Hydrogen storage alloys

Abstract

Hydrogen storage alloys comprising a metal oxide containing 60 at % oxygen; and/or comprising a metal region adjacent to a boundary region, which boundary region comprises at least one channel; and/or comprising a metal region adjacent to a boundary region, where the boundary region has a length and an average width, where the average width is from about 12 nm to about 1100 nm; and/or comprising a metal oxide zone comprising a metal oxide, which oxide zone is aligned with at least one channel; and/or comprising a Ni/Cr metal oxide have improved electrochemical properties, for instance improved low temperature electrochemical performance.

Claims

1. A hydrogen storage alloy comprising i) at least one main phase and ii) a secondary phase comprising La and Ni, wherein the alloy comprises a bulk metal region adjacent to a metal oxide boundary region, which boundary region comprises at least one channel capable of allowing transport of electrolyte to the bulk metal region, wherein the alloy comprises about 11 at % to about 13 at % Ti, about 18 at % to about 23 at % Zr, about 9 at % to about 11 at % V, about 6 at % to about 9 at % Cr, about 6 at % to about 9 at % Mn, about 31 at % to about 34 at % Ni, about 0.3 at % to about 0.6 at % Al, about 2 at % to about 8 at % Co and about 1 at % to about 7 at % La, based on the total alloy, and wherein the alloy exhibits a charge transfer resistance (R) at 40 C. of from about 5 to about 20 .Math.g; and/or a surface catalytic ability for the main phase or main phases at 40 C. of from about 1 to about 5 seconds; and/or a charge transfer resistance for the main phase or main phases (R) at 40 C. of 10 .Math.g.

2. A hydrogen storage alloy according to claim 1, where the boundary region comprises a Ni/Cr metal oxide.

3. An alloy according to claim 2 where the Ni/Cr oxide contains 60 at % oxygen.

4. An alloy according to claim 2 where the Ni/Cr oxide contains from about 2 at % to about 8 at % Cr.

5. An alloy according to claim 2 where the Ni/Cr oxide contains from about 16 at % to about 23 at % Ni.

6. An alloy according to claim 2 where the Ni/Cr oxide contains from about 64 at % to about 71 at % oxygen, from about 3 at % to about 8 at % Cr and from about 16 at % to about 21 at % Ni.

7. An alloy according to claim 2 where the Ni/Cr oxide contains oxygen, Ni, Cr and one or more further elements selected from the group consisting of Al, Ti, V, Mn, Co and Zr.

8. An alloy according to claim 1 where the boundary region has a length and an average width and comprises at least one channel which runs along the length of the boundary region.

9. An alloy according to claim 1 where the boundary region comprises at least one channel which has an average width of from about 4 nm to about 40 nm.

10. An alloy according to claim 1 where the boundary region has a length and an average width and further comprises a transition oxide zone adjacent to a metal region which transition zone runs along the length of the boundary region.

11. An alloy according to claim 10 where the transition zone has an average width of from about 4 nm to about 30 nm.

12. An alloy according to claim 1 where the boundary region has a length and an average width and comprises a metal oxide zone which runs along the length of the boundary region.

13. An alloy according to claim 12 where the metal oxide zone which has an average width of from about 5 nm to about 500 nm.

14. An alloy according to claim 1 where the boundary region has a length and an average width and comprises across the width a first transition oxide zone, a metal oxide zone and a second transition oxide zone, each running along the length of the boundary region.

15. An alloy according to claim 1 where the boundary region has a length and an average width and comprises across the width a first transition oxide zone, a channel and a second transition oxide zone, each running along the length of the boundary region.

16. An alloy according to claim 1 where the boundary region has a length and an average width and comprises across the width a first transition oxide zone, a metal oxide zone, a channel and a second transition oxide zone, each running along the length of the boundary region.

17. An alloy according to claim 1 where the boundary region has a length and an average width, where the length is 4 times the average width and where the width is substantially uniform along the length.

18. An alloy according to claim 1 where the boundary region has an average width of from about 17 nm to about 600 nm.

19. An alloy according to claim 1 comprising from about 1.5 at % to about 7.0 at % La.

20. An alloy according to claim 1 comprising a C14 or C15 main Laves phase or comprising C14 and C15 main Laves phases.

21. An alloy according to claim 1 comprising a C14 or C15 main Laves phase or C14 and C15 main Laves phases, >0.5 wt % of a storage secondary phase comprising La and Ni and from about 0.3 wt % to about 15 wt % of a catalytic secondary phase comprising Ti and Ni.

22. A metal hydride battery, a solid hydrogen storage media, an alkaline fuel cell or a metal hydride air battery comprising a hydrogen storage alloy according to claim 1.

23. An alloy according to claim 1, which exhibits a charge transfer resistance (R) at 40 C. of from about 5 to about 20 .Math.g; and a surface catalytic ability for the main phase or main phases at 40 C. of from about 1 to about 5 seconds.

24. An alloy according to claim 1, which exhibits a surface catalytic ability for the main phase or main phases at 40 C. of from about 1 to about 5 seconds; and a charge transfer resistance (R) at 40 C. for the main phase or main phases of 10 .Math.g.

25. An alloy according to claim 1, which exhibits a charge transfer resistance (R) at 40 C. of from about 5 to about 20 .Math.g; a surface catalytic ability for the main phase or main phases at 40 C. of from about 1 to about 5 seconds; and a charge transfer resistance (R) at 40 C. for the main phase or main phases of 10 .Math.g.

26. An alloy according to claim 1, comprising from about 2.0 to about 7.0 atomic percent La.

27. An alloy according to claim 1, comprising from about 4.0 to about 7.0 atomic percent La.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 represents SEM/EDS results of alloy 0 of Example 1.

(2) FIG. 2 represents SEM/EDS results of alloy 5 of Example 1.

(3) FIG. 3 is a darkfield transmission electron micrograph (TEM) of a boundary region of alloy 0 of Example 1. The oxide interface is dark and the metal regions are bright.

(4) FIGS. 4a and 4b are a brightfield/darkfield TEM image pair of a grain boundary region for inventive alloy 5 of Example 1. In the brightfield 4a the oxide interface is white and the metal regions are dark.

(5) FIG. 5 is a brightfield TEM of a single channel boundary region of alloy 5 of Example 1. The oxide interface is bright and the metal regions are dark.

(6) FIG. 6 is an amplified TEM of the single channel boundary region of FIG. 5.

(7) FIG. 7 contains Cole-Cole plots of alloys 0-5 of Example 1 and show that two semi-circles emerge with increasing La content. This indicates two distinct phases participating in the electrochemistry.

(8) FIG. 8 is the circuitry employed to determine the charge transfer resistance (R2 and R4) and double layer capacitance (C1 and C2) of each phase from the Cole-Cole plots. The base alloy 0 exhibits only a single semi-circle in the Cole-Cole plot, therefore only R4 and C2 are calculated for alloy 0.

(9) FIG. 9 is a schematic of showing present narrow boundary regions throughout the bulk metal alloy (metal) and comprising transition oxide zones (transition amorphous oxide), metal oxide zones (oxide layer) and an open channel. The nickel hydroxide and nanoporous oxide layers are conventional metal oxides.

EXAMPLE 1

La Modified TiZrVCrMnNiAlCo Alloys

(10) Arc melting is performed under a continuous argon flow with a non-consumable tungsten electrode and a water-cooled copper tray. Before each run, a piece of sacrificial titanium undergoes a few melting/cooling cycles to reduce the residual oxygen concentration in the system. Each 12 g ingot is re-melted and turned over a few times to ensure uniformity in chemical composition. The chemical composition of each sample is examined using a Varian LIBERTY 100 inductively coupled plasma optical emission spectrometer (ICP-OES).

(11) The alloys below are designed together with the actual compositions as found by ICP.

(12) TABLE-US-00001 alloy Ti Zr V Cr Mn Ni Al Co La 0 design 12.0 22.8 10.0 7.5 8.1 32.2 0.4 7.0 0.0 ICP 11.9 22.9 10.0 7.5 8.0 32.2 0.4 7.1 0.0 1 design 12.0 21.8 10.0 8.1 8.1 32.2 0.4 7.0 1.0 ICP 11.9 22.2 10.2 7.6 7.5 32.1 0.4 7.0 0.9 2 design 12.0 20.8 10.0 7.5 8.1 32.2 0.4 7.0 2.0 ICP 12.2 20.7 10.3 6.4 8.0 32.5 0.6 7.2 2.1 3 design 12.0 19.8 10.0 7.5 8.1 32.2 0.4 7.0 3.0 ICP 11.9 20.2 9.9 6.8 7.9 32.8 0.5 6.9 3.1 4 design 12.0 18.8 10.0 7.5 8.1 32.2 0.4 7.0 4.0 ICP 12.0 19.0 9.9 7.3 8.0 32.1 0.5 7.2 3.9 5 design 12.0 17.8 10.0 7.5 8.1 32.2 0.4 7.0 5.0 ICP 11.8 17.9 9.9 7.4 7.9 32.6 0.4 7.1 4.9 Alloys 2-5 are inventive. Alloys 0-1 are comparative.

(13) Besides main C14 and C15 phases, two additional phases are identified with a Philips X'PERT PRO X-ray diffractometer (XRD). The abundance of the C14, C15, catalytic secondary TiNi phase and storage secondary LaNi phases are below (XRD, analyzed by JADE 9 software). All alloys are C14 predominant. Abundance is in weight percent, based on the alloy.

(14) TABLE-US-00002 alloy C14 C15 TiNi LaNi 0 85.4 11.2 3.4 0.0 1 75.6 21.5 2.4 0.5 2 80.8 15.5 3.1 0.6 3 80.7 15.8 2.3 1.2 4 82.8 14.3 1.2 1.7 5 88.7 8.4 0.9 2.0

(15) A JEOL-JSM6320F scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS) capability is used to study the phase distribution and corresponding compositions. The crystal structure of the TiNi phases, although containing significant amounts of Zr, exhibit a TiNi (B2) structure according to XRD. Inventive alloys 2-5 contain TiNi phases containing from 21.6 to 27.5 at % Ti, from 43.5 to 45.3 at % Ni, from 13.5 to 20.6 at % Zr and from 40.1 to 42.6 at % (Ti+Zr).

(16) A SEM/EDS spectra for alloy 0 is shown in FIG. 1. Results are below for the indicated locations.

(17) TABLE-US-00003 location Ti Zr V Ni Co Mn Cr Al La phase 1 21.8 22.7 1.6 45.6 5.0 2.5 0.4 0.3 0.0 TiNi 2 11.1 22.7 12.0 31.0 7.5 9.1 6.0 0.6 0.0 AB.sub.2 3 11.7 22.6 11.3 31.7 7.4 8.9 5.6 0.6 0.0 AB.sub.2 4 10.4 23.1 12.6 27.8 7.9 9.7 7.9 0.4 0.0 AB.sub.2 5 10.4 23.1 12.7 26.2 7.8 9.8 9.5 0.5 0.0 AB.sub.2 6 10.2 53.2 3.9 23.7 3.4 3.4 1.7 0.3 0.0 ZrO.sub.2

(18) A SEM/EDS spectra for inventive alloy 5 is shown in FIG. 2. Results are below for the indicated locations.

(19) TABLE-US-00004 location Ti Zr V Ni Co Mn Cr Al La phase 1 0.0 0.2 0.4 49.3 0.2 0.0 0.1 0.3 49.6 LaNi 2 0.1 0.2 0.4 49.7 0.3 0.0 0.1 0.2 49.2 LaNi 3 27.3 13.7 3.0 43.7 6.5 3.4 1.3 0.6 0.4 TiNi 4 11.6 19.7 12.5 29.0 8.3 8.9 9.3 0.5 0.1 AB.sub.2 5 12.1 19.8 12.4 29.2 8.0 8.7 9.3 0.5 0.0 AB.sub.2

(20) Transmission electron micrograph (TEM) results show that in alloy 0, only random Ni/Ti/Zr oxide is found, lightly oxidized. In alloy 5, both random Ni/Cr oxide (large gap grain boundary) and aligned Ni/Cr oxide (small gap grain boundary) are found, heavily oxidized. TEM analysis is performed with a TECNAI TF-30 Super-Twin TEM with an Oxford X-MAX EDS and a Gatan QUANTUM SE (963) electron energy loss spectrometer (EELS).

(21) FIG. 3 is a darkfield TEM of a boundary region of alloy 0. The oxide composition of alloy 0, determined by EDS is below.

(22) TABLE-US-00005 O Al Ti V Cr Mn Co Ni Zr 21.15 0.40 16.62 1.24 0.60 1.82 4.03 37.05 17.09

(23) FIGS. 4a and 4b are a brightfield/darkfield TEM image pair of a grain boundary region for inventive alloy 5. A nano-scaled boundary region separating metal regions is visible. A transition zone adjacent to the metal region is visible. The metal region is bright and the metal oxide is dark in the darkfield 4b. Energy loss spectroscopy shows that nickel of the metal region and the transition zone is in the zero oxidation state (Ni.sup.0) and that nickel in the oxide region is oxidized (Ni.sup.2+/.sup.3+). The oxide composition of alloy 5, determined by EDS is below.

(24) TABLE-US-00006 O Al Ti V Cr Mn Co Ni Zr 69.5 0.4 2.2 0.8 4.2 0.5 0.9 19.6 1.9

(25) FIG. 5 is a brightfield TEM of present alloy 5 showing a single channel boundary region between metal regions. The boundary region is bright and the metal regions are dark. The nano-scaled boundary region contains transition zones adjacent to the metal regions, a Ni/Cr oxide zone and an aligned channel. The width of the boundary region is substantially uniform along the length. The transition zones, channel and oxide zone run along the length of the boundary region.

(26) FIG. 6 is an amplified TEM of the single channel boundary region of FIG. 5.

(27) The low temperature electrochemical results are below. FIG. 7 shows in the Cole-Cole plots that two semi-circles emerge with increasing La content. This indicates two distinct phases participating in the electrochemistry. The charge transfer resistance (R2 and R4) and double layer capacitance (C1 and C2) of each phase are calculated from the Cole-Cole plots using the circuitry shown in FIG. 8. The base alloy 0 exhibits only a single semi-circle in the Cole-Cole plot, therefore only R4 and C2 are calculated for alloy 0.

(28) The R and C values are calculated from the Cole-Cole plot of AC impedance measurements. AC impedance measurements are conducted with a SOLARTRON 1250 Frequency Response Analyzer with sine wave of amplitude 10 mV and frequency range of 0.1 mHz to 10 kHz. Prior to the measurements, the electrodes are subjected to one full charge/discharge cycle at 0.1 C rate using a SOLARTRON 1470 Cell Test galvanostat, charged to 100% SOC, discharged to 80% SOC, then cooled to 40 C.

(29) TABLE-US-00007 alloy R1 R2 R4 R2 + R4 C1 C2 0 0.57 158 158 0.18 1 0.76 4.07 154 158.1 1.69 1.02 2 0.41 9.64 5.62 15.26 2.59 0.31 3 0.28 10.40 4.43 14.83 4.20 0.48 4 0.28 9.45 3.25 12.70 7.12 0.53 5 0.27 7.31 3.69 11.00 6.75 0.57

(30) Charge transfer resistance, R is in .Math.g. Double layer capacitance, C is in Farad/g. The R and C values are calculated from the Cole-Cole plot of AC impedance measurements performed at 40 C.

(31) It is seen that La-modified alloys 2-5 have vastly improved charge transfer resistance (R2+R4) relative to the comparative alloys (lower values desired).

(32) High rate dischargeability results are below.

(33) TABLE-US-00008 3.sup.rd cycle cap. 3.sup.rd cycle cap. activation cycles to alloy 50 mA/g 4 mA/g HRD (%) reach 92% HRD 0 300 376 80 6 1 340 371 92 4 2 349 365 96 1 3 347 364 95 1 4 331 345 96 1 5 307 321 96 1

(34) Half-cell HRD is defined as the ratio of discharge capacity measured at 50 mA g.sup.1 to that measured at 4 mA g.sup.1. The discharge capacity of an alloy is measured in a flooded cell configuration against a partially pre-charged Ni(OH).sub.2 positive electrode. No alkaline pretreatment is applied before the half-cell measurement. Each sample electrode is charged at a constant current density of 50 mA g.sup.1 for 10 h and then discharged at a current density of 50 mA g.sup.1 followed by two pulls at 12 and 4 mA g.sup.1. Capacities and HRD are measured at the 3.sup.rd cycle.

(35) BET (Brunauer-Emmett-Teller) surface area for alloy 0 is 1.89 m.sup.2/g. BET surface are for alloy 5 is determined to be 4.92 m.sup.2/g. BET surface area is measured by the liquid nitrogen dipping BET method.

EXAMPLE 2

Sc, Y or Mischmetal Modified TiZrVCrMnNiAlCo Alloy

(36) Example 1 is repeated, replacing La with Sc, Y and mischmetal.