Seawater electrolyte electrochemical cell

Abstract

An improved seawater electrochemical cell with a consumable anode and an oxygen reducing cathode is provided with a reduced distance between anode and cathode surfaces. The reduced distance does not impede the ingress of oxygen dissolved in water and the egress of reaction products from the cell and causes an increase in the volumetric energy and power density of such dissolved oxygen seawater cells.

Claims

1. A galvanic cell employing ambient seawater as electrolyte, the galvanic cell comprising: an oxidizing metal anode electrode selected from the group consisting of magnesium, aluminum, zinc, and mixtures thereof, and an oxygen reducing cathode electrode, wherein the electrodes are flat electrodes arranged parallel to each other such that all electrode surfaces do not contact each other and allow the seawater to flow between the electrodes, and all around the electrodes, such that all electrode surfaces come in contact with the seawater, wherein the electrodes are stacked atop one another to form an assembly and the electrodes are separated apart with spacing means, the spacing means holding the assembly together as a rigid structure open to ingress and egress of the seawater on all peripheral edges, wherein a thickness of the spacing means is such that the electrodes are at most 2.0 cm apart.

2. The galvanic cell of claim 1, wherein the assembly comprises multiples of the oxidizing metal anode electrode and multiples of the oxygen reducing cathode electrode, wherein all oxidizing metal anode electrodes are electrically connected together and all oxygen reducing cathode electrodes are electrically connected together.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is an overall view showing the assembly of anodes and cathodes, stacked and held apart by spacers.

(2) FIG. 2 shows the construction of an anode with plastic frame and lead wire.

(3) FIG. 3 shows the construction of a cathode with plastic frame and lead wire.

(4) FIG. 4 shows the voltage of a dissolved oxygen cell with magnesium anodes and copper screen cathodes while the cell anodes and cathodes were connected together with a resistor in a natural marine environment. The y axis is the voltage of the cell and the x axis is elapsed time in hours.

DRAWINGSREFERENCE NUMERALS

(5) 1 Cathode Assembly 2 Anode Assembly 3 Spacer 4 Cathode Wire 5 Cathode Frame 6 Cathode Screen 7 Anode 8 Anode Frame 9 Anode Wire

FIG. 1First Embodiment

(6) The first embodiment dissolved oxygen cell is shown in FIG. 1. In FIG. 2 a sheet 7 of 0.78 mm thick magnesium alloy AZ61 (6% aluminum and 1% zinc) is cut to 15.2 cm22.8 cm in size. Alternate thicknesses of anode metal can be used, depending upon the desired ampere-hour capacity. A lead wire 9 is connected to sheet 7. The connection is covered with epoxy resin. I contemplate that the epoxy be 3M two part epoxy 2216 (3M Corp, U.S.A.) but other materials compatible with seawater or freshwater are also suitable.

(7) Anode electrode frames 8 were machined of polyvinylchloride (PVC) but other plastic, non-conductive such as but not limited to acrylonitrile butadiene styrene (ABS), and polyacetal may be used to advantage provided they are compatible with magnesium and seawater. The anode and wire assembly was held between two electrode frames 8 which are bonded together with any epoxy resin compatible with seawater and fresh water.

(8) Referring to FIG. 3, a cathode 6 sized 15.2 cm22.8 cm is cut from 40 mesh copper screen. Lead wire 4 is attached to the copper screen. The wire connection was covered with epoxy resin. The cathode assembly 1 was held between two electrode frames 5 which were bonded together with epoxy compatible with seawater and fresh water.

(9) Referring to FIG. 1, electrode spacers 3 were machined from PVC tubing. The length of the spacers 3 determines the spacing between the anode surfaces and the cathode surfaces. I contemplate that the spacing between anode and cathode surfaces should be 0.3-0.8 cm but distances less than 0.2 cm are useable. The cell in FIG. 1 was assembled as follows: Two anode assemblies 2 and three cathode assemblies 1 are used.

(10) A cell described in this embodiment was discharged at a current density of 50 a/cm.sup.2 in artificial seawater (29 PSU) at 5.9 C. at a flow velocity of 3.4 cm/s. In this embodiment the spacer length 3 was such that the spacing between each anode and cathode surface is 0.8 cm. The test results are presented in TABLE 2.

(11) TABLE-US-00003 TABLE 2 Elapsed Time (Hours) Cell Voltage 1 hour 1.114 V 4 hours 1.106 V 8 hours 1.103 V 12 hours 1.101 V 16 hours 1.099 V

Second Embodiment

(12) A cell described in FIG. 1 was discharged at a current density of 50 a/cm.sup.2 in artificial seawater (45.4 ms/cm) at 6.0 C. at a flow velocity of 2.5 cm/s. In this embodiment the spacer length 3 was such that the spacing between each anode and cathode is 1.5 cm. The test results are presented in TABLE 3.

(13) TABLE-US-00004 TABLE 2 Elapsed Time (Hours) Cell Voltage 1 hour 1.178 V 4 hours 1.085 V 8 hours 1.080 V 10 hours 1.079 V 20 hours 1.073 V 30 hours 1.068 V 40 hours 1.065 V

(14) At present I believe that dissolved oxygen cells with spacing between anode and cathode surfaces less than 2 cm operate most efficiently.

Third Embodiment

(15) A cell described in FIG. 1 was placed in a natural marine environment at Monterey Calif. in a protected harbor. In this embodiment the spacer length 3 was such that the spacing between each anode and cathode is 0.8 cm. The cell was electrically discharged through a resistive load such that the average current density was equivalent to 43 A/cm.sup.2. The cell voltage over a 1290 hour discharge period is shown as FIG. 4.

(16) During the discharge the water velocity ranged from 2 to 5 cm/s, the temperature ranged from 13.5 to 17 C., the dissolved oxygen concentration ranged from 4.5 to 7.0 ppm, and the salinity ranged from 33 to 33.3 PSU. Four (4) times during the discharge the cell was removed from the water for inspection. During those times the voltage approached zero volts, as shown in FIG. 4.

(17) For the 1290 hour discharge period the average cell voltage was 1.2077V with a 1 standard deviation of 0.0643V.

Alternate Embodiments

(18) The shape of anodes and cathodes can be varied to accommodate different form factors such as but not limited to round and square. Expanded metal, woven, wool, and welded metals can be used as a cathode surface. Other cathode metals than copper can be used, including stainless steel and titanium. Other cathode screen mesh sizes can be also be used as well as solid foil and perforated foils.

(19) Alternate anode metals are aluminum, zinc, and their alloys. Expanded metal configurations can also be used.

CONCLUSION, RAMIFICATION, AND SCOPE

(20) The reader will see that the embodiments provide dissolved oxygen cells with greatly increased volumetric power density. Contrary to the prior art, a large spacing between anode and cathode is not needed or desired to properly supply dissolved oxygen to the oxygen reducing cathode and to remove the hydroxyl ions which can cause precipitation of calcium carbonate from the seawater or freshwater. I have found that a constricted design operates efficiently, resulting in significantly higher volumetric power density.

(21) While the description of the embodiments contains specificities, these should not be construed as limitations on the scope, but rather as an exemplification of several embodiments thereof. Many other variations are possible such as shape of the electrodes and materials for the electrodes and the electrode frames. Accordingly, the scope should be determined not by the embodiments illustrated, but by the appended claims and other legal equivalents.