REVERSIBLE ELECTROCHEMICAL GRAPHITE SALT FORMATION FROM AQUEOUS SALT ELECTROLYTES

Cyclic electrochemical intercalation/deintercalation of anions from aqueous salt solutions in crystalline graphite electrodes has been investigated. The practical electrode was polypropylene bound natural graphite ″CPP″ . The main candidates for the salts were NaClO//4, NaBF//4, Na//2SO//4 and KF in the concentration range of 0. 1 - 12 M. Current efficiencies alpha with ClO//4** minus and BF//4** minus are lower as in aqueous acids due to side reactions, which increase with increasing dilution and temperature. No pH-effect on alpha has been found between pH 1 - 12. Under favorable conditions (8 M NaClO//4 at 20 degree C or 4 M NaClO//4 at 0 degree C), alpha 's as high as 80% have been observed. A pronounced formation effect is found upon galvanostatic cycling. In Na//2SO//4, alpha drops to zero at pH 3 due to the lack of HSO//4** minus -ions. No intercalation of F** minus ions is detected from aqueous KF. Intercalation potential E//I shows Nernst behavior with regard to anions in solution and intercalated anions.