Compounding betweenNiO and La2O3 protects the latter from water and molten salt attack, and ensures successful direct electrolytic conversion of the oxide precursors, in the solid state, to more affordable LaNi5-type hydrogen storage materials.

A thin layer model is proposed to assist in the understanding of the electrochemical conversion of insulator to conductor at the conductor/insulator/electrolyte three-phase interline (3PI) when the influence of mass diffusion in the electrolyte phase is negligible. The model predicts, under potentiostatic conditions, a linear variation of the current or the length of the 3PI with time. When polarization is sufficiently large, the logarithm of the current/time ratio or the 3PI-length/time ratio, according to the model, increases linearly with the applied potential. These predictions were tested against and agreed very well with two practical systems: the electroreduction of solid AgCl to Ag in aqueous KCl and of solid SiO2 to Si in molten CaCl2. Kinetic parameters were derived from experimental data using the model. Particularly, the electron transfer coefficient, R, was found to be about 0.29 for the reduction of AgCl to Ag in the aqueous KCl solution at room temperature but about 10-2 for the reduction of SiO2 to Si in molten CaCl2 at 850℃.

Sintered (300℃) porous pellets of MoS2 were electrolysed to elemental S and Mo in molten CaCl2 (800-900℃) under argon at 1.0-3.0V for 1-20h. On a graphite anode, the product was primarily S (but traces of CS2 could not yet be excluded by this work) and evaporated from the molten salt, allowing the electrolysis to continue. It then condensed to solid at the lower temperature regions of the system. The anode remained intact after repeated uses. The MoS2 pellet was highly conducting at high temperatures and could be fast electroreduced to fine Mo powders (0.1-1.0lm) in which the S content could be below 1000ppm. No reduction occurred at voltages below 0.5V. Partial reduction was seen at 0.5-0.7V, and converted MoS2 to a mixture of MoS2 and Mo3S4, orMo3S4 and Mo with the Mo content increasing with the voltage. Cyclic voltammetry of the MoS2 powder in a Mo-cavity electrode, together with the electrolysis results, revealed the reduction mechanism to include two steps: MoS2 to Mo3S4 at 0.28V (potential vs. Ag/AgCl), and then to Mo at -0.43V.

Cyclic voltammetry of the CuCl powder in a cavity microelectrode revealed direct electro-reduction in solid state in 1-butyl-3-methylimidazolium hexafluorophosphate. Potentiostatic electrolysis of the salt powder (attached to a current collector) in the ionic liquid produced Cu nanoparticles as confirmed by X-ray diffraction, energy dispersive X-ray analysis, scanning and transmission electron microscopy. The particle size decreased down to 10 nm when the electrode potential was shifted from -0.9V to -1.8V (versus Ag/Ag+). The electro-reduction and the nanoparticle formation mechanisms were investigated in the ionic liquid and also in aqueous 0.1mol L 1 KCIO4 in which larger Cu particles were obtained.

Chromates conversion coatings provide very effective corrosion protection for many metals. However, the high toxicity of chromate leads to an increasing interest in using non-toxic alternatives such as molybdates, silicates, rare earth metal ions and etc. In this work, quartz crystal microbalance (QCM) was applied as an in-situ technique to follow the film formation process on zinc (plated on gold) in acidic solutions containing an inorganic inhibitor, i.e. potassium chromate, sodium silicate, sodium molybdate or cerium nitrate. Using an equation derived in this work, the interfacial mass change during the film formation process under different conditions was calculated, indicating three different film formation mechanisms. In the presence of K2CrO4 or Na2SiO3, the film growth follows a mix-parabolic law, showing a process controlled by both ion diffusion and surface reaction. The apparent kinetic equations are 0.4t=-17.4+20Dmf+(Dmf)2 and 0.1t=19.0+8.4Dmf+10(Dmf)2 respectively (t and Dm arein seconds and lg/cm2). In solutions containing Na2MoO4, a logarithmic law of Dmf=-24.7+6.6 lnt was observed. Changing the inhibitor to Ce(NO3)3, the film growth was found to obey an asymptote law that could be fit into the equation of Dmf=55.1(1-exp(-2.6×10-3t)).