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Young K.,Energy Conversion Devices Inc. | Regmi R.,Wayne State University | Lawes G.,Wayne State University | Ouchi T.,Energy Conversion Devices Inc. | And 3 more authors.
Journal of Alloys and Compounds | Year: 2010

The effects of aluminum substitution to the structural, electrochemical, and gas phase hydrogen storage properties of C14-rich alloys are reported. Minor phases, including C15 and TiNi, were identified by X-ray diffraction analysis. Entropy and enthalpy were estimated from equilibrium pressure at a fixed hydrogen concentration due to the large slope factor in pressure-concentration-temperature isotherms. The stability of hydrides from these materials, determined from the pressure-concentration isotherm equilibrium pressure and maximum storage capacities has a better correlation with the change in entropy than that in enthalpy. Alloys having smaller unit cell volume, relatively low hydride heat of formation, and relatively higher degree of disorder exhibit lower plateau pressure, higher storage capacity, and smaller hydrogen diffusion coefficient. Comparing to the Co substitution in the same base alloy, Al substitution makes better contribution to both bulk hydrogen transport and surface reaction. Substituting 0.4% Al and 1.5% Co to AB2 alloy is found to be the best combination in terms of general nickel metal hydride battery performance. © 2009 Elsevier B.V. All rights reserved. Source


Young K.,Energy Conversion Devices Inc. | Ouchi T.,Energy Conversion Devices Inc. | Reichman B.,Energy Conversion Devices Inc. | Mays W.,Energy Conversion Devices Inc. | And 4 more authors.
Journal of Alloys and Compounds | Year: 2010

The structural, electrochemical, and gas phase hydrogen storage properties of predominantly C14 crystalline phase alloys with partial replacement by Co (up to 2.5 at%) are reported. Minor phases, including C15 and cubic TiNi, were found by X-ray diffraction and contributed to the improved hydrogen diffusion through the alloy. The optimal Co-content of between 1.0 and 1.5 at% provides easy activation, high gas phase capacity, and a high discharge capacity. An optimized alloy formula also provided the smallest metallic nickel cluster size embedded in the surface oxide and the largest number of nickel clusters. In sealed cell studies, a Co-content of 1.5% gives the best performance in formation, cycle life, and charge retention, but has worse specific power and low temperature performance than some other compositions. The high-rate dischargeabilities at lower rates were found to be limited by surface reactions, not bulk diffusion. © 2009 Elsevier B.V. All rights reserved. Source


Young K.,Ovonic Battery Company | Wu A.,Shida Battery Company | Qiu Z.,Shida Battery Company | Tan J.,Shida Battery Company | Mays W.,Ovonic Battery Company
International Journal of Hydrogen Energy | Year: 2012

In this paper we have compared nickel/metal hydride batteries made from AB 5 and Nd-only A 2B 7 alloys with or without addition of hydrogen peroxide (H 2O 2). The biggest advantages Nd-only A 2B 7 alloys have over AB 5 alloys are: a higher positive electrode utilization rate, lower initial internal resistance and less resistance increase after a 60°C storage, and higher capacity and resistance degradation during cycling. The hydrogen peroxide was used as an oxidation agent and was added into the electrolyte before closing the cells. The H 2O 2 can oxidize both Co(OH) 2 in the positive electrode and MH alloy in the negative electrode. From the test results, H 2O 2 oxides the MH alloy preferentially over the Co(OH) 2 in the case of AB 5 alloy. This preferential oxidation is reversed in the case of the A 2B 7 alloy in which Co(OH) 2 is oxidized first. In cells made from both alloys, the addition of H 2O 2 prevented the venting of cells during formation, increased the utilization of positive electrode, improved the 60°C charge retention, and increased the mid-point voltage after 300 cycles. Additionally the H 2O 2 also improved the cell balance for A 2B 7 alloy by decreasing the over-discharge reservoir in the negative electrode and reducing the capacity degradation in A 2B 7 alloy. However, the addition of H 2O 2 in cells made with AB 5 alloy deteriorated the cell balance by increasing the over-discharge reservoir in the negative electrode. The different cell balance and failure mechanisms for the two alloy compositions and H 2O 2 additive were compared and discussed. © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. Source

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