In situ X-ray absorption spectroscopy studies of metal hydride electrodes
- Brookhaven National Laboratory, Upton, NY (United States). Dept. of Applied Science
- Texas A and M Univ., College Station, TX (United States). Center for Electrochemical Systems and Hydrogen Research
In situ X-ray absorption spectroscopy (XAS) studies were done on three metal hydride electrodes, LaNi{sub 5}, LaNi{sub 4.8}Sn{sub 0.2}, La{sub 0.8}Ce{sub 0.2}Ni{sub 4.8}Sn{sub 0.2}, in 6M KOH. Ex situ measurements were also made on dry uncycled electrodes and on material from an La{sub 0.8}Ce{sub 0.2}Ni{sub 4.8}Sn{sub 0.2} electrode that had been cycled 25 times. Comparison of the in situ XAS at the Ni K and at the La L{sub 3} edge of charged and discharged electrodes indicates large changes in the electronic and structural characteristics on introduction of hydrogen. Results at the Ce L{sub 3} edge in La{sub 0.8}Ce{sub 0.2}Ni{sub 4.8}Sn{sub 0.2} show a transition from a mixed valent to {alpha} to a {gamma}-like Ce state as the lattice expands during charge. Ex situ x-ray absorption near-edge structures (XANES) at the Ni K edge indicate that the additions of either Ce or Sn fill empty Ni 3d states. The Ni K edge extended x-ray absorption fine structures (EXAFS) for all three alloys in the dry uncharged state were similar, indicating that minor substitutions for either the A or B component does not substantially change the structure. The Sn substitution causes an increase both in a and c axis as evidenced from increase in the Ni-Ni and the Ni-La distances. Partial substitution of La by Ce causes a slight contraction in the Ni-La distance. The Ni XANES and EXAFS indicate that about 6% of the Ni in the La{sub 0.8}Ce{sub 0.2}Ni{sub 4.8}Sn{sub 0.2} corroded after 25 cycles. Ce XANES on the cycled electrode indicates some corrosion of Ce and the formation of Ce (III) state. The results indicate that XAS is a very useful technique for the study of alloy hydrides, particularly the role of electronic structure, the environment around minor constituents, and the corrosion of individual components.
- Research Organization:
- Brookhaven National Laboratory (BNL), Upton, NY
- DOE Contract Number:
- AC02-76CH00016
- OSTI ID:
- 99618
- Journal Information:
- Journal of the Electrochemical Society, Journal Name: Journal of the Electrochemical Society Journal Issue: 7 Vol. 142; ISSN JESOAN; ISSN 0013-4651
- Country of Publication:
- United States
- Language:
- English
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