Anodic behaviour of carbon materials in NaCl saturated NaAlCl4 fused electrolyte at low temperatures: A cyclic voltammetric study

The anodic behaviour of compacted graphite, graphite powder, glassy carbon and reticulated vitreous carbon electrodes in basic sodium chloroaluminate melt in the temperature range 428-573 K was studied using cyclic voltammetr y. Chlorine evolution (> + 2.1 V vs Al) alone was the predominant reaction on the compact glassy carbon and fresh RVC electrodes. On compacted graphit e, chlorine-assisted chloroaluminate intercalation was found to be a compet itive process to the chlorine evolution. At high sweep rates, intercalation /deintercalation near the graphite lattice edges occur faster than chlorine evolution. Subsequent intercalation, however, is a slow process. Chlorine evolution predominates at higher temperatures and at higher anodic potentia ls. On graphite powders, a more reversible free radical chlorine adsorption /desorption process also occurs in the potential region below chlorine evol ution. The process occurs at the grain boundaries, edges and defects of the graphite powder material. Intercalation/deintercalation processes are main ly responsible for the disintegration of graphitic materials in low-tempera ture chloroaluminate melts. Repeated intercalation/deintercalation cycles r esult in the irreversible transformation of the electrode surface and elect rode characteristics. The surface area of the electrode is increased substa ntially on cycling. Electrode materials and operating conditions suitable f or chlorine generation, intercalation/deintercalation and chlorine adsorpti on/desorption and power sources based on these processes are identified in this work.