Superior catalytic effect of TiF3 over TiCl3 in improving the hydrogen sorption kinetics of MgH2 : Catalytic role of fluorine anion

• Published in: Acta materialia Vol. 57; no. 7; pp. 2250 - 2258
• Main Authors: MA, L.-P, KANG, X.-D, DAI, H.-B, LIANG, Y, FANG, Z.-Z, WANG, P.-J, WANG, P, CHENG, H.-M
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier 01.04.2009
• Subjects: Applied sciences; Exact sciences and technology; Metals. Metallurgy; Hydrogen storage; Storage; Fluorine; Hydrogen; Hydrides; Catalysis; Kinetics; X-ray photoelectron spectroscopy
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2009.01.025

TiF3 shows a superior catalytic effect over TiCl3 in improving the hydrogen sorption kinetics of MgH2. Combined phase analysis and microstructure characterization suggest that both titanium halide additives react with host MgH2 in a similar way. However, systematic X-ray photoelectron spectroscopy studies reveal that the incorporated fluorine (F) differs significantly from its analog chlorine (Cl) in terms of bonding state. The asymmetry of F 1s spectra and the sputtering-induced peak shift suggest that, in addition to the Mg-F bond, a new Ti-F-Mg bonding is formed in the TiF3-doped MgH2. In contrast, only one stable binding state of Cl is identified in the form of MgCl2 for the TiCl3-doped MgH2. In combination with the designed experiments, these findings suggest that the generation of active F-containing species may be responsible for the advantage of TiF3 over TiCl3 in improving both the absorption and desorption kinetics of MgH2. Fundamentally, it emphasizes the functionality of F anion in tuning the activity of compound catalyst.