Chemistry: electrical current producing apparatus – product – and – Fluid active material or two-fluid electrolyte combination... – Active material in solution
Reexamination Certificate
2000-07-28
2002-10-15
Chaney, Carol (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Fluid active material or two-fluid electrolyte combination...
Active material in solution
C429S101000
Reexamination Certificate
active
06465124
ABSTRACT:
CROSS REFERENCE TO OTHER PATENT APPLICATIONS
Not applicable.
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a new electrochemical system based on a magnesium anode and an electrocatalyst of palladium and iridium catalyzed on carbon paper.
(2) Description of the Prior Art
Magnesium seawater batteries have been successfully demonstrated whereby oxygen saturated in the seawater electrolyte is reduced on a catalytic cathode surface opposite a magnesium anode. Early magnesium seawater battery systems are shown in U.S. Pat. No. 3,462,309 to Wilson and U.S. Pat. No. 3,481,790 to Duddy.
Magnesium seawater battery systems generally are highly energy dense systems due to the fact that there is no sodium hydroxide required, greatly reducing the system's weight. However, limited oxygen availability limits specific energies to 220 Watt hr/kg.
Other magnesium-seawater batteries have been developed, all of which include solid electrodes, including silver chloride, cuprous chloride, lead chloride, cuprous iodide, cuprous thiocyanate, and manganese dioxide.
Testing has been accomplished with a magnesium anode in a seawater/hydrogen peroxide electrolyte opposite electrocatalysts of silver foil or planar nickel foil catalyzed with palladium and iridium. All testing was performed in neutral media. The reduction of the hydrogen peroxide took place at the electrocatalytic surface. Cell voltages of 1.1 to 1.2V were observed at an applied current density of 25 mA/cm
2
for these tests with durations up to sixty minutes.
The reduction-oxidation (redox) potentials versus Standard Hydrogen Electrode (SHE) associated with the magnesium-hydrogen peroxide system are:
Anode
Mg → Mg
2+
+ 2e
−
2.37 V
(1)
Cathode
HO
2
+ H
2
O + 2e− → 30H
−
0.88 V
(2)
Cell Reaction
Mg + HO
2
−
+ H
2
O → Mg
2+
+ 30H
−
3.25 V
(3)
Unfortunately, these theoretical open circuit potentials are reduced and the electrochemical performance inhibited by the following parasitic reactions:
Decomposition Reaction
2 H
2
O
2
→ 2 H
2
O + O
2
↑
(4)
Direct Reaction
Mg + HO
2
−
+ H
2
O → Mg
2+
+ 30H
−
(5)
Precipitation Reactions
Mg
2+
+ 20H
−
→ Mg(OH)
2
(s)
(6)
Mg
2+
+ CO
3
−
→ MgCO
3
(s)
(7)
Where (s) stands-for solid precipitate
The precipitation reactions produce solid magnesium hydroxide and magnesium carbonate. The magnesium hydroxide results from the interaction of the magnesium cation with the hydroxyl group produced during the reduction of the catholyte, whereas the magnesium carbonate is a result of the magnesium interacting with the carbonates in seawater.
The system is limited by the production of the precipitates in the electrolyte resulting in electrolytic flow blockages, increased gassing rates and internal pressure rates with decreased cell voltages.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an improved magnesium semi-fuel cell.
It is a further object of the present invention to provide a magnesium semi-fuel cell as above which is a high energy density source for underwater vehicle applications with energy densities approaching 6 to 7 times that of silver-zinc.
The foregoing objects are attained by the semi-fuel cell of the present invention.
In accordance with the present invention, the semi-fuel cell comprises a magnesium anode, a seawater/catholyte electrolyte, preferably containing acid to solubilize solid precipitates, and an electrocatalyst composed of palladium and iridium catalyzed onto carbon paper. The acid added to the electrolyte is preferably selected from the group consisting of sulfuric acid, hydrochloric acid, phosphoric acid, acetic acid, and mixtures thereof.
Other details of the semi-fuel cell of the present invention, as well as other objects and advantages attendant thereto, are set forth in the following detailed description and the accompanying drawings.
REFERENCES:
patent: 5445905 (1995-08-01), Marsh et al.
Bessette Russell R.
Dow Eric G.
Medeiros Maria G.
Chaney Carol
Lall Prithvi C.
McGowan Michael J.
Oglo Michael F.
The United States of America as represented by the Secretary of
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