Electrochemical intercalation of sodium ions into poly(para-phenylene) in carbonate-based electrolytes

Electrochemical intercalation of sodium ions into poly(para-phenylene) (PPP) has been carried out in NaClO4-carbonate electrolytes (EC, PC and their mixture in the volumic ratio of 1/1). The same electrochemical behavior has been observed in the three electrolytes. The galvanostatic curves exhibit potential slope changes which are characteristic of multiphase system; this behavior is confirmed by cyclic voltammetry. Our experimental conditions allow the obtainment of rich compounds Na-0.5(C6H4) which do not contain co-inserted solvent molecules. This is due to a passivating layer formed at the electrode surface during the first discharge that prevents the co-insertion of solvent. Analysis of this layer by transmission electron microscopy reveals the presence of Na,CO, at potentials higher than 0.75 V and sodium alkylcarbonates at potentials lower than 0.75 V. A two-step mechanism of electrolyte decomposition is proposed by analogy with the case of the reduction of graphite in carbonate electrolytes containing LiClO4 salt. (C) 1997 Elsevier Science S.A.