Electrochemical hydrogen storage properties of Mg2−xAlxNi (x = 0, 0.3, 0.5, 0.7) prepared by hydriding combustion synthesis and mechanical milling

Mg_2−xAl_xNi (x = 0, 0.3, 0.5, 0.7) hydrogen storage alloys used as the negative electrode in a nickel–metal hydride (Ni–MH) battery were successfully prepared by means of hydriding combustion synthesis (HCS) and the selected alloy Mg_1.5Al_0.5Ni was further modified by mechanical milling (MM). The structural and electrochemical hydrogen storage properties of Mg_2−xAl_xNi alloys have been investigated in detail. XRD results show that a new phase Mg₃AlNi₂ that possesses an excellent cycling stability is observed with the substitution of Al for Mg. A short-time mechanical milling has a significant effect on improving the discharge capacity of the HCS product of Mg_1.5Al_0.5Ni. The maximum discharge capacity of Mg_1.5Al_0.5Ni ascends with increasing mechanical milling time and reaches the maximum 245.5 mAh/g when milled for 10 h. The alloy milled for 5 h shows the best electrochemical kinetics, which is due to its smaller mean particle size and uniform distribution of the particles. Further increasing in mechanical milling time could not bring about better electrochemical kinetics, which might be attributed to the agglomeration of the alloy particles and thus the charge-transfer reaction and hydrogen diffusion are restrained. It is suggested that the novel method of HCS + MM is promising to prepare ternary Mg-based intermetallic compound for electrochemical hydrogen storage.     

Effects of metal additive on electrochemical performances of Mg-based hydrogen storage materials prepared by hydriding combustion synthesis and subsequent mechanical milling (HCS+MM)

Mg₂Ni-based hydride was prepared by hydriding combustion synthesis (HCS), and subsequently modified with various metal elements (Ti, Co, Cr and Y) by mechanical milling. The effects of the modifications on electrochemical properties of the hydride were investigated. Both of the maximum discharge capacity and the high rate dischargeability (HRD) are increased by the modification of Co, while the cycling stability is improved for the hydride modified with Ti, Cr and Y. The Tafel polarization shows that the addition of the metals has a positive effect on improving the anti-corrosion ability. The electrochemical kinetics was also characterized by linear polarization, electrochemical impedance spectroscopy and potentiostatic discharge. The results show that the hydrogen diffusion coefficient and the electrochemical reaction resistance are increased by the modifications, but the exchange current density decreases.     

Hydrogen storage properties of Mg–30 wt.% LaNi5 composite prepared by hydriding combustion synthesis followed by mechanical milling (HCS + MM)

A Mg–30 wt.% LaNi₅ composite was prepared by hydriding combustion synthesis followed by mechanical milling (HCS + MM), and the hydriding and dehydriding properties of the HCS + MM product were compared with those of the HCS product and the MM product. The dehydriding temperature onsets of the MM and HCS + MM products were both 470 K, which were lower than that of the HCS product by 100 K. Moreover, the HCS + MM product desorbed faster than the MM product, e.g., the former desorbed completely upon heating to 510 K, whereas the latter did not decompose completely until 590 K. Additionally, the HCS + MM product reached a saturated hydrogen absorption capacity of 3.80 wt.% at 373 K in 50 s, but both the HCS product and the MM product absorbed less than 1.50 wt.% of hydrogen at 373 K in 1800 s. These results suggest the potential of the HCS + MM processing in preparing Mg-based hydrogen storage materials.     

Effect of multi-wall carbon nanotubes supported palladium addition on hydrogen storage properties of magnesium hydride

To improve the hydrogen storage performance of magnesium hydride, multi-wall carbon nanotubes supported palladium (Pd/MWCNTs) was introduced to the magnesium-based materials. Pd/MWCNTs catalysts with different amounts of Pd (20 wt.%, 40 wt.%, 60 wt.%, 80 wt.%) were synthesized by a solution chemical reduction method. Afterwards, Mg₉₅–Pd_m/MWCNTs_5−m (m = 0, 1, 2, 3, 4, 5) were prepared for the first time by hydriding combustion synthesis (HCS) and mechanical milling (MM). It is determined by X-ray diffraction (XRD) analysis that Pd/MWCNTs can significantly increase the hydrogenation degree of magnesium during the HCS process. The microstructures of the composites obtained by transmission electron microscope (TEM) and field emission scanning electronic microscopy (FESEM) analyses show that Pd nanoparticles are well supported on the surface of carbon nanotubes and the Pd/MWCNTs are dispersed uniformly on the surface of MgH₂ particles. Moreover, it is revealed that there is a synergistic effect of MWCNTs and Pd on the hydrogen storage properties of the composites. The Mg₉₅–Pd₃/MWCNTs₂ shows the optimal hydriding/dehydriding properties, requiring only 100 s to reach its saturated hydrogen absorption capacity of 6.67 wt.% at 473 K, and desorbing 6.66 wt.% hydrogen within 1200 s at 573 K. Additionally, the dehydrogenation activation energy of MgH₂ in this system is decreased to 78.6 kJ/mol H₂, much lower than that of as-received MgH₂.     

Superior hydrogen storage properties of Mg95Ni5 + 10 wt.% nanosized Zr0.7Ti0.3Mn2 + 3 wt.% MWCNT prepared by hydriding combustion synthesis followed by mechanical milling (HCS + MM)

Significant improvement of the hydrogen storage property of the magnesium-based materials was achieved by the process of hydriding combustion synthesis (HCS) followed by mechanical milling (MM) and the addition of nanosized Zr_0.7Ti_0.3Mn₂ and MWCNT. Mg₉₅Ni₅ doped by 10 wt.% nanosized Zr_0.7Ti_0.3Mn₂ and 3 wt.% MWCNT prepared by the process of HCS + MM absorbed 6.07 wt.% hydrogen within 100 s at 373 K in the first hydriding cycle and desorbed 95.1% hydrogen within 1800 s at 523 K. The high hydriding rate remained well and the hydrogen capacity reached 5.58 wt.% within 100 s at 423 K in the 10th cycle. The dehydrogenation activation energy of this system was 83.7 kJ/mol, which was much lower than that of as-received MgH₂. A possible hydrogenation–dehydrogenation mechanism was proposed in terms of the structural features derived from the HCS + MM process and the synergistic catalytic effects of nanosized Zr_0.7Ti_0.3Mn₂ and MWCNT.     

Electrochemical properties of Mg-based hydrogen storage materials modified with carbonaceous materials prepared by hydriding combustion synthesis and subsequent mechanical milling (HCS + MM)

Mg₂Ni-based hydride was prepared by hydriding combustion synthesis (HCS), and subsequently modified with various carbonaceous materials including graphite, multi-walled carbon nanotubes (MWCNTs), carbon aerogels (CAs) and carbon nanofibers (CNFs) by mechanical milling (MM) for 5 h. The structural properties of the modified hydrides were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). All of the modified hydrides show amorphous or nanocrystalline-like phases. The hydride modified with graphite exhibits the most homogenous distribution of particles and the smallest particle size. The effects of the modifications on electrochemical properties of the hydride were investigated by galvanostatic charge/discharge, linear polarization, Tafel polarization, electrochemical impedance spectroscopy and potentiostatic discharge measurements. The results show that the maximum discharge capacity, the high rate dischargeability (HRD), the exchange current density and the hydrogen diffusion ability of the hydride modified with the carbonaceous materials are all increased. Especially, the hydride modified with graphite possesses the highest discharge capacity of 531 mAh/g and the best electrochemical kinetics property.     

Catalytic mechanism of Nb2O5 and NbF5 on the dehydriding property of Mg95Ni5 prepared by hydriding combustion synthesis and mechanical milling

The catalytic mechanism of Nb₂O₅ and NbF₅ on the dehydriding property of Mg₉₅Ni₅ prepared by hydriding combustion synthesis and mechanical milling (HCS + MM) was studied. It was shown that NbF₅ was more efficient than Nb₂O₅ in improving the dehydriding property. In particular, the dehydriding temperature onset decreases from 460 K for Mg₉₅Ni₅ to 450 K for Mg₉₅Ni₅with 2.0 at.% Nb₂O₅, whereas it decreases to 410 K for that with 2.0 at.% NbF₅. By means of X-ray diffraction and X-ray photoelectron spectroscopy, it was confirmed that the interaction between the Nb ions and the H atoms and that between the anions (O²⁻ or F⁻) and Mg²⁺ existed in Mg₉₅Ni₅ doped with Nb₂O₅ or NbF_5. Further, the pressure–concentration-isotherms analysis clarified that these interactions destabilized the Mg–H bonding, and that NbF₅ had a better effect on the destabilization of the Mg–H bonding than Nb₂O₅ contributing to the better dehydriding property of (Mg₉₅Ni₅)2.0−NbF₅.     

Improvement on hydrogen storage thermodynamics and kinetics of the as-milled SmMg11Ni alloy by adding MoS2

In this experiment, the Mg-based hydrogen storage alloys SmMg₁₁Ni and SmMg₁₁Ni + 5 wt.% MoS₂ (named SmMg₁₁Ni-5MoS₂) were prepared by mechanical milling. By comparing the structures and hydrogen storage properties of the two alloys, it could be found that the addition of MoS₂ has brought on a slight change in hydrogen storage thermodynamics, an obvious decrease in hydrogen absorption capacity, an obvious catalytic action on hydrogen desorption reaction, and a lowered onset desorption temperature from 557 to 545 K. Additionally, the addition of MoS₂ could dramatically improve the alloy in its hydrogen absorption and desorption kinetics. To be specific, the hydrogen desorption times of 3 wt.% H₂ at 593, 613, 633 and 653 K were measured to be 1488, 683, 390 and 192 s respectively for the SmMg₁₁Ni alloy, which were reduced to 938, 586, 296 and 140 s for the MoS₂ catalyzed SmMg₁₁Ni alloy at identical conditions. The activation energies of the alloys with and without MoS₂ for hydrogen desorption are 87.89 and 100.31 kJ/mol, respectively. The 12.42 kJ/mol decrease is responsible for the ameliorated hydrogen desorption kinetics by adding catalyst MoS₂.     

Stability of transition metals on Mg(0001) surfaces and their effects on hydrogen adsorption

The interactions of a hydrogen atom with clean, vacancied, and transition metal-doped (TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Au, Pt) Mg(0001) surfaces are investigated using first-principles calculations. The H adsorption on Mg(0001) with TMs doped within the second layer is generally more stable than that on clean Mg but clearly weaker than that on Mg surfaces with TM in the first layer. We find, however, that all these TM atoms prefer to substitute for the Mg atoms in the second layer rather than for those in the outermost layer of the Mg surface. To enhance the catalytic effect of the TM dopants, we investigated various co-doping conditions of TMs, and we found that i) Ti is a good “assistant” that stabilizes co-doped Co, Ni, Pd, Ag, Pt, and Au within the first layers and that ii) Ni and Co are more easily incorporated into the first layer of a Mg surface when co-doped with Ti, V, and Nb. These observations may lead to a possible approach to stabilize the TM dopants within the first layer and thus promote the hydrogenation of Mg accordingly.     

First principles study towards the influence of interstitial nitrogen on the hydrogen storage properties of the Mg2Ni (0 1 0) surface

Doping light elements into Mg-based alloy has been viewed as an effective method for improving the hydrogen storage properties without remarkably reducing hydrogen capacity. The influences of interstitial nitrogen doping on the crystal structure, thermal stability, hydrogen adsorption energy and electronic properties of Mg₂Ni (0 1 0) surface were investigated by first principles calculations. The calculation results showed that the addition of interstitial N results in an anisotropic expansion in the crystal structure and a better improvement effect on lowering thermal stability of the Mg₂Ni surface than the commonly used transition metal. Three stable sites including the NiNi bridge site, the top sites of Mg and Ni atoms, were determined to take in hydrogen in the pure surface. When the nonmetal N is doped into the pure surface, the number of the stable adsorption sites is increased and the adsorption energy of H in the NiNi bridge site is also increased from ?0.9614 eV for the pure to ?0.5441 eV for the N-doped counterpart. The increases in both the stable adsorption sites and the energy caused by the addition of N indicate that more hydrogen could be adsorbed in the weaker NiH bonds of the N-doped Mg₂Ni alloy, thereby improving the hydrogen storage behaviors of Mg-based alloy.     

Study on the eutectic formation and its correlation with the hydrogen storage properties of Mg98Ni2-xLax alloys

Transition metals and rare-earth elements have excellent catalytic effects on improving the de-/hydrogenation properties of Mg-based alloys. In this study, a small amount of La is used to substitute the Ni in Mg₉₈Ni₂ alloy, and some Mg₉₈Ni_2-xLa_x (x = 0, 0.33, 0.67, and 1) alloys show the better overall hydrogen storage properties. The effects of La on the solidification and de-/hydrogenation behaviors of the alloys are revealed. The results indicate that different factors dominate the processes of hydrogen absorption and desorption. The Mg₉₈Ni_1·67La_0.33 alloy absorb 7.04 wt % hydrogen at 300 °C, with the highest isothermal absorption rate, the Mg₉₈Ni_1·33La_0.67 hydride show the highest isothermal desorption rates and the lowest peak desorption temperature of 327 °C. The La addition can increase the driving force of hydrogenation, thus the hydrogenation rates and capacities of the Mg₉₈Ni_1·67La_0.33 and Mg₉₈Ni_1·33La_0.67 alloys are improved. The formation of refined eutectic structures is a key factor that facilitates the desorption processes of the Mg₉₈Ni_2-xLa_x hydrides with x = 0.67 and 1. High-density LaH₃ nanophses are in-situ formed from the LaMg_x (8.5 < x < 12) phase, which results in the improved de-/hydrogenation properties. The further La addition deteriorates the hydrogen storage properties of Mg₉₈Ni_2-xLa_x alloy.     

Kinetics and electrochemical characteristics of Mg2NiH4-x wt.% MmNi3.8Co0.75Mn0.4Al0.2 (x = 5, 10, 20, 40) composites for Ni-MH battery

The structure, kinetics and electrochemical characteristics of Mg₂NiH₄-x wt.% MmNi_3.8Co_0.75Mn_0.4Al_0.2 (x = 5, 10, 20, 40) composites prepared by mechanical milling have been investigated in this paper. XRD results indicate that the as-milled Mg₂NiH₄ shows nanocrystalline or amorphous-like structure, and it does not react with MmNi_3.8Co_0.75Mn_0.4Al_0.2 during mechanical milling. As the amount of MmNi_3.8Co_0.75Mn_0.4Al_0.2 increases, the maximum discharge capacity decreases initially from 508 mAh/g (x = 5) to 440 mAh/g (x = 10) and then increases to 509 mAh/g (x = 40). Meanwhile, the capacity retention (R₁₀) increases from 12.8% (x = 5) to 23.4% (x = 40), and the corrosion potential of electrode (E_corr) increases from −0.930 V to −0.884 V (vs. Hg/HgO). Especially, the more MmNi_3.8Co_0.75Mn_0.4Al_0.2 content the composite contains, the higher high rate dischargeability (HRD) the electrode exhibits, which could be attributed to the catalytic reaction and reduction of the Mg₂NiH₄ grain size brought by MmNi_3.8Co_0.75Mn_0.4Al_0.2. The improvement in electrode kinetics has been depicted from the bulk hydrogen diffusion coefficient (D), the exchange current density (I₀) and the charge transfer resistance (R_ct) on the alloy surface.     

Lithium metal hydrides (Li2CaH4 and Li2SrH4) for hydrogen storage; mechanical,electronic and optical properties

Hydrogen storage is a critical step for commercialisation of hydrogen consumed energy production. Among other storage methods, solid state storage of hydrogen attracts much attention and requires extensive research. This study rationally and systematically designs novel solid state hydrides; Li₂CaH₄ (GHD is obtained as −6.95 wt %) and Li₂SrH₄ (GHD is obtained as −3.83 wt %) using computational method. As a first step, we suggest and predict crystal structures of solid state Li₂CaH₄ and Li₂SrH₄ hydrides and look for synthesizability. Then, the mechanical stabilities of hydrides are identified using elastic constants. Both hydrides fulfil the well-known Born stability criteria, indicating that both Li₂CaH₄ and Li₂SrH₄ are mechanically stable materials. Several critical parameters, bulk modulus, shear modulus, Cauchy pressures, anisotropy factors of hydrides and bonding characteristics are obtained and evaluated. Furthermore, electronic and optical band structures of hydrides are computed. Both Li₂CaH₄ and Li₂SrH₄ have indirect bands gaps as 0.96 eV (Г-U) and 1.10 eV (Г-R). Thus, both materials are electronically semiconducting. Also, Bader charge analysis of hydrides have been carried out. Charge density distribution suggests an ionic-like (or polarized covalent) bonding interaction between the atoms.     

Destabilization of LiBH4 by MH2 (M = Ce, La) for hydrogen storage: Nanostructural effects on the hydrogen sorption kinetics

Destabilization of LiBH₄ by addition of metal hydrides or borohydrides is a powerful strategy to develop new promising hydrogen storage systems. In this study, we compare the destabilization behavior of the LiBH₄ by addition of MH₂ (M = La, Ce). A notable improvement in the hydrogen desorption temperature, the rate and the weight percentage of hydrogen released is observed for LiBH₄-MH₂ with respect to LiBH₄. Formation of LaB₆ and CeB₆ after dehydriding of the composites is proved by PXRD. Remarkable hydrogen storage reversibility of LiBH₄-MH₂ composites is confirmed under moderate conditions: 400 °C and 6.0 MPa of hydrogen pressure for 4 h without catalyst. The LiBH₄-LaH₂ composite exhibits improved hydrogen desorption performance compared with LiBH₄-CeH₂ composite, but the hydrogen storage reversibility is inferior. Notably, the LiBH₄-CeH₂ nanocomposite produced by in situ formation of CeH₂ from Ce(BH₄)₃-LiH displays excellent hydrogen storage properties. The addition of ZrCl₄ as a catalyst improves dehydriding kinetics. The mechanism underlying the enhancement in the LiBH₄-MH₂ composites is also discussed. Our study is the first work about reversible hydrogen storage in LiBH₄-LaH₂.     

Synergistic catalytic effects of ZIF-67 and transition metals (Ni,Cu, Pd,and Nb) on hydrogen storage properties of magnesium

MgTM/ZIF-67 nanocomposites were prepared by the deposition-reduction method using ZIF-67, MgCl₂, and TMCl_x (TM = Ni, Cu, Pd, Nb) as raw materials. The dehydrogenation activation energies of MgTM/ZIF-67 (TM = Ni, Cu, Pd, Nb) nanocomposites were calculated to be 115.4 kJ mol⁻¹ H₂, 115.7 kJ mol⁻¹ H₂, 113.6 kJ mol⁻¹ H₂, and 75.8 kJ mol⁻¹ H₂, respectively; hence, the MgNb/ZIF-67 nanocomposite manifested the best comprehensive hydrogen storage performance. The hydrogen storage capacity of the MgNb/ZIF-67 nanocomposite was hardly attenuated after the 100th hydrogen absorption-desorption cycle. The dehydrogenated enthalpies of MgH₂ and CoMg₂H₅ in MgNb/ZIF-67 hydride were calculated to be 72.4 kJ mol⁻¹ H₂ and 81.0 kJ mol⁻¹ H₂, respectively, which were lower than those of additive-free MgH₂ and Mg/ZIF-67. The improved hydrogen storage properties of MgNb/ZIF-67 can be ascribed to the CoMg₂–Mg(Nb) core-shell structure and the catalytic effects of NbH and niobium oxide nanocrystals.     

The effects of the nanometric interstitial compounds TiC,ZrC and TiN on the mechanical and thermal dehydrogenation and rehydrogenation of the nanocomposite lithium alanate (LiAlH4) hydride

Profuse mechanical dehydrogenation occurs during controlled high energy ball milling of LiAlH₄ containing 5 wt.% of the nanometric interstitial compounds such as n-TiC, n-TiN and n-ZrC which involves a gradual decomposition of LiAlH₄ to the mixture of Li₃AlH₆ and Al (Stage I) followed by a further decomposition of Li₃AlH₆ to the mixture of Al and LiH (Stage II). XRD reveals that the interstitial compounds remain stable in the hydride matrix during entire ball milling duration. The effectiveness of the nanometric interstitial compound additives for mechanical dehydrogenation increases on the order of n-TiN > n-TiC > n-ZrC. X-ray diffraction (XRD) reveals that there is no measurable change in a unit cell volume of LiAlH₄ after ball milling which indicates that an accelerated mechanical dehydrogenation of LiAlH₄ containing the nanometric interstitial compounds is unrelated to the lattice expansion as we have already reported for the nanometric metal Fe (n-Fe). In addition, the observed strong catalytic activity of the nanometric interstitial compounds for mechanical dehydrogenation is not related to their valence electron concentration (VEC) number. However, the n-TiN additive, which is the most effective one for mechanical dehydrogenation, has the smallest average particle size of 20 nm and the largest Specific Surface Area (SSA > 80 m²/g). For thermal dehydrogenation in Stage I the average apparent activation energy, E_A, for the interstitial compound additives is within the range of 87–96 kJ/mol whereas, for comparison, the nanometric metallic additives, n-Fe and n-Ni, exhibit drastically smaller apparent activation energy on the order of 55–70 kJ/mol. The average apparent activation energy for thermal dehydrogenation in Stage II is in the range of 63–80 kJ/mol in the order of E_A(n-ZrC) < E_A(n-Ti = n-TiC) and is lower than that for the nanometric metal additives n-Ni and n-Fe. In summary, the nanometric interstitial compounds do not substantially affect the apparent activation energy of Stage I but are able to reduce the apparent activation energy of thermal dehydrogenation in Stage II. XRD reveals that the interstitial compounds remain stable in the hydride matrix up to the dehydrogenation temperature of at least 165 °C. Ball milled LiAlH₄ containing 5 wt.% n-TiC, n-TiN and n-ZrC is able to slowly discharge large quantities of H₂ up to 5–6 wt.% during storage at 40 °C. Unfortunately, the results of rehydrogenation at 165 °C under 95 bar for 5 h indicate that LiAlH₄ containing the nanometric interstitial compounds exhibits no rehydrogenation.     

Effect of Al on the hydrogen storage properties of Mg(BH4)2

The various Mg–B–Al–H systems composed of Mg(BH₄)₂ and different Al-sources (metallic Al, LiAlH₄ and its decomposition products) have been investigated as potential hydrogen storage materials. The role of Al was studied on the dehydrogenation and the rehydrogenation of the systems. The results indicate that the different Al-sources exhibit a similar improving effect on the dehydrogenation properties of Mg(BH₄)₂. Taking the Mg(BH₄)₂ + LiAlH₄ system as an example, at first LiAlH₄ rapidly decomposes into LiH and Al, then Mg(BH₄)₂ decomposes into MgH₂ and B, finally the MgH₂ reacts with Al, LiH and B, which forms Mg₃Al₂ and MgAlB₄. The system starts to desorb H₂ at 140 °C and desorbs 3.6 wt.% H₂ below 300 °C, while individual Mg(BH₄)₂ starts to desorb H₂ at 250 °C and desorbs only 1.3 wt.% H₂ below 300 °C. The isothermal desorption kinetics of the Mg–B–Al–H systems is about 40% faster than that of Mg(BH₄)₂ at the hydrogen desorption ratio of 90%. In addition, the Mg–B–Al–H systems show partial reversibility at moderate temperature and pressure. For Al-added system, the product of rehydrogenation is MgH₂, while for LiAlH₄-added system the product is composed of LiBH₄ and MgH₂.     

Density functional and microkinetic study of CO2 hydrogenation to methanol on subnanometer Pd cluster doped by transition metal (M= Cu,Ni, Pt,Rh)

We study the CO₂ hydrogenation to methanol on subnanometer Pd₇ and transition metal doped Pd₆M (M = Cu, Ni, Pt, and Rh) clusters using a combination of density functional theory and microkinetic calculations. We find that, in general, the inclusion of transition metal dopants could decrease the activation energy of several important elementary reactions. This condition results in a significant improvement in the activity of the catalyst, especially for the Pd₆Ni cluster. We find that the Pd₆M clusters are more selective toward the formate pathway than the RWGS + CO hydrogenation pathway. We also compare the turnover frequency profiles of the clusters with that of the Cu(111) surface, representing the standard industrial catalyst. We find that the Pd₆Ni cluster can successfully overcome the TOF of Cu(111) surface, even at the low-pressure condition.     

Effects of annealing on Zr8Ni19X2 (X = Ni,Mg, Al,Sc, V,Mn, Co,Sn, La,and Hf): Hydrogen storage and electrochemical properties

The effects of 8-h annealing at 960 °C on the gaseous phase hydrogen storage and electrochemical properties of partial-Ni substituted Zr₈Ni₂₁ alloys were studied. The substituting elements included Mg, Al, Sc, V, Mn, Co, Sn, La, and Hf. Only the main phase of the annealed Sn-substitution remained Zr₈Ni₂₁-structured while those of other substitutions turned into Zr₇Ni₁₀ or Zr₂Ni₇. The observed trend in maximum gaseous phase hydrogen storage capacity followed the increasing order of B/A ratio of the main phase as orthogonal Zr₇Ni₁₀ > tetragonal Zr₇Ni₁₀ > Zr₈Ni₂₁ > Zr₂Ni₇. After annealing, due to the increase in abundance of the main phase, the maximum gaseous phase hydrogen storage capacities of alloys with higher capacities before annealing increased while others decreased. The full discharge capacity also improved in the same increasing order of B/A ratio in the main phase. Hf-substitution showed the highest electrochemical discharge capacity at 200 mAh g⁻¹. After annealing, all alloys with the same main phase as the as-cast alloys showed degradation in full electrochemical capacity due to the reduction in both number and abundance of the catalytic secondary phases. All supplements assisted in improving surface exchange current from the base binary Zr₈Ni₂₁ alloy. Except for La- and Hf-substitutions, annealing reduced the surface exchange current density. The bulk hydrogen diffusion coefficient decreased with most of the supplements except for V- and Sn-substitutions. All supplements, except for Sc, showed improvement in the bulk diffusion after annealing. Furthermore, the maximum gaseous phase hydrogen storage capacity showed a strong correlation to the full electrochemical discharge capacity. Among all alloys in this study, the as-cast Hf-substituted Zr₈Ni₂₁ alloy demonstrated the best overall gaseous hydrogen storage and electrochemical properties.