Hydrogen Storage Properties Of Composites Research Articles

Enhanced electrochemical hydrogen storage performance of Ti[sbnd]V[sbnd]Ni composite employing NaAlH4

The Ti1.4V0.6Ni doped with NaAlH4 composites were prepared by ball-milling method and the phase composition and electrochemical hydrogen storage properties of the composites were investigated. The phase contains icosahedral quasicrystalline (i-phase), Ti2Ni and V-based solid-solution phase primarily. The NaAlH4 phase is not evident for the composite, and the NaAlH4 phase should be decomposed to help form porous structure on the surface of the composites. The electrochemical hydrogen storage properties of composites has been enhanced with doped NaAlH4, and the maximum electrochemical hydrogen discharge capacity is 299.2 mAh/g, and keeps above 220 mAh/g after 80 cycles for 1 wt.% doping. The high-rate discharge ability of the composite electrode could achieve 79.8% at the discharge current density of 240 mA/g compared with that of 30 mA/g. The enhancement could be attributed to decoration of the composites surface, increase of entropy variation and improvement of H-kinetics on the strength of new porous structure in the composites.

The catalysis mechanism of La hydrides on hydrogen storage properties of MgH2 in MgH2+xwt.% LaH3 (x=0,10,20, and 30) composites

Abstract A systematic investigation was performed on the hydrogen storage properties of composites which were prepared by ball milling MgH2 with different amounts of LaH3 and the catalysis mechanism of La hydride on MgH2 was reported in this paper. Pressure–Composition–Temperature (P–C–T) curves showed that the reversible hydrogen storage capacity of MgH2 + 20 wt.% LaH3 composite was 5.1 wt.% at 548 K, while the pure MgH2 hardly released any H2 under the same conditions. The addition of LaH3 also significantly improved the hydriding/dehydriding kinetics, and led to the rate-controlling steps of MgH2 becoming altered from a three-dimensional interfacial reaction to a one-dimensional diffusion process. The XRD pattern indicated that the LaH3 phase partially transformed to LaH2.3 phase during the dehydriding process. TEM micrograph images revealed that the LaH2.3 phase was distributed homogeneously throughout the Mg phase and that the Mg crystals were coated with LaH2.3 crystals in the matrix. This microstructure exhibited an obvious volume contraction and resulted in a distinct strain of MgH2 when the LaH3 phase released H2. DSC curves proved that the addition of LaH3 could decrease the temperature at which the onset of the dehydrogenation of MgH2 occurred by approximately 20.4 K.

Structure, morphology and hydrogen storage properties of composites prepared by ball milling [formula omitted] with La–Mg-based alloy

Hydrogen storage alloy composites Ti 0.9 Zr 0.2 Mn 1.5 Cr 0.3 V 0.3 - x wt % La 0.7 Mg 0.25 Zr 0.05 ( Ni 0.85 Co 0.15 ) 3.5 ( x = 0 , 5 , 10 ) were prepared by ball milling method. Their structures, morphologies and the hydrogen storage characteristics were intensively studied in the present work. It was found that the bulk of composites maintained the hexagonal C14 Laves phase structure after ball milling with additional La–Mg-based alloy for two hours. Scanning electron microscopy (SEM) observations revealed that the average size of Ti 0.9 Zr 0.2 Mn 1.5 Cr 0.3 V 0.3 and La 0.7 Mg 0.25 Zr 0.05 ( Ni 0.85 Co 0.15 ) 3.5 particles were reduced to several hundred nanometers after ball milling process. Energy dispersive X-ray spectrometer (EDS) patterns of the composites showed that the La 0.7 Mg 0.25 Zr 0.05 ( Ni 0.85 Co 0.15 ) 3.5 phase was uniformly distributed on the surface of Ti 0.9 Zr 0.2 Mn 1.5 Cr 0.3 V 0.3 . The hydrogen absorption–desorption characteristics of the composites were improved with increasing dispersivity of the La 0.7 Mg 0.25 Zr 0.05 ( Ni 0.85 Co 0.15 ) 3.5 alloy particles. Pressure–composition–temperature (PCT) measurements revealed that the pressure plateau and the hysteresis decreased with increasing x. Among these composites, the sample of x = 10 exhibited more significant hydrogen storage performances. Its hydrogen absorption and desorption plateau pressure were 0.547 and 0.302 MPa, respectively, which were much lower than those of the Ti 0.9 Zr 0.2 Mn 1.5 Cr 0.3 V 0.3 alloy. Moreover, it took only 200 and 2500 s to reach the constant pressure for the hydrogen absorption and desorption reaction. These improvements can be attributed to the preferable dispersivity of La–Mg-based alloy particles and also the formation of micro-crack after ball milling. Both factors synergetically facilitate the diffusion of hydrogen atoms in the composites and accelerate the dissociation of hydrogen molecules and recombination of hydrogen atoms on the surface of composites during the hydrogen absorption–desorption process.