The solar thermal electrolytic production of Zn from ZnO was studied in the temperature range of 1275–1500 K in a cavity-solar receiver located at the focal point of a concentrating solar furnace. This study establishes how cathode material, solvent, current levels, and operating temperature influence the electrolytic cell’s performance. For a nominal current density of 0.1 A cm− 2 at temperatures from 1275 to 1425 K, we found that our performance parameters, the back work ratio and substituted-solar fraction, are within 25% and 20% of the ideal values, respectively. This behavior was true whether the cathode was Mo or W and whether the electrolyte was pure cryolite or a 35 mol. % cryolite-CaF2 mixture. When the electrolytes were cryolite-CaF2 mixtures in the temperature range of 1275–1425 K, there was no measurable difference in the performance, but at 1500 K with a MgF2 electrolyte, the performance dropped significantly. We have some evidence that the performance of the cell is better at current densities above 0.1 A cm− 2 when the cathode is Mo as opposed to W. Furthermore, the difference in the performance values can be attributed to higher kinetic over voltages associated with W versus Mo as a cathode. Our data also suggest that kinetic over voltages increase as the operating temperature increases. The experimental evidence suggests the reaction mechanism at the cathode for ZnO in cryolite involves a reaction between Na+  and ZnF2, and the anode reaction involves a reaction between the anions Al2OF62−  and ZnO22− . Both Mo and W worked as cathode materials, but both the Mo and the W became brittle. Pt worked well as an anode without showing any evidence of degradation. Our SiC crucible may have suffered some carbothermic reaction with ZnO at temperatures exceeding 1275 K, with solvent mixtures of cryolite, CaF2, and MgF2.

References

References
1.
Venstrom
,
L.
,
Krueger
,
K.
,
Leonard
,
N.
,
Tomlinson
,
B.
,
Duncan
,
S.
, and
Palumbo
,
R. D.
, 2009, “
Solar Thermal Electrolytic Process for the Production of Zn from ZnO: An Ionic Conductivity Study
,”
J. Sol. Energy Eng.
,
131
, p.
031005
.
2.
Fletcher
,
E. A.
, and
Noring
,
J. E.
, 1983, “
High Temperature Solar Electrothermal Processing—Zinc From Zinc Oxide
,”
Energy
,
8
(
3
), pp.
247
254
.
3.
Fletcher
,
E. A.
,
Macdonald
,
F. J.
, and
Kunnerth
,
D.
, 1985,“
High Temperature Solar Electrothermal Processing II—Zinc From Zinc Oxide
,”
Energy
,
10
(
12
), pp.
1255
1272
.
4.
Palumbo
,
R. D.
, and
Fletcher
,
E. A.
, 1988, “
High Temperature Solar Electrothermal Processing III—Zinc From Zinc Oxide at 1200–1675 K Using a Non-Consumable Anode
,”
Energy
,
13
(
4
), pp.
319
332
.
5.
Parks
,
D. J.
,
Scholl
,
K. L.
, and
Fletcher
,
E. A.
, 1988, “
A Study of the Use of Y2O3 Doped ZrO2 Membranes for Solar Electrothermal and Solar Thermal Separation Technologies
,”
Energy
,
13
, pp.
121
136
.
6.
Krenzke
,
P.
,
Krueger
,
K.
,
Leonard
,
N.
,
Duncan
,
S.
,
Moeller
,
S.
, and
Palumbo
,
R. D.
, 2010, “
A Solar Thermal Electrolytic Reactor for Studying the Production of Metals From Their Oxides
,”
J. Sol. Energy Eng.
,
132
, p.
034501
.
7.
Steinfeld
,
A.
, and
Palumbo
,
R.
, 2002, “
Solar Thermochemical Process Technology
,”
Encyclopaedia of Physical Science and Technology
,
3rd ed.
,
Vol. 15
,
Academic Press
,
New York
.
8.
Levin
,
E. M.
,
Robbins
,
C. R.
, and
McMurdie
,
H. F.
, 1979,
Phase Diagrams for Ceramists
,
The American Ceramic Society
,
Columbus, Ohio
, 4th printing, Figure 1567.
9.
Thonstad
,
J
,
Fellner
,
P.
,
Haarberg
,
G. M.
,
Hives
,
J.
,
Kvande
, and
H.
Sterten
,
A.
, 1982,
Aluminum Electrolysis, Fundamentals of the Hall-Héroult Process
,
3rd ed.,
Aluminum-Verlag, Dusseldorf
.
You do not currently have access to this content.