Kinetic Enhancement in the Sorption Properties by Forming Mg–x wt % ZrCrCu Composites

Abstract

Composite formation with Zr-based Laves phase alloys, especially the ZrCr 2 family, is an effective method to improve the hydriding properties of MgH 2 . The present paper describes a systematic study of the reaction pathway of Mg−x wt % ZrCrCu composites (x = 25, 50) in terms of their structural, morphological, and hydrogenation properties. XRD and SEM results show no interaction between Mg and the ZrCrCu alloy phase during composite preparation by high-energy ball-milling. However, hydriding/annealing cycles lead to the formation of the Mg 2 Cu phase at grain boundaries of the Mg−ZrCrCu matrix. This Mg 2 Cu phase does not interact with the hydrogen at the studied condition, but provides several diffusion paths and stable nucleation sites for the formation of MgH 2 , and thus enhances the sorption kinetics. Pressure composition temperature (PCT) analysis shows a reduction in desorption temperature down to 250 °C for these composites.

Effect of ZrCrCo alloy on hydrogen storage properties of Mg

“…As mentioned above, at higher temperatures only Mg counterpart plays active role towards hydrogen sorption, the enthalpy values of the hydrogenation process for Mg counterpart of Mg-x wt% ZrCrCo composites are found to be À64.54 ± 2.0 and À62.59 ± 4.5 kJ mol À1 for x = 25 and 50 respectively. These values are close to that of pure Mg [27], which is actually in line with the XRD findings according to which there is no additional phase formation which could affect the thermodynamics. However a small variation in the enthalpy values may be related to the defects created into the material during the ball milling.…”

“…4. Similar to the earlier works [26][27][28][29] on the other composites with ZrCrM (M = Ni, Cu, Fe) alloys, activation cycles are required for the present composite, but less number of cycles (in comparison to 20 cycles for ZrCrNi composite) i.e. 5 absorption/desorption activation cycles are found necessary to get the stabilized results.…”

“…These values are in agreement with the theoretical value of MgH 2 counterpart [2]; which suggest a silent behavior of ZrCrCo alloy towards hydrogenation reaction. This must be due to separate PCT windows of Mg and ZrCrCo alloy as reported in our recent work [27,28]. The absorption curve for Mg-25% ZrCrCo composite shows several steps at the end of pressure plateau, which must be correlated to the irregular particle size as can be seen in the micrographs of Fig.…”

“…4 and ZrNiCr systems over their crystalline states respectively. [25][26][27][28]. For Mg-ZrCrNi system [26], we concluded that 10 wt% ZrCrNi alloy content is sufficient to attain improved characteristics.…”

“…The dual property of ZrCrFe alloy, catalytic at high temperature and hydriding at low temperature is found to be responsible for higher content of 4.5 wt% hydrogen in MgZrCrFe composite [28]. In case of Mg-ZrCrCu composite, the formation of Mg 2 Cu alloy due to diffusion of Mg in ZrCrCu phase during sorption cycles helps in improved kinetics by providing diffusion paths and nucleation sites for hydrogen [27]. These results suggest that changing M in ZrCrM systems has varying effects on hydrogenation properties of Mg.…”