Synergistic effects of transition metal halides and activated carbon nanofibers on kinetics and reversibility of MgH2. (January 2019)

• Record Type: Journal Article
• Authors: Plerdsranoy, Praphatsorn; Thiangviriya, Sophida; Dansirima, Palmarin; Thongtan, Puttimate; Kaewsuwan, Dechmongkhon; Chanlek, Narong; Utke, Rapee
• Is Part Of: Journal of physics and chemistry of solids. Volume 124(2019)
• Page Start: 81
• Page End: 88
• Publication Date: 2019-01
• Subjects: Solid state hydrogen storage -- Carbon -- Dehydrogenation -- Activation energy -- Mg hydride; Solids -- Periodicals; Solides -- Périodiques; Solids; Periodicals; 530.41
• DOI: 10.1016/j.jpcs.2018.09.001
• Languages: English
• ISSNs: 0022-3697

Abstract

Abstract: MgH2 doped with transition metal halides (TiF4, NbF5, and ZrCl4 ) and activated carbon nanofibers (ACNF) for reversible hydrogen storage is prepared by ball milling technique. Transition metal halides provide catalytic effects for de/rehydrogenation kinetics, while ACNF benefits thermal conductivity and hydrogen permeability as well as prevents particle agglomeration during cycling. Significant reduction of onset and main dehydrogenation temperatures of MgH2 (Δ T = 243 and 158 °C, respectively) are achieved by doping with 5–10 wt % of NbF5, ACNF-TiF4 and ACNF-NbF5 . During the 1 st cycle, the latter samples liberate 4.7–5.0 wt % H2 within 1 h 30 min, whereas MgH2 doped with ACNF reaches only 1.5 wt % H2 . The reaction between MgF2 and NbHx (x < 1) (MgH2 -NbF5 and MgH2 -ACNF-NbF5 ) during dehydrogenation results in the formation of new catalytic active species of Nb-F-Mg favoring kinetics. Upon four hydrogen release and uptake cycles, kinetics and reversibility within 1 h 30 min of MgH2 -ACNF-NbF5 are preserved at 5.0 wt % H2, while those of MgH2 -NbF5 and MgH2 -ACNF-TiF4 decay to 4.4 wt % H2 . Activation energy ( E A ) for dehydrogenation of MgH2 considerably decreases from 140.0 ± 10.2 to 37.8 ± 1.5 kJ/mol after doing with ACNF-NbF5 . Superior performance of MgH2 -ACNF-NbF5 to MgH2 -NbF5 is due to synergistic effects of NbF5 and ACNF. In the case of MH2 -ACNF-TiF4, the disappearance of active species benefiting kinetic properties and the formation of thermally stable TiH2 account for inferior hydrogen content reversible. Highlights: Enhanced kinetics of MgH2 by doping with transition metal halides and ACNF. Reduction of desorption temperature by 243 °C after doping ACNF-NbF5 into MgH2 . Decrease of E A by 102 kJ/mol after doping ACNF-NbF5 into MgH2 . Upon four H2 de/absorption cycles, 5 wt % H2 preserved from MgH2 -ACNF-NbF5 . Formation of new active species (Nb-F-Mg) favoring H2 storage performances of MgH2 .