Changpin Chen

Studies on the electrochemical properties of MlNi4.3−xCoxAl0.7 hydride alloy electrodes

Abstract In this paper, the electrochemical properties of MlNi 4.3− x Co x Al 0.7 electrode alloys, including high rate dischargeability, exchange current density I 0 , limiting current density I L , and diffusion coefficient of hydrogen in the hydride D α by means of linear polarization, anodic polarization, and electrochemical impedance spectroscopy were systematically studied. The results indicate that, with the increase of Co content, the cyclic stability is improved markedly, which agrees with previous investigation. However, activation becomes more difficult, and the high rate dischargeability decreases. The linear polarization and anodic polarization results suggest that the exchange current density I 0 and limiting current density I L decrease from the 395 ( x =0) to 33 mA g −1 ( x =1.3) and from 2263 ( x =0) to 308 mA g −1 , respectively. The electrochemical impedance spectroscopy result also reveals that the diffusion coefficient of hydrogen in the alloys decreases rapidly with the increase in Co content in MlNi 4.3− x Co x Al 0.7 hydride alloy electrodes.

Metal hydride beds and hydrogen supply tanks as minitype PEMFC hydrogen sources

Abstract In order to improve the properties of hydrogen tanks for hydrogen fuel cells, we studied the effect of two different matrix configurations, one being pellet pressed by Cu coating hydrogen storage alloy powders and the other foam nickel sheets filled with hydrogen storage alloy powders, on the heat and mass transfer properties of metal hydride beds. AB5-type alloy Ml0.85Ca0.15Ni5 and AB2-type alloy Ti0.9Zr0.15Mn1.6Cr0.2V0.2 were used as hydrogen storage materials, respectively. Comparison with general metal hydride powder beds shows that the heat transfer property of the beds with these two new matrix configurations is well improved. Based on these two new matrix configurations of metal hydride beds, hydrogen tanks with different structures and capacities were designed and prepared. For the prototype tanks of 500 l hydrogen storage capacity, the gravimetric and volumetric density of the tanks with AB5-type and AB2-type materials can attain values of the order of 1.1 wt % , 25 kg H 2 / m 3 and 1.3 wt % , 40 kg H 2 / m 3 , respectively.

Electrochemical properties of the ball-milled La1.8Ca0.2Mg14Ni3+xwt%Ni composites (x=0, 50, 100 and 200)

Abstract The electrochemical characteristics of the as-cast and ball-milled La 2 Mg 17 type alloy La 1.8 Ca 0.2 Mg 14 Ni 3 + x wt%Ni ( x =0, 50, 100 and 200) were investigated. After 50 h ball-milling the amorphous La 1.8 Ca 0.2 Mg 14 Ni 3 +100wt%Ni composite exhibited a large discharge capacity of 1004 mAh g (La 1.8 Ca 0.2 Mg 14 Ni 3 ) −1 at 298 K. Compared with the as-cast La 1.8 Ca 0.2 Mg 14 Ni 3 alloy, the remarkable improvement in electrochemical capacity of the ball-milled composite is due to the formation of an amorphous composite. The addition of Ni is an important factor for the earlier formation of an amorphous alloy. The cycling degradation of the composite is influenced by the degree of amorphorization and the amount of Ni added.

Direct synthesis of nanocrystalline NaAlH4 complex hydride for hydrogen storage

Nanocrystalline NaAlH4 was directly synthesized by ball milling NaH/Al with TiF3 catalyst under hydrogen pressure of 15–25 bar within 50 h. It is found that the synthesized NaAlH4 exhibits a high reversible hydrogen capacity of 4.7 wt % with fast reaction kinetics. It can absorb about 3.5 wt % hydrogen even at ambient temperature. The Ti–Al–H active species formed during reactive ball milling may act as catalyzing agent for hydrogen dissociation/recombination during in situ hydrogenation process and subsequent hydriding/dehydriding cycle.

The hydrogen storage properties of Ti–Mn-based C14 Laves phase intermetallics as hydrogen resource for PEMFC

Abstract In this paper, the hydrogen storage properties of Ti–Mn based Laves phase alloys, including Ti 0.8 Zr 0.2 Mn 2−x Cr x (x=0.2,0.4,0.6,0.8,1.0) , Ti–Zr–Mn–V–M(M=Ni,Cr), Ti–Zr–Mn–(VFe)–M(M=Ni,Cr), were investigated using gas–solid reaction. And its structure was analyzed by X-ray diffraction. The results show that the reversible hydrogen capacity of Ti0.9Zr0.2Mn1.6V0.2Ni0.2 alloy is 212.7 ml / g . VFe replacing V causes a little decrease in the reversible hydrogen capacity. The hydrogen capacity and activation behavior of Ti0.8Zr0.2Mn2−xCrx alloys increase as the content of Cr element increases.

The Thermal Stability of Amorphous Hydride Mg50Ni50H54and Mg30Ni70H45

The thermal stability of amorphous ternary hydrides Mg5oNi5oH54 and Mg3oNi7oH45 and their corresponding amorphous binary alloys Mg5oNi5o and Mg30Ni7o were studied with X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Samples of the amorphous alloys were prepared by mechanical alloying and the amorphous hydrides were obtained by charging the alloys with gaseous hydrogen at 3.0 MPa and 423 K. It was found that the amorphous hydrides released most of their hydrogen before the crystallization of the essentially hydrogen depleted amorphous alloy began. The crystallization temperature of amorphous Mg5oNi5oH54 was elevated and that of amorphous Mg30Ni7oH45 did not change relative to that of the original binary amorphous alloys. This is very exceptional for amorphous hydrides. The reason for the effects of hydrogen absorption/desorption on the crystallization of amorphous alloys was discussed.

Investigation of magnetic properties of NdMn2-xCoxGe2 compounds (x = 0 to 1.0)

The structure and the magnetic properties for the NdMn2-xCoxGe2 compounds (x = 0 to 1.0) have been investigated. All the compounds crystallize in the ThCr2Si2-type structure. Substitution of Co for Mn led to a linear decrease in the lattice constants and the unit cell volume. From the magnetic measurement we have determined two concentration regions of qualitatively different low temperature behavior. Increasing substitution of Co for Mn in NdMn2Ge2 shows a depression of ferromagnetic ordering and a gradual development of antiferromagnetic ordering. For compounds with x < 0.6 ferromagnetic ordering occurs, while for compounds with x greater than or equal to 0.6 antiferromagnetic ordering occurs. The saturation magnetization at 1.5 K for these compounds decreases monotonously with increasing Co content.

The recovery, purification, storage and transport of hydrogen separated from industrial purge gas by means of mobile hydride containers

In this paper the experiment results of the recovery, purification to a high purity and transport of the hydrogen abstracted from the purge gas of a synthetic ammonia plant and the application of the hydrogen to the tin bath in a float glass factory 25 km away from the ammonia plant by means of mobile metal hydride hydrogen container are reported. Four hydride containers loaded on a truck were used to store and transport 200 Nm3 of high-purity hydrogen on each journey. The hydrogen was abstracted from purge gas of 45–50% hydrogen content and purified to a purity of 99.999% hydrogen with a maximum recovery ratio above 70%. The influence of gas pressure and the flow rate scheme of the pretreated purge gas through the container on the hydrogen storage capacity of the container and the ratio of hydrogen recovery was reported. This process is proved to be of merit economically, environmentally and in the safety aspect. It is believed that this technology is also applicable to other industries, where high purity hydrogen in large quantities is used.

INVESTIGATION OF MAGNETIC PROPERTIES OF TB2FE17-XMNX COMPOUNDS

The effect of Mn on structure and magnetic properties of Tb2Fe17−xMnx compounds has been investigated. Substitution of Mn for Fe does not change the structure of Tb2Fe17. All compounds crystallize in the Th2Ni17-type structure. The Curie temperature of Tb2Fe17−xMnx compounds decreases monotonically with increasing Mn content. The saturated magnetic moment and the magnetic moment of the transition metal sublattice of the Tb2Fe17−xMnx compounds decrease with increasing Mn concentration. A point without zero moment similar to the compensation point was observed in the temperature dependence of magnetization for the Tb2Fe17−xMnx compound with x=4.0, which is explained by a three-sublattice model.

Structure and magnetic properties of Y2Fe17−xMnx compounds (x = 0–6)

The effect of Mn on structure and magnetic properties of Y2Fe17−xMnx compounds has been studied. Substitution of Mn for Fe does not change the structure of Y2Fe17, and all the Y2Fe1−xMnx compounds crystallize in Th2Ni17 structure. The lattice constants first increase, then slightly decrease, and finally increase again. The Curie temperature of Y2Fe17−xMnx compounds first increases, shows a maximum atx = 0.3, the decreases again. The saturation magnetization of Y2Fe1−xMnx compounds decreases dramatically with increasing Mn content. The moments of Mn atoms in these compounds are also discussed.