Electrochemical and in situ neutron diffraction investigations of La-Ni-Al-H alloys Page: 4 of 4
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The stability of the selected hydride alloys was studied
by electrochemical cycling. Figure 3 shows plots of specific
capacity (as x value) of the three investigated alloy
compositions versus the cycle number for cycles 1-20. The
LaNi5 electrode has low, but very stable, capacity. The
LaNi44Al06 alloy electrode has the highest capacity
(x < 4.4) with a relatively small drop. The alloy with a low
concentration of Al, LaNi4 87Alo 12, however, has a rather
poor stability indicated by a large capacity decay. One
possible reason for this behavior is the selective dissolution
of aluminum. Analysis of the electrolyte solutions from the
cells indicated the presence of dissolved aluminum.
Electrolytes from cells made with the LaNi457A1o12 alloy
contained 5 ppm Al after 12 cycles, 14 ppm after 29 cycles.
Lanthanum was not detectable in these electrolytes. The
higher concentration of Al in the LaNi44Alo.6 alloy,
however, can compensate for the corrosion loss of Al for a
longer time than in the case of the LaNi487A1012 alloy.
Thus, electrodes with higher Al content have longer cycle
life. These experiments show that the Al-alloying
component is very important to produce a high specific
capacity, but, also increases the sensitivity to corrosion.
Surface modification of the alloy particles or introduction of
other corrosion-suppressing alloying elements are necessary
to achieve longer cycle life.
To explain the variation in electrochemical performance
among the Al-containing alloys, the in situ neutron
diffraction data were analyzed to gain insight on
relationships between structural and electrochemical
phenomena of these alloys. Preliminary results show
correlations between electrochemical measurements and
neutron diffraction refinements for endmember states.
This research was sponsored by the U.S. Army
Research Office, Research Triangle Park, NC, through the
ARO Fuel Cell / Battery Research Hub at the Illinois
Institute of Technology. The research was conducted at
Argonne National Laboratory, which is operated by the
University of Chicago for the U.S. Department of Energy
under Contract No. W-31-109-Eng-38.
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* Illinois Institute of Technology
Working Electrode Lead
Counter Electrode Lead
Fig. 1 Schematic diagram of the electrochemical cell for
in situ neutron diffraction measurements.
2 3 4
x value, H/M
Fig. 2 Open-circuit voltage for MHx/NiO(OH) cells as
function of discharge capacity.
0 5 10
Fig. 3 Cycling behavior of the La-Ni-Al-H alloys for
three aluminum composition.
U aNi4.4Alo. Hx
LaNisH. U x 3
f.*.0 ***- -.04. **.
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Peng, W.; Redey, L.; Vissers, D.R.; Myles, K.M.; Carpenter, J.; Richardson et al. Electrochemical and in situ neutron diffraction investigations of La-Ni-Al-H alloys, article, May 1, 1996; Illinois. (digital.library.unt.edu/ark:/67531/metadc668074/m1/4/: accessed February 17, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.