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The catalysis of NiFe2O4 nanoparticles on the hydrogen storage performances of magnesium hydride synthesized by high-energy ball milling was studied for the first time. The H-2 storage performances and catalytic mechanism were studied by pressurecompositiontemperature (PCT), differential scanning calorimetry (DSC), X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The nonisothermal dehydrogenation results display that the initial dehydrogenation temperature of 7 mol % NiFe2O4-doped MgH2 is 191 degrees C, which is 250 degrees C lower than that of pristine MgH2. The desorption kinetics displays that the MgH2+7 mol % NiFe2O4 sample could desorb 3.79 wt % H-2 within 1 h at 300 degrees C under H-2 pressure of 0.1 MPa. The absorption kinetics displays that the MgH2+7 mol % NiFe2O4 sample could absorb 2.06 wt % H-2 within 3 h near room temperature under H-2 pressure of 4 MPa. The desorption activation energy of the MgH2+7 mol % NiFe2O4 sample is 59.6 kJ/mol, decreasing 195.3 kJ/mol as compared with pristine magnesium hydride. The reaction enthalpy and entropy of the MgH2+7 mol % NiFe2O4 sample during the dehydrogenation process are improved. The enhancement in the H-2 storage performances of MgH2 by adding NiFe2O4 nanoparticles is primarily ascribed to intermetallic Fe7Ni3 and (Fe,Ni) phases during the desorption procedure, which act as the real catalyzer in the 7 mol % NiFe2O4-doped sample., Peer Reviewed, Postprint (published version)

Nanostructured tungsten carbide with high surface area and containing amorphous carbon is prepared by a low temperature combustion synthesis method. The nanostructured tungsten carbide is used as the catalyst in a gas diffusion electrode. The obtained WC with different carbon content was investigated by XRD, FESEM, TG-DTA, BET and XPS. When the molar ratio of C/W is 19/3, the WC particles with different carbon content are obtained after a carbonizing process between 900 and 1400 C, and the content of free carbon in WC also increases gradually with temperature. The carbon content is tested by the high frequency combustion-infrared absorption method in a carbon sulfur analyzer. The electrochemical properties of the tungsten carbide for the oxygen reduction reaction are characterized by its polarization curves and electrochemical impedance. The results show that the presence of the appropriate amorphous carbon is beneficial for improving the conductivity and dispersibility of the tungsten carbide catalyst, and more active centers can be provided by the catalyst, Postprint (published version)

The structural relaxation, glass transition and crystallization processes of Mg65Cu25Y10 metallic glass are studied by Differential Scanning Calorimetry (DSC) and Mechanical spectroscopy. The relaxation model derived from the mechanical measurements is compared with the kinetics of these transformations obtained from the DSC curves. The structural relaxation kinetics is found to be controlled by the glassy dynamics following an Adams-Gibbs-Vogel function. The glass transition and crystallization kinetics are controlled by the dynamics of the supercooled melt following a Vogel-Fulcher-Tammann behaviour. The results suggest that the microscopic processes responsible of structural relaxation and aging below the glass transition correspond to the same processes generating the a-relaxation peak. (C) 2013 Elsevier B.V. All rights reserved., Peer Reviewed, Postprint (author’s final draft)

A new Fe-based bulk metallic glass with superior glass-forming ability (GFA), Fe46Cr15Mo14C15B6Nb4, was developed based on the Fe-Cr-Mo-C-B alloy system by minor addition of Nb. The effects of Nb addition on glass formation of the Fe-50 xCr15Mo14C15B6Nbx (x = 0, 2, 4 and 6 at.%) alloys were investigated. The optimum addition content of Nb was determined as 4 at.% by X-ray diffraction and differential scanning calorimeter analysis. A fully amorphous rod sample with 3 mm in diameter was produced by using commercial-grade raw materials and a copper mold casting technique. This alloy shows an ultimate compressive strength of 1920 MPa and Vicker's hardness 1360 H-V, which is two to three times that of conventional high strength steel and suggests a promising potential for applications combining outstanding corrosion and wear resistance properties. The crystallization kinetics studies found that the activation energies for glass transition, onset of crystallization and crystallization peak were higher than those of other reported Fe-based bulk metallic glasses. The value of the fragility parameter m for the Fe46Cr15Mo14C15B6Nb4 alloy was calculated to be 34, indicating that the Fe-Cr-Mo-C-B-Nb alloy system is a strong glass former according to the Angell's classification scheme. It is inferred that the more sequential change in the atomic size, the generation of new atomic pairs with large negative heats of mixing and the amount of oxygen in the molten liquid neutralized into Nb oxides provide a synergetic effect for the remarkably improved GFA and thermal stability. (C) 2014 Elsevier B.V. All rights reserved., Peer Reviewed, Postprint (published version)

CoFe2O4 nanoparticles are added to magnesium hydride (MgH2) by high-energy ball milling in order to improve its hydriding properties. The hydrogen storage properties and catalytic mechanism are investigated by pressure-composition-temperature (PCT), differential thermal analysis (DTA), X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The nonisothermal desorption results show that the onset desorption temperature of the MgH2 + 7 mol% CoFe2O4 is 160 degrees C, which is 200 degrees C lower than of the as-received MgH2. The dehydrogenation process of the MgH2 doped with the CoFe2O4 nanoparticles includes two steps. DTA curves and XRD patterns reveal that a chemical reaction happens between MgH2 and CoFe2O4, forming the final products of the ternary combination, corresponding to Co3Fe7, MgO and Co. The onset desorption temperature of the ball-milled MgH2 doped with Co3Fe7, MgO and Co is about 260 degrees C, approximately 100 degrees C lower than the un-doped MgH2, demonstrating that the ternary combination (Co3Fe7, MgO, and Co) also has a great catalytic effect on the MgH2 hydrogen storage properties. It is also confirmed that the various methods of adding the ternary combination have different effects on the MgH2 hydriding-dehydriding process. (C) 2014 Elsevier B.V. All rights reserved., Peer Reviewed, Postprint (published version)

The catalytic effects of CoFe2O4 nanoparticles on the hydrogen storage properties of LiAlH4 prepared by ball milling were investigated. The onset desorption temperature of the LiAlH4 + 2 mol% CoFe2O4 sample is 65 °C, which is 90 °C lower that of the as-received LiAlH4, with approximately 7.2 wt% hydrogen released at 250 °C. The isothermal desorption results show that for the 2 mol% CoFe2O4 doped sample dehydrogenated at 120 °C, 6.8 wt% of hydrogen can be released within 160 min, which is 6.1 wt% higher than that of the as-received LiAlH4 under the same conditions. Through the differential scanning calorimetry (DSC) and the Kissinger desorption kinetics analyses, the apparent activation energy, Ea, of the 2 mol% CoFe2O4 doped sample is calculated as 52.4 kJ mol -1 H2 and 86.5 kJ mol-1 H2 for the first two decomposition processes. This is 42.4 kJ mol-1 H 2 and 86.1 kJ mol-1 H2 lower compared with the pristine LiAlH4, respectively, indicating considerably improved dehydrogenation kinetics by doping the CoFe2O4 catalyst in the LiAlH4 matrix. From the Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses, a series of finely dispersed Fe and Co species with a range of valence states, produced from the reactions between LiAlH4 and CoFe2O4, play a synergistic role in remarkably improving LiAlH4 dehydrogenation properties. The rehydrogenation properties of the LiAlH4 + 2 mol% CoFe 2O4 sample have also been investigated at 140 °C under 6.5 MPa pressure held for 2.5 h, Peer Reviewed, Postprint (published version)

The catalytic effects of MnFe2O4 nanoparticles on the dehydrogenation properties of NaAlH4, prepared by ball milling, are investigated. The onset temperatures for NaAlH4 + 7 mol% MnFe2O4 are 95 C, 152 C and 327 C for the three dehydrogenation steps, significantly lower compared with as-received NaAlH4. The isothermal dehydriding kinetics shows that adding MnFe2O4 to NaAlH4 could significantly enhance the desorption kinetics of NaAlH4, 7 mol% MnFe2O4-doped sample also displays the well-maintained kinetics and only a slight capacity loss for the three cycles. From the differential scanning calorimetry and the Kissinger desorption kinetics analysis, the apparent activation energy of the 7 mol% MnFe2O4-doped sample for the three steps is 57.74 kJ mol(-1), 75.06 kJ mol(-1) and 117.22 kJ mol(-1), resulting in 56.05 kJ mol(-1), 67.53 kJ mol(-1) and 59.12 kJ mol(-1) reduction, respectively, compared with the as-received NaAlH4. Based on the Fourier Transform Infrared Spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy, Fe0.9536O and amorphous Mn or Mn-containing species together play a synergistic role in remarkably improving NaAlH4 dehydriding properties, Peer Reviewed, Postprint (published version)

Tungsten carbide powder, which is used as the catalyst for a gas diffusion electrode, has been prepared by low-temperature combustion synthesis for the first time. The average particle size of the prepared tungsten carbide is 200 nm, determined by X-ray diffraction and field-emission scanning electron microscopy. The effects of the carbon/tungsten (C/W) molar ratio on the formation of tungsten carbide and carbon content on the complete carbonization temperature are discussed. The optimal synthesis temperature is 1100 °C, and the optimal C/W molar ratio is 19/3. The electrocatalytic properties of tungsten carbide for the oxygen reduction reaction are evaluated through the use of polarization curves and electrochemical impedance spectroscopy in neutral and alkaline electrolytes. The current density of the tungsten carbide-based gas diffusion electrode is as high as 350 mA cm-2 at 0.4 V versus Hg/HgO. It is demonstrated that the tungsten carbide catalyst exhibits excellent electrocatalytic performance, comparable with that of Pt., Peer Reviewed, Postprint (published version)