Effect of Oxide Layers on the Absorption Kinetics of Hydrogen by Metals at Room Temperature*

Abstract

Hydrogen in metals / Absorption kineticsOxide layers on metal surfaces impede or prevent hydrogen absorption at temperatures below 400°C. This passivation can be caused by slow dissociation of H2 molecules on the surface, slow transfer of chemisorbed H atoms into the oxide, or by slow H permeation through the oxide layer. Experiments on the H2 absorption kinetics of film samples with known oxygen precoverage yield a direct access to reaction models if relevant results of other techniques are regarded appropriately as well as inherent thermochemical and atomistic limits. Typical examples are discussed to elucidate this approach for the investigation of complex reaction mechanisms in H2 absorption kinetics at room temperatures.Oxidschichten auf Metalloberflachen behindern oder unterdnicken die Wasserstoffaufnahme bei Temperaturen unterhalb 400°C. Diese Passivierung kann durch langsame Dissoziation von H2-Molekiilen auf der Oberflache, durch einen langsamen Durchtritt chemisorbierter H-Atome ins Oxid oder durch eine langsame Permeation der H-Atome durch die Oxidschicht verursacht werden. Experimente an Filmproben mit bekannter Sauerstoffvorbelegung ermoglichen die Uberprufung von Reaktionsmodellen, die aufgrund von Ergebnissen mit anderen Verfahren und in Abstimmung mit bekannten thermochemischen und atomistischen Daten aufgestellt worden sind. Dieses Vorgehen zur Aufkliirung komplexer Reaktionsmechanismen bei der Wasserstoffaufnahme von Metallen bei Raumtemperatur wird durch einige typische Beispiele aufgezeigt.

Thermochemical Energy Storage through De/Hydrogenation of Organic Liquids: Reactions of Organic Liquids on Metal Hydrides

“…We believe that the catalytically active surface sites important for the association of absorbed hydrogen atoms are blocked by the adsorbed species. Similar passivation and poisoning mechanisms of metal hydrides have been reported in the literature for gaseous impurities, such as O 2 , H 2 O, hydrocarbons, CO, or CO 2 , which form blocking layers on transition metal hydride surfaces and hereby inhibit the hydrogen sorption reactions. ,− The acetone-treated hydrides are stabilized through this kinetic barrier for extended time periods up to several weeks, as demonstrated by XRD.…”

Deactivation of titanium during temperature-induced hydrogen absorption–desorption cycling

“…In order to promote hydrogen absorption, temperature has to be risen up to 673 K for the SPL covered specimen. Oxide layers on titanium surface prevented hydrogen dissociation and transfer of hydrogen atoms into metal [14]. Oxygen may penetrate into metal forming a solution.…”

Effect of Mischmetal Introduction on Hydrogen Storage Properties in Impure Hydrogen Gas of Ti-Fe-Mn-Co Alloys

“…Facts have proved that rare-earth metals can significantly improve the cyclic stability under impure hydrogen gas of V-based hydrogen storage alloys. Fromm [14] studied the effect of the oxide layer on the hydrogen absorption kinetics of the alloy. Modi and Aguey-Zinsou [15] studied the recovery method of the poisoned TiFe-based alloys.…”