High temperature hydrogenation of Ti-V alloys: The effect of cycling and carbon monoxide on the bulk and surface properties

In the present work, the high temperature (425-575 °C) hydrogen storage properties of Ti-V alloys have been studied, both at static conditions and in a flow of hydrogen gas. The selected isothermal temperature range is considered as an optimal condition for hydrogen sorption enhanced steam reforming. When hydrogenation and dehydrogenation were performed in pure hydrogen gas and in vacuum, a large reversible hydrogen capacity of 3.95 wt. % H was obtained, demonstrating completeness of the formation and decomposition of (Ti,V)-dihydrides. However, when cycling was performed in a flow of hydrogen gas, the reversible hydrogen capacity decreased to ∼2 wt. % H caused by the formation of stable lower (Ti,V)-hydrides. A further decrease in the reversible hydrogen storage capacity took place when pure hydrogen gas was replaced by a mixture of hydrogen and carbon monoxide CO. This decrease was caused by the formation of an oxygen rich layer on the surface of the alloy, which was partially blocking the hydrogen exchange between the surface and the bulk of the sample.