Reversible hydrogen storage in the Li–Mg–N–H system – The effects of Ru doped single walled carbon nanotubes on NH3 emission and kinetics

• NH3 emission and kinetics are closely related to ball milling parameters.
• SWCNTs doping of the Li–Mg–N–H system increases NH3 emission by 4 fold.
• Ru doped SWCNTs are effective in NH3 decomposition in the Li–Mg–N–H system.

In this study, the LiNH2–MgH2 (2:1.1) complex hydride system (Li–Mg–N–H is investigated in terms of hydrogen ab/desorption kinetics and the concomitant NH3 emission levels. By selecting more intense ball milling parameters, the hydrogen ab/desorption kinetics were improved and the NH3 emission reduced. However, it is shown that NH3 emission cannot be completely eliminated during ball milling. Single walled carbon nanotubes (SWCNTs) and 20 wt.% Ru doped SWCNTs are utilized as catalysts to study their effects on NH3 emission and kinetics characteristics of the Li–Mg–N–H system. The SWCNT doped sample did not show any kinetics improvement, whereas the SWCNT-20Ru doped sample showed similar kinetics performance as that of the base sample. More importantly, the presence of SWCNT increased the NH3 emission as compared to the base sample. On the other hand, SWCNT-20Ru doping reduced the NH3 emission compared to the SWCNT doping, but did not eliminate it completely. As revealed from the mass spectrometry signals, the SWCNT-20Ru catalyst starts to decompose NH3 at a temperature as low as 200 °C.

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