Synergistic Effect of New ZrNi5/Nb2O5 Catalytic Agent on Storage Behavior of Nanocrystalline MgH2 Powders

Abstract

Due to its availability and high storage capacity, Mg is an ideal material in hydrogen storage applications. In practice, doping Mg/MgH2 with catalyst(s) is necessary in enhancing the de/rehydrogenation kinetics and minimizing both of decomposition temperature and its related apparent activation energy. The present study proposed a new heterogeneous catalytic agent that consisted of intermetallic compound (ZrNi5)/metal oxide (Nb2O5) binary system for using with different concentrations (5−30 wt%) to improve MgH2. Doping MgH2 powders with low concentration (5, 7, 10 wt%) of this new catalytic system led to superior absorption/desorption kinetics, being indexed by the short time that is required to absorb/desorb 4.2−5.6 wt% H2 within 200 s to 300 s. Increasing the doping dose to 15–30 wt% led to better kinetic effect but a significant decrease in the hydrogen storage capacity was seen. The dependent of apparent activation energy and decomposition temperature of MgH2 on the concentration of ZrNi5/Nb2O5 has been investigated. They tended to be linearly decreased with increasing the catalyst concentrations. The results elucidated the crucial role of catalytic additives on the disintegration of MgH2 into ultrafine powders (196 nm to 364 nm diameter). The formation of such nanoparticles enhance the hydrogen diffusion and shorten the time that is required for the hydrogenation/dehydrogenation process. Moreover, this refractory catalytic system acted as a grain growth inhibitor, in which Mg/MgH2 powders maintained their submicron level during the cycle-life-test that was extended to 100 h at 200 °C.

Mechanically-Induced Catalyzation of MgH2 Powders with Zr2Ni-Ball Milling Media

“…Shimadzu Thermal Analysis System/TA-60WS, Saitama, Japan, using normal differential scanning calorimeter (DSC) was employed to investigate the decomposition temperatures of MgH 2 powders with a heating rate of 5 • C/min. The apparent activation energy of decomposition (E a ) for the powders obtained after different RBM time were investigated, using the Arrhenius approach with different heating rates (5,10,20,30,40 • C/min).…”

“…Reactive ball milling (RBM), which was investigated in the beginning of the 1990s [1,2] is a cost effective process, employed for conducting gas-solid reactions at ambient temperature, starting from pure metal and desired gas. Since then, RBM has been intensively used to produce large amounts of high quality MgH 2 nanocrystalline powders, starting from Mg metal and hydrogen gas [3][4][5].…”

“…Severe plastic deformation (SPD) technique [15], including high energy ball milling [16], cold rolling (CRing) [17,18], high pressure torsion (HPT) [19] and equal channel angular pressing (ECAP) [20] were employed to improve the hydrogen storage properties of MgH 2 . Apart from the mechanical treatment approach, catalyzation MgH 2 powders with proper volume fractions of catalytic agents [21], including pure metals [22], intermetallic compounds [23][24][25][26], metal-oxides [27,28], metal/metal oxide composites [5,29], -carbides [30,31], metallic glassy alloys [32][33][34] and chlorides [35] have shown outstanding effects on enhancing the hydrogen storage properties of MgH 2 and infer its apparent activation energy of decomposition [36]. More recently, self-assembled MgH 2 and metal borohydride nanoparticles on graphene technique has shown great enhancement of the behavior of the metal hydride phase [37][38][39].…”

Selective Catalytic Reduction of NOx by CO over Doubly Promoted MeMo/Nb2O5 Catalysts (Me = Pt, Ni, or Co)

“…Indeed, our previous work reported that Mo oxide The niobium pentoxide exists in several structures with the polymorphs mostly being derived from the ReO 3 type structure. The main phase for Nb 2 O 5 occurs upon calcination of the amorphous niobium oxide in the 600-800 • C range with predominance of orthorhombic structure e.g., T-Nb 2 O 5 while the pseudohexagonal one, e.g., TT-Nb 2 O 5 is observed at lower temperatures [23][24][25][26][27][28].…”

Review on Hydrogen Storage Performance of MgH2: Development and Trends

“…It takes 425 s to absorb 6.2 wt % H 2 at 200 °C and 3 MPa, and 700 s to dehydrogenate 6.2 wt % H 2 at 225 °C. The research team also developed ZrNi 5 /Nb 2 O 5 [22b] and Zr 70 Ni 20 Pd 10 [22c] alloy catalysts, which not only have faster hydrogen absorption and desorption properties (Zr 70 Ni 20 Pd 10 can release 6 wt % H 2 within 3.8 min at 200 °C), but also maintain a good hydrogen storage capacity over hundreds of cycles. L.T.…”