Electrochemical formation and stability of CrO3HClO4graphite bi-intercalation compounds

Abstract

Abstract The present paper concerns CrO3HClO4graphite bi-intercalation compounds (CrO3 HClO4GBCs) synthesized upon the subsequent intercalation of 70 wt% HClO4 into stage-3 and stage-5 CrO3graphite intercalation compounds. On the basis of the results of the potentiodynamic and galvanostatic measurements and the XRD analysis, it has been shown that the formation of stage-1 CrO3HClO4 GBC occurs for both CrO3GICs but the overoxidation and deintercalation processes, as well as the cycling behaviour of the ternary GBCs, depend on the structure of the original CrO3GIC. In contrast to the binary HClO4GIC, which is readily deintercalated to the pure graphite upon cathodic reduction, CrO3HClO4 GBCs and the products of their overoxidation are only partially deintercalated despite cathodic reduction followed by washing with water. After such a treatment, CrO3HClO4GBCs retain the stage structure characteristic of the original CrO3GIC but surprisingly exhibit a new chemical composition. A role of the CrO3 intercalate in the mechanism of the intercalation/deintercalation reactions occurring within CrO3HClO4GBCs is discussed. The results of this work lend credence to the assumption that bi- and co-intercalation phases coexist in the product of the subsequent intercalation of HClO4 into CrO3GIC.