Journal of Applied Electrochemistry

Recent improvements in container materials for Na/S cells (central sodium type) have led to greatly enhanced cell life and performance. Although problems with rapidly decreasing capacity are no longer observed, cells appear to exhibit a slowly increasing resistance with time. This paper describes anin situ technique for assessing the electrical stability of various container materials and determining the extent that corrosion processes influence cell resistance changes. Potentials within the sulphur electrodes of operating cells were measured over prolonged cycling times. Results indicate that chromized steel possesses excellent electrical stability compared to 347 stainless steel and that container corrosion accounts for only a fraction of the increase in total cell resistance.

Three different liquid electrode/sodiumβ″-alumina interfaces were investigated. The NaNO3/β″-alumina interface displays ohmic behaviour although the resistance is somewhat larger than expected. The sodium/β″-alumina interface exhibits asymmetric resistance with respect to d.c. current flow. Cyclic voltammetry results suggest that a Na2O film is being modified electrochemically during the sweeps. When a sodium amalgam electrode is utilized, the film, if it is present, has very little effect. The asymmetric resistance is not observed and there is good agreement between d.c. and a.c. resistances after only a small amount of sodium deposition.

This paper describes a study of the deposition of lithium from lithium salts (LiNO3, LiCl, and LiClO4) in organic solvents (CH3CN, (CH3)2SO, HCONH2, HCON(CH3)2, CH3CON(CH3)2, and THF) using the potential-sweep technique. The current efficiency for lithium deposition was found to depend on both the solvent used and the particular anion in the electrolyte. In CH3CON(CH3)2, (CH3)2SO, and HCON(CH3)2 solutions, the current efficiency for lithium deposition increased in the order: lithium chloride < lithium perchlorate < lithium nitrate whereas in CH3CN it increased on addition of chloride. Addition of water to the LiNO3-DMF solution also increased the current efficiency for lithium deposition. The solution which gave the highest efficiency was LiNO3 in CH3CON(CH3)2, in which efficiencies higher than 70% were obtained. The lithium metal deposited electrolytically from the LiNO3-HCON(CH3)2 solution consisted of fine grains and had a high degree of crystallinity with very smooth deposit surfaces.

Electrochemical reduction of nitrate ions in synthetic regenerating solutions after ion exchange column regeneration was studied. The influence of current density on the current efficiency was determined in the range 2.8–7.6 mA cm−2 in a diaphragmless flow-through electrolyser in a batch recirculation mode. A Cu cathode and a Ti/Pt anode was used, the temperature being maintained at 25 ∘C. Highest integral current efficiency occurred at 2.8 mA cm−2. The presence of about 6 mg dm−3 Cu ions in treated solution was found to prevent a decrease in cathode activity and, consequently, in electrolysis efficiency. The catalytic influence of Cu ions was verified by potentiodynamic polarisation experiments on a copper rotating disc electrode and by chronopotentiometry performed during the course of electrolysis.