ELECTROCHEMICAL PROCESSES ON DISPERSE GRAPHITE ELECTRODES IN HNO3 SOLUTIONS

Abstract

The mechanism and kinetics of anodic processes on a dispersed graphite electrode are investigated by a potentiodynamic method. Variation of the reversal potential in the anode zone on potentiodynamic curves PDC allow to estimate the ratio of the anode and cathode capacities and to determine the coefficient of reversibility of electrochemical reactions. By the degree of reversibility of electrochemical reactions, three potential zones are distinguished: Ist - E ... 1.15 V; II-1,15 ... 1,4V; III -> 1.4B corresponding to the sequential course of the intercalation of graphite with nitrate ions, oxidation of the surface functional groups, the formation of oxide-like graphite compounds. In the zone of potentials I, the maximum reversibility of the anodic process is noted, due to the intercalation-deintercalation process, with the formation of graphite intercalation compounds. Then, a regular decrease in the coefficient of reversibility associated with the occurrence of reactions involving surface oxygen-containing groups and reactions involving oxygen is noticed. This complex of electrochemical processes is accompanied by the formation of graphite intercalation compounds of non-stoichiometric composition and, probably, the oxide of similar structures. The transition to the potential of zone III is characterized by an abrupt decrease in the coefficient of reversibility and the growth of anode currents, which decrease with cycling. Under these conditions, oxidation reactions of the graphite matrix are likely to occur with the formation of CO and CO2. An increase in the rate of irreversible reactions is revealed with a decrease in the concentration of HNO3. In 45% HNO3, the re-oxidation reactions of graphite intercalation compound and the formation of oxide compounds of graphite are significantly accelerated. In 30% HNO3, the highest anode currents of the first cycle from the solutions studied are recorded on a dispersed graphite electrode, and the reversibility of the anode processes is lower than in 60% HNO3. It has been shown that in HNO3 with a concentration of less than 15%, the intercalation of graphite proceeds at a low rate and is accompanied by the surface reactions involving oxygen.For citation:Yakovlev A.V., Yakovleva E.V., Rakhmetulina L.A., Solovyova N.D., Lopukhova M.I. Electrochemical processes on disperse graphite electrodes in HNO3 solutions. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 7. P. 121-128