Electron Irradiation
means. Based on thermal heating experiments conducted in a DSC [2], it was established that full de-protonation of Ni(OH)2 proceeds by de-hydroxylation in a single stage by the loss of water molecules during heating at ∼300° C (equation 1):
Ni OH NiOHO2 ()2 =+ (1)
It was also shown that NiO could be produced by mechanical grinding of dry Ni(OH)2
Ni(OH)2
each cycle of charge [3], according to equation 2. ββ
-NiOOH HO e-Ni OH OH forward is discharge, reverse
++ () +22 (2) − (iis charge)
Tis reaction is the essential process by which the positive Ni electrode operates in a rechargeable NiMH battery. Te charge cycle of de-hydroxylation operates from the recombination of a hydroxyl ion from a dissociated water molecule and hydrogen coming from the de-protonated hydroxide. In this research we found that NiOOH is produced in the powder during electron irradiation in the TEM,
dry Ni(OH)2
with an extra peak in the ELNES spectrum at about 527eV. We can attribute this peak to NiOOH because its near-edge energy 527eV is close to 529eV for the binding energy of O2-
in the
O1s peak [8]. Moreover, the careful perusal of the spectrum suggests that the NiOOH coming from the irradiation process in this study may be somewhat disordered. Tis is shown by the substantial intensity of the O1s peak of the oxide group O2-
hydroxyl OH- Ni(OH)2 powders, also with no evidence for an
intermediate stage [2]. In contrast, electrochemical charge-discharge cycling of in a fresh battery electrode does create NiOOH on
can readily supply the bond-breaking energy needed for the transformation.
Acknowledgements It is a pleasure to thank Prof. David McComb of the Ohio
State University for invaluable discussions and advice on optimizing the EELS spectra, when he was a summer visitor at Natural Resources Canada (Ottawa).
References [1] J McBreen, “Nickel Hydroxides” in Handbook of Battery Materials (1997) JO Besenhard, ed., Wiley-VCH, Germany.
https://www.osti.gov/servlets/purl/757095.
[2] GJC Carpenter and ZS Wronski, Nanostruct Mat 11 (1999)
https://doi.org/10.1016/S0965-9773(99)00020-3.
[3] ZS Wronski et al., J Nanosci Nanotech 9 (2009) https://doi .org/10.1166/jnn.2009.M09.
[4] C Suryanarayana, Prog Mater Sci 46 (2001) https://doi .org/10.1016/S0079-6425(99)00010-9.
[5] GJC Carpenter et al., Microscopy Today 29 (2021) https://
doi.org/10.1017/S1551929521000869.
[6] MT Shehata and GJC Carpenter, Proc 28th Ann Tech Mtg
IMS Symp (1996) DW Stevens et al., eds., ASM International, Materials Park, OH. ISBN-13: 978-0871705709.
[7] GJC Carpenter and Z Wronski, Microsc Microanal 21 (2015)
https://doi.org/10.1017/S1431927615015470.
[8] BP Payne et al., J Electron Spectrosc Rel Phenomena 175 (2009)
https://doi.org/10.1016/j.elspec.2009.07.006.
[9] EL Ratcliff et al., Chem Mater 23 (2011) https://doi .org/10.1021/cm202296p.
, as compared to the very weak peak characteristic of the group, which should be visible at approximately
231eV for the disordered γ form of NiOOH [5]. For the NiOOH intermediate phase to occur in dry , the decomposition process would have to occur by
the following reaction (equation 3): 22 2
Ni OH 2() NiOOH H=+ (3)
Tis reaction would require the diffusion of protons to the sur- faces of the hydroxide crystals followed by the recombination of the hydrogen atoms and the release of hydrogen (equation 4):
HH H+= 2 (4)
For the intermediate phase to occur (as in a fresh electrode) in dry Ni(OH)2
under irradiation by 200kV electrons in a TEM,
it is likely that this is a result of the experiment being carried out in situ using a very thin specimen. Tus, we would expect that the hydrogen atoms could readily diffuse out through the nearby specimen surfaces and recombine into H2
, to be lost in
the vacuum of the microscope. If this experiment were carried out using thicker specimens, for example, in a high-voltage electron microscope, it is possible that recombination of the H ions would result in the formation of small hydrogen bubbles within the thin foil specimen. Te de-protonation process under the electron beam leads
to an intermediate phase, one which is not created from Ni(OH)2 by either heating or mechanical grinding. We conclude that the dissociation reaction to form protons is caused primarily by ionization damage from the 200kV charged electrons, which
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