Reduction In Hydrogen Storage Capacity Research Articles

Stoichiometry and annealing condition on hydrogen capacity of TiCr2-x AB2 alloys

This study presents the effect of stoichiometry and annealing condition on Ti–Cr AB2-type hydrogen storage alloys. Prior to annealing the majority phase of the as-cast alloys was the C14 Laves phase, with separate Ti and Cr phases. Annealing treatment (1273 K/14 d) led to a transition from C14 to C15 Laves phase structure. Both C14 (as-cast) and C15 (annealed) cell size increased with Ti content, up to a ratio (Cr/Ti) of 1.6, due to B-site Ti substitution in the lattice up to a limit. Pressure composition isotherm (PCI) measurements demonstrated alloys containing a greater Ti content had a better maximum hydrogen storage capacity (1.5 vs. 1.03 wt%) and lower plateau pressure (9.4 vs. 15.8 bar) at 253 K. Annealing resulted in a lower storage capacity (1.05 vs. 1.49 wt%), greater plateau pressure (ca. 30 bar) and flatter plateau slope (25 % reduction in plateau slope). Reduction in hydrogen storage capacity of annealed alloys could be due to diffusion of residual Cr in the alloy into the C15 Laves phase during the annealing process, thereby changing the local composition as confirmed through X-ray diffraction (XRD).

Parametric investigations on LCC1 based hydrogen storage system intended for fuel cell applications

Considering the necessity for compact hydrogen storage system for fuel cell stacks, 41 embedded cooling tube (ECT) reactor with an outer cooling jacket (OCJ) is designed, fabricated and tested with 3.75 kg of LCC1® alloy. To analyse the sensitivity of the system performance at various operating conditions and the applicability of this prototype as storage system, an extensive parametric investigation was carried out at varying supply pressure (Ps), absorption temperature (Ta) and desorption temperature (Td). LCC1® alloy achieved maximum hydrogen storage capacity (HSC) of 1.6 wt% within 420 s at Ps of 25 bar, Ta of 25 °C and heat transfer fluid (HTF) flow rate (HTFa) of 6 LPM. Supply pressure is found to have greater influence than absorption temperature over absorption performance and heating output. With Ta of 25 °C, HTFa of 6 LPM, HSC of 1.58 wt% and 1.6 wt% were achieved at Ps of 20 bar and 30 bar, respectively, resulting in corresponding specific heating power (SHP) of 497.7 W/kg and 544.9 W/kg. Varying Ta from 25 °C to 35 °C at Ps of 20 bar and HTFa of 6 LPM resulted in 3% reduction in HSC. During desorption, desorption temperature of above 20 °C is found to be favourable with more than 95% of stored hydrogen being desorbed. It is further observed that the dehydriding rate of LCC1® was nearly steady which is potentially suitable for fuel cell applications, as the average dehydriding rate is estimated to be about 15.75 NLPM and 22.91 NLPM at Td of 20 °C and 25 °C, respectively, with 6 LPM of HTF flow rate. The analysed module is proposed as a potential hydrogen supply unit for a 1 kW fuel cell reported in literature.

Magnesium and iron loaded hollow glass microspheres (HGMs) for hydrogen storage

The development of a safe and efficient method for hydrogen storage is essential for the use of hydrogen with fuel cells for vehicular applications. Hollow glass microspheres (HGMs) have characteristics suitable for hydrogen storage and are expected to be a potential hydrogen carrier to be used for energy release applications. The HGMs with 10–100 μm diameters, 100–1000 Å pore width and 3–8 μm wall thicknesses are expected to be useful for hydrogen storage. In our research we have prepared HGMs from amber glass powder of particle size 63–75 μm using flame spheroidisation method. The HGMs samples with magnesium and iron loading were also prepared to improve the heat transfer property and thereby increase the hydrogen storage capacity of the product. The feed glass powder was impregnated with calculated amount of magnesium nitrate hexahydrate salt solution to get 0.2–3.0 wt% Mg loading on HGMs. Required amount of ferrous chloride tetrahydrate solution was mixed thoroughly with the glass feed powder to prepare 0.2–2 wt% Fe loaded HGMs. Characterizations of all the HGMs samples were done using FEG-SEM, ESEM and FTIR techniques. Adsorption of hydrogen on all the Fe and Mg loaded HGMs at 10 bar pressure was conducted at room temperature and at 200 °C, for 5 h. The hydrogen adsorption capacity of Fe loaded sample was about 0.56 and 0.21 weight percent for Fe loading 0.5 and 2.0 weight percentage respectively. The magnesium loaded samples showed an increase of hydrogen adsorption from 1.23 to 2.0 weight percentage when the magnesium loading percentage was increased from 0 to 2.0. When the magnesium loading on HGMs was increased beyond 2%, formation of nano-crystals of MgO and Mg was seen on the HGMs leading to pore closure and thereby reduction in hydrogen storage capacity.

Degradation Mechanism against Hydrogenation Cycles in Mg2–xPrxNi4 (x = 0.6 and 1.0)

A long cycle life of metal hydrides is paramount for applications. We present an investigation of the degradation mechanism against hydrogenation cycles in Mg2–xPrxNi4 (x = 0.6 and 1.0). Mg1.0Pr1.0Ni4 shows significant degradation and loss of capacity after only a few cycles. In stark contrast, Mg1.4Pr0.6Ni4 did not show any reduction of hydrogen storage capacity until 100 cycles at 313 K. The peak broadening of X-ray diffraction (XRD) patterns and accumulation of lattice strain were observed concomitantly with an increase of hydrogenation cycles only in Mg1.0Pr1.0Ni4. These changes were not observed in Mg1.4Pr0.6Ni4. In pair distribution function (PDF) patterns, r-dependent peak broadening was observed and it became significant with an increasing number of cycles in Mg1.0Pr1.0Ni4, suggesting an increase of the dislocation density. Mg1.4Pr0.6Ni4 showed higher hardness and more pulverization upon hydrogenation than Mg1.0Pr1.0Ni4. These results suggest that the dominant mechanism, the stress induced by hydr...

Characterization and analyses of degradation and recovery of LaNi4.78Sn0.22 hydrides following thermal aging

LaNi4.78Sn0.22Hx hydride samples were held at a hydrogen content of x > 5.0 (x is H/La atomic ratio) and temperatures above 465 K to accelerate the intrinsic degradation processes. Although Sn-substituted alloys are much more resistant to disproportionation than nearly all other LaNi5 alloys, the present test conditions did produce substantial degradation. Effects observed included reduction in hydrogen storage capacity, decreases in the plateau pressures, increased slopes of the plateaus, and smaller hysteresis ratios. A regeneration process nearly completely restored the behavior of the degraded LaNi4.78Sn0.22 hydride to its initial value. First-principles chemical reaction kinetics and statistical thermodynamics simulations have replicated experimental pressure–composition hydrogen gas absorption isotherms for both initial and degraded LaNi4.78Sn0.22 hydride. Neutron diffraction characterization of phase compositions, crystal structures, and hydrogen content have been performed on undamaged, degraded, and regenerated LaNi4.78Sn0.22 deuterides.

The effect of chromium (III) oxide (Cr 2O 3) nanopowder on the microstructure and cyclic hydrogen storage behavior of magnesium hydride (MgH 2)

High energy ball milling in a Fritsch P6 planetary ball mill was used for the synthesis of the nanocomposite of MgH 2 with 10 wt.% of Cr 2O 3 nanopowder catalyst (particle size <50 nm). After ball milling for 1 h the resulting grain size of β-MgH 2 was equal to ∼30 nm. Subsequently, the nanocomposite was subjected to 150 desorption/absorption cycles at 325 °C. A gradual loss of hydrogen storage capacity upon cycling from ∼5.2 wt.% after 1 cycle to ∼4.6 wt.% after 150 cycles is observed on respective PCT curves obtained at 325 °C after every 25 cycles. The TPD curves temperature maxima are gradually shifted to a higher temperature range with increasing number of cycles which may indicate a lowering of the overall rate of transformation. Thorough microstructural investigations using such techniques as X-ray diffraction (XRD), scanning transmission electron microscopy (STEM) and X-ray photoelectron spectroscopy (XPS) of the samples after 150 cycles of desorption/absorption show profound microstructural changes such as sintering of individual powder particles into agglomerates, increase in grain/crystallite size (>100 nm), segregation of the Cr 2O 3 particles to the interfaces between the sintered Mg particles and some reduction of Cr 2O 3 to Cr and MgO. All these microstructural changes seem to be responsible for the reduction of hydrogen storage capacity upon cycling and lowering the overall rate of transformation.

Electrochemical Evaluation of LaNi5 − xGex Metal Hydride Alloys

We report a detailed evaluation of Ge‐substituted for electrochemical application as a negative electrode in alkaline rechargeable cells. Alloys with small substitutions of Ge for Ni show operating pressures, chargeability, cyclic lifetime, and kinetics for hydrogen absorption and desorption all superior to those found in many other substituted alloys. These improved properties were achieved with a minimal reduction in hydrogen storage capacity.

Thermodynamic properties and cyclic hydriding-dehydriding stability of LaNi5 thin films

Pressure-composition isotherms (P-C-T relations) for thin film LaNi5-H systems were measured volumetrically. The film samples were prepared by flash evaporation of LaNi5 powder. The deposited film had a very fine grain or amorphous-like structure and exhibited almost no temperature dependence of the isotherms whereas recrystallization of the film by annealing increased the maximum hydrogen storage capacity and the thermodynamic stability of the hydrided film. The first 10–20 hydriding-dehydriding reactions markedly increased the residual electrical resistance of the film sample and reduced the maximum hydrogen storage capacity by 60%. The reduction in hydrogen storage capacity during cycling may be attributed to the generation and accumulation of a high density of defects in the film caused by cyclic hydriding and dehydriding reactions.

Thermodynamic properties and cyclic hydriding-dehydriding stability of LaNi5 thin films

Pressure-composition isotherms ( P - C - T relations) for thin film LaNi 5 -H systems were measured volumetrically. The film samples were prepared by flash evaporation of LaNi 5 powder. The deposited film had a very fine grain or amorphous-like structure and exhibited almost no temperature dependence of the isotherms whereas recrystallization of the film by annealing increased the maximum hydrogen storage capacity and the thermodynamic stability of the hydrided film. The first 10–20 hydriding-dehydriding reactions markedly increased the residual electrical resistance of the film sample and reduced the maximum hydrogen storage capacity by 60%. The reduction in hydrogen storage capacity during cycling may be attributed to the generation and accumulation of a high density of defects in the film caused by cyclic hydriding and dehydriding reactions.