Potentials of graphite nitrate formation during spontaneous and electrochemical graphite intercalationстатья

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[1] Potentials of graphite nitrate formation during spontaneous and electrochemical graphite intercalation / N. E. Sorokina, L. A. Monyakina, N. V. Maksimova et al. // Inorganic Materials. — 2002. — Vol. 38, no. 5. — P. 482–489. Earlier and new results on spontaneous and electrochemical intercalation reactions of highly oriented pyrolytic graphite and nitric acid in a wide range of HNO3 concentrations are summarized and analyzed. The oxidizing capacity of the solution is shown to determine the extent of intercalation and the stage index of the resulting graphite intercalation compound (GIC), as in the graphite-H2SO4 system. The final potential of graphite nitrate after spontaneous intercalation coincides with the potential E-Ag/AFCl in HNO3. During the reaction of graphite with an HNO3 solution, the potential of graphite nitrate varies monotonically, in contrast to the steplike variation in E in the C-H2SO4-oxidant system. The behaviors of Bronsted acids which can and cannot spontaneously intercalate into graphite are compared. It is shown that the anodic polarization of graphite in HNO3 offers the possibility of controlling the potential and stage index of the resulting GIC by varying the HNO3 concentration and current. During anodic polarization in 75-98% HNO3 at I = 30- 100 muA, the interplay between the spontaneous and electrochemical oxidation processes leads to the formation of stage 11 graphite nitrate. irrespective of the charge passed, and notably reduces the intercalation rate. This effect is interpreted in terms of the intercalation mechanism and sorption processes. The data on the anodic polarization of graphite at small currents point to fundamental differences in electrochemical behavior between the intercalants that can (HNO3) and cannot (H2SO4) spontaneously intercalate into graphite. The concentration ranges and potentials of the formation of stage I and II graphite nitrates via anodic oxidation in HNO3 are determined. The electric current is shown to influence the potential of formation of the stage I GIC: the minimal potential of graphite nitrate formation in 98% HNO3 is E-Ag/AgCl = 1.34 V (I = 500 muA). The potentialities of the spontaneous and electrochemical intercalation reactions for the controlled synthesis of graphite nitrate with a particular stage index are compared. [ DOI ]

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