KINETICS OF HYDROGEN ABSORPTION BY NICKEL POWDER WITH ADDED PALLADIUM, COPPER, AND NICKEL FROM NICKEL-CHLORIDE REDUCTION BY HYDROGEN

Absorption of hydrogen by nickel powder, obtained from a reduction of dehydrated nickel-chloride by hydrogen, in the presence of 0.1 mass.% of palladium, copper, and nickel from nickel-formate decomposition has been investigated. A stereological analysis of the powders revealed r elatively rounded and similar shaped particles of sizes in the range D -x = 0.321-2.085 mu m. The largest value of the mean particle diameter is observed for the pure nickel powder (D-x = 2.085 mu m), and the lo west for the powder with added palladium (D-x = 0.321 mu m). Kinetics of hydrogen absorption in a temperature interval of 80-350 degrees C h ave been investigated and the activation energy, absorption enthalpy, rate constants of the reactions, and the frequency factors determined. Enthalpy of hydrogen absorption by pure nickel powder amounts -Delta H = 588 J/g, increasing in the presence of additives, being -Delta H = 2916 J/g in the case of palladium added, -Delta H = 1454 J/g and -Del ta H = 1228 J/g when copper and nickel were added. The maximum absorpt ion enthalpy of the sample with added palladium can be explained by th e influence of the ''spillover'' effect and the particle sizes (the sm allest ones), while a positive effect of added copper is thought to be a consequence of the weakening of bonds in the lattice of nickel due to copper solubility and somewhat smaller particles. The influence of added nickel, obtained by nickel-formate decomposition, on the absorpt ion increase resulted from a decrease in the particle size. (C) 1997 I nternational Association for Hydrogen Energy.