Kinetics of hydrogen absorption by nickel powder with added palladium, copper, and nickel from nickel-chloride reduction by hydrogen

Abstract

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 relatively rounded and similar shaped particles of sizes in the range D x = 0.321–2.085 μm. The largest value of the mean particle diameter is observed for the pure nickel powder ( D x = 2.085 μm), and the lowest for the powder with added palladium ( D x = 0.321 μm). Kinetics of hydrogen absorption in a temperature interval of 80–350 °C have 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 − Δ H = 588 J/g, increasing in the presence of additives, being −Δ H =2916 J/g in the case of palladium added, −Δ H = 1454 J/g and −Δ H = 1228 J/g when copper and nickel were added. The maximum absorption enthalpy of the sample with added palladium can be explained by the influence of the “spillover” effect and the particle sizes (the smallest 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 absorption increase resulted from a decrease in the particle size.