Advancement in the Hydrogen Absorbing and Releasing Kinetics of MgH2 by Mixing with Small Percentages of Zn(BH4)2 and Ni

Young Jun Kwak,Hye Ryoung Park,Myoung Youp Song 대한금속·재료학회 2018 METALS AND MATERIALS International Vol.24 No.2

Zn(BH4)2 made in our former investigation and Ni were mixed with MgH2to promote the hydrogen absorption and releasefeatures of Mg. A 96 w/o MgH2+ 2 w/o Ni + 2 w/o Zn(BH4)2 sample [named MgH2–4NZ] was prepared by milling in aplanetary ball mill in a hydrogen atmosphere. The proportion of the additive was small (4 w/o) in order to increase hydrogenabsorbing and releasing rates without majorly sacrificing the hydrogen-storage capacity. The hydrogen absorption andrelease features of the MgH2–4NZ were inspected in detail and compared with those of 99 w/o MgH2+ 1 w/o Zn(BH4)2[named MgH2–1Z] and 95 w/o MgH2+ 2.5 w/o Ni + 2.5 w/o Zn(BH4)2 [named MgH2–5NZ] samples. The activation of theMgH2–4NZ was not required. The MgH2–4NZ had a useful hydrogen-storage capacity (the quantity of hydrogen absorbedafter 60 min) of about 5.5 w/o at the first cycle. At the first cycle, the MgH2–4NZ absorbed 3.84 w/o hydrogen after 5 minand 5.47 w/o hydrogen after 60 min at 593 K in 12 bar hydrogen. The MgH2–4NZ had a higher releasing rate, larger amountsof hydrogen absorbed and released after 60 min, and a better cycling capability than the MgH2–1Z. Staying of Ni (as Mg2Ni)and a larger amount of Zn among particles is believed to have led to the better cycling capability of the MgH2–4NZ.

Effects of Zn(BH4)2, Ni, and/or Ti Doping on the Hydrogen-Storage Features of MgH2

송명엽,곽영준 대한금속·재료학회 2019 대한금속·재료학회지 Vol.57 No.3

In the present work, MgH2 was doped with Zn(BH4)2, Ni, and/or Ti to improve its hydrogen absorption and release features. Samples were prepared by grinding in a planetary ball mill in a hydrogen atmosphere. To increase the hydrogen absorption and release rates without significantly sacrificing hydrogenstorage capacity the additive percentages were less than 10 wt%. The activation of these samples was not necessary. M2.5Z2.5N had the largest quantity of hydrogen absorbed in 60 min, Qa (60 min), at the number of cycles, NC, of one (NC=1), followed in descending order by M5Z2.5N2.5T and M1Z. M5Z2.5N2.5T had the highest initial release rate, followed in descending order by M2.5Z2.5N and M1Z. M5Z2.5N2.5T had the highest initial release rate and M1Z had the largest quantity of hydrogen released in 60 min, Qd (60 min) at NC=2. The sample without Ni (M1Z) had the lowest initial release rate at NC=2. Among these samples, M2.5Z2.5N had the best hydrogen absorption and release properties. Grinding MgH2 with Zn(BH4)2, Ni, and/ or Ti in hydrogen is believed to create defects, induce lattice strain, generate cracks, and reduce the particle sizes. The formed hydrides β-MgH2, γ-MgH2, and TiH1.924 are believed to help produce finer particles in the sample by being pulverized during grinding in hydrogen. The formed Zn and TiH1.924 and the NaCl remained unreacted during cycling. It was deemed that the formed Mg2Ni phase contributed to the increases in the initial hydrogen absorption and release rates and the improvement in cycling performance by absorbing and releasing hydrogen itself.

Raising the Dehydrogenation Rate of a Mg-CMC (Carboxymethylcellulose, Sodium Salt) Composite by Alloying Ni via Hydride-Forming Milling

송명엽,최은호,곽영준 대한금속·재료학회 2018 대한금속·재료학회지 Vol.56 No.8

In our previous work, samples with a composition of 95 wt% Mg + 5 wt% CMC (Carboxymethylcellulose, Sodium Salt, [C6H7O2(OH)x(C2H2O3Na)y]n) (named Mg-5 wt%CMC) were prepared through hydride-forming milling. Mg-5 wt%CMC had a very high hydrogenation rate but a low dehydrogenation rate. Addition of Ni to Mg is known to increase the hydrogenation and dehydrogenation rates of Mg. We chose Ni as an additive to increase the dehydrogenation rate of Mg-5 wt%CMC. In this study, samples with a composition of 90 wt% Mg + 5 wt% CMC + 5 wt% Ni (named Mg-5 wt%CMC-5 wt%Ni) were made through hydride-forming milling, and the hydrogenation and dehydrogenation properties of the prepared samples were investigated. The activation of Mg-5 wt%CMC-5 wt%Ni was completed at the 3rd hydrogenation-dehydrogenation cycle (N=3). Mg-5 wt%CMC-5 wt%Ni had an effective hydrogen-storage capacity (the quantity of hydrogen stored for 60 min) of 5.83 wt% at 593 K in 12 bar hydrogen at N=3. Mg-5 wt%CMC-5 wt%Ni released hydrogen of 2.73 wt% for 10 min and 4.61 wt% for 60 min at 593 K in 1.0 bar hydrogen at N=3. Mg-5 wt%CMC-5 wt%Ni dehydrogenated at N=4 contained Mg and small amounts of MgO, β-MgH2, Mg2Ni, and Ni. Hydride-forming milling of Mg with CMC and Ni and Mg2Ni formed during hydrogenation-dehydrogenation cycling are believed to have increased the dehydrogenation rate of Mg-5 wt%CMC. As far as we know, this study is the first in which a polymer CMC and Ni were added to Mg by hydride-forming milling to improve the hydrogenation and dehydrogenation properties of Mg.

Hydrogen storage properties of pure Mg

( Myoung Youp Song ),( Young Jun Kwak ),( Seong Ho Lee ),( Hye Ryoung Park ) 대한금속재료학회(구 대한금속학회) 2014 대한금속·재료학회지 Vol.52 No.4

The hydrogen storage properties of pure Mg are investigated at 573 K under 12 bar H2. In addition, in order to increase the hydriding and dehydriding rates of pure Mg, it is ground under hydrogen (reactive mechanical grinding, RMG), and its hydrogen storage properties are investigated. The pure Mg absorbs hydrogen very slowly. At n = 1, the pure Mg absorbs 0.05 wt.% H for 5 min, 0.08 wt.% H for 10 min, and 0.29 wt.% H for 60 min at 573 K under 12 bar H2. The hydriding rate decreases as the number of cycles increases from n = 7. At n = 7, the pure Mg absorbs 0.96 wt.% H for 5 min, 1.29 wt.% H for 10 min, and 2.20 wt.% H for 60 min. At n = 1, the pure Mg after RMG does not absorb hydrogen. The hydriding rate of pure Mg after RMG increases as the number of cycles increases from n = 1 to n = 11. The pure Mg after RMG absorbs 1.91 wt.% H for 5 min, 2.61 wt.% H for 10 min, and 3.65 wt.% H for 60 min at n = 11. The reactive mechanical grinding of the pure Mg and the hydriding-dehydriding cycling of the pure Mg after RMG are believed to create defects on the surface and in the interior of Mg particles and to form cracks in Mg particles.

Hydriding/Dehydriding Behavior of MgH_x-Iron Oxides Composites

Kyeong-Il Kim,Tae-Whan Hong 대한금속·재료학회 2011 METALS AND MATERIALS International Vol.17 No.6

Hydrogen has considerable potential as a renewable substitute for fossil fuels due to its high gravimetric energy density and environment friendliness. In particular, metal hydrides were attracted much interest given that its hydrogen capacity exceeds. One approach that can improve the kinetics is the addition of iron oxide. In this study, the hydrogen absorption/desorption properties of Mg were improved. The effect of the iron oxide concentration on the kinetics of the Mg hydrogen absorption reaction was investigated. MgHx-iron oxide composites were synthesized by hydrogen-induced mechanical alloying. The synthesized powder was characterized by XRD, SEM, and simultaneous TG/DSC analysis. The hydriding behaviors were evaluated,using an automatic Sievert’s-type PCT apparatus. The absorption and desorption kinetics of Mg catalyzed with 5 and 10 wt.% Fe2O3/Fe3O4 were determined at 423, 473, 523, 573, and 623K, respectively. The results of hydrogenation properties on MgHx-Iron oxide composites were measured to be about 1.0~4.7 wt.% under 1 MPa H2 atmosphere.

MgH2 and Ni-Coated Carbon-Added Mg Hydrogen-Storage Alloy Prepared by Mechanical Alloying

( Seong Hyeon Hong ),( Myoung Youp Song ) 대한금속재료학회(구 대한금속학회) 2016 대한금속·재료학회지 Vol.54 No.2

In this work, MgH2, which is brittle, and Ni-coated carbon were added to Mg in order to improve the hydrogen absorption and release properties of magnesium. Carbon has a relatively low density, and it is thus considered that the interfacial area between Mg and an added catalyst will increase when Ni-coated carbon is added to Mg. In this research, the quantity of added Ni-coated carbon was smaller than that in the previously reported studies. A mixture with a composition of 85 wt% Mg+10 wt% MgH2+5 wt% (Ni-coated carbon) was milled in a hydrogen atmosphere in a planetary ball mill (alloyed mechanically in a hydrogen atmosphere). The hydrogen absorption and release properties of the prepared sample were investigated. Mechanical alloying in a hydrogen atmosphere of Mg with MgH2 and Ni-coated carbon and hydrogen absorption-release cycling are believed to create defects on the surface and in the inside of the Mg particle, to make clean surfaces, to increase the interfacial area between Mg and additives, and to diminish the particle size of Mg. The sample released 0.03 wt% H for 2 min, 1.50 wt% H for 9 min, 2.69 wt% H for 16 min, and 2.86 wt% H for 60 min at 648 K under an initial hydrogen pressure of 0 bar.(Received May 8, 2015)

Enhancement of the Hydrogen-Storage Characteristics of Mg by Adding Mg2Ni and Ni to MgH2 via High Energy Ball Milling in Hydrogen Atmosphere

홍성현,곽영준,송명엽 대한금속·재료학회 2018 대한금속·재료학회지 Vol.56 No.1

In this work, Mg2Ni and Ni were added to MgH2 in order to improve the hydrogen-storage properties of Mg. A 94 wt% MgH2+5 wt% Mg2Ni+1wt% Ni (named 94MgH2+5Mg2Ni+1Ni) sample was prepared by milling in a hydrogen atmosphere in a planetary ball mill for 5 h. The Mg2Ni was hydrided during milling in a hydrogen atmosphere. The 94MgH2+5Mg2Ni+1Ni had an effective hydrogen-storage capacity (the quantity of hydrogen absorbed for 60 min) of near 5 wt%. At n=1, the sample released 0.18 wt% for 2 min, 2.14 wt% for 5 min, 4.65 wt% for 10 min, and 5.46 wt% for 60 min at 648 K. The reactive mechanical grinding of MgH2 with Mg2Ni and Ni is believed to facilitate nucleation (by creating defects, which serve as active sites for nucleation, on the surfaces and inside the Mg particles), increase reactivity with hydrogen (by making clean surfaces), and decrease the diffusion distances of hydrogen atoms (by reducing the particle size of Mg).

Hydrogen Sorption of Pure Mg and Niobium (V) Fluoride-Added Mg Alloys Prepared by Planetary Ball Milling in Hydrogen

( Hye Ryoung Park ),( Young Jun Kwak ),( Seong Ho Lee ),( Myoung Youp Song ) 대한금속재료학회(구 대한금속학회) 2016 대한금속·재료학회지 Vol.54 No.12

In this work, niobium (V) fluoride was selected as an additive to heighten the hydrogen sorption rates of Mg. Specimens of pure Mg, 5 wt% niobium fluoride-added Mg, and 10 wt% niobium fluorideadded Mg were prepared by planetary ball milling in hydrogen. The hydrogen sorption properties of the specimens were then examined. An Mg-based hydrogen-storage alloy with an effective hydrogenstorage capacity of about 5.5 wt% was developed. At 593 K in 12 bar hydrogen at the first cycle (Cn = 1), the 5 wt% niobium fluoride-added Mg stored 4.37 wt% hydrogen in 5 min and 5.50 wt% hydrogen in 30 min. At 593 K in 1.0 bar hydrogen at Cn = 1, the 5 wt% niobium fluoride-added Mg released 2.11 wt% hydrogen in 10 min, 4.66 wt% hydrogen in 30 min, and 5.43 wt% hydrogen in 60 min. The planetary ball milling of Mg with NbF5 in hydrogen, which generated MgF2, NbH2, and NbF3, is believed to have produced imperfections both on the surface and in the interior of the Mg particles, created clean surfaces, and diminished the particle size of the Mg. The 5 wt% niobium fluoride-added Mg specimen stored a larger quantity of hydrogen in 30 min and a larger quantity of hydrogen was released in 60 min compared with the 10 wt% niobium fluoride-added Mg, or the pure Mg. †(Received April 5, 2016; Accepted June 27, 2016)

Hydrogen Storage and Release Properties of Transition Metal-Added Magnesium Hydride Alloy Fabricated by Grinding in a Hydrogen Atmosphere

( Sung Nam Kwon ),( Hye Ryoung Park ),( Myoung Youp Song ) 대한금속재료학회(구 대한금속학회) 2016 대한금속·재료학회지 Vol.54 No.7

90 wt% MgH2+5 wt% Ni+2.5 wt% Fe+2.5 wt% Ti (called MgH2+Ni+Fe+Ti), a hydrogen storage and release material, was fabricated by grinding in a hydrogen atmosphere, and then its quantities of stored and released hydrogen as a function of time were examined. A nanocrystalline MgH2+Ni+Fe+Ti specimen was made by grinding in a hydrogen atmosphere and subsequent hydrogen storage-release cycling. The crystallite size of Mg and the strain of the Mg crystallite after ten hydrogen storage-release cycles, which were obtained using the Williamson-Hall method, were 38.6 (±1.4) nm and 0.025 (±0.0081) %, respectively. The MgH2+Ni+Fe+Ti sample after the process of grinding in a hydrogen atmosphere was highly reactive with hydrogen. The sample exhibited an available storage capacity of hydrogen (the amount of hydrogen stored during 60 minutes) of about 5.7 wt%. At the first cycle, the MgH2+Ni+Fe+Ti sample stored hydrogen of 5.53 wt% in 5 minutes, 5.66 wt% in 10 minutes and 5.73 wt% in 60 minutes at 573 K and 12 bar of hydrogen. The MgH2+Ni+Fe+Ti after activation released hydrogen of 0.56 wt% in 5 minutes, 1.26 wt% in 10 minutes, 2.64 wt% in 20 minutes, 3.82 wt% in 30 minutes, and 5.03 wt% in 60 minutes. †(Received November 6, 2015; Accepted February 13, 2016)

Increase in the Hydrogen-Sorption Rates and the Hydrogen-Storage Capacity of MgH2 by Adding a Small Proportion of Zn(BH4)2

박혜령,곽영준,송명엽 대한금속·재료학회 2017 대한금속·재료학회지 Vol.55 No.9

In this work, Zn(BH4)2 was added to improve the hydrogen-storage properties of MgH2. A 99 wt% MgH2+1 wt% Zn(BH4)2 sample was prepared by milling in a planetary ball mill in a hydrogen atmosphere. The proportion of the added Zn(BH4)2 was small (1 wt%) in order to increase hydriding and dehydriding rates without reducing the hydrogen-storage capacity too much. Changes in the released hydrogen quantity, Hd, with temperature, T, for as-milled 99MgH2+1Zn(BH4)2 was obtained by heating the sample from room temperature to 683 K with a heating rate of 5 K/min under 1.0 bar of gas. Activation of the sample was not required. 99MgH2+1Zn(BH4)2 had an effective hydrogen-storage capacity (the quantity of hydrogen absorbed in 60 min) of 4.83 wt% in the first cycle. The as-purchased MgH2 absorbed hydrogen slowly, absorbing 0.04 wt% H in 60 min. On the other hand, in the first cycle, 99MgH2+ 1Zn(BH4)2 absorbed 3.97 wt% H in 5 min, 4.49 wt% H in10 min, and 4.83 wt% H in 60 min at 593 K under 12 bar H2.