Improvements in metal-gas batteries and fuel cells

Abstract

An improved reactor of the type having a cathode to which a gas is introduced and whereat the gas is involved in a reaction, the improvement comprising: a liquid which introduces the gas to the cathode.

Description

Improvements in metal-gas batteries and fuel cellsCross-Reference to Related Applications

[0001] This application claims priority to United States Provisional Patent Application Serial No. 63 / 573080, filed April 2, 2025.Field

[0002] The invention relates to the field of anode-gas batteries and fuel cells.Background

[0003] Anode-gas batteries and fuel cells, which are commonly metal-gas based, can have high-energy densities, low cost of production and long service life. Because of this, these devices have been considered as candidates for adoption in utility, or grid, scale energy storage but the cost associated with the extensive number of batteries / fuel cells that are required to provide sufficient power output has limited their adoption. While many metals such as aluminum, germanium, calcium, iron, lithium, and magnesium can be reacted in a metal-gas battery / fuel cell, the most common type utilizes zinc: this is driven by its good energy density, low toxicity, low cost and widespread availability. An alternate, non-metal type of anode-gas battery is a silicon-oxygen battery. With respect to the gas, most utilize the oxygen in air at the cathode but other types are known, for example, lithium-carbon dioxide batteries have been disclosed, wherein the carbon dioxide in air acts at the cathode.

[0004] In a typical zinc-oxygen battery, a separator divides a volume of electrolyte between a portion that is in contact with a zinc anode and portion that is in contact with a gas-diffusing cathode that is exposed to atmosphere. The separator serves to stop migration of zincate (Zn(OH)4-2), but the electrolyte is free to cross the separator. At the anode, zinc metal and hydroxide in converted into Zn(OH)T2and electrons are released. At the cathode, O2 combines with H2O and electrons to produce hydroxide. Within the electrolyte Zn / OH y2converts into ZnO + H2O + 2 OH' . [The overall reaction is : 2 Zn + O2 => 2 ZnO],

[0005] FIG. 1 shows a schematic prior art zinc-oxygen battery.Summary of the invention

[0006] Forming one aspect of the invention is an improved reactor of the type having a cathode to which a gas is introduced and whereat the gas is involved in a reaction. The improvement comprises: a liquid which introduces the gas to the cathode.

[0007] According to another aspect, the reactor can be in the form of one of an anode-gas battery and an anode-gas fuel cell.

[0008] According to another aspect, the cathode can be fully permeable to the liquid.

[0009] According to another aspect, the liquid can be an electrolyte.

[0010] According to another aspect, the cathode can have a portion that is impermeable to the liquid and the electrolyte.

[0011] According to another aspect, the electrolyte can differ from the liquid.

[0012] A system using the reactor forms another aspect of the invention. In the system, the reactor can be a metal-gas fuel cell, the system can comprise a regeneration device which converts the reaction product of the gas and metal into the metal and the gas, and the gas, the metal and the electrolyte can be recycled for subsequent use in the discharge state.

[0013] According to another aspect, the gas can be oxygen.

[0014] According to another aspect, the metal can be Zinc.

[0015] According to another aspect, the gas can be entrained in the liquid.

[0016] According to another aspect, the gas can be dissolved in the liquid.

[0017] According to another aspect, the gas can be constantly replenished in use.

[0018] According to another aspect, the gas can be provided in the liquid by molecular infusion.

[0019] According to another aspect, the reactor can be a zinc-oxygen battery using an aqueous electrolyte based on potassium hydroxide with a pH in the range of 9 to 14 or higher.

[0020] According to another aspect, the oxygen can be dissolved in an aqueous solution.

[0021] According to another aspect, the oxygen can be dissolved in the electrolyte.

[0022] According to another aspect, the gas can be dissolved to a level above saturation and total gas pressure is above atmospheric.

[0023] According to another aspect, the liquid can be non-aqueous.

[0024] According to another aspect, in the reactor, the cathode can be immersed: on the input side of the cathode, in a solution in which the gas has been provided by infusion; and on the output side of the cathode, in an electrolyte.

[0025] According to another aspect, the cathode can be impermeable.

[0026] According to another aspect, the cathode can be permeable and allow throughflow of an electrolyte in which the gas has been provided by infusion.

[0027] Advantages, features and characteristics of the invention will become evident upon review of description which follows, with reference to the accompanying drawings, the latter being briefly described hereinafter.BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In the drawings:FIG. l is a schematic view of a prior art zinc-oxygen battery;FIG. 2 is a schematic view of a prior art zinc-oxygen battery;FIG. 3 is a schematic view of a battery according to an embodiment of the invention utilizing a permeable and an impermeable cathode;FIG. 4 is a plot of current output of the battery of FIG. 3;FIG. 5 is a plot of optimum current vs. oxygen;FIG. 6 is a schematic view of an anode-air battery;FIG. 7 is a schematic view of the battery of FIG. 6 improved according to an embodiment of the invention;FIG. 8 is a schematic of a battery according to a further embodiment of the invention utilizing an impermeable cathode;FIG. 9 is a schematic of a battery according to a further embodiment of the invention utilizing an impermeable cathode;FIG. 10 is a schematic of a battery according to a further embodiment of the invention utilizing an impermeable cathode;FIG. 11 is a schematic of a battery according to a further embodiment of the invention utilizing a permeable cathode;FIG. 12 is a schematic of a battery according to a further embodiment of the invention utilizing a permeable cathode;FIG. 13 is a schematic showing an alternative embodiment of an infusion system;FIG. 14 is a schematic showing an infusion process;FIG. 15 is a schematic showing an infusion device;FIG. 16 is a schematic showing manifolds;FIG. 17 is a schematic showing individual serviceable multi -impermeable cathodes;FIG. 18 is a schematic showing an anode packing and supply arrangement;FIG. 19 is a schematic of a continuous cycle fuel cell according to a further embodiment of the invention utilizing a permeable cathode;FIG. 20 is a schematic showing a continuous cycle fuel cell embodiment utilizing a permeable cathodes;FIG. 21 is a schematic showing a further embodiment for a continuous cycle fuel cell utilizing a permeable cathodes and multiple anode metals;FIG. 22 is a schematic showing a fuel cell embodiment with an impermeable cathode;FIG. 23 is a schematic showing a further fuel cell embodiment with impermeable cathodes;DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

[0029] This embodiment is a battery capable of three modes of operation (i) in air (ii) with pure O2 supplied to the cathode, or (iii) with pH 13 potassium hydroxide (KOH) electrolyte infused with various levels of oxygen supplied to the input side of the cathode. In all modes, pH 13 KOH forms the remainder of the electrolytic volume. FIG. 2 is a schematic for this battery in mode (i) and (ii). In the schematic, GDL represents a gas diffusion layer. A 9-by-9 cm Alkaline Air Diffusion Electrode (ADE) with a non-precious metal catalyst was used. The electrode is based on nickel foam with the back side laminated with a porous PTFE film. This permeable cathode was paired with a wire-mesh stainless steel conductive grid, and a gas diffusion layer to make an impermeable cathode. An anion exchange membrane (PiperlON AEM 60 micron, self- supporting) acts the separator and immediately follows the cathode. Each anode contained 300g of zinc pellets. KOH electrolyte was fed to the anodes at 180 ml / minute. Infusion was done using a Biotherm Solutions TOOB, injecting 1.5 l / min of oxygen into 25.5 1 / m of fluid. All fluid flow was driven by pneumatic diaphragm pumps.EXPERIMENTAL

[0030] The battery of FIG. 2 was tested. For testing, the voltage was measured with no circuit load. To measure current, a simple circuit was assembled consisting of the battery and a 5-ohm linear resistor. For this configuration, both cathode / anode pairs produced a voltage of 1.2V, and a 0.17 mA current. Note that because neither cathode was able to produce the current required at the no-load voltage, the battery naturally derated so the voltage under load was 0.17 mA X 5 ohm = 0.87V. So based on power being I2R, the power output is 0.172(5) = 0.1445 W for each cathode / anode pair.

[0031] The battery was also tested in mode (ii). For this test, a cap was placed over both GDLs, and oxygen was supplied to the cap from a pressurized oxygen tank through a 5 PSIG regulator. Note that the cap was not sealed to prevent the gas pressure from damaging the cathode apparatus. Based on pressure gage readings, the pressure upon the cathode was estimated to be in the range of 1 to 2 PSIG. Under this scenario, the voltage remained at 1.2V, but the current grew to 0.2 mA, representing a power output of 0.2 W.

[0032] Following this, the GDL was removed on Cathode 2 and a cap was sealed to the remaining cathode apparatus to enable oxygen-infused KOH electrolyte to be supplied. Electrolyte was supplied to the cathode at 750 ml / min, and to the anode at 180 ml / min. The schematic for this version of the battery is shown in FIG. 3

[0033] The following table provides the results of Cathode 2 / Anode 2 for this configuration along with the magnification of power output compared to the conventional battery with air. Note that DO is an acronym for “dissolved oxygen” and Magnification Factor = Power measured / Conventional battery power with air.Table 1

[0034] Fitting a curve to the current data yields a very close fit (error at data points is less than 0.04%) as shown in FIG. 4:Current (mA) = 0.17 + .25952(1 - exp [-(DO-85) / (93)]

[0035] Based on this curve fit, the maximum current output for these cathodes is projected to be 0.431mA, for a power output of 0.92 W, which represents a maximum power magnification factor relative to a conventional battery of 6.43.

[0036] Analyzing the data demonstrates that the power output at 85% dissolved oxygen (DO) matches the power output for the conventional battery in air. Appealing to the model, at 100% DO the current would be 0.21 mA and the power output would be 0.2205W which is 10% higher than the results for the conventional battery with pure oxygen. These results are surprising when one considers the relatively small amount of dissolved oxygen that is associated with 100% of saturation in a liter of pH 13 electrolyte. Nonetheless, the results show that the cathode is more efficient at extracting the small amount of dissolved oxygen in an aqueous electrolyte than it is at processing oxygen from a stream of pure oxygen gas. When one considers that the current produced at 100% DO is greater than the current produced for pure oxygen gas, it means that the cathode is taking in more oxygen from the electrolyte than from either air or pure oxygen gas.

[0037] Given the leveling out of the current curve and the slow performance of metal-air cathodes, it appears that the cathode is reaching its limit to take in more oxygen. However, based on the amount of dissolved oxygen in the water, there is ample oxygen to draw more current from the anode so long as the current capacity of the anode hasn’t been reached. Assuming the anode has more capacity (which is the case here), the leveling off of the cathode curve simply shows that greater current, and hence power output, can be achieved by either implementing a larger cathode with a greater surface area for reacting with oxygen, or adding additional cathode capacity in parallel to effectively enlarge the original cathode. Put in other words, the goal is to add more cathode capacity to stay as close as possible to the target line based on the slope of the model at 85% DO which is 0.028 mA / (%D0) until the reaction limit for the anode is met which will cause the current output to level out again.

[0038] If this is done, then on a normalized basis the power output per unit mass of anode metal can be driven higher than the roughly six times power magnification of an immersed cathode over a conventional cathode in air that was observed here. While the anode reaction limit was not determined, the following plot in FIG. 5 illustrates the capacity for adding cathode capacity as it shows the 0.028 slope target line versus the current output model and the measured data. The natural goal is to stay as close to the 0.028 slope target as possible until the anode capacity has been reached.

[0039] While the data here indicates that permeable cathodes should be immersed with high DO to improve power output, and more or bigger cathodes should be used with high DO to reach the maximum current capacity of an anode and drive power output to a maximum, the question of impermeable cathode performance remains. While a power curve was not developed for an impermeable anode, a test was run test at 240% DO on Cathode 1 where the GDL was in place (rendering it impermeable). This resulted in a current of 0.25 mA versus the expected 0.38 mA current from a permeable cathode. While this points to a 34% reduction in performance, the power output with a 5-ohm resister is still 2.16 times greater than for a conventional battery. Note the lower performance is simply caused by the oxygen having to go through the gas diffusion layer to get to the cathode. So, the GDL is simply a path of resistance for dissolved oxygen.

[0040] Given the greater current and power output that was observed with the GDL removed (permeable cathode case), then higher output for an impermeable cathode should be achievable by either implementing a larger cathode or adding more cathodes in parallel to process the infused oxygen in the electrolyte feeding the cathode. Another option is to increase the total gas pressure of the liquid feeding the target gas to the cathode to create a pressure differential to force additional oxygen across the GDL. A further means of improving the performance across a gas diffusion layer is to utilize a cathode apparatus where the spacing between the gas diffusion layer and the catalytic surface for target gas ionization is minimized and preferably is a single integrated structure. Note that for this example, the cathode assembly consisted of three distinct sandwiched layers: gas diffusion layer, stainless steel wire-mesh conductor, and the permeable oxygen ionization catalyst.Example 2:

[0041] This example used the same apparatus as Example 1 to test the effect of electrolyte flow rate on anode performance. For each flow rate, the anode current output and no-load voltage across the cathode / anode pair was measured after 4 minutes of operation at the specific flow rate. The testing was done with the combination of Cathode 2 / Anode 2. The flowrate to the cathode was fixed at 250 ml / minute. The results below show that over the flowrate regime tested, there was no appreciable change in the no-load voltage or the current across the 5-ohm resister.Table 2

[0042] The experimental examples show that immersing the cathode and exposing it to an aqueous solution with a high concentration of dissolved oxygen results in a dramatically higher power output.Example 3:

[0043] Two embodiments were tested to demonstrate the performance with high pH of up to 15, and to observe performance as the total gas pressure was increased from 1 atmosphere. Once again, potassium hydroxide (KOH) electrolyte was used.

[0044] The cathode assembly consists of a GDL (AvCarb MGL370), a current collector (18 Mesh stainless steel, an electrode (9-by-9 cm high performance alkaline diffusion electrode with non-precious metal catalyst based on a nickel foam with the back side laminated with a porous PTFE film cut down to a 6.35 cm diameter circle), and an anion exchange membrane (PiperlON AEM 60 micron, self-supporting) which acts as the separator. The anodes were loaded with 225 g of metal pellets, which were either zinc, iron, or aluminum depending on the trial. Using a pneumatic diaphragm pump, the KOH electrolyte flowrate in the cathode-anode loop was 200 ml / minute. For this example, only one cathode and one anode were used.

[0045] The infusion membrane for this example is a custom-made unit from Southern Stainless in Tennessee. The unit shell is stainless steel with approximately 2500 30-cm long polypropylene fibers that are wrapped around a central stainless-steel shaft. The oxygen flow rate into the membrane was 1.5 liters / minute, and the liquid flow rate through the membrane 25.5 liters / minute, driven by a pneumatic diaphragm pump. The flow rates were the same when atmospheric air was infused for one experiment.

[0046] The embodiments used for this example are shown in FIG. 6 and 7. Using these embodiments, the following experiments were conducted: a. Baseline test: Dry air only at the cathode with zinc (FIG. 6 embodiment) b. Distilled water with 02 infusion, pH 14, running from 1 atm to 50 psi with zinc (FIG. 7 embodiment) c. Distilled water with 02 infusion, pH 15, running from 1 atm to 50 psi with zinc (FIG. 7 embodiment) d. Distilled water with air infusion, pH 15, 1 atm to 50 psi with zinc (FIG. 7 embodiment) e. Distilled water with 02 infusion with iron anode, pH 15, running 1 atm to 30 psi with iron (FIG. 7 embodiment)

[0047] The results for each experiment are in the following table:Table 3

[0048] The table shows that for pH 15 with iron or zinc that the battery power output with infused oxygen or even infused air at any pressure, including atmospheric pressure, is substantially greater than for a conventional battery based on dry air. This clearly shows that the catalyst is more efficient at taking in dissolved oxygen than atmospheric oxygen.

[0049] Note that in some cases, as the pressure goes up, the power goes slightly down. This was attributed to a small issue in the infusion device as a part was being forced to occlude the water output that diminished the flow through the infuser. A spacer was added into the infuser to prevent the occlusion, and the results with zinc for pH 15 and infused oxygen were obtained.

[0050] The following table presents the maximum power magnification results relative to the baseline reading in dry air for a conventional battery.Table 4

[0051] Note that these results show that infused air is quite competitive with infused oxygen in terms of magnification of power. Also, compared with the data from the previous example, the data here shows, as expected, that the power and power magnification go up dramatically as pH is increased.

[0052] As counterintuitive as it may be, this explicitly demonstrates how physical materials can more efficiently draw in a dissolved gas than draw in the same gas that is plentiful in air. Hence, to improve efficiency, it is better to utilize immersed cathodes to draw in dissolved gas than operate with a cathode that draws from normal atmospheric air. These results show the invention can be applied to alternate anodic materials and achieve improved performance by immersing the cathode in the manner disclosed in this invention.

[0053] A test was run with aluminum, where the amount of metal in the anode was reduced by more than 90%. The reduction in anode mass was needed to address the production of hydrogen that rapidly made its way to the cathode, where it joined with oxygen ions to make hydroxide and maintain the pH in the electrolyte.Example 4

[0054] This example uses the same system as the previous example for FIG. 7 with zinc with pH 15 and 02 infused to 40 psig. For this example, all three cathodes were used. Following this test, the cathodes were opened and examined, and it was determined that Cathode 1 and possibly 2 had a hole and were leaking electrolyte, which reduced the system power output. As expected, the power increased as each cathode was engaged. Note that only Anode 1 was engaged for this experiment. The following table shows the results as each cathode was sequentially engaged by connecting it in parallel with Cathode 1.Table 5Variations in Cell Design

[0055] As will be apparent to those skilled in the art, the invention disclosed here can be implemented in a variety of ways. FIG. 8-10 illustrate strategies using an impermeable cathode. Note that using an impermeable cathode, in turn, enables the use of a non-electrolyte liquid solution on the input side of the cathode. As such, any liquid with a capacity for carrying entrained target gas can be used as long as it won’t result in degradation of the cathode. In this way, the solution could theoretically be distilled and deionized water, an electrolyte, pressurized liquid ammonia, mineral oil, etc. Note that each embodiment in the following figures will utilize a molecular infusion device to entrain the target gas in the liquid. However, molecular infusion is the preferred method of entraining target gas but can be replaced by other methods.

[0056] FIG. 8 illustrates a standard zinc-oxygen battery with a single cathode and anode. The infused liquid here is driven by a pump coming off the drain of the input chamber to the cathode. The pump could just as well be positioned at the supply to the input chamber for the cathode. FIG. 9 illustrates a zinc-oxygen battery with dual cathodes and anodes. The number of anodes and cathodes can be extended arbitrarily.

[0057] FIG. 10 illustrates a zinc-oxygen battery with dual cathodes and anodes wherein each anode is fed independently by its own pump (Pl and P2). Note that cathodes can also be plumbed in a variety of ways, such as having a single infuser supply a separate pump for each cathode, or one could have a dedicated infusion system and pump for each cathode. Also, it is clear that pumps can be used to supply the input sides of the cathodes and anodes or draw from the output drains of the respective cathode and anode assemblies.

[0058] FIG. 11-12 illustrate strategies involving the use of a permeable cathode which allows liquid transfer across the cathode. Because liquid can flow across the cathode, it is apparent that the liquid should be the same electrolyte with the same concentration used throughout the rest of the battery / fuel cell.

[0059] FIG. 11 below represents a modification of FIG. 8 where excess electrolyte is drained on the cathode output side and returned to the infuser (or other means of entraining the target gas in the liquid). The permeable nature of the cathode combined with the flow pressure from the input side of the cathode will force liquid transfer across the cathode. Note that in the same way, the schematics in FIG. 9 and 10 can be altered to accept a permeable cathode.

[0060] FIG. 12 presents an embodiment that enables electrolyte to cyclically flow throughout the entire battery by using zincate separators to protect both sides of the cathode assembly.

[0061] In each of these drawings, an infusion system has been shown where a liquid is pumped through while a target gas is injected for infusion. However, many alternate arrangements are possible. FIG. 13 shows an alternative where excess liquid is stored at the infuser and is continuously charged with the target gas by the infusion system. Note that in practice the infuser may be subject to a controller that shuts off the infuser if the target gas concentration level is over a desired set point and then cycles the infuser back on when a lower set point is reached. Other control algorithms may also be desirable.Variations in Gas Supply

[0062] Gas may be dissolved into a liquid in many ways, such as sparging, packed towers, tray or plate towers, laminar jet contactors, wetted wall contactors, stirred cell contactors, or membranes.

[0063] For this invention, the preferred method for entraining gas into an aqueous solution is molecular infusion.

[0064] One method of molecular infusion involves injecting gas into an aqueous solution through microporous, hydrophobic hollow fiber as taught by Glassford in US Patent 6,209,855. This method provides efficient, rapid gas mass transfer at a molecular level and displaces existing dissolved gases, which are rejected through a gas vent, so a beneficial dissolved gas environment can be established. Other methods of molecular infusion are known.

[0065] As disclosed by Semmons in US Patent 5,034,164, if the gas pressure is controlled to be less than the dynamic pressure of the aqueous solution, then bubbleless molecular infusion will occur, which, in turn, eliminates infused gas losses due to bubble buoyancy.

[0066] Injecting gas into a non-aqueous liquid can be done by the same process except the microporous hollow fiber must be modified to reject the liquid. If this is not done, then the liquid can easily move past the liquid / fiber barrier and flood the gas components of the system, rendering them non-functional and possibly destroying them.

[0067] FIG. 14 shows a schematic for a molecular infusion process that can be used. For this system, liquid is circulated via a low-turbulence pump, such as a progressive cavity pump, through the infusion device as gas is dissolved into the liquid. This is done in two stages.During the first stage, the tank top control valve C2 is open, which leads to a gas vent. Control valve C2 is left open until the previously existing dissolved gas environment in the liquid has been substantially forced out by infusion of the target gas. Since the gas vent is exposed to the atmosphere, it causes the total gas pressure in the liquid to remain at atmospheric pressure, which forces the existing dissolved gases to come out of solution as the target gas is infused based on Henry’s Law. Of course, as the concentration of infused target gas within the liquid increases, then based on Henry’s Law, an increasing level of the infused target gas will be expelled in response to further target gas being infused. As such, the first stage ends when a user or control algorithm decides that the pre-existing dissolved gas atmosphere has been sufficiently replaced by the infused target gas required for battery / fuel cell discharge.

[0068] The second stage begins by closing valve C2 so that target gas can be further infused as the total dissolved gas pressure is driven to the desired level. While the gas vent has been depicted as being attached to the storage tank, it can also be located at the top of the enclosure containing the gas infusion system. Viable locations for the gas vent will depend on the exact embodiment. Also, note that the safety valve, S, is set to release based on the tank’s pressure limit.

[0069] Through both stages, the target gas is infused at a pressure to ensure rapid molecular infusion without bubble generation, while also preventing backflow of liquid to the gas side of the liquid-fiber membrane. If the target gas pressure is too low (typically more than 5 psi lower than the dynamic pressure of the recirculating liquid), then back-flow can occur, and if the pressure is greater than the dynamic pressure of the recirculating liquid, then bubble generation can occur at the interface of the liquid / fiber membrane.

[0070] Bubble generation is not desirable because it results in greater volumes of gas being vented from the system during the first stage. Bubble generation is also not desirable because it can lead to pockets of gas being trapped and either creating gas locks or preventing the target gas from being delivered to the cathode for ionization. Far more importantly, bubble formation is not desirable because even if gas bubbles are delivered to the cathode, the productivity of the cathode will be significantly diminished because cathodes extract and process dissolved target gas from liquid far more efficiently than they can extract and process the target gas in air, or even simply process a flow of pure target gas. The substantial lack of productivity of a cathode that processes a stream of pure target gas as compared to an immersed cathode extracting dissolved target gas was demonstrated in the examples.

[0071] Note that the two-stage process for infusing target gas to achieve a total gas pressure above 1 atm, can be reduced to a one-stage process, where the gas vent remains closed at all times, by starting with a degassed liquid. In this case, the target gas is simply infused until the target total gas pressure is reached. In general, no matter what the desired total gas pressure may be, it is desirable to start the infusion process with a degassed liquid to eliminate unwanted dissolved gas species and any detrimental effects that they might have.

[0072] The gas infusion system typically involves a membrane which, in turn, is primarily composed of a bundle of perforated hollow fiber as shown in FIG. 15. Gas comes into the gas inlet chamber and flows down the hollow fiber bores and then exits through the fiber perforations into the liquid. The hollow fiber bundle is potted at both ends to prevent liquid from entering the gas inlet and the bore of the hollow fiber ends. The potting is such that the bores are open on the gas inlet chamber end and plugged on the opposite end. With respect to the schematic in FIG. 23, note that the enclosure containing the infusion system could contain multiple gas infusion membranes. In addition, multiple infusion systems could be connected in series or parallel to enable a higher rate of molecular infusion into the liquid. Again, note that the hollow fiber naturally repels the liquid, and the liquid cannot push past the natural repelling nature of the fiber unless the differential between the dynamic liquid pressure and the target gas pressure is too large (generally 5 or more PSI).

[0073] The schematic shown in FIG. 15 can be improved for higher dissolving efficiency by designing the infusion unit such that the liquid flow is parallel to the fibers. This is easily done by enclosing the gas infusion module within an enclosure and orienting the bundles of fiber with their associated gas inlet chamber such that the liquid flows along and through the bundles. To that end, the bundles and gas inlet chamber can be arranged as an annulus, so the water naturally and passively flows on the outside and inside of the annulus. A further option is to have a recirculation pump within the gas infusion chamber, which takes the liquid and then re-injects it through an eductor, which is integrated with the separate gas inlet chamber, so that the liquid is forced along the fibers.[

[0074] Preferably, the storage tank in FIG. 14 will either have a flexible water-tight interior bladder surrounded by air which can freely enter or leave the space between the bladder and tank walls as the bladder fills or empties with the liquid, or else it will have a control system that maintains a pressurized environment of the same target gas that was infused to maintain pressure so dissolved gas is not released, and to prevent a tank rupture as liquid is drained.Variations in anode metals and non-metals

[0075] Metals other than zinc and non-metals such as silicon, can be used at the anode. Of note in this regard is aluminum, which has an energy / mass density ten times that of zinc.Aluminum very rapidly corrodes above pH 7.5. Aluminum can be used as a viable anode metal in a high pH electrolyte according to the present invention in high load applications; in such applications, it reacts so quickly that the problems of corrosion are manageable.Fluid management variations

[0076] Rather than individually connecting hundreds of cathodes or anodes with separate input and output lines between their associated input and output tanks, manifolds can be used to efficiently enable large numbers of easily accessible cathodes or anodes to be utilized. FIG. 16 shows how manifolds can be used to efficiently plumb a large number of anodes between preanode and post-anode tanks. (A similar approach could be applied to permeable cathodes.)

[0077] For this schematic, each anode apparatus is shown with an input and output control valve. Note that besides the functioning anode, the anode apparatus may include a pump and other equipment associated with refilling, controlling, or maintaining the anode apparatus, as well as monitoring all aspects of anode productivity.

[0078] FIG. 17 shows a schematic for individually controllable and serviceable impermeable cathodes. For this schematic, a liquid carrying the target gas is individually delivered from the Pre-Cathode Manifold to each impermeable cathode apparatus and is then returned to the PostCathode Manifold such that the gas-carrying liquid can be re-entrained with the target gas. The apparatus associated with each cathode may contain control valves to enable a cathode to be isolated for maintenance, along with pumps and sensors for controlling and monitoring liquid flow into each cathode, as well as sensors to measure cathode productivity.Variations in Anode Design

[0079] The design of the anode for this invention is flexible and can range from simple to complex. The simplest design is a solid anode with passive flow by the anode. Alternative designs can utilize anodes in the form of packed nuggets, ingots, grains, or powders. Electrolyte flow through the anode can be in any orientation; however, when the anode is made up of nuggets, ingots, grains, or powders, a downward flow may be advisable to work with gravity to help keep the anode material tightly packed against the conductor.

[0080] To aid in maintenance and power control, it is useful to have input and output control valves around the anode. In this way, an anode can be isolated for maintenance or turned off to save metal when the power output is not needed.

[0081] To maintain consistent power output at a given anode, the associated apparatus at the anode may include a loading system to incrementally add anode material for reaction to compensate for anode metal or non-metal that has been lost due to reaction. In addition, the anode apparatus may include a mechanical means of ensuring the anode metal remains well packed to ensure good electrical current flow.

[0082] For those skilled in the art, this may be accomplished in many ways. The schematic in FIG. 18 shows a motor-driven threaded shaft connected to a perforated plate through which the electrolyte can flow. The shaft has position and pressure control to keep the anode metal sufficiently compacted to ensure current flow and to enable the shaft to retract when additional anode metal is supplied to the anode for reaction.

[0083] For anode metals that feature high corrosion rates in the presence of a strong base, the apparatus may have additional systems to protect the anode metal and prevent corrosion when the anode is not being actively used to generate power output. Specifically, a control mechanism can be implemented to close the input and output electrolyte flow control valves when the anode is not active. Then, after the anode is isolated, an acid can be added to neutralize the pH in the anode. Following this, the anode can be washed with pH 7 water, followed by dry air being blown through to dry the anode metal. In this way, the anode metal and anode apparatus will be saved from corrosion while waiting for the anode to be cycled back to active duty.

[0084] The process described here is advantageous because by isolating the anode, the acid and water used to clean the anode will not alter the chemistry of the electrolyte used in the rest of the battery / fuel cell. Of course, when the anode is activated and the electrolyte is brought back in, then a vent system will be needed to allow air / gas in the anode to escape as the anode is flooded prior to opening the anode drain valve to fully allow the electrolyte to flow through the discharge system.Variations in control modes

[0085] Given the intricacies of the battery discharge systems disclosed here, many means of controlling the power output during discharge are possible.• Flow rate of the gas-entrained liquid at the cathode input: Flow rate can be controlled to regulate cathode access to dissolved target gas.• The quantity of entrained gas maintained in the liquid feeding the cathode input: In general, the higher the entrained gas level, the higher the power output. This trend is stronger where the entrained gas is dissolved.• Controlling the amount of mass and / or surface area of anode metal within the anode. This presumes that, as the anode metal is consumed, there is a means of placing additional metal into the anode. Then the greater the surface area of anode metal available for contact with the electrolyte, the greater the potential power output given suitable access to electrolyte. In general, as the mass of metal in the anode increases, the amount of surface area available for reaction increases, and this, in turn, increases the potential power output, or productivity, for that anode.• The number and type of anodes that are energized: The power output can be controlled by adjusting the number of energized anodes through which the electrolyte is flowing.• In addition, for embodiments using multiple types of anode metals, the power output can be adjusted by controlling the types of anode metal being consumed at a given point in time. As a practical example of this, consider a grid-scale fuel cell which features hundreds of anodes of Metal A and Metal B, where the power output from Metal B is four times that of Metal A. Therefore, as power usage increases, more Metal A anodes can be brought online. However, when a fourth Metal A anode is required, then rather than bringing the fourth Metal A anode online, a single Metal B anode can be brought online while three Metal A anodes are shut down.• Controlling the number of energized cathodes and their association with specific anodes: The number of cathodes electrically connected in parallel and assigned to a single or group of energized anodes, which are also electrically connected in parallel, can be controlled. This is important because cathodes tend to be the limiting step in maximizing the potential current generation from an anode. In principle, these features allow operators or automatic control systems to quickly match the power output to the electrical power demand.Variation in form: operation as a fuel cell

[0086] While the invention can be operated as a pure battery, for grid-scale applications, this invention is likely to be part of a fuel cell. In general, any battery embodiment can be extended into a fuel cell by adding regeneration capability. In addition, fuel cell embodiments can be based on batch or simultaneous discharge / regeneration operation.Batch operation as a fuel cell

[0087] In batch operation, when the operator or control system determines that the discharge cycle has run to a point where a regeneration cycle is warranted (anode metal may or may not be completely exhausted), the regeneration process begins where some or all of the electrolyte, which contains reacted anode metal, is transferred to the regeneration system.

[0088] The regeneration system generally consists of a plating apparatus where a charge is applied to the plates causing the reacted anode metal to break down into the original anode metal (such as zinc) and the original target gas (such as oxygen). The anode metal is then harvested from the plates. Once the metal is harvested, it is stored and made available to the anode metal supply system back on the discharge side of the fuel cell. In an advanced system, the anode metal may first be passed to a cleaning system prior to being stored for reuse. In the cleaning system, an acid can be added to neutralize the pH of any remaining electrolyte. Following this, the anode can be washed with pH 7 water, followed by a dry gas being blown through to dry the anode metal. In this way, the anode metal and the fuel cell apparatus will be saved from corrosion while waiting for the anode metal to be cycled back to active duty.

[0089] In many modern regeneration systems, the recovered target gas is simply vented into the atmosphere. This has the disadvantage of also releasing a slight electrolyte mist, which typically has a toxic and corrosive high pH. Given the scalability of the invention and the resulting economy of scale, this invention allows the dissolved gas to be recovered. To enable this, the recovered target gas is gathered and sent through a drying system, which may include condensing plates for gathering and returning electrolyte to storage. Once the gas is dried, it is then pressurized and stored for reuse by the infusion system on the discharge side of the fuel cell. Finally, the regeneration system may include an electrolyte chemical conditioning system to correct any impurities or other deficiencies in the chemical properties of the recycled electrolyte.

[0090] By including gas and electrolyte conditioning systems within the fuel cell, this invention is intended to be self-contained and only require minor target gas, electrolyte, and anode metal makeup supply.

[0091] Note that depending upon the capacities and constraints for the components in the metal regeneration process, it may be preferable to feed the electrolyte to multiple redundant regeneration units where each unit handles a portion of the electrolyte. This has the advantage of allowing excess regeneration capacity to be provided that can sit in reserve for maintenance periods when a particular regeneration unit is taken down for repair or scheduled maintenance.

[0092] Finally, note that alternative batch fuel cell designs are possible based on using solid anodes that are directly replated. However, these and other more traditional batch fuel-cell designs are generally prone to dendrite formation from repeated discharge / charge cycles that can lead to separator perforation.Continuous operation as a fuel cell

[0093] One issue with batch-design fuel cells is that the discharge side of the fuel cell stops while the anode metal is regenerated, and the associated electrolyte is recycled. This is a problem because it means the system has no steady-state output capacity on its own.

[0094] The issue of capacity is enormous in the power industry. For example, a windmill farm may have the potential to generate Gigawatts, but its capacity is zero because it can’t produce anything if the wind stops. As a result, utilities must hedge wind power production with alternate sources of power capacity that can deliver if the wind stops. The surprising end result is that in many circumstances, wind power, which in and of itself is extremely cheap, becomes the most expensive power source once the hedging contract is added to the production cost.

[0095] This invention has the ability to help address some of the capacity problems in the power industry. Specifically, this invention has natural embodiments that enable it to be linked with a zero-capacity power source, such as a windmill farm, to convert it from a zero-capacity intermittent power supply to a reliable high-capacity power supply. The key to this is designing the discharge side of the fuel cell to produce electrical energy at a steady rate that is a portion of the statistically expected annual energy generation from the intermittent power supply. Under this scenario, the intermittent power supply will drive the regeneration system and store excess electrolyte, anode metal, and reaction gas for times when the intermittent power source is in a down state. A further benefit of this approach is that if there is excess electrolyte, anode metal, and reaction gas beyond what is required, including contingencies, then the power output on the discharge side of the fuel cell can be increased to help meet peak power needs.

[0096] As with the battery schematics shown earlier, fuels cells can be implemented in a variety of ways and use either permeable or impermeable cathodes.

[0097] Starting with permeable cathodes, FIG. 19 shows a basic schematic for extending a battery to yield fuel cell functionality. Note that the oxygen recovery and drying process, or any electrolyte reconditioning process, has been lumped in with the Regeneration System.

[0098] For the following embodiment in FIG. 20, the electrolyte runs in a continuous cycle from the discharge side of the fuel cell to the regeneration side of the fuel cell and back again. Under this scenario, the entire electrolyte flow passes across the cathode assembly. (Pumps are not shown in the schematic.)

[0099] An advantage of this design is that it can be modified to handle multiple anode metals. As previously discussed, the advantage here is in terms of dynamic power management. To implement this embodiment with the type of dynamic power management previously described, it is preferable for each type of anode metal to be handled as a group by dedicated manifolds that will lead to individual regeneration systems for each type of anode metal. One possible schematic for such a system is presented in FIG. 21.

[0100] While for this embodiment, Anode Metal 1 (or 2) can represent a single anode, it can also represent a manifold servicing hundreds of Metal 1 anodes where all of these anodes drain spent electrolyte into a Metal 1 output manifold, which provides a pathway to the Metal 1 regeneration infrastructure. From this schematic, it is apparent that the invention can be extended for an arbitrary number of anode metals.

[0101] For those skilled in the art, it is also apparent that variations on this embodiment are easily contemplated. For example, one could choose to implement a separate target gas and electrolyte storage system for each metal. Furthermore, while the discussion has contemplated a singular Anode Metal Regeneration system for each type of metal, one could easily choose to implement a manifold to supply a number of Anode Metal Regeneration systems, all handling one type of metal. By doing this, sufficient regeneration could be implemented to enable maintenance on a given regeneration system while the remaining systems maintain the regeneration process without having to derate the overall power output from the fuel cell. Once again, a key advantage of this invention is the operational redundancy and flexibility that can be integrated into a physical embodiment.

[0102] Note that for FIG. 20 and 21, the components in the schematics represent summaries for system components that are consistent with the invention presented in FIG. 7-12Impermeable cathode

[0103] FIG. 22 shows a basic schematic for extending a zinc-oxygen battery with an impermeable cathode to yield fuel cell functionality.

[0104] Once again, there are many ways to modify a battery to achieve fuel cell functionality. While this embodiment takes spent electrolyte from the tank that feeds the anodes, the following schematic demonstrates an embodiment for a zinc-oxygen fuel cell that regenerates the electrolyte immediately following the anodes.

[0105] Once again, note that in both FIG. 22 and 23, the stage of O2 drying and recovery has been lumped in with the Electrolyte Regeneration System. For those skilled in the art, it is apparent that the embodiments in FIG. 22 and 23 can be extended to utilize multiple anode metals in the same manner this was accomplished for permeable cathodes.Variations in scale

[0106] The invention disclosed here is extensively scalable and flexible. It can be used with any liquid that won’t foul the cathode input and can carry a sufficient quantity of, preferentially dissolved, target gas. It can be used with any anode material that is part of an anode-gas battery.

[0107] Whereas the description focuses on fuel cells and batteries, the invention can be used in other reactors wherein a gas reacts at a cathode, for example, CO2 reduction into ethanol.

[0108] The invention can be implemented on a power-plant scale where a building houses a number of discharge units that are electrically connected in series to produce sufficient voltage to drive an efficient inverter. In addition, each discharge unit can contain an arbitrary number of cathodes and anodes that share a common electrolyte vessel, and where each discharge unit has access to recycled supplies of electrolyte, target gas, and a particular anode material. This enables flexible power output control strategies within a discharge unit where multiple cathodes can be electrically connected in parallel and paired to a number of anodes that are electrically connected in parallel to maximize the current generated per unit mass of anode material.

[0109] For this discussion, a discharge unit works with a specific target gas and a specific anode metal or non-metal. This is because each anode-gas pair will have a characteristic voltage across the cathode / anode. So, while cathodes and anodes can respectively be dynamically energized and connected in parallel within a discharge unit to control power output, in the end, all of the power outputs within a discharge unit will be electrically connected in parallel to sum all of the individual current contributions. This is because it is not possible to electrically connect cathode / anode pairs in series if they are all in fluid connection with the same central electrolyte vessel.

[0110] Alternate target gas and anode metal and non-metal combinations are typically contained in separate discharge units with their own specific output voltage. Since this invention can work with multiple anode metals and non-metals, where they each have their own energy densities and output voltage, then different anode metals and non-metals can be dynamically activated and paired with cathodes as a means of power management and thereby match the electrical load as previously discussed.

[0111] The ability to use multiple anodes and cathodes also aids scalability and reliability by enabling singular or arbitrary groups of anodes or cathodes to be taken out of service for maintenance and repair. Likewise, multiple independent electrolyte regeneration systems can be implemented to enable individual regeneration systems to be brought down for maintenance, and to enable regeneration to take place concurrently while the discharge units are operating.

[0112] In scaling the invention, there is no practical limitation on the spacing of components due to fire risk. As a result, the invention can be scaled horizontally and vertically.Variations in industrial application

[0113] The invention has many large-scale power grid applications:• Grid-scale storage: o The invention enables renewable power sources to be converted into base capacity power sources with peaking capability that eliminates the need for expensive hedging programs when the renewable source stops producing. o The invention enables the storage of excess electrical output from thermal power plants that can’t be efficiently throttled down to zero when not needed. Hence, their off-hours energy production can be stored for later high-demand periods.• Industrial peaking power o The invention enables energy to be stored to provide peaking power for large intermittent processes. o The invention enables large industrial users to flatten their demand and thereby minimize the demand charge on their power bills.Variations in electrolyte

[0114] In the designs of commercial grid-scale batteries, the electrolyte pH is typically 14 or higher. At such a high pH, the solubility of oxygen, the most common target gas, is severely diminished. This problem can be overcome in two ways.

[0115] In the first case, where a permeable cathode is used, the total gas pressure of the electrolyte can be dramatically increased. The capacity of the electrolyte to carry target gas increases proportionately as the total gas pressure increases. In this way, the total gas pressure can be increased to the point that ample supplies of the target gas can be entrained, and preferentially infused, into the electrolyte. With respect to oxygen, this can mean pushing the total gas pressure to 10 atmospheres or higher. For immersed components, this is not a major issue; instead, it requires proper design of pressure vessels, piping, valves, pumps, and connectors, etc.

[0116] The second alternative is to use an impermeable cathode. By doing this, the liquid feeding the target gas to the cathode doesn’t have to be an electrolyte. As such, it can be a lower-pH electrolyte or even water. The concern in this alternative is that the impermeable cathode will have a gas diffusion layer that the entrained target gas in the liquid will have to cross. As the examples show, the gas diffusion layer is a point of resistance to oxygen flow and results in lower power output as compared to the power output for the same level of dissolved oxygen in combination with a permeable cathode. However, this can again be addressed by driving high levels of target gas via infusion, or other means, into the liquid such that the total gas pressure rises to the point that there exists a sufficient pressure differential across the gas diffusion layer such that an ample supply of target gas is driven through the gas diffusion layer. The only remaining issue here is that the physical support required for the gas diffusion layer and other cathode components to handle the higher-pressure loading on the input side of the cathode must be designed accordingly. One approach to this is to raise the pressure of the electrolyte and then have the extensive differential in the concentration of target gas on the input side of the cathode to the output side drive the target gas flow through the cathode.Miscellaneous features

[0117] For each of the previous embodiments, they may be further enhanced via the following:• The use of an automatic control algorithm to optimize power output, discharge cycle start-up, and ramp-up conditions for load management. This may be done by suitably monitoring and controlling the electrolyte flow rate and pressure, the cathode input liquid flow rate and pressure, the dissolved oxygen level, the total dissolved gas pressure, and Reynolds number (laminar or turbulent flow conditions). These may be controlled through the active control of pumps, valves, veins, variable nozzles, diffusers, and orifice plates, along with additional control surfaces.• The regeneration and discharge portions of each schematic can optionally be enhanced by adding automated temperature control systems to maintain optimum operating conditions based on temperature.• For a battery, or on the discharge side of a fuel cell, the order of the Gas Infusion System and the Liquid Recirculation System components is not critical to the process. The Liquid Recirculation System refers to the pumps, sensors, controls, and other components that are engaged to provide the operational fluid pressure and flow rate for the cathode input. Hence, the various mechanical, sensing, and control components of the Liquid Recirculation System can be distributed throughout the device in accordance with the actual design. The same is true for the Electrolyte Recirculation System.• Gas infusion can be enhanced through the use of low-intensity pulsed ultrasound (LIPUS) to irradiate the hollow fiber in the gas infusion systems. The hollow fiber in the gas infusion systems mimics the perforated hydrophobic nature of skin on mammals. Recent research has shown that irradiating skin with LIPUS enhances gas transfer through the skin. This is especially helpful with passing oxygen into the skin, which is critical for wound healing. As such, it is logical to irradiate perforated hollow fiber with LIPUS to enhance gas flow through the walls of the hollow fiber. The number of LIPUS actuators and their positioning will depend on the actual physical configuration of the gas infusion system. While the LIPUS actuator is expected to operate in the 20KHz to lOOKHz range, the actual optimum settings for frequency, pulse frequency, and pulse width will be based on the actual physical infusion configuration. [3-10]

[0118] Whereas fiber-based infusion membranes were used in the examples, alternative nonfiber designs are possible. In general, any membrane design that is compatible Glassford’s apparatus in US Patent 6,209,855 can be used. One such alternative includes the concentric- cylinder non-fiber membranes by Southern Stainless. These systems utilize concentric liquid and gas chambers, where the gas chamber is an annulus surrounding the central liquid chamber, and the chambers are separated by a non-fiber microporous membrane. Moleaer also sells infusion membranes with a similar geometry. Yet further variations are of course possible. Accordingly, the invention should be understood to be limited only by the accompanying claims, purposively construed.

Claims

Claims:

1. An improved reactor of the type having a cathode to which a gas is introduced and whereat the gas is involved in a reaction, the improvement comprising: a liquid which introduces the gas to the cathode.

2. The reactor of claim 1 in the form of one of an anode-gas battery and an anode-gas fuel cell.

3. The reactor of claim 2, wherein the cathode is fully permeable to the liquid.

4. The reactor of claim 1, wherein the liquid is an electrolyte.

5. The reactor of claim 2, wherein the cathode has a portion that is impermeable to the liquid and the electrolyte.

6. The device of claim 5, wherein the electrolyte differs from the liquid.

7. A system using the reactor of claim 4, wherein the reactor is a metal-gas fuel cell, the system comprising a regeneration device which converts the reaction product of the gas and metal into the metal and the gas, and wherein the gas, the metal and the electrolyte are recycled for subsequent use in the discharge state.

8. The system of claim 7, wherein the gas is oxygen.

9. The system of claim 8, wherein the metal is Zinc.

10. The reactor of claim 1, wherein the gas is entrained in the liquid.

11. The reactor of claim 1, wherein the gas is dissolved in the liquid.

12. The reactor of claim 1, wherein the gas is constantly replenished in use.

13. The reactor of claim 1, wherein the gas is provided in the liquid by molecular infusion.

14. The reactor of claim 1, wherein the reactor is a zinc-oxygen battery using an aqueous electrolyte based on potassium hydroxide with a pH in the range of 9 to 14 or higher.

15. The reactor of claim 14, wherein the oxygen is dissolved in an aqueous solution.

16. The reactor of claim 14, wherein the oxygen is dissolved in the electrolyte.

17. The reactor of claim 1, wherein the gas is dissolved to a level above saturation and total gas pressure is above atmospheric.

18. The reactor of claim 1, wherein the liquid is non-aqueous.

19. The reactor of claim 1, where the cathode is immersed: on the input side of the cathode, in a solution in which the gas has been provided by infusion; and on the output side of the cathode, in an electrolyte.

20. The reactor of claim 1, wherein the cathode is impermeable.

21. The reactor of claim 1, wherein the cathode is permeable and allows throughflow of an electrolyte in which the gas has been provided by infusion.

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