The kinetics of the absorption of hydrogen by LaNi5Hx-n-undecane suspensions

Abstract

Abstract Isothermal kinetics studies of the absorption of hydrogen by LaNi5Hx suspended in n-undecane have been performed. The rate-limiting process is the dissolution of hydrogen in the solvent. The following general rate equation is given: d[H 2 ] dt = 1 2 k s (a′'−a′) where ks is the rate constant for the absorption of hydrogen by the solvent and a′'−a′ represents a thermodynamic driving force which is determined by the equilibrium solubility of hydrogen in the solvent and the equilibrium absorption plateau pressure of the solid. The rate constant is defined as k s = A s exp(− E s RT) where Es is the activation energy for dissolution of hydrogen in the solvent and is equal to 11.0 ± 1.1 kJ (molH2)−1. The pre-exponential As is a function of the efficiency of the gas-liquid contact. The rate equation should have general utility and can be used with other hydrides suspended in n-undecane as long as the rate-limiting process is unchanged. A new method for the study of fast reactions involving the dissolution of hydrogen in liquids is discussed. The hydrogen absorption and desorption rates are well within the range required for practical applications.