Electrode Processes in Sodium Polysulfide Melts

Results are reported of three-electrode measurements in sodium polysulfide melts. The composition range covered was Na2S3-Na2S5 and the temperature range 300~176 The electrode material used was vitreous carbon. Voltam-metric, chronopotentiometric, and current interruption techniques were used to investigate cathodic and anodic processes. Evidence is produced that sulfide films are formed at the cathode and that these result in l imiting currents. The lowest value of l imiting current density was 28 mA 9 cm-2 obtained for Na2S3 at 350 ~ At the anode the current appears to be limited by accumulation of liquid sulfur. The value of the l imiting current density in Na2S5 was I00 mA 9 cm-2 at 350 ~ A reaction scheme which best fits our results is suggested. Interest in the electrochemistry of sodium polysul-tides has recently been stimulated by the development of the sodium/sulfur battery (1-3), in which the over-all process at the cathode is the reduction of sulfur t