The role of solvate acid in the electrochemical behaviour of graphite intercalation compounds

Abstract

Anodic intercalation of anions into graphite and the reverse reaction are fast electrochemical processes, characterized by charge transfer through anions and cointercalation of undissociated acid molecules, HA. The reversible intercalation potential, U I, for primary intercalation into pristine graphite is found to be greatly influenced by the molar acid concentration, c. U I decreases linearly with increasing c for H 2SO 4, HClO 4, HBF 4 and H 2F 2 by −56, −64, −54 and −27 mV mol −1 l, respectively. This is interpreted in terms of depolarization by HA molecules, whose concentration c HA rises exponentially with increasing c. A quantitative fit with spectroscopic data for c HA could be obtained for H 2SO 4 and HClO 4 at low and medium acid concentrations using the Nernst equation. Diffusion potential effects are lower by one order of magnitude. Practical implications of our findings, e.g., potentiometric determination of acid concentration, are discussed briefly.