Since 1968 when Reilly and Wiswall [1] discovered the reversible hydro the alloy Mg2Ni to form th... more Since 1968 when Reilly and Wiswall [1] discovered the reversible hydro the alloy Mg2Ni to form the ternary hydride Mg2NiH4, its hydriding-dehydr thermal and kinetic properties have been investigated by many resea years, Mg2NiH4 has continued to surprise the researchers by exhibiting s [2] and resistivity anomalies [3], seemingly unpredictably dependent on sample history. Mg2NiH4 has been regarded as a promising metal hydride for hyd increasing the negative electrode capacity in nickel metal hydride (NiM under normal conditions Mg2NiH4 is too stable, i.e. at room temperature is so low that Mg2NiH4 practically does not desorb hydrogen. Therefor stability of Mg2NiH4 be decreased to produce a suitable material for practi Results and discussion On heating and cooling, Mg2NiH4 exhibits a reversible phase transfo accompanied by a distinct colour change from orange grey-black ( Mg2NiH4 exhibits a monoclinic distorted low-temperature (LT) modifi temperature (HT) phase, where magnesium ions f...
New high pressure synthesized ternary Mg-TM hydrides (Ti, Zr, Hf, V, Nb and Ta) with metastable F... more New high pressure synthesized ternary Mg-TM hydrides (Ti, Zr, Hf, V, Nb and Ta) with metastable FCC structures
Low cost rechargeable iron-air alkaline batteries have all essential attributes to adapt for larg... more Low cost rechargeable iron-air alkaline batteries have all essential attributes to adapt for large scale energy storage applications. To actualize this implementation needs to overcome the challeng ...
Alkaline iron electrodes present some challenges for use in secondary batteries that are associat... more Alkaline iron electrodes present some challenges for use in secondary batteries that are associated with low coulombic efficiency and discharge utilization. Low coulombic efficiency is correlated t ...
Abstract A large active specific surface area is a very efficient way to improve charge/discharge... more Abstract A large active specific surface area is a very efficient way to improve charge/discharge rate capabilities of metal hydride electrodes. This can be promoted by washing oxidized, pre-hydrided AB 5 alloy particles in a hot KOH solution. This leads to magnetization of the alloy powder, making it possible to lift the powder with a simple permanent magnet, indicating that nickel liberated in the surface layer is essential for the improved kinetics. The overpotential of each step in the discharge process is analysed in detail using both half cells and sealed cells. The electrode polarisation depends inversely on the current density per active area. Untreated and treated alloy powders have similar current densities per active area, but treated powder exhibits superior kinetics due to its larger surface area. A NiMH cell with a surface-treated alloy has very good rate capability, only limited by the kinetics of the Ni electrode. At low overpotential, the electrochemical reaction gives the main contribution to the electrode polarisation. If the discharge current is increased to give an overpotential of more than 0.1 V, concentration polarisation will become important and a limiting factor at high current densities.
ABSTRACT Feeling the pressure: Hydrogenation of C70 at 100 bar H2 pressure and 400 °C for 72 h ha... more ABSTRACT Feeling the pressure: Hydrogenation of C70 at 100 bar H2 pressure and 400 °C for 72 h has enabled isolation of C70H38. Full structural assignment was achieved by 2D NMR spectroscopic studies, which show C70H38 to have C2 symmetry and contain five benzenoid rings and two protonated carbon atoms on the equator (see picture). The proposed protonation scheme for the formation of this isomer shows a high similarity to reported C70F38isomers.
ABSTRACT Zr-based AB2-type hydrogen storage alloys as dual catalysts for hydrogen adsorption and ... more ABSTRACT Zr-based AB2-type hydrogen storage alloys as dual catalysts for hydrogen adsorption and oxidation reactions in alkaline fuel cells were investigated. A hydrogen-diffusion electrode composed of this hydride alloy was constructed, and its performance in terms of catalytic activities and durability was evaluated. Results demonstrated that the hydrogen-diffusion electrode had not only good activity but also excellent stability at a current density of 40−60 mA/cm2 after surface treatments using a 1.0 M HF solution. XPS analyses showed that the improvement in catalytic activity is related to the formation of a nickel-rich layer and the removal of other oxides on the catalyst surface. The novel possible application of Zr-based hydride alloys could lead to an attempt to exploit new catalysts to lower material cost for hydrogen fuel cells.
Products of the reaction of C(60) with H(2) gas have been monitored by high-resolution atmospheri... more Products of the reaction of C(60) with H(2) gas have been monitored by high-resolution atmospheric pressure photoionization Fourier transform ion cyclotron resonance mass spectrometry (APPI FT-ICR MS), X-ray diffraction, and IR spectroscopy as a function of hydrogenation period. Samples were synthesized at 673 K and 120 bar hydrogen pressure for hydrogenation periods between 300 and 5000 min, resulting in the formation of hydrofullerene mixtures with hydrogen content ranging from 1.6 to 5.3 wt %. Highly reduced C(60)H(x) (x > 36-40) and products of their fragmentation were identified in these samples by APPI FT-ICR MS. A sharp change in structure was observed for samples with at least 5.0 wt % of hydrogen. Low-mass (300-500 Da) hydrogenation products not observed by prior field desorption (FD) FT-ICR MS were detected by APPI FT-ICR MS and their elemental compositions obtained for the first time. Synthetic and analytical fragmentation pathways are discussed.
Rechargeable batteries are essentially unstable systems with respect to charging/discharging. The... more Rechargeable batteries are essentially unstable systems with respect to charging/discharging. The main electrode reactions of all battery chemistries are well known but are valid and reversible only at small currents. When batteries are used with nonzero current, gradients in voltage, current, and temperature will arise and initiate a number of less understood parasitic reactions. If all these rather complicated and interconnected reactions are not reversible upon charging/discharging, the battery will derail after a number of charging/discharging cycles. This article describes two ways to improve performance. One is to choose applications where the battery is not deeply discharged, such as in hybrid electric vehicles. In battery electric vehicle applications, this would correspond to working with a significantly oversized battery. The second way is to improve uniformity and quality of design and materials of metal hydride electrodes; however, this will also drastically increase cost, and for a battery application, the total throughput of available energy over the lifetime cost of the battery must be maximized. Uniform metal hydride particles with a large and uniform reaction surface are examples of how to increase battery performance by making the electrodes work under more ideal conditions, which slows down the deteriorating influence from the parasitic reactions.
The stability and electronic structure of perovskite hydrides ABH3 were investigated by means of ... more The stability and electronic structure of perovskite hydrides ABH3 were investigated by means of first-principles density functional calculations. Two types of perovskite hydrides are distinguished: (1) When A and B are alkali and alkaline earth metals, the hydrides are ionic compounds with calculated band gaps of around 2eV and higher. Their stability trend follows basically the concept of Goldschmidt's tolerance
Abstract The kinetics of oxygen and hydrogen gas recombination on the metal hydride electrode in ... more Abstract The kinetics of oxygen and hydrogen gas recombination on the metal hydride electrode in a NiMH cell is investigate as function of gas pressure, temperature, cycling and a hydrophobic additive. Both oxygen and hydrogen gas recombination rates in the NiMH cells are found to be linearly proportional to the gas pressure, indicating that surface processes with a constant number of reaction sites could be the rate limiting step. The rate of oxygen gas recombination is, however, more than 10 times faster than that of hydrogen at the same pressure. As the temperature increases, both reaction rates increase very rapidly, even though the solubilities of the gases in the KOH electrolyte decrease with temperature. The activation energies for oxygen and hydrogen gas recombination are 32.6 kJ mol −1 and 27.0 kJ mol −1 , respectively. The reactions rates also increase as the cells are cycled. This indicates, that the number of active sites increases, as the surface area increases, due to the continuously decrepitating of the alloy particles. The hydrogen gas absorption rate increases dramatically after a large number of cycles due the drying of the MH electrode. A hydrophobic PTFE additive in the MH electrode can significantly improve hydrogen absorption efficiency in NiMH cells.
Since 1968 when Reilly and Wiswall [1] discovered the reversible hydro the alloy Mg2Ni to form th... more Since 1968 when Reilly and Wiswall [1] discovered the reversible hydro the alloy Mg2Ni to form the ternary hydride Mg2NiH4, its hydriding-dehydr thermal and kinetic properties have been investigated by many resea years, Mg2NiH4 has continued to surprise the researchers by exhibiting s [2] and resistivity anomalies [3], seemingly unpredictably dependent on sample history. Mg2NiH4 has been regarded as a promising metal hydride for hyd increasing the negative electrode capacity in nickel metal hydride (NiM under normal conditions Mg2NiH4 is too stable, i.e. at room temperature is so low that Mg2NiH4 practically does not desorb hydrogen. Therefor stability of Mg2NiH4 be decreased to produce a suitable material for practi Results and discussion On heating and cooling, Mg2NiH4 exhibits a reversible phase transfo accompanied by a distinct colour change from orange grey-black ( Mg2NiH4 exhibits a monoclinic distorted low-temperature (LT) modifi temperature (HT) phase, where magnesium ions f...
New high pressure synthesized ternary Mg-TM hydrides (Ti, Zr, Hf, V, Nb and Ta) with metastable F... more New high pressure synthesized ternary Mg-TM hydrides (Ti, Zr, Hf, V, Nb and Ta) with metastable FCC structures
Low cost rechargeable iron-air alkaline batteries have all essential attributes to adapt for larg... more Low cost rechargeable iron-air alkaline batteries have all essential attributes to adapt for large scale energy storage applications. To actualize this implementation needs to overcome the challeng ...
Alkaline iron electrodes present some challenges for use in secondary batteries that are associat... more Alkaline iron electrodes present some challenges for use in secondary batteries that are associated with low coulombic efficiency and discharge utilization. Low coulombic efficiency is correlated t ...
Abstract A large active specific surface area is a very efficient way to improve charge/discharge... more Abstract A large active specific surface area is a very efficient way to improve charge/discharge rate capabilities of metal hydride electrodes. This can be promoted by washing oxidized, pre-hydrided AB 5 alloy particles in a hot KOH solution. This leads to magnetization of the alloy powder, making it possible to lift the powder with a simple permanent magnet, indicating that nickel liberated in the surface layer is essential for the improved kinetics. The overpotential of each step in the discharge process is analysed in detail using both half cells and sealed cells. The electrode polarisation depends inversely on the current density per active area. Untreated and treated alloy powders have similar current densities per active area, but treated powder exhibits superior kinetics due to its larger surface area. A NiMH cell with a surface-treated alloy has very good rate capability, only limited by the kinetics of the Ni electrode. At low overpotential, the electrochemical reaction gives the main contribution to the electrode polarisation. If the discharge current is increased to give an overpotential of more than 0.1 V, concentration polarisation will become important and a limiting factor at high current densities.
ABSTRACT Feeling the pressure: Hydrogenation of C70 at 100 bar H2 pressure and 400 °C for 72 h ha... more ABSTRACT Feeling the pressure: Hydrogenation of C70 at 100 bar H2 pressure and 400 °C for 72 h has enabled isolation of C70H38. Full structural assignment was achieved by 2D NMR spectroscopic studies, which show C70H38 to have C2 symmetry and contain five benzenoid rings and two protonated carbon atoms on the equator (see picture). The proposed protonation scheme for the formation of this isomer shows a high similarity to reported C70F38isomers.
ABSTRACT Zr-based AB2-type hydrogen storage alloys as dual catalysts for hydrogen adsorption and ... more ABSTRACT Zr-based AB2-type hydrogen storage alloys as dual catalysts for hydrogen adsorption and oxidation reactions in alkaline fuel cells were investigated. A hydrogen-diffusion electrode composed of this hydride alloy was constructed, and its performance in terms of catalytic activities and durability was evaluated. Results demonstrated that the hydrogen-diffusion electrode had not only good activity but also excellent stability at a current density of 40−60 mA/cm2 after surface treatments using a 1.0 M HF solution. XPS analyses showed that the improvement in catalytic activity is related to the formation of a nickel-rich layer and the removal of other oxides on the catalyst surface. The novel possible application of Zr-based hydride alloys could lead to an attempt to exploit new catalysts to lower material cost for hydrogen fuel cells.
Products of the reaction of C(60) with H(2) gas have been monitored by high-resolution atmospheri... more Products of the reaction of C(60) with H(2) gas have been monitored by high-resolution atmospheric pressure photoionization Fourier transform ion cyclotron resonance mass spectrometry (APPI FT-ICR MS), X-ray diffraction, and IR spectroscopy as a function of hydrogenation period. Samples were synthesized at 673 K and 120 bar hydrogen pressure for hydrogenation periods between 300 and 5000 min, resulting in the formation of hydrofullerene mixtures with hydrogen content ranging from 1.6 to 5.3 wt %. Highly reduced C(60)H(x) (x > 36-40) and products of their fragmentation were identified in these samples by APPI FT-ICR MS. A sharp change in structure was observed for samples with at least 5.0 wt % of hydrogen. Low-mass (300-500 Da) hydrogenation products not observed by prior field desorption (FD) FT-ICR MS were detected by APPI FT-ICR MS and their elemental compositions obtained for the first time. Synthetic and analytical fragmentation pathways are discussed.
Rechargeable batteries are essentially unstable systems with respect to charging/discharging. The... more Rechargeable batteries are essentially unstable systems with respect to charging/discharging. The main electrode reactions of all battery chemistries are well known but are valid and reversible only at small currents. When batteries are used with nonzero current, gradients in voltage, current, and temperature will arise and initiate a number of less understood parasitic reactions. If all these rather complicated and interconnected reactions are not reversible upon charging/discharging, the battery will derail after a number of charging/discharging cycles. This article describes two ways to improve performance. One is to choose applications where the battery is not deeply discharged, such as in hybrid electric vehicles. In battery electric vehicle applications, this would correspond to working with a significantly oversized battery. The second way is to improve uniformity and quality of design and materials of metal hydride electrodes; however, this will also drastically increase cost, and for a battery application, the total throughput of available energy over the lifetime cost of the battery must be maximized. Uniform metal hydride particles with a large and uniform reaction surface are examples of how to increase battery performance by making the electrodes work under more ideal conditions, which slows down the deteriorating influence from the parasitic reactions.
The stability and electronic structure of perovskite hydrides ABH3 were investigated by means of ... more The stability and electronic structure of perovskite hydrides ABH3 were investigated by means of first-principles density functional calculations. Two types of perovskite hydrides are distinguished: (1) When A and B are alkali and alkaline earth metals, the hydrides are ionic compounds with calculated band gaps of around 2eV and higher. Their stability trend follows basically the concept of Goldschmidt's tolerance
Abstract The kinetics of oxygen and hydrogen gas recombination on the metal hydride electrode in ... more Abstract The kinetics of oxygen and hydrogen gas recombination on the metal hydride electrode in a NiMH cell is investigate as function of gas pressure, temperature, cycling and a hydrophobic additive. Both oxygen and hydrogen gas recombination rates in the NiMH cells are found to be linearly proportional to the gas pressure, indicating that surface processes with a constant number of reaction sites could be the rate limiting step. The rate of oxygen gas recombination is, however, more than 10 times faster than that of hydrogen at the same pressure. As the temperature increases, both reaction rates increase very rapidly, even though the solubilities of the gases in the KOH electrolyte decrease with temperature. The activation energies for oxygen and hydrogen gas recombination are 32.6 kJ mol −1 and 27.0 kJ mol −1 , respectively. The reactions rates also increase as the cells are cycled. This indicates, that the number of active sites increases, as the surface area increases, due to the continuously decrepitating of the alloy particles. The hydrogen gas absorption rate increases dramatically after a large number of cycles due the drying of the MH electrode. A hydrophobic PTFE additive in the MH electrode can significantly improve hydrogen absorption efficiency in NiMH cells.
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