HOPG as a host for redox reactions with FeCl4− in water medium

An ionic graphite intercalation compound (GIC) with FeCl4− was prepared electrochemically under controlled charge from an FeCl3HCl solution using highly oriented pyrolytic graphite (HOPG) and a graphitized polyimide film as hosts. From the X-ray diffraction (XRD) 00l lines, the stage of the GIC was determined and the unstable properties of the samples were examined. Gradual transformation of stage-s GIC to stage-(s + 1) GIC confirmed their instability after exposure to air or pumping under vaccum at 120 °C. Thermogravimetry analysis of the samples and IR spectra of the gas evolving during GIC drying allowed the quantitative estimation of the co-intercalated species (H2O, HCl) and, hence, the formula of the second-stage GIC was established to be C20–36+FeCl4−, 1.5H2O, 0.5HCl. Electrochemical reduction of the second-stage FeCl4−GIC to higher stages and/or Fe0 particles dispersed on exfoliated graphite was performed in aprotic solution. The influence of co-intercalated molecules on the reduction behaviour of FeCl4−GIC is discussed.