Electrochemical carbyne from perfluorinated hydrocarbons: Synthesis and stability studied by Raman scattering

The synthesis of electrochemical carbyne from perfluorinated hydrocarbons was optimized. The relative yield of carbyne was monitored by Raman spectroscopy using the CC stretching mode. The position and relative intensity of this band depend on the type of fluorocarbon and reducing agent used. Optimum conditions were attained for electrochemical reduction of poly(tetrafluoroethylene) with K- or Na-amalgams. Poly(tetrafluoroethylene) oriented by mechanical stretching gives partly oriented polyyne chains with a conjugation length of 16 carbon atoms. Electrochemical carbyne is stabilized against interchain crosslinking (graphitization) by interspersed microcrystalline alkali metal fluoride (reaction byproduct). Carbyne decomposes spontaneously if the alkali metal fluoride is extracted from the composite by leaching out with water. The final salt-free product is a highly disordered carbon material resembling diamond-like amorphous carbon; it graphitizes after thermal and pressure treatments.