Air stability and surface passivation of acceptor-type graphite intercalation compounds

The environmental stabilities of graphite intercalation compounds (GICs) containing bifluoride, nitrate, sulfate, C8F17SO3-, N(CF3SO2)(2)(-), or N(CF2CF3SO2)(2)(-) are determined at 20 degrees C in air, at 50 degrees C and 100% relative humidity, and at 20 degrees C in liquid water. The GICs containing large perfluoroanions are significantly less reactive towards moisture than those with bifluoride, nitrate or sulfate. Graphite nitrates and graphite sulfates prepared in the corresponding parent acids are less stable than those prepared in hydrofluoric acid. Evacuation of these GICs for 24 h generally reduces the content of neutral intercalates, decreases the intercalate gallery dimension, and enhances the GICs environmental stability. The stability of graphite bifluoride is increased significantly by formation of a passive surface following reaction with dilute solutions containing large perfluoroanions. The GICs derived from natural graphite powder (1-mu m particle diameter) show decomposition rates one to two orders of magnitude higher than those derived from SP-1 graphite powder (100-mu m diameter). (C) 2000 Elsevier Science Ltd. All rights reserved.