Patent Description:
This invention generally relates to systems and methods for extracting oxygen from an aqueous ambient environment and, more particularly, to systems and methods of generating an electrical current using the extracted oxygen.

A battery converts the chemical energy of active materials into electrical energy by means of an electrochemical oxidation-reduction reaction. A battery includes an electrolyte, a cathode, and an anode. Water-activated metal batteries (such as Li-H<NUM>O, Na-H<NUM>O, Al-H<NUM>O, and Mg-H<NUM>O galvanic cells)<NUM> oxidize a metal at the anode (negative electrode) and reduce water at a cathode (positive electrode). These systems in general could achieve much higher energy storage densities if there were a way to continuously extract dissolved oxygen from seawater, and to transfer this oxygen to the battery electrolyte to be used as an oxidant in the place of water.

As shown in the above table, seawater-activated Al-H<NUM>O power systems could offer nearly two times their presently-attainable energy density if they were able to reduce the O<NUM> dissolved in seawater, rather than if the Al-H<NUM>O power systems reduced only the seawater itself.

Alternately, a system capable of transferring dissolved O<NUM> from seawater into the electrolyte of a metal-air battery (such as Li-O<NUM>, Na-O<NUM>, Al-O<NUM>, Zn-O<NUM> and Mg-O<NUM> galvanic cells) could allow these batteries to function in ocean environments, whereas they are now restricted to operate only in environments with a ready supply of gaseous oxygen.

Prior batteries that oxidize reactive metals, and reduce the oxygen dissolved in seawater, have operated without self-contained electrolytes i.e. at least one of the components of the electrochemical cell, including at least one of the cathode, anode, and electrolyte are open to seawater and are not separated by any barrier to the surrounding environment. In some prior batteries, the electrochemical cell uses the ocean as the electrolyte. This configuration allows these batteries to reduce the O<NUM> present in seawater at low rates. However, without a contained electrolyte, the batteries suffer from high internal resistances, and are prone to biofouling and calcareous deposits on their positive electrodes. Additionally, such battery systems must operate at very low voltages (often a single cell), as series combinations of cells for higher voltages will result in shunt losses between cells though the shared electrolyte.

The document <CIT> describes an oxygen/CO<NUM> air membrane. In the document <CIT> is proposed a membrane that will selectively remove CO<NUM>(g) from the air so as to prevent carbon dioxide in the air dissolves in the electrolytic solution and the battery from being poisoned.

This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description section. This summary is not intended to identify or exclude key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

The present disclosure is related to systems and methods for extracting oxygen from an aqueous ambient environment and, more particularly, to systems and methods of generating an electrical current using the extracted oxygen. The subject matter of the present invention involves, in some cases, interrelated products, alternative solutions to a particular problem, and/or a plurality of different uses of one or more systems and/or articles.

In one aspect, embodiments relate to a method of generating an electrical current. The method includes extracting oxygen from an aqueous ambient environment surrounding an electrochemical system; transporting the extracted oxygen through a selectively oxygen-permeable membrane to an enclosed electrolyte configured to surround an anode and a cathode in the electrochemical system, wherein the electrolyte is separated from the aqueous ambient environment; transporting the oxygenated electrolyte to the cathode; reducing the oxygen at the cathode; and oxidizing a metal at the anode.

In one embodiment, the electrolyte has a pH above <NUM>.

In one embodiment, the method further includes extracting metal-hydroxide waste from the electrolyte.

In one embodiment, the membrane is salt-selective.

In one embodiment, the anode comprises at least one of Li, Mg, Na, Zn, and Al.

In one embodiment, the system comprises a plurality of selectively oxygen-permeable membranes.

In one embodiment, the aqueous ambient environment comprises seawater.

In one embodiment, a pump actively transports the oxygenated electrolyte to the cathode.

In one embodiment, the oxygenated electrolyte is passively transported to the cathode.

It is not part of the invention a multi-cell metal-dissolved oxygen electrochemical device. The device includes a metal anode; a cathode; an enclosed electrolyte configured to surround the cathode and the anode, wherein the electrolyte is separated from an aqueous ambient environment surrounding the electrochemical device; and a selectively oxygen-permeable membrane configured to extract oxygen from the aqueous ambient environment; wherein the electrochemical device is configured to: transport the oxygen to the electrolyte; transport the oxygenated electrolyte to the cathode; reduce the oxygen at the cathode; oxidize a metal at the metal anode; and generate an electrical current.

In one embodiment, the device further includes a plurality of selectively oxygen-permeable membranes.

In one embodiment, the aqueous ambient environment includes seawater.

In one embodiment, the device includes a pump configured to actively transport the oxygenated electrolyte to the cathode.

In one embodiment, the cells are arranged electrically in series.

In one embodiment, the cells are arranged fluidically in parallel.

In yet another aspect, embodiments relate to a multi-cell electrochemical device. The device includes a metal anode; a cathode; an enclosed electrolyte configured to surround the cathode and the anode, wherein: the electrolyte is separated from an aqueous ambient environment surrounding the electrochemical device, and the electrolyte comprises an anolyte and a catholyte; a selectively oxygen-permeable membrane configured to extract oxygen from the aqueous ambient environment; and an anolyte flow loop separate from a catholyte flow loop, wherein the electrochemical device is configured to: transport the oxygen to the catholyte; transport the oxygenated catholyte to the cathode; reduce the oxygen at the cathode; oxidize a metal at the metal anode; and generate an electrical current.

Other advantages and novel features of the present invention will become apparent from the following detailed description of various non-limiting embodiments of the invention when considered in conjunction with the accompanying figures.

Non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying figures, which are schematic and are not intended to be drawn to scale. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the invention shown where illustration is not necessary to allow those of ordinary skill in the art to understand the invention. In the figures:.

Various embodiments are described more fully below with reference to the accompanying drawings, which form a part hereof, and which show specific exemplary embodiments. However, the concepts of the present disclosure may be implemented in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided as part of a thorough and complete disclosure, to fully convey the scope of the concepts, techniques and implementations of the present disclosure to those skilled in the art. Embodiments may be practiced as methods, systems or devices. Accordingly, embodiments may take the form of a hardware implementation, an entirely software implementation or an implementation combining software and hardware aspects. The following detailed description is, therefore, not to be taken in a limiting sense.

Reference in the specification to "one embodiment" or to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiments is included in at least one example implementation or technique in accordance with the present disclosure.

In addition, the language used in the specification has been principally selected for readability and instructional purposes and may not have been selected to delineate or circumscribe the disclosed subject matter. Accordingly, the present disclosure is intended to be illustrative, and not limiting, of the scope of the concepts discussed herein.

Embodiments described herein scavenge O<NUM> gas dissolved in an aqueous environment, such as seawater, and supply the O<NUM> into the battery electrolyte for use as an oxidizing agent. Combined with modification to the battery electrolyte and operating parameters, the inclusion of this scavenging subsystem significantly increases the energy density of metal-dissolved oxygen batteries in some embodiments. Furthermore, in some embodiments, this scavenging subsystem may allow metal-air batteries to operate in underwater environments.

Some embodiments include a set of artificial 'gills' that comprise a manifold or array of O<NUM> permeable membranes. This 'gill' subunit may be placed in the internal flow of electrolyte in a battery with a reactive metal (Li, Na, Mg, Zn, Al, or alloys or any combination thereof) anode(s) in some embodiments. In some embodiments, the electrochemical cell may use an anode comprising a reactive metal, including metals selected from Groups 1A and 2A of the Periodic Table, alloys, or any combinations thereof. A parallel flow, cross-flow, or counterflow arrangement between an aqueous ambient environment on one side of the membranes, and the electrolyte of the electrochemical cell on the other side of the membranes, may facilitate the transport of dissolved O<NUM> from seawater into the battery electrolyte without allowing significant transport of dissolved species in either direction across the membrane. In some embodiments, a counterflow or cross-flow arrangement between an aqueous environment on one side of the membranes and the electrolyte of the electrochemical cell on the other side of the membranes may facilitate a larger transport of dissolved O<NUM> into the battery electrolyte over a set period of time than a parallel flow. Once in the battery electrolyte, the oxygen species may be carried along an electrolyte flow loop to the cathode(s) of the battery, where they are reduced.

In some embodiments, the membranes may be arranged in a high surface area configuration that facilitates the maximum throughput of oxygen, much like the lamellae in the gills of a shark. In some embodiments, once the system is deployed, the gill subunit may expand, unfurl or unfold into the sea or other aqueous environment in order to maximize the mass transfer surface area. The membranes may be arranged in tubes or channels and may enable a crossflow or counterflow arrangement between the battery electrolyte and the aqueous ambient environment in some embodiments. In some embodiments, the battery electrolyte may comprise a separate catholyte and anolyte. In some embodiments, the membranes may enable a crossflow or counterflow arrangement between the battery catholyte and the aqueous ambient environment. The membranes may be nonpolar small-pore membranes or polymer composite membranes in some embodiments. The membranes may comprise silicone rubber, polytetrafluoroethylene or other fluoropolymers (with or without sulfonyl group substitutions), an alkylcellulose, an acetylcellulose, polysulfone, polyamide, polypropylene, polyethylene, polyethersulfone, polybenzimidazolone, or a combination thereof. In some embodiments, the membranes may comprise zeolites, clays, or a combination thereof.

<FIG> illustrates an aluminum-based battery <NUM> in accordance with one embodiment. In some embodiments, the battery <NUM> may use a selectively oxygen-permeable membrane <NUM> to extract O<NUM> <NUM> from the aqueous ambient environment and allow the O<NUM> to pass into the electrolyte <NUM>. In some embodiments, this selectively oxygen-permeable membrane <NUM> may be a gill subunit and may use a plurality of filtration layers to extract O<NUM> <NUM> from the ambient environment. This 'gill' subunit, an embodiment of which is shown in <FIG>, may be placed in the internal flow of electrolyte <NUM> on the battery <NUM>. In some embodiments, other reactive metals (such as Li, Na, Mg, Zn, Al, or any combination of metals) thereof may be used as anodes in the battery <NUM>. In some anodes, In, Ga, Sn, or Mn may be present in concentrations of less than <NUM>% wt. In some embodiments, a lithium-aluminum alloy wherein the lithium comprises more than <NUM>% wt may be used as anodes in the battery <NUM>.

In some embodiments, the electrolyte <NUM> containing the extracted O<NUM> may be transported to the at least one electrochemical cell <NUM>. In some embodiments, the electrolyte <NUM> may be transported to a plurality of electrochemical cells <NUM>. In some embodiments, the electrolyte <NUM> within the system may be aqueous and alkaline. In some embodiments, the electrolyte may contain additional agents to facilitate the transport of O<NUM>, such as an emulsion of perfluorocarbon liquids, such as perfluorooctyl bromide, perfluorodecyl bromide, other perfluoroalkyl bromides, <NUM>,<NUM>,<NUM>-perfluoro-<NUM>-hexene, perfluoro(methylcyclohexane), or redox shuttles containing the Fe<NUM>+/<NUM>+, Cr<NUM>+/<NUM>+, Co<NUM>+/<NUM>+, V<NUM>+/<NUM>+, V<NUM>+/<NUM>+, or other redox centers, such as Fe(II) protoporphyrin IX, hemoglobin, or substituted viologen or quinone species. In some embodiments, the electrolyte may also contain additional agents to raise the pH of the electrolyte, including hydroxide compounds such as potassium hydroxide or sodium hydroxide. In other embodiments, the battery <NUM> may use barriers or selective ion exchange resins to filter salts, such as magnesium and calcium salts, from the aqueous ambient environment to preserve the alkalinity of the electrolyte. In some embodiments, the electrolyte may be sea water. In embodiments, the electrolyte may have a high pH. In embodiments, the electrolyte may be non-aqueous.

In embodiments, the electrolyte <NUM> may be transported to the at least one electrochemical cell <NUM>. At the cell stack, two half-reactions may occur in some embodiments. At the anode, the half reaction may be:.

wherein M represents a metal, such as aluminum in some embodiments. The number of hydroxide molecules used at the anode oxidation process per cycle is dependent upon the type of metal used. For a generalized metal M, the half reaction at the anode may be:.

and a different amount of energy may be produced in the oxidation process. The anode gives up electrons to the external circuit.

In embodiments, the cathode half reaction may be:.

<NUM>/<NUM> O<NUM> + <NUM>/<NUM><NUM>O + 3e- → 3OH-.

wherein the H<NUM>O and O<NUM> are initially present in the electrolyte <NUM> and the electrons originate from the half reaction at the anode. In embodiments, the O<NUM> is co-reduced with H<NUM>O at the cathode. In embodiments, the ratio rate of reduction for H<NUM>O:O<NUM> is <NUM>: <NUM>.

The hydroxide may react with the anode at the at least one electrochemical cell <NUM> to produce waste in the form of a metal hydroxide, such as Al(OH)<NUM>. In some embodiments, the O<NUM> in the electrolyte may react with the water at the cathode and the electrons produced at the anode of the at least one electrochemical cell <NUM> to produce hydroxide ions and an electrical current.

In embodiments, metal-hydroxide waste may be removed from the system through a waste removal system, such as a filter <NUM>. In some embodiments, the filter is a semi-permeable membrane or a porous membrane. In some embodiments, the filter is an ultrafiltration membrane or a nanofiltration membrane. In another embodiment, waste is removed in a settling chamber. In some embodiments, the waste is removed in precipitate form. In some embodiments, the waste is removed in crystallized form.

The waste removal system <NUM> can be placed in the internal flow of the electrolyte <NUM>. In some embodiments, the waste removal system <NUM> can be placed between the selectively oxygen-permeable membrane <NUM> and the at least one electrochemical cell <NUM>. In some embodiments, the electrolyte <NUM> may flow in a direction such that the electrolyte <NUM> may first pass by the selectively oxygen-permeable membrane <NUM> and then pass the waste removal system <NUM> before passing through the at least one electrochemical cell <NUM> of the battery <NUM>. In some embodiments, the electrolyte <NUM> may flow in a direction such that the electrolyte <NUM> may first pass by the selectively oxygen-permeable membrane <NUM> and then pass through the at least one electrochemical cell <NUM> before passing through the waste removal system <NUM> of the battery <NUM>.

In some embodiments, the electrolyte <NUM> may be contained within the battery <NUM>. In embodiments, the selectively oxygen-permeable membrane <NUM> may be a selective membrane permeable to O<NUM> and may add additional O<NUM> to the electrolyte <NUM>. To add O<NUM> to the electrolyte <NUM>, embodiments may use an active counterflow O<NUM> exchange, as shown in <FIG> below. In embodiments, the only loss from the electrolyte <NUM> may be the filtered waste removed. In embodiments, both the waste removal <NUM> and the selectively oxygen-permeable membrane <NUM> may be equipped with at least one semi-permeable membrane. In embodiments, the membrane at the selectively oxygen-permeable membrane <NUM> may also be salt-selective, in that the selectively oxygen-permeable membrane <NUM> would not allow salts from the aqueous ambient environment to enter the electrolyte <NUM>. In some embodiments, the membrane <NUM> may also be configured to prevent salt in the electrolyte <NUM> from leaving the electrolyte <NUM>.

In some embodiments, the electrolyte <NUM> may contain agents to boost O<NUM> solubility. In some embodiments, the electrolyte <NUM> may contain perfluorocarbons, such as perfluorooctyl bromide, perfluorodecyl bromide, other perfluoroalkyl bromides, <NUM>,<NUM>,<NUM>-perfluoro-<NUM>-hexene, perfluoro(methylcyclohexane), or redox shuttles comprising Fe<NUM>+/<NUM>+, Cr<NUM>+/<NUM>+, Co<NUM>+/<NUM>+, V<NUM>+/<NUM>+, V<NUM>+/<NUM>+, or other redox centers, such as Fe(II) protoporphyrin IX, hemoglobin, or substituted viologen or quinone species to boost O<NUM> solubility.

In embodiments, the electrolyte <NUM> may be transported actively through the battery <NUM>. Flow over the membranes and filters <NUM>, <NUM> of both the electrolyte <NUM> (internal to the system) and the ambient aqueous environment external to the battery <NUM> may be pumped by active mechanical means <NUM>. In some embodiments, the active mechanical means <NUM> may be a pump. In some embodiments, the active mechanical means <NUM> may comprise at least one of a centrifugal, gear, lobe, diaphragm, peristaltic, or rotary vane pump. The electrolyte <NUM> may flow from the counterflow exchange at the gill subunit <NUM>. In embodiments, the electrolyte <NUM> may also flow under the influence of ocean currents or wave motion. In some embodiments, the electrolyte <NUM> may flow with the assistance of one-way valves, as shown in <FIG>.

To increase the energy density of a battery <NUM>, the battery <NUM> may reduce the extracted O<NUM> from the aqueous ambient environment rather than only the H<NUM>O itself. In some embodiments, reducing the extracted O<NUM> may offer approximately twice the attainable energy density of a battery reducing solely H<NUM>O. In some embodiments, the battery <NUM> may switch to a system reducing only H<NUM>O instead of both H<NUM>O and O<NUM>. This change may produce a higher power density for a short period of time in some embodiments, as a tradeoff for the higher energy density offered by the extracted O<NUM>. In embodiments, reducing only H<NUM>O may be referred to as a "water breathing metabolism" because the battery <NUM> only reduces water. In embodiments, the selectively oxygen-permeable membrane <NUM> may not continue to actively supply O<NUM> to the electrolyte <NUM> when the battery <NUM> is set on this high-power density mode. This switch may occur if, for example, the load attached to the battery <NUM> requires more power than the membrane <NUM> can provide by filtering O<NUM> into the electrolyte <NUM>.

<FIG> illustrates a schematic diagram of a metal-based battery system <NUM> with a gill subunit <NUM> having a plurality of electrochemical cells <NUM> wherein each chemical cell is arranged electrically in series and fluidically in parallel, in accordance with one embodiment. In some embodiments, the gill subunit <NUM> may comprise a selectively oxygen-permeable membrane. In some embodiments, the battery system <NUM> may use a selectively oxygen-permeable membrane <NUM> to extract O<NUM> <NUM> from the aqueous ambient environment <NUM>. In some embodiments, the aqueous ambient environment <NUM> is at least one of brackish water, salt water, sea water, or fresh water. In some embodiments, the selectively oxygen-permeable membrane <NUM> may be a gill subunit and may use a plurality of filtration layers to extract O<NUM> <NUM> from the ambient environment <NUM>.

In some embodiments, the electrolyte <NUM> containing the extracted O<NUM> may be transported to at least one electrochemical cell or a plurality of electrochemical cells <NUM>. In embodiments, waste may be removed from the system through a filter <NUM>. The waste may be metal-hydroxide waste. In some embodiments, the filter is a semi-permeable membrane or a porous membrane. In some embodiments, the waste is removed in precipitate form. In some embodiments, the waste is removed in crystallized form.

The waste removal system <NUM> can be placed in the internal flow of the electrolyte <NUM>. In some embodiments, the waste removal system <NUM> can be placed between the selectively oxygen-permeable membrane <NUM> and the electrochemical cells <NUM>. In some embodiments, the electrolyte <NUM> may flow in a direction such that the electrolyte <NUM> may first pass by the selectively oxygen-permeable membrane <NUM> and then pass the waste removal system <NUM> before passing through the electrochemical cells <NUM> of the system <NUM>. In some embodiments, the electrolyte <NUM> may flow in a direction such that the electrolyte <NUM> may first pass through the selectively oxygen-permeable membrane <NUM> and then pass through the electrochemical cells <NUM> before passing through the waste removal system <NUM> of the battery system <NUM>.

In some embodiments, the electrochemical cells <NUM> are arranged electrically in series and fluidically in parallel. The cells may be arranged such that the anode <NUM> of one cell is closer in proximity to the cathode <NUM> of the next cell than the anode <NUM> of the next cell. In some embodiments, a divider <NUM> may be placed between the individual cells <NUM>. Although <FIG> shows a plurality of electrochemical cells <NUM> used in the battery system <NUM>, embodiments may use only one electrochemical cell. The number of electrochemical cells <NUM> represented in the figure should not be interpreted as a maximum or minimum number of electrochemical cells <NUM> in other embodiments.

In some embodiments, the divider <NUM> may comprise polytetrafluoroethylene, nylon, polypropylene, polyamide, polyethylene, polyether ether ketone, polyethylene terephthalate, silicone, acrylonitrile butadiene styrene, polyvinyl chloride, polyvinyl difluoride, ethylene propylene diene monomer rubber, acrylonitrile butadiene rubber, or any combination thereof. The divider <NUM> may comprise a polymer chemically compatible with an alkaline electrolyte. In some embodiments, the divider <NUM> may comprise a material capable of being ultrasonically welded together with a cell housing (shown in <FIG>).

In embodiments, the electrochemical cells <NUM> may be connected such that each cell has electrolyte <NUM> flowing around both the anode <NUM> and the cathode <NUM>. In embodiments, the electrochemical cells <NUM> are connected fluidically in parallel, such that the electrolyte <NUM> may freely flow between the electrochemical cells <NUM> through the electrolyte circulation cycle. In embodiments, no electrochemical cell <NUM> may impede the flow of the electrolyte <NUM>.

In embodiments, the reactive metal anode <NUM> may comprise Li, Na, Mg, Zn, Al, or any combination thereof. In some anodes, In, Ga, Sn, or Mn may be present in concentrations of less than <NUM> wt. In some embodiments, a lithium-aluminum alloy wherein the lithium comprises more than <NUM>% wt may be used as anodes in the battery <NUM>. In some embodiments, the cathode <NUM> may comprise metallic oxides, such as manganese oxide, chromium oxide, copper oxide, or any combination thereof. In some embodiments, the cathode <NUM> may comprise Pt, Ir, Pd, Ni, Mo, Co, Fe, N, C, or any combinations thereof. In some embodiments, high specific surface area substrates of Ni, C, or stainless steel may be used as conductive catalyst supports.

<FIG> is a schematic diagram of an aluminum-based water-activated battery <NUM> with a gill subunit <NUM> and separate anolyte <NUM> and catholyte <NUM> flow loops, in accordance with one embodiment. In some embodiments, the battery system <NUM> may use a selectively oxygen-permeable membrane <NUM> to extract O<NUM> <NUM> from the aqueous ambient environment <NUM>. In some embodiments, the aqueous ambient environment <NUM> is at least one of brackish water, salt water, sea water, or fresh water. In some embodiments, the selectively oxygen-permeable membrane <NUM> may be a gill subunit and may use a plurality of filtration layers to extract O<NUM> <NUM> from the ambient environment <NUM>.

In some embodiments, the catholyte <NUM> may contain agents to boost O<NUM> solubility. In some embodiments, the catholyte <NUM> may contain perfluorocarbons, such as perfluorooctyl bromide, perfluorodecyl bromide, other perfluoroalkyl bromides, <NUM>,<NUM>,<NUM>-perfluoro-<NUM>-hexene, perfluoro(methylcyclohexane)), or redox shuttles comprising Fe<NUM>+/<NUM>+, Cr<NUM>+/<NUM>+, Co<NUM>+/<NUM>+, V<NUM>+/<NUM>+, V<NUM>+/<NUM>+, or other redox centers, such as Fe(II) protoporphyrin IX, hemoglobin, or substituted viologen or quinone species to boost O<NUM> solubility.

In some embodiments, the catholyte <NUM> containing the extracted O<NUM> may be transported to the cathode <NUM>, such that the cathode <NUM> is exposed to an oxygen-rich catholyte <NUM>. In some embodiments, the catholyte <NUM> is separated from the anolyte <NUM> in the system <NUM> by an ion-conducting membrane <NUM>. In some embodiments, the membrane <NUM> may comprise a ceramic material or glassy material, such as alumina, titania, zirconia oxides, silicon carbide, or any combination thereof. In some embodiments, the membrane <NUM> may comprise LISICON (lithium super ionic conductor) or NASICON (sodium (Na) super ionic conductor. The membrane <NUM> may be ion-selective and may only allow ions to pass from the catholyte <NUM> to the anolyte <NUM>. In other embodiments, the membrane <NUM> may only allow ions to pass from the anolyte <NUM> to the catholyte. For example, in some embodiments, the half reaction at the cathode <NUM> may be <NUM>/<NUM> O<NUM> + <NUM>/<NUM><NUM>O + 3e- → 3OH-. In some embodiments, the half reaction at the anode <NUM> may be M + 3OH- → M(OH)<NUM> + 3e-. The membrane <NUM> may be configured to conduct the hydroxide ions from the catholyte <NUM> to the anolyte <NUM> to facilitate the anode half-reaction. In some embodiments, the membrane <NUM> may also be salt-selective to reduce or prevent corrosion of the anode <NUM>.

In some embodiments, the cathode <NUM>, anode <NUM>, catholyte <NUM>, and anolyte <NUM> may all be chosen for their compatibility. In some embodiments, the anolyte <NUM> may be a fluorocarbon solvent or dimethyl carbonate. In some embodiments, the catholyte <NUM> may be non-aqueous, such as dimethyl sulfoxide, dimethyl carbonate, THF, or an ionic liquid. In some embodiments, a dimethyl carbonate anolyte <NUM> may be used with a Li anode <NUM> because the dimethyl carbonate anolyte <NUM> may be configured to transport Li+ ions but may not be configured to transport sufficient OH- ions.

In some embodiments, both the catholyte <NUM> and the anolyte <NUM> may be water-based. The battery system <NUM> may be assembled with powdered substances contained in the anolyte <NUM> and/or catholyte <NUM> flow loops. The anolyte <NUM> and/or catholyte <NUM> flow loops may be connected to fill ports <NUM>, <NUM>. The fill ports <NUM>, <NUM> may also contain semi-permeable membranes. If the system <NUM> is submerged in an ambient aqueous environment <NUM>, the fill ports <NUM>, <NUM> may fill the catholyte <NUM> and the anolyte <NUM> flow loops with water. The powders contained in the flow loops may then mix with the water to form the catholyte <NUM> and anolyte <NUM>.

In embodiments, waste may be removed <NUM> from the system <NUM> through a filter to the ambient environment <NUM>. The waste may be metal-hydroxide waste. In some embodiments, the filter is a semi-permeable membrane or porous membrane. In some embodiments, the waste may be removed in precipitate form. In some embodiments, the waste may be removed in crystallized form. Some embodiments may contain a plurality of waste removal systems <NUM>, such that waste in the catholyte <NUM> that cannot be transported across the membrane <NUM> may be removed from the system <NUM>. In some embodiments, waste in the catholyte <NUM> may be removed through the gill subunit <NUM>.

<FIG> is a schematic diagram of a lithium-based water-activated battery system <NUM> with a separate gill subunit <NUM>, in accordance with one embodiment. In some embodiments, the separate gill subunit <NUM> may include a selectively oxygen-permeable membrane. In some embodiments, the battery system <NUM> may have separate anolyte <NUM> and catholyte <NUM> flow loops, separated by an ion-conducting membrane <NUM>. In some embodiments, the battery system <NUM> may use a selectively oxygen-permeable membrane <NUM> to extract O<NUM> <NUM> from the aqueous ambient environment <NUM>. In some embodiments, the aqueous ambient environment <NUM> is at least one of brackish water, salt water, sea water, or fresh water. In some embodiments, the selectively oxygen-permeable membrane <NUM> may be a gill subunit and may use a plurality of filtration layers to extract O<NUM> <NUM> from the ambient environment <NUM>. In some embodiments, the membrane <NUM> may use counterflow to extract O<NUM> <NUM> from the ambient environment <NUM>.

In some embodiments, Li is used as the anode <NUM>. In some embodiments, the anode <NUM> may comprise Al, Li, Na, Mg. Zn, or any combination thereof. The cathode <NUM> may comprise materials stable at potentials up to <NUM> V with respect to a reversible hydrogen electrode (RHE). The cathode <NUM> may also comprise materials that are catalytically active for oxygen reduction reactions, hydrogen evolution reactions, or both oxygen reduction reactions and hydrogen evolution reactions in some embodiments. In some embodiments, the cathode <NUM> may comprise Pt, Ir, Pd, Ni, Mo, Co, Fe, N, C, or any combinations thereof. In some embodiments, high specific surface area substrates of Ni, C, or stainless steel may be used as conductive catalyst supports. In embodiments where the anode <NUM> comprises Li, the half-reaction at the anode <NUM> may produce lithium ions. The membrane <NUM> may be an ion-conducting membrane and may transport the lithium ions from the anolyte <NUM> to the catholyte <NUM>. In some embodiments, the membrane <NUM> may be semi-permeable and may be salt-selective.

In embodiments, waste may be removed from the battery system <NUM> through a filter <NUM> to the ambient environment <NUM>. The waste may comprise metal hydroxide. In some embodiments, the filter <NUM> is a semi-permeable membrane or a porous membrane. In some embodiments, the waste may be removed in precipitate form. In some embodiments, the waste may be removed in crystallized form. Some embodiments may contain a plurality of waste removal systems <NUM>, such that waste in the catholyte <NUM> that cannot be transported across the membrane <NUM> may be removed from the system <NUM>. In some embodiments, waste in the catholyte <NUM> may be removed through the gill subunit <NUM>. In some embodiments, a waste removal system <NUM> may be present to filter the anolyte <NUM>.

<FIG> is a schematic diagram of the gill subunit <NUM>, in accordance with one embodiment. In some embodiments, the gill subunit <NUM> may contain a plurality of O<NUM> permeable membranes <NUM>. The O<NUM>-rich seawater <NUM> may pass through or over the O<NUM>-permeable membranes <NUM>. In the process, the O<NUM>-permeable membranes <NUM> may extract O<NUM> from the O<NUM>-rich seawater <NUM> and the extracted O<NUM> may enrich the electrolyte <NUM> to form an O<NUM>-rich electrolyte <NUM>. In some embodiments, the gill subunit <NUM> only enriches a catholyte with O<NUM>. The gill subunit <NUM> may extract O<NUM> through counterflow. In some embodiments, the gill subunit <NUM> may extract O<NUM> from fresh water, brackish water, or another ambient aqueous environment.

In some embodiments, a battery having the gill subunit <NUM> may be assembled with the membranes <NUM> in a folded or otherwise collapsed configuration. Upon submersion of the gill subunit <NUM> in an aqueous ambient environment, the gill subunit <NUM> may expand. In embodiments, the gill subunit <NUM> may expand to up to <NUM> times its initial volume to facilitate exchange of O<NUM> between the battery electrolyte and the aqueous ambient environment. In some embodiments, the gill subunit <NUM> may expand up to <NUM> times its initial volume. In some embodiments, the gill subunit <NUM> may expand up to <NUM>,<NUM> times its initial volume.

<FIG> is a schematic diagram of an individual cell <NUM> in a pre-deployed configuration, in accordance with one embodiment. <FIG> is a schematic diagram of an individual cell <NUM> in a deployed configuration, in accordance with one embodiment. In some embodiments, the cell <NUM> has at least one cathode <NUM>. In some embodiments, the cell <NUM> has two cathodes <NUM><NUM>, <NUM><NUM>. The cell <NUM> may have an anode <NUM> placed between the cathodes <NUM> and an outer housing <NUM> to contain the electrolyte <NUM>. The electrolyte <NUM> may also be encased in an inner housing made of an insulating material, such as plastic. In other embodiments, the inner housing further comprises a semi-permeable membrane <NUM> to allow O<NUM> to permeate through the electrolyte <NUM> and between cells <NUM>.

<FIG> is a cell stack <NUM> in a pre-deployed configuration, in accordance with one embodiment. 6D is a cell stack <NUM> in a deployed configuration, in accordance with one embodiment. The individual cells <NUM> may be arranged in a cell stack <NUM>. In some embodiments, the cells <NUM> may have semi-permeable membranes <NUM> to allow O<NUM> to pass from the ambient aqueous environment to the electrolyte <NUM>. In some embodiments, the O<NUM> is transported passively from the environment to the electrolyte. The membrane <NUM> may also be salt-selective and may not allow salt to pass from the ambient environment to the electrolyte <NUM>.

In some embodiments, the cell stack <NUM> may be used as a static cell configuration and may allow O<NUM> to be transported passively, such as by wave movement, into the electrolyte <NUM>.

In some embodiments, the cell stack <NUM> may begin in a pre-deployed configuration such that any significant gaps between the anode <NUM> and the cathode(s) <NUM> are initially removed. In some embodiments, the cell stack <NUM> may expand during a cell startup phase or may, alternatively, expand during cell operation. The pre-deployed configuration shown in <FIG> may be several times less voluminous than the deployed configuration shown in FIG. 6D and, thus, may save space upon transport of the cell stack <NUM>.

<FIG> is a schematic diagram of a counterflow gill subunit <NUM>, in accordance with one embodiment. In some embodiments, the gill subunit <NUM> has an inlet <NUM> for fluid to enter and pass through the subunit <NUM>. In embodiments, this fluid may be the ambient aqueous environment and may comprise ocean water, seawater, brackish water, or fresh water. In some embodiments, the counterflow gill subunit <NUM> may have an outlet <NUM> for the fluid to exit from the subunit <NUM>. When the fluid passes through the gill subunit <NUM>, the fluid may pass around at least one membrane tube <NUM>. In embodiments, the membrane tube <NUM> may contain electrolyte. The electrolyte may flow in a direction <NUM> through the inlet <NUM>, through the tubes <NUM>, and towards the outlet <NUM>.

In some embodiments, the membrane tubes <NUM> may be semi-permeable and may be permeable to O<NUM>. The membrane tubes may not be permeable to salt in some embodiments. The membrane tubes <NUM> may facilitate extraction of O<NUM> from the fluid entering from the inlet <NUM> and may enrich the electrolyte flowing through the membrane tube <NUM> with O<NUM>. The enriched electrolyte may then flow from outlet <NUM> towards a cathode. In some embodiments, the fluid depleted from O<NUM> may then pass through the outlet <NUM>.

<FIG> is a schematic diagram of a passive-flow gill subunit <NUM>, in accordance with one embodiment. In some embodiments, the O<NUM>-rich aqueous ambient environment <NUM> may surround the subunit <NUM>. Through passive movement of the ambient aqueous environment <NUM>, such as wave movement, the ambient environment <NUM> may contact the membrane <NUM> of the subunit <NUM>. In some embodiments, the membrane <NUM> may be a selectively O<NUM>-permeable membrane and may allow O<NUM> to pass through the membrane <NUM> and into the electrolyte <NUM>. In some embodiments, the electrolyte <NUM> may then be transported to the electrochemical cells <NUM>. In some embodiments, the membrane <NUM> is flexible, such that flexible filaments <NUM> surround the electrochemical cells <NUM>. In some embodiments, the flexibility of the membrane <NUM> enables the one-way valves <NUM>, <NUM> to convert movement of the ambient environment <NUM>, including ocean currents, waves, and hydroelastic flutter, into circulation of the electrolyte <NUM>.

In some embodiments, the O<NUM>-rich electrolyte <NUM> may be transported to the electrochemical cells <NUM>. The electrochemical cells may use the O<NUM> to generate power. In some embodiments, once the electrochemical cells <NUM> generate power, the cells <NUM> may deplete the electrolyte <NUM> of O<NUM>. In some embodiments, the depleted electrolyte <NUM> may then be transported to the membrane filaments <NUM> to be replenished with O<NUM> from the ambient environment <NUM>. In some embodiments, the depleted electrolyte <NUM> may be separated from the O<NUM>-rich electrolyte by a membrane <NUM> or other divider. In some embodiments, the filaments <NUM> may expand in contact with an aqueous ambient environment <NUM>. In some embodiments, the membrane <NUM> may be impermeable to salt.

One-way valve <NUM> may help prevent the oxygen-enriched electrolyte <NUM> from flowing away from the electrochemical cells <NUM>. The one-way valve <NUM> may enable a forward ocean current to propel the oxygen-enriched electrolyte <NUM> to flow towards the electrochemical cells <NUM>, and the valve <NUM> may stop a backward flowing ocean current from propelling the oxygen-enriched electrolyte away from the electrochemical cells in some embodiments. Similarly, one-way valve <NUM> may help prevent the oxygen-depleted electrolyte <NUM> from flowing towards the electrochemical cells <NUM>. One-way valve <NUM> may enable a backwards ocean current to propel the oxygen-depleted electrolyte <NUM> away from the electrochemical cells <NUM>, and the valve <NUM> may stop a forward flowing ocean current from propelling the oxygen-depleted electrolyte <NUM> towards the electrochemical cells <NUM>.

<FIG> is a schematic diagram of a ram ventilation gill subunit <NUM>, in accordance with one embodiment. Ram ventilation is used by some fish, such that water flows through the mouth of the fish and across the gills when the fish is swimming forward. Similarly, during forward propulsion of a unit <NUM> comprising a gill subunit <NUM> and electrochemical cells <NUM>, the aqueous environment <NUM> may flow through the gill subunit <NUM>. In some embodiments, the O<NUM>-rich aqueous environment <NUM><NUM> may enter the gill subunit <NUM> and may leave as an O<NUM>-depleted fluid <NUM><NUM>, <NUM><NUM> through different sides of the gill subunit <NUM>.

In some embodiments, the gill subunit <NUM> may comprise a semi-permeable membrane <NUM>, wherein the membrane is permeable to O<NUM>. In some embodiments, the membrane <NUM> may be selectively impermeable to salt. When the unit <NUM> moves forward, the aqueous environment <NUM> may pass through the gill subunit <NUM>. In some embodiments, O<NUM> from the ambient environment <NUM> may pass through the membrane <NUM> and enrich the electrolyte. The enriched electrolyte <NUM> may then be propelled to the electrochemical cells <NUM> to supply the cells with O<NUM>.

In some embodiments, O<NUM> may flow through the membrane <NUM> at a rate of at least <NUM> ng/cm<NUM>/min. In some embodiments, O<NUM> may flow through the membrane <NUM> at a rate of at least <NUM> ng/cm<NUM>/min. In some embodiments, O<NUM> may flow through the membrane <NUM> at a rate of at least <NUM> ng/cm<NUM>/min. In some embodiments, O<NUM> may flow through the membrane <NUM> at a rate of at least <NUM>µg/cm<NUM>/min. In some embodiments, O<NUM> may flow through the membrane <NUM> at a rate of at least <NUM>µg/cm<NUM>/min. In some embodiments, O<NUM> may flow through the membrane <NUM> at a rate of at least <NUM>µg/cm<NUM>/min. In some embodiments, O<NUM> may flow through the membrane <NUM> at a rate of at least <NUM>µg/cm<NUM>/min. In some embodiments, O<NUM> may flow through the membrane <NUM> at a rate of at least <NUM>µg/cm<NUM>/min. In some embodiments, O<NUM> may flow through the membrane <NUM> at a rate of at least <NUM>/cm<NUM>/min. In some embodiments, O<NUM> may flow through the membrane <NUM> at a rate of at most <NUM> ng/cm<NUM>/min. In some embodiments, O<NUM> may flow through the membrane <NUM> at a rate of at most <NUM> ng/cm<NUM>/min. In some embodiments, O<NUM> may flow through the membrane <NUM> at a rate of at most <NUM> ng/cm<NUM>/min. In some embodiments, O<NUM> may flow through the membrane <NUM> at a rate of at most <NUM>µg/cm<NUM>/min. In some embodiments, O<NUM> may flow through the membrane <NUM> at a rate of at most <NUM>µg/cm<NUM>/min. In some embodiments, O<NUM> may flow through the membrane <NUM> at a rate of at most <NUM>µg/cm<NUM>/min. In some embodiments, O<NUM> may flow through the membrane <NUM> at a rate of at most <NUM>µg/cm<NUM>/min. In some embodiments, O<NUM> may flow through the membrane <NUM> at a rate of at most <NUM>µg/cm<NUM>/min. In some embodiments, O<NUM> may flow through the membrane <NUM> at a rate of at most <NUM>/cm<NUM>/min.

In some embodiments, O<NUM> flow rates may vary based on ambient environment <NUM> temperature. Both flow configuration and temperature of the ambient environment may affect the diffusion rate of O<NUM>. For example, the directional flow configuration, such as a cross-flow, parallel flow, or counter-flow may affect the flow rate of O<NUM> through the membrane <NUM>. In some embodiments, cross-flow or counter-flow will draw more O<NUM> through the membrane <NUM> than parallel flow. In embodiments, the solubility of O<NUM> in the electrolyte <NUM> may increase as the temperature of the electrolyte <NUM> decreases.

In embodiments, the total surface area of the membrane <NUM> may be adjusted to control the flow rate of O<NUM> through the membrane <NUM>. For example, in some embodiments, gills may be expanded or contracted to increase or decrease the total surface area of the membrane <NUM> exposed to the ambient environment <NUM> (shown in <FIG>).

In some embodiments, the flow rate of O<NUM> through the membrane <NUM> may depend on the type of membrane <NUM> used in the subunit <NUM>. In embodiments utilizing a dense solid polymer membrane <NUM>, wherein the membrane has no pores of appreciable diameter, O<NUM> may adsorb into the polymer matrix of the membrane <NUM>, diffuse through the polymer matrix along the concentration gradient, and then desorb into the electrolyte <NUM>. In some embodiments, O<NUM> may desorb into a catholyte separate from the anolyte (shown in <FIG>). In embodiments, the diffusion coefficient of O<NUM> in the polymer membrane <NUM> may vary based on the polymer material selected.

In some embodiments, the membrane <NUM> may comprise a small-pore propylene membrane comprising small, fixed pores physically traversing the thickness of the membrane. In a small-pore propylene membrane, capillary forces and hydrophobic surface interactions may act as a barrier to H<NUM>O and allow small, non-polar molecules such as O<NUM> to pass through the membrane. In some embodiments, the O<NUM> transfer rate may depend on the physical configuration of the hydrophobic small-pore membrane. Physical configuration may include the porosity and pore size distribution within the membrane <NUM>. In some embodiments, the membrane <NUM> may comprise a mixture of dense solid polymer membranes and small-pore propylene membranes.

In some embodiments, the unit <NUM> may comprise a tank of perfluorocarbons (PFCs) <NUM>. In some embodiments, the tank <NUM> may have a controlled release valve for the PFCs such that the PFCs could be released slowly or quickly into the electrolyte <NUM>. In some embodiments, the PFCs may increase the amount of O<NUM> absorbed into the electrolyte <NUM>.

In some embodiments, the rate of diffusion of O<NUM> may be proportional to the concentration difference across the membrane <NUM>. In some embodiments, the speed of the unit <NUM> may be increased to direct the unit <NUM> to an ambient environment <NUM> having more dissolved oxygen. In some embodiments, the pump flow rate of the electrolyte <NUM> may change with the speed of the unit <NUM>. In some embodiments, the residence time of the ambient environment <NUM> in the gill may affect the O<NUM> concentration in the electrolyte <NUM>. For example, at a low speed, the unit <NUM> may have a low flow rate of a highly oxygenated electrolyte <NUM> because the aqueous environment <NUM> resided in the gill subunit <NUM> for an extended period of time and thus, more O<NUM> permeated through the membrane of the gill subunit <NUM>. Conversely, at a high speed, the unit <NUM> may have a high flow rate of a moderately-oxygenated electrolyte <NUM> because the aqueous environment <NUM> resided in the gill subunit <NUM> for a shorter period of time.

<FIG> is a graphical comparison of the cell voltages of a metal-dissolved oxygen cell having a de-oxygenated electrolyte <NUM>, a partially-oxygenated electrolyte <NUM>, a fully-oxygenated electrolyte <NUM>, and a fully-oxygenated electrolyte with perfluorocarbons <NUM>.

The de-oxygenated electrolyte <NUM> current-voltage chart tracks an electrolyte <NUM> flushed with a pure N<NUM> gas environment to remove O<NUM>. The partially-oxygenated electrolyte <NUM> current-voltage chart tracks an electrolyte <NUM> held in an ambient atmospheric gas environment comprising approximately <NUM>% N<NUM> and <NUM>% O<NUM>. The fully-oxygenated electrolyte <NUM> current-voltage chart tracks an electrolyte <NUM> held in an ambient pure O<NUM> gas environment. The fully-oxygenated electrolyte with perfluorocarbons <NUM> current-voltage chart tracks a <NUM>%-<NUM>% electrolyte-perfluorocarbon mixture <NUM> held in an ambient pure O<NUM> gas environment.

When current (mA) was initially applied to the cell having partially-oxygenated, non-enriched electrolyte <NUM>, the electrolyte <NUM> in cell was not completely void of O<NUM>. During experimental procedures, the electrolyte may be opened to atmospheric conditions in some embodiments, which results in a small O<NUM> concentration initially present in the partially-oxygenated, non-enriched electrolyte <NUM>. Through Henry's law, the initial concentration of O<NUM> of the electrolytes <NUM>, <NUM> at room temperature is approximately <NUM> ppm in some embodiments. The fully-oxygenated electrolyte <NUM> has a concentration of approximately <NUM>-<NUM> ppm.

As the current increased to approximately <NUM> mA, the cell having a partially-oxygenated, non-enriched electrolyte <NUM> reduced the O<NUM> initially present in the electrolyte and began to reduce H<NUM>O at the cathode. The curve at <NUM> mA for the standard electrolyte <NUM> demonstrates that the O<NUM> was exhausted and the fraction of H<NUM>O reduced at the cathode increased. As shown by <FIG>, fully-oxygenated electrolyte cells, enriched with dissolved O<NUM>, have a higher cell potential than non-enriched cells in some embodiments. At <NUM> mA, the fully-oxygenated electrolyte <NUM>, <NUM> cells have a higher cell potential than the non-enriched and partially-enriched cells at <NUM> mA. This greater potential indicates that the cathode is reducing O<NUM>.

Other elements may optionally be present other than the elements specifically identified by the "and/or" clause, whether related or unrelated to those elements specifically identified unless clearly indicated to the contrary. Thus, as a non-limiting example, a reference to "A and/or B," when used in conjunction with open-ended language such as "comprising" can refer, in one embodiment, to A without B (optionally including elements other than B); in another embodiment, to B without A (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc..

Claim 1:
A method of generating an electrical current comprising:
extracting oxygen from an aqueous ambient environment surrounding an electrochemical system;
transporting the extracted oxygen through a selectively oxygen-permeable membrane to an enclosed electrolyte surrounding an anode and a cathode in the electrochemical system, wherein the electrolyte is separated from the aqueous ambient environment;
transporting the oxygenated electrolyte to the cathode;
reducing the oxygen at the cathode; and
oxidizing a metal at the anode.