Rate determining step in the absorption and desorption of hydrogen by magnesium

Effects of BaRuO3 addition on hydrogen desorption in MgH2

“…5) can be normalized by the driving force, g(P/P eq ), so that a purely kinetic constant, h(T), can be obtained. The driving force depends on the ratio P/P eq , where P is the pressure of the desorption experiment (0.1 MPa in these experiments) and P eq is the equilibrium pressure at the temperature of the experiment [44,45]. Attempts to apply the correction for the driving force led to a significant decrease of the correlation coefficient for the linear regression in the Arrhenius plot of Figure 5, with the consequence of unreasonable values for the activation energy.…”

“…Due to the progressive approaching of the equilibrium temperature at the desorption pressure (0.1 MPa) on decreasing temperatures [26], a correction of the kinetic constants obtained at various temperatures with a constant pressure has been suggested [44].…”

Direct synthesis of MgH2 nanofibers at different hydrogen pressures

“…Each of these steps can influence the other two steps and make the overall hydrogenation process increasingly complex [4]. Further, the hydrogen diffusion in bulk Mg is slow enough to be the rate-determining step in the conventional gas-solid reaction [12].…”

Electronic Principles of Hydrogen Incorporation and Dynamics in Metal Hydrides

“…Despite somewhat larger values obtained for defects formation and diffusion in [87], it is H desorption from the MgH 2 surfaces that is usually considered [88,89] as the rate-limiting step for dehydrogenation process of MgH 2 . The common, and to a great extent, correct explanation for this is a strong ionic interaction between Mg and H. But, as can be seen in Figure 6a, besides the bonding between Mg (red spheres) and H (blue spheres), H-H bonding interaction also exists in the system (see also Figure 3b in [84]).…”

“…One attempt in this direction is presented in Figure 7a Although all mentioned [80,82,[85][86][87][88][89]91,92] and other numerous investigations deal with only some particular aspects of the process (e.g., distinct points on the MgH 2 dehydrogenation curve), they are accurate enough to justify the expectation that the entire process (as well as the process of Mg hydrogenation) will be resolved "from the first principles" in the near future. Also, the investigations have "located'' the main obstacles that should be resolved in the further attempts to improve the performances of the Mg-H system.…”