A kinetic study on the mechanism of hydrogen evolution in Ni–P coated titanium hydride powder

• We coated TiH2 powder by Ni–P compounds using an electroless plating technique.
• We suggested a comprehensive mechanism for hydrogen evolution process.
• It was shown that the coating can increase dehydrogenization temperature up to 900 °C.
• This coating prevents H2 from diffusing out of the powder till 900 °C.
• A 400 °C delay is reported for gas release process of Ni–P coted TiH2.

In this work, titanium hydride powder (TiH2) was coated by an electroless method through an aqueous coating bath consisting of nickel-phosphorus compounds. Energy Dispersive Spectroscopy (EDS) was utilized for characterization of nickel compounds in the coated layer. Also, DTA, XRD and TGA patterns were determined in order to take different stages of hydrogen release process into consideration. In conformity with the results, only 1.25 wt% Ni–P coating was deposited on the as-received TiH2, so that its great majority includes Ni5P2 compound. Also, the hydrogen gas release process, in this case, occurs at seven stages, exactly similar to that in TiH2 heat treated in air. The coating causes various stages of hydrogen evolution to undergo a temperature delay roughly equal to 400 °C. It means that the coating displaces various stages of hydrogen release process to higher temperatures thereby delaying efficiently the starting time of the reaction approximately for 40 min. It implies that Ni–P coating can act as an effective diffusion barrier to hydrogen gas evolution. Also, activation energy values for these seven stages were calculated. It was shown that only active mechanism in Ni–P coated TiH2 is internal diffusion, i.e. the diffusion of hydrogen atoms into titanium lattice.

Figure optionsDownload as PowerPoint slide