Comment on graphite intercalated with H/sub 2/SO/sub 4/

Salaneck, Brucker, Fischer, and Metrot (Phys Rev. B 24, 5037 (1981)) have stated that x-ray-photoelectron spectroscopic data indicate that the intercalant of the graphite-sulfuric acid system consists of species containing a variety of S/sub n/O/sub 4n/ /sup 2 -/ ions. We question the evidence for these peroxy sulfate species, since C/sub 17/ /sup +/ can be formed at potentials 0.23 to 0.38 V below that necessary to make S/sub 2/O/sub 8/ /sup 2 -/. The reaction of the chemically similar SO/sub 4/F/sup -/ species with graphite yields a product which does not contain SO/sub 4/F/sup -/, suggesting that strong chemical oxidants will not be stable with respect to graphite.