Dehydrogenation kinetics and modeling studies of MgH2 enhanced by NbF5 catalyst using constant pressure thermodynamic forces

In this research, the effect of NbF5 as an additive on the hydrogen desorption kinetics of MgH2 was investigated and compared to TiH2, Mg2Ni and Nb2O5 catalysts. The kinetics measurements were done using a method in which the ratio of the equilibrium plateau pressure to the opposing pressure was the same for all the reactions. The data showed NbF5 to be vastly superior to the other catalysts for improving the desorption kinetics of MgH2. The rates of desorption were found to be in the order NbF5 ≫ Nb2O5 > Mg2Ni > TiH2 > Pure MgH2. Kinetic modeling measurements showed that chemical reaction at the phase boundary to be the likely process controlling the reaction rates. TPD analyses showed the mixture with NbF5 has the lowest desorption temperature although it was accompanied with some weight penalty.

► Kinetic measurements were done using constant pressure thermodynamic forces. ► NbF5 is a vastly superior catalyst for improving the desorption kinetics of MgH2. ► Kinetic modeling done by two methods gave the same result. ► Chemical reaction at the phase boundary is the rate-controlling process.