E170
Journal of The Electrochemical Society, 156 ͑11͒ E167-E170 ͑2009͒
Table I. Thermodynamical data (a) obtained in this study and (b)
calculated data from the solubility of Li2O for Reaction 14. (The
error values denote the 95% confidence intervals.)
0
0
0
Ј
Ј
Ј
⌬G
͑kJ mol−1
⌬S
⌬H
͑kJ mol−1
͒
͒
͑J K−1 mol−1
͒
͑a͒
͑b͒
−456.3 Ϯ 0.5
−456.7 Ϯ 2.3
−151 Ϯ 3
−161 Ϯ 3
−573.5 Ϯ 0.1
−581.0 Ϯ 0.2
fore the standard formal free energy change, ⌬G0 ͑14͒, is calculated
Ј
as follows
0
0
0
Ј
Ј
Ј
⌬G ͑14͒ = ⌬Gf ͑solid Li2O͒ + ⌬G ͑23͒
͓28͔
Here, ⌬G0f ͑solid Li2O͒ is the standard formal free energy of for-
mation of crystalline Li2O, which is available from reported thermo-
Ј
2Li͑l͒ + 1 O2͑g͒ = Li2O͑s͒
͓29͔
Figure 6. Temperature dependence of the standard formal free energy
change of Reaction 12: in a LiCl–KCl eutectic melt. Calculated results are
shown by a broad gray line, considering the error values which denote the
95% confidence intervals in our previous data on Li2O solubility.
2
Figure 6 shows ⌬G0 ͑14͒ obtained in the present study, which in-
creases with the elevation of temperature. The calculated values are
also shown in Fig. 6 by a gray line, taking into account the error
values which denote the 95% confidence intervals in our previous
data on Li2O solubility. As a typical result, the obtained thermody-
namic quantities at 773 K are summarized in Table I. These values
are in good agreement within the experimental error, indicating the
validity of successive measurements in this study.
Ј
0
Ј
ͩ ͪ
0
Ј
⌬S ͑14͒ = −
͓18͔
͓19͔
p
0
0
0
Ј
Ј
Ј
⌬H ͑14͒ = ⌬G ͑14͒ + T⌬S ͑14͒
Conclusion
The obtained formal thermodynamic quantities are given as follows
The standard formal potential of O2/O2− was measured precisely
using the BDD electrode as an IPE in a LiCl–KCl eutectic melt. The
standard formal free energy change for Reaction 14 is in good agree-
ment with the calculated value from our solubility data on Li2O
obtained previously, indicating the validity of successive measure-
ments in this study. Thus, this study has enabled thermodynamic
consideration on chemical and electrochemical processes involving
oxide ion, such as electrochemical reduction of metal oxides, with
higher accuracy than before.
0
−3
⌬G ͑14͒ = − 573.5͑ Ϯ 0.1͒ + 151͑ Ϯ 3͒ ϫ 10 T kJ mol−1
Ј
͓20͔
⌬S ͑14͒ = − 151͑ Ϯ 3͒ J K−1 mol−1
͓21͔
͓22͔
0
Ј
⌬H ͑14͒ = − 573.5͑ Ϯ 0.1͒ kJ mol−1
0
Ј
The error values denote the 95% confidence intervals. ⌬G0 ͑14͒
increases as the temperature increases. ⌬G0 ͑14͒ and ⌬S ͑14͒ are
Ј
0
Ј
Ј
Kyoto University assisted in meeting the publication costs of this article.
constant in this temperature range.
The standard formal free energy change for Reaction 14, ⌬G0
Ј
References
͑14͒, was calculated as follows. The solution equilibrium of Li2O is
described by Reaction 23 and the free energy change is given by Eq.
24, where aLi+ is the activity of the Li+ cation
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͓23͔
͓24͔
⌬G͑23͒ = ⌬G0͑23͒ + RT ln͑aL2i+aO2−
͒
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⌬G0͑23͒ = − RT ln͑aL2i+aO2−
͒
͓25͔
Here we introduce the standard formal free energy, ⌬G0 ͑23͒, de-
Ј
scribed by the following equation
0
0
Ј
⌬G ͑23͒ = ⌬G ͑23͒ + RT ln͑␥O2−
͒
͓26͔
Thus ⌬G0 ͑23͒ is given by the following equation
Ј
2
⌬G ͑23͒ = − RT ln͑␥Li+X2 +XO2−
͒
͓27͔
0
Ј
Li
This is a similar concept as the standard formal potential in Eq. 9
and is calculated from our previous solubility data on Li2O.12 There-