Analyzing the kinetic behavior of hydrides applying the Markov Chain Monte Carlo (MCMC) method

Analyzing the kinetic behavior of hydrides applying the Markov Chain Monte Carlo (MCMC) method Authors J. Puszkiel1, 2,*, V. R. Hosseini3, A. Neves1, 2, T. Carraro3, T. Klassen1, 2, J. Jepsen1, 2 Affiliations 1Materials Technology, Helmut-Schmidt University (HSU), University of the Federal Armed Forces, Holstenhofweg 85, 22043, Hamburg, Germany 2Institute of Hydrogen Technology, Helmholtz-Zentrum Hereon GmbH (hereon), Max-Planck-Str. 1, 21502, Geesthacht, Germany 3Applied Mathematics, Helmut-Schmidt University (HSU), University of the Federal Armed Forces, Holstenhofweg 85, 22043, Hamburg, Germany * Lead presenter Abstract Hydrogen is considered the most promising energy vector for an energy matrix based on renewable energy sources. There are several bottlenecks for the broad utilization of hydrogen; among them, its storage poses a challenge. Hydrogen storage in solid materials can provide a more compact, efficient, and safer alternative than the conventional physical storage methods in gaseous or liquid state [1]. These hydrogen storage systems comprise a vessel containing a hydride-forming material whose hydrogenation and dehydrogenation kinetic behaviors require appropriate characterization and modeling to gain a deeper understanding of the reaction mechanism [2]. This work explores a novel application of the Markov Chain Monte Carlo (MCMC) method to determine the rate-limiting step (RLS) of an AB2 hydride-forming alloy (Ti0.9Zr0.1)1.25Cr0.85Mn1.1Mo0.05 to which 10 wt.% of expanded natural graphite (ENG) was added [3]. Results obtained from measurements in Sieverts apparatus in broad ranges of temperature and hydrogen pressures (from -25 ºC to about 40 ºC and from 1 bar to about 160 bar) have been analyzed through this method to evaluate the JMAK equation (Johnson-Mehl-Avrami-Kolmogorow) [4]. To determine their most probable values, the MCMC approach focuses on the statistical distribution of the exponential factor n, describing the RLS, and the kinetic rate constant k for each kinetic curve. Considering the obtained n, the RLS mechanisms for the hydrogenation and dehydrogenation processes show a clear dependence on the T and P conditions. On the one hand, for the hydrogenation process, the RLS changes from a mixed mechanism (interphase movement and diffusion control, n= 0.7-0.8) to a pure interphase movement control mechanism as the temperature and pressure increase (n= 1.0-1.24). On the other hand, for the dehydrogenation process, the RLS is mainly the interphase movement at low temperatures and pressures (n= 1.0-1.25) and changes to a mixed mechanism as the temperature and pressure increase (n= 0.8-0.9). However, the interphase movement dominates the mixed mechanism in the T and P range. This analysis provides novel insights into the determination of the RLS, something impossible to reach with the application of the traditional gas-solid model determination methods (linearization of the gas-solid equations and reduced time method [4]). References [1] J. Bellosta von Colbe, et al., Application of Hydrides in Hydrogen Storage and Compression: Achievements, Outlook and Perspectives, International Journal of Hydrogen Energy 44 (2019) 7780. [2] L. Pasquini, et al., Magnesiumand intermetallic alloys-based hydrides for energy storage: modelling, synthesis and properties, Progress in Energy 4 (2022) 032007. [3] J. Puszkiel, et al., Designing an AB2-Type Alloy (TiZr-CrMnMo) for the Hybrid Hydrogen Storage Concept. Energies 13 (2020) 2751 [4] J. A. Puszkiel, Tailoring the Kinetic Behavior of Hydride Forming Materials for Hydrogen Storage, ed. IntechOpen, London, 2018, ISBN: 978-1-78984-957-8.