battery using V (Ⅴ)/V (Ⅳ) as positive active material and Ti(Ⅳ)/Ti(Ⅲ) as negative active material was set up, and its charge-discharge performance was tested in a simple H-type cell. The voltage efficiency is 90.91%, and the energy efficiency reaches 83.44% at 10 mA/cm2, therefore, it shows a potential application value in RFB. |
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