Patent Publication Number: US-8974939-B2

Title: Fluid-surfaced electrode

Description:
RELATED APPLICATIONS 
     For purposes of the USPTO extra-statutory requirements, the present application constitutes a continuation-in-part of U.S. patent application Ser. No. 12/462,205, entitled FLUID-SURFACED ELECTRODE, naming Geoffrey F. Deane, Bran Ferren, William Gates, W. Daniel Hillis, Roderick A. Hyde, Muriel Y. Ishikawa, Edward K. Y. Jung, Jordin T. Kare, Nathan P. Myhrvold, Clarence T. Tegreene, David B. Tuckerman, Thomas A. Weaver, Charles Whitmer, Lowell L. Wood, Jr., Victoria Y. H. Wood as inventors, filed Jul. 29, 2009, now U.S. Pat. No. 8,460,814, which is entitled to the benefit of the filing date. 
     For purposes of the USPTO extra-statutory requirements, the present application constitutes a continuation-in-part of U.S. patent application Ser. No. 12/589,309, entitled FLUID-SURFACED ELECTRODE, naming Geoffrey F. Deane, Bran Ferren, William Gates, W. Daniel Hillis, Roderick A. Hyde, Muriel Y. Ishikawa, Edward K. Y. Jung, Jordin T. Kare, Nathan P. Myhrvold, Clarence T. Tegreene, David B. Tuckerman, Thomas A. Weaver, Charles Whitmer, Lowell L. Wood, Jr., Victoria Y. H. Wood as inventors, filed Oct. 20, 2009, which is currently co-pending, or is an application of which a currently co-pending application is entitled to the benefit of the filing date. 
     For purposes of the USPTO extra-statutory requirements, the present application constitutes a continuation-in-part of U.S. patent application Ser. No. 12/589,323, entitled FLUID-SURFACED ELECTRODE, naming Geoffrey F. Deane, Bran Ferren, William Gates, W. Daniel Hillis, Roderick A. Hyde, Muriel Y. Ishikawa, Edward K. Y. Jung, Jordin T. Kare, Nathan P. Myhrvold, Clarence T. Tegreene, David B. Tuckerman, Thomas A. Weaver, Charles Whitmer, Lowell L. Wood, Jr., Victoria Y.H. Wood as inventors, filed Oct. 20, 2009, which is currently co-pending, or is an application of which a currently co-pending application is entitled to the benefit of the filing date. 
     For purposes of the USPTO extra-statutory requirements, the present application constitutes a continuation-in-part of U.S. patent application Ser. No. 12/589,310, entitled FLUID-SURFACED ELECTRODE, naming Geoffrey F. Deane, Bran Ferren, William Gates, W. Daniel Hillis, Roderick A. Hyde, Muriel Y. Ishikawa, Edward K.Y. Jung, Jordin T. Kare, Nathan P. Myhrvold, Clarence T. Tegreene, David B. Tuckerman, Thomas A. Weaver, Charles Whitmer, Lowell L. Wood, Jr., Victoria Y. H. Wood as inventors, filed Oct. 20, 2009, which is currently co-pending, or is an application of which a currently co-pending application is entitled to the benefit of the filing date. 
     The United States Patent Office (USPTO) has published a notice to the effect that the USPTO&#39;s computer programs require that patent applicants reference both a serial number and indicate whether an application is a continuation or continuation-in-part. Stephen G. Kunin,  Benefit of Prior - Filed Application , USPTO Official Gazette Mar. 18, 2003, available at http://www.uspto.gov/web/offices/com/sol/og/2003/week11/patbene.htm. The present Applicant Entity (hereinafter “Applicant”) has provided above a specific reference to the application(s)from which priority is being claimed as recited by statute. Applicant understands that the statute is unambiguous in its specific reference language and does not require either a serial number or any characterization, such as “continuation” or “continuation-in-part,” for claiming priority to U.S. patent applications. Notwithstanding the foregoing, Applicant understands that the USPTO&#39;s computer programs have certain data entry requirements, and hence Applicant is designating the present application as a continuation-in-part of its parent applications as set forth above, but expressly points out that such designations are not to be construed in any way as any type of commentary and/or admission as to whether or not the present application contains any new matter in addition to the matter of its parent application(s). 
    
    
     CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is related to and claims the benefit of the earliest available effective filing date(s) from the following listed application(s) (the “Related Applications”) (e.g., claims earliest available priority dates for other than provisional patent applications or claims benefits under 35 USC §119(e) for provisional patent applications, for any and all parent, grandparent, great-grandparent, etc. applications of the Related Application(s)). All subject matter of the Related Applications and of any and all parent, grandparent, great-grandparent, etc. applications of the Related Applications is incorporated herein by reference to the extent such subject matter is not inconsistent herewith. 
     BACKGROUND 
     Recent attention to “green” generation of energy has produced a variety of new processes and refinements of existing methods for providing electrical power. However, many renewable energy sources (e.g., solar power and wind power) may be only intermittently available, thus possibly requiring substantial storage capacity in order to provide electricity on demand. Even continuously-available power sources (e.g., nuclear) may benefit from electrical storage allowing intermittent peak loading in excess of continuously-available average capacity. Existing batteries for these purposes can be expensive, especially on a lifetime basis (considering limited cycle lifetimes). 
     Further, existing batteries may have energy densities substantially below those of fossil fuels, thus motivating continued primary use of hydrocarbon fuels for personal transport despite known negative effects of the use of hydrocarbons for such purposes. Improved battery technology could enable more widespread use of electric vehicles and “green” power generation. 
     SUMMARY 
     In one aspect, an electrochemical device includes two electrodes (an anode and a cathode) and an electrolyte arranged to conduct an ionic current from a surface in contact with one electrode to a surface in contact with the other electrode. At least one (or optionally both) of the electrodes includes an electrochemically active fluid layer having fluid properties that permit at least a portion of it to cling to a substantially smooth solid support by a surface energy effect, a surface of the electrochemically active fluid layer being in contact with the electrolyte. 
     If both electrodes include an electrochemically active fluid layer, these layers may be in contact with a common surface of the solid support. The solid support may include a fluid-directing structure such as a surface channel, conduit, or pattern of regions having different wetting properties, any of which may be configured to direct fluid flow via surface tension. The fluid-directing structure may be configured to adjust a fluid surface area in response to pressure, and may be configured to control flow rate or flow direction of a fluid. The fluid-directing structure may be configured to distribute fluid according to a flow pattern selected to optimize an electrical property of the electrochemical device (e.g., by maximizing or minimizing the property, or by adjusting it to obtain a selected value). The device may be configured to dynamically change a property of the fluid-directing structure, such as surface energy, wetting behavior, shape, or temperature, for example in response to a property of the device such as global current, global voltage, local current, local voltage, current density, amount or composition of electrochemically active fluid, or amount or composition of reaction products, and such dynamic change may alter a flow characteristic of the electrochemically active fluid layer. 
     At least a portion of the electrochemically active fluid layer may cling to the substantially smooth solid support in a manner that varies spatially. The substantially smooth solid support may include an electrical contact, and may be curved. The solid support and the fluid layer may differ in composition. 
     The electrolyte may conduct an ionic current by motion of positive ions, negative ions, or both, and may conduct current from cathode to anode, anode to cathode, or both. The electrolyte may include a solid surface which may be impervious to the electrochemically active fluid, and may include a fluid-directing structure configured to direct fluid flow of the electrochemically active fluid layer. The electrolyte may include an ion-transport fluid through which an ion can move to produce the ionic current, and may further include a solid structure, such as a porous structure infiltrated by the ion-transport fluid (e.g., a sponge, a wick, a plurality of fibers, a fabric, a partially sintered body, a mesh, a perforated sheet, a textured surface, or an agglomeration of particles). The ion-transport fluid may wet the porous structure, and the electrochemically active fluid may wet the ion-transport fluid more than it wets the solid structure, including not wetting the solid structure. If the cathode and the anode each include an electrochemically active fluid layer, the ion-transport fluid may wet each of the electrochemically active fluid layers more than they wet one another (including a case in which they do not wet one another). The ion-transport fluid may be supercritical, and may contact an electrochemically active fluid at one or both electrodes. The ion-transport fluid may be immiscible with the electrochemically active fluid. The ion-transport fluid may be connected to an external reservoir, and may be configured to remove heat by flow of the ion-transport fluid. 
     The electrolyte may have a thickness of less than about 1 cm, 1 mm, 100 μm, 10 μm, 1 μm, 100 nm, or 10 nm. It may include a reaction product of at least a portion of the cathode with at least a portion of the anode. If the reaction product is a fluid, it may wet a solid surface of the electrolyte or of at least one of the electrodes, or may cling to a solid surface of at least one of the electrodes. The reaction product may be connected to a reservoir, and the electrolyte may be configured to remove heat by flow of the reaction product. A reaction product of at least a portion of the cathode with at least a portion of the anode may be intermixed with the electrochemically active fluid. Either the electrolyte or one of the electrodes may include a fluid-reacting structure configured to direct a reaction product of at least a portion of the cathode with at least a portion of the anode. 
     The electrochemically active fluid layer may include a liquid, a paste, a gel, an emulsion, a thixotropic fluid, a supercritical fluid, or a non-Newtonian fluid, and may be an ionic or an electronic conductor. It may include a carrier fluid that is not electrochemically active. It may wet or cling to the electrolyte. The fluid layer may include a dissolved gas such as oxygen, or a liquid metal such as an alloy. The liquid metal may be liquid at about 100° C., 50° C., 25° C., or 0° C. The electrochemically active fluid may be connected to an external reservoir, and may be configured to transport heat energy away from the battery. 
     The anode may include lithium, sodium, mercury, tin, cesium, rubidium, potassium, or an alloy, solution, amalgam, or intermetallic compound of any of these. The cathode may include gallium, iron, mercury, tin, sulfur, chlorine, or an alloy, solution, amalgam, or intermetallic compound of any of these. The electrolyte may include perchlorate, ether, graphene, polyimide, succinonitrile, polyacrylonitrile, polyethylene oxide, polyethylene glycol, ethylene carbonate, beta-alumina, or an ion-conducting glass. The electrochemical device may include a cooling system, which may include a heat pipe, a heat exchanger, or a microchannel. 
     In another aspect, a method of supplying electrochemical energy includes connecting an electrical load to a first and a second electrode separated by an electrolyte arranged to conduct an ionic current from a first electrolyte surface in contact with the first electrode to a second electrolyte surface in contact with the second electrode. At least one of the electrodes includes an electrochemically active fluid sheet that clings to a solid support by a surface energy effect in opposition to an acceleration field, such as a gravitational field. A surface of the fluid sheet is in contact with the electrolyte. 
     In another aspect, a method of charging a battery includes connecting an electrical potential to a first and a second electrode separated by an electrolyte arranged to conduct an ionic current from a first electrolyte surface in contact with the first electrode to a second electrolyte surface in contact with the second electrode. At least one of the electrodes includes an electrochemically active fluid sheet that clings to a solid support by a surface energy effect in opposition to an acceleration field, such as a gravitational field. A surface of the fluid sheet is in contact with the electrolyte. 
     In another aspect, a method of charging a battery having an electrode including an electrochemically active fluid layer that clings to a substantially smooth solid support by a surface energy effect includes refreshing the electrochemically active fluid layer by flowing the electrochemically active fluid along the substantially smooth solid support. Refreshing may include removing fluid depleted of an electrochemical species and introducing fluid containing the electrochemical species, and may include flowing the fluid in a substantially laminar flow. 
     In another aspect, a method of refreshing a battery having an electrolyte layer including an ion transport fluid includes refreshing the ion transport fluid by flowing it through the electrolyte layer. Refreshing the ion transport fluid may include removing fluid depleted of an electrochemical species and introducing fluid containing the electrochemical species. 
     In another aspect, a method of refreshing a battery that produces a fluid reaction product of an electrochemical reaction includes refreshing the battery by flowing the fluid reaction product. 
     In another aspect, an electrode for a battery includes an electrochemically active fluid layer that clings to a substantially smooth solid support by a surface energy effect, the electrochemically active fluid layer being configured for contact with an electrolyte. 
     In another aspect, a method of making a battery includes coupling an electrolyte with two electrodes, at least one of the electrodes being configured to support an electrochemically active fluid layer in ionic communication with the electrolyte by a surface energy effect on a substantially smooth solid support. 
     In another aspect, an electrochemical device includes two electrodes (an anode and a cathode), and an electrolyte arranged to conduct an ionic current from one electrode to the other. At least one of the electrodes includes an electrochemically active fluid layer having a surface in contact with the electrolyte, and a micropatterned support including a fluid-directing structure configured to direct the electrochemically active fluid according to a predetermined flow pattern. The micropatterned support may be constructed by micromachining, lithography, molding, printing, stamping, or replica-printing, and may include fluid-directing structures configured to direct a plurality of fluids, each according to a predetermined flow pattern. It may include a first fluid-directing structure configured to direct an electrochemically active fluid of the anode, and a second fluid-directing structure configured to direct an electrochemically active fluid of the cathode. The micropatterned support may include a first fluid-directing structure configured to wet an electrochemically active fluid of the anode, and a second fluid-directing structure configured to wet an electrochemically active fluid of the cathode. It may be configured to spatially vary the contact between the electrochemically active fluid and the electrolyte. 
     The micropatterned support may include a fluid channel, which may have a surface that wets the electrochemically active fluid or may be configured to retain the electrochemically active fluid by surface tension. A dimension of the fluid channel may vary along its length, and it may be parallel to the surface of the electrochemically active fluid in contact with the electrolyte or not parallel to it (e.g., perpendicular). The micropatterned support may include a plurality of fluid channels, which may be interconnected. The micropatterned support may include first and second regions that differ in their wetting behavior with the electrochemically active fluid layer. The fluid-directing structure may include a defined surface topology on the micropatterned support, such as a plurality of surface projections. 
     The electrochemical device may be configured to dynamically change a property of the fluid-directing structure, such as surface energy, wetting behavior, shape, or temperature, for example to alter a flow characteristic of the electrochemically active fluid layer. Dynamically changing the property of the fluid-directing structure may be in response to a property of the device, such as global current, global voltage, local current, local voltage, current density, amount or composition of electrochemically active fluid, or amount or composition of reaction products. 
     In another aspect, a method of supplying electrochemical energy includes connecting an electrical load to first and second electrodes separated by an electrolyte arranged to conduct an ionic current from a first electrolyte surface in contact with the first electrode to a second electrolyte surface in contact with the second electrode, at least one of the electrodes including a micropatterned support including an fluid-directing structure, and flowing an electrochemically active fluid along the micropatterned support in a configuration in which the electrochemically active fluid contacts the electrolyte and is directed by the fluid-directing structure to flow according to a predetermined flow pattern. 
     In another aspect, a method of charging a battery includes connecting an electrical potential to first and second electrodes separated by an electrolyte arranged to conduct an ionic current from a first electrolyte surface in contact with the first electrode to a second electrolyte surface in contact with the second electrode, at least one of the electrodes including a micropatterned support including an fluid-directing structure, and flowing an electrochemically active fluid along the micropatterned support in a configuration in which the electrochemically active fluid contacts the electrolyte and is directed by the fluid-directing structure to flow according to a predetermined flow pattern. 
     In another aspect, a method of charging a battery having an electrode including an electrochemically active fluid layer that flows along a micropatterned solid support and contacts an electrolyte includes refreshing the electrochemically active fluid by flowing it along the solid support according to a predetermined flow pattern. Refreshing the electrochemically active fluid may include removing electrochemically active fluid depleted of an electrochemical species and introducing electrochemically active fluid containing the electrochemical species. Flowing the electrochemically active fluid may include flowing it in a substantially laminar flow. 
     In another aspect, an electrode for a battery includes an electrochemically active fluid layer that clings to a micropatterned solid support by a surface energy effect, the electrochemically active fluid being configured for contact with an electrolyte, and the micropatterned solid support including a fluid-directing structure configured to direct the electrochemically active fluid according to a predetermined flow pattern. 
     In another aspect, a method of making a battery includes coupling an electrolyte with two electrodes including an anode and a cathode, wherein at least one of the electrodes is configured to support an electrochemically active fluid layer in ionic communication with the electrolyte on a micropatterned solid support, the micropatterned solid support including a fluid-directing structure configured to direct the electrochemically active fluid according to a predetermined flow pattern. 
     In another aspect, an electrochemical device includes two electrodes (a cathode and an anode), and an electrolyte arranged to conduct an ionic current from a first electrolyte surface in contact with one of the electrodes to a second electrolyte surface in contact with another of the electrodes. At least one of the electrodes includes an electrochemically active fluid layer having a surface in contact with the electrolyte and a micropatterned support including a fluid-directing structure configured to retain the electrochemically active fluid at a predetermined location. 
     In another aspect, a method of supplying electrochemical energy includes connecting an electrical load to a first and second electrode separated by an electrolyte arranged to conduct an ionic current from a first electrolyte surface in contact with the first electrode to a second electrolyte surface in contact with the second electrode. At least one of the first and second electrodes includes a micropatterned support including a fluid-directing structure. The method further includes flowing an electrochemically active fluid along the micropatterned support in a configuration in which the electrochemically active fluid contacts the electrolyte and is retained by the fluid-directing structure at a predetermined location. 
     In another aspect, a method of charging a battery includes connecting an electrical potential to a first and second electrode separated by an electrolyte arranged to conduct an ionic current from a first electrolyte surface in contact with the first electrode to a second electrolyte surface in contact with the second electrode. At least one of the first and second electrodes includes a micropatterned support including a fluid-directing structure. The method further includes flowing an electrochemically active fluid along the micropatterned support in a configuration in which the electrochemically active fluid contacts the electrolyte and is retained by the fluid-directing structure at a predetermined location. 
     In another aspect, a method of charging a battery having an electrode including an electrochemically active fluid layer that flows along a micropatterned solid support and contacts an electrolyte includes refreshing the electrochemically active fluid layer by flowing the electrochemically active fluid along the solid support while retaining electrochemically active fluid at a predetermined location. Refreshing the electrochemically active fluid layer may include removing electrochemically active fluid depleted of an electrochemical species and introducing electrochemically active fluid containing the electrochemical species. Flowing the electrochemically active fluid may include flowing the electrochemically active fluid in a substantially laminar flow. 
     In another aspect, an electrode for a battery includes an electrochemically active fluid layer that clings to a micropatterned solid support by a surface energy effect, the electrochemically active fluid layer being configured for contact with an electrolyte, and the micropatterned solid support including a fluid-directing structure configured to retain electrochemically active fluid at a predetermined location. 
     In another aspect, a method of making a battery includes coupling an electrolyte with two electrodes (an anode and a cathode). At least one of the electrodes is configured to support an electrochemically active fluid layer in ionic communication with the electrolyte on a micropatterned solid support, the micropatterned solid support including a fluid-directing structure configured to retain the electrochemically active fluid at a predetermined location. 
     In another aspect, an electrochemical device includes two electrodes (a cathode and an anode), and an electrolyte arranged to conduct an ionic current from a first electrolyte surface in contact with one of the electrodes to a second electrolyte surface in contact with another of the electrodes. The cathode includes a first electrochemically active fluid layer configured to cling to a first microfeatured fluid-directing structure arranged to engage the electrolyte, and the anode includes a second electrochemically active fluid layer configured to cling to a second microfeatured fluid-directing structure arranged to engage the electrolyte. The first microfeatured fluid-directing structure may be configured to direct the first electrochemically active fluid according to a first predetermined flow pattern, while the second microfeatured fluid-directing structure may be configured to direct the second electrochemically active fluid according to a second predetermined flow pattern. The first microfeatured fluid-directing structure may be configured to retain the first electrochemically active fluid at a first predetermined location, while the second microfeatured fluid-directing structure may be configured to retain the second electrochemically active fluid at a second predetermined location. The first microfeatured fluid-directing structure may be micromachined, constructed by lithography, or constructed by molding, printing, stamping, or replica-printing. 
     The first microfeatured fluid-directing structure may include a plurality of fibers or a plurality of particles, which may be affixed to a surface of the electrolyte. The first microfeatured fluid-directing structure may includes a fluid channel, which may have a dimension that varies along its length, and may be parallel or not parallel to a surface of the electrolyte. The first microfeatured fluid-directing structure may include a plurality of fluid channels, at least two of which may be interconnected. It may have a property that varies spatially. The electrochemical device may be configured to dynamically change a property of the first microfeatured fluid-directing structure. 
     In another aspect, a method of supplying electrochemical energy includes connecting an electrical load to a cathode and an anode separated by an electrolyte, the electrolyte arranged to conduct an ionic current from a first electrolyte surface in contact with the cathode to a second electrolyte surface in contact with the anode. The cathode includes a first microfeatured fluid-directing structure arranged to engage the electrolyte and the anode includes a second microfeatured fluid-directing structure arranged to engage the electrolyte. The method further includes flowing a first electrochemically active fluid along the first microfeatured fluid-directing structure in engagement with the electrolyte, and flowing a second electrochemically active fluid along the second microfeatured fluid-directing structure in engagement with the electrolyte. 
     In another aspect, a method of charging a battery includes connecting an electrical potential to a cathode and an anode separated by an electrolyte, the electrolyte arranged to conduct an ionic current from a first electrolyte surface in contact with the cathode to a second electrolyte surface in contact with the anode. The cathode includes a first microfeatured fluid-directing structure arranged to engage the electrolyte and the anode includes a second microfeatured fluid-directing structure arranged to engage the electrolyte. The method further includes flowing a first electrochemically active fluid along the first microfeatured fluid-directing structure in engagement with the electrolyte, and flowing a second electrochemically active fluid along the second microfeatured fluid-directing structure in engagement with the electrolyte. 
     In another aspect, a method of charging a battery having an electrode including a first electrochemically active fluid layer that clings to a first microfeatured fluid-directing structure arranged to engage an electrolyte and a second electrochemically active fluid layer that clings to a second microfeatured fluid-directing structure arranged to engage the electrolyte includes refreshing the first electrochemically active fluid layer by flowing the first electrochemically active fluid along the first microfeatured fluid-directing structure. Refreshing the first electrochemically active fluid layer may include removing electrochemically active fluid depleted of a charge carrier and introducing electrochemically active fluid containing the charge carrier. Flowing the first electrochemically active fluid may include flowing the first electrochemically active fluid in a substantially laminar flow. 
     In another aspect, a pair of electrodes for a battery includes a first microfeatured fluid-directing structure arranged to engage an electrolyte and to support a first electrochemically active fluid layer, and a second microfeatured fluid-directing structure arranged to engage the electrolyte and to support a second electrochemically active fluid layer. 
     In another aspect, a method of making a battery includes coupling an electrolyte with two electrodes (a cathode and an anode), the cathode including a first microfeatured fluid-directing structure arranged to engage the electrolyte and to support a first electrochemically active fluid layer and the anode including a second microfeatured fluid-directing structure arranged to engage the electrolyte and to support a second electrochemically active fluid layer. 
     In another aspect, an electrochemical device includes two electrodes (a cathode including a first electrochemically active fluid layer and an anode including a second electrochemically active fluid layer), an electrolyte arranged to conduct an ionic current from a first electrolyte surface in contact with one of the electrodes to a second electrolyte surface in contact with another of the electrodes via an ion-transport fluid, and a fluid control structure configured to engage a controlled fluid through surface tension, the controlled fluid being the first electrochemically active fluid, the second electrochemically active fluid, or the ion-transport fluid. The cathode and/or the anode may further include a solid support, and the electrochemically active fluid layer(s) may cling to the solid support by a surface energy effect. The first and/or second electrochemically active fluid layer may be configured to flow along a surface of the electrolyte. The ion-transport fluid may be configured to flow within or through the device. The electrolyte may further include a solid structure, such as a porous structure infiltrated by the ion-transport fluid. The porous structure may include a sponge, a wick, a plurality of fibers, a fabric, a partially sintered body, a mesh, a perforated sheet, a textured surface, or an agglomeration of particles. The ion-transport liquid may wet the porous structure. At least one of the first and second electrochemically active fluids may wet the ion-transport fluid more than it wets the solid structure, including not wetting the solid structure. The ion-transport fluid may wetseach of the first and second electrochemically active fluid layers more than the electrochemically active fluid layers wet one another, and the electrochemically active fluid layers may not wet one another. The ion-transport fluid may be supercritical. The ion-transport fluid may be in contact with only one of or with both of the first and second electrochemically active fluid layers. It may be immiscible with the electrochemically active fluid, and may be connected to an external reservoir. 
     The electrolyte may be configured to remove heat by flow of the ion-transport fluid. The fluid control structure may configured to retain or to direct flow of the controlled fluid, and may be microfeatured, micropatterned, or substantially smooth. 
     In another aspect, a method of supplying electrochemical energy includes connecting an electrical load to a first and second electrode separated by an electrolyte arranged to conduct an ionic current from a first electrolyte surface in contact with the first electrode to a second electrolyte surface in contact with the second electrode via an ion-transport fluid. The first electrode includes a first electrochemically active fluid layer and the second electrode includes a second electrochemically active fluid layer. The method further includes controlling via surface tension flow of the ion-transport fluid, the first electrochemically active fluid layer, or the second electrochemically active fluid layer. 
     In another aspect, a method of charging a battery includes connecting an electrical potential to a first and second electrode separated by an electrolyte arranged to conduct an ionic current from a first electrolyte surface in contact with the first electrode to a second electrolyte surface in contact with the second electrode via an ion-transport fluid. The first electrode includes a first electrochemically active fluid layer and the second electrode includes a second electrochemically active fluid layer. The method further includes controlling via surface tension flow the ion-transport fluid, the first electrochemically active fluid layer, or the second electrochemically active fluid layer. 
     In another aspect, a method of charging a battery having a first electrode including a first electrochemically active fluid layer, a second electrode including a second electrochemically active fluid layer, and an electrolyte including an ion-transport fluid includes refreshing by flowing the ion-transport fluid, the first electrochemically active fluid layer, or the second electrochemically active fluid layer. Refreshing by flowing may include removing fluid depleted of an electrochemical species and introducing fluid containing the electrochemical species, and may include flowing the fluid in a substantially laminar flow. 
     In another aspect, a method of making a battery includes coupling an electrolyte with two electrodes (an anode and a cathode), the first electrode being configured to support a first electrochemically active fluid layer in ionic communication with the electrolyte and the second electrode being configured to support a second electrochemically active fluid layer in ionic communication with the electrolyte. 
     The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a schematic of an electrochemical device. 
         FIG. 2  is a schematic of an electrode surface for another electrochemical device. 
         FIG. 3  is a schematic of another electrode surface for an electrochemical device. 
         FIG. 4  is a schematic of another electrochemical device. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. 
     As used herein, the term “fluid” includes any condensed phase lacking substantial shear strength, including liquids, pastes, gels, emulsions, and supercritical fluids. Unless context dictates otherwise, materials within electrochemical devices that are described as “fluids” have a fluidic character at the working temperature and pressure of the device, which may be room temperature or another temperature (e.g., 0° C., 25° C., 50° C., 75° C., 100° C., or any other suitable temperature), and ambient pressure or another suitable working pressure. 
     As used herein, the term “smooth,” when used to describe a surface wetted by a fluid layer, includes a surface having a local radius of curvature significantly greater than the thickness of the fluid layer. 
     As used herein, the term “cling,” when used to describe a fluid in contact with a solid, includes a fluid that wets or otherwise substantially adheres to the solid, for example with a force sufficient to maintain contact with the solid in opposition to a gravitational force. 
     As used herein, the term “ionic current” includes any movement of electrical charge created by bulk diffusion or flow of ions. An “ionic current” is said to flow from a positive potential to a negative potential, even if it is produced in part or in whole by a movement of (negatively charged) ions in the opposite direction. A material “conducts” ionic current if it permits ions to pass through it to create a net flow of charge. These ions may be already present in the material or may enter through an interface. 
     As used herein, the term “micropatterned” includes surfaces exhibiting structures of roughly submillimeter size (including micron-scale and nanoscale structures), where these structures form predetermined shapes or have a predetermined effect on fluid flow in their vicinity. Micropatterned surfaces may, but need not, include repeating arrays of features, and may be constructed, for example, by micromachining, lithography, molding (including extrusion), printing, stamping, replica-printing, or other processes. 
     As used herein, the term “microfeatured” includes surfaces exhibiting structures of roughly submillimeter size (including micron-scale and nanoscale structures), where the shapes or flow characteristics of the structures may (but need not) have a random component. 
     As used herein, the term “impervious” includes substances that resist flow of a specified fluid. A substance may still be termed “impervious” to a fluid if it is gradually degraded by the fluid over time. 
       FIG. 1  is a schematic of an electrochemical device such as a battery. As shown, the device includes cathode  100 , anode  102 , and electrolyte  104 . Cathode  100  includes a solid support  106  and a fluid layer  108  that clings to the solid support. In some embodiments, fluid layer  108  may also wet electrolyte  104 . The illustrated electrolyte  104  includes an ion-transport fluid  110  infiltrated into a porous layer  112  (e.g., a sponge, a wick, a plurality of substantially parallel fibers, a fabric, a partially sintered body, a mesh, a perforated sheet, a textured surface such as a surface including a plurality of projections, or an agglomeration of particles of any appropriate shape or size). In some embodiments, ion-transport fluid  110  may wet porous layer  112 . In other embodiments (not shown), electrolyte  104  may be a fluid, a solid, or a combination other than the infiltrated solid illustrated in  FIG. 1  (e.g., a fluid layer that clings to a solid layer). While both cathode  100  and anode  102  are in contact with electrolyte  104  during operation of the device, in some embodiments, either electrode may be in contact only with the solid or only with the liquid portions of the electrolyte  104 , or with both (if both are present). In the illustrated embodiment, anode  102  is a solid structure. In other embodiments (not shown), anode  102  may include a fluid layer and a solid support analogous to those shown in the cathode  100  of  FIG. 1 , and may further include one or more reservoirs as discussed below in connection with cathode  100 . While the illustrated embodiment is substantially flat, in other embodiments the device may be curved, with one or two radii of curvature. 
     In the illustrated embodiment, cathode  100  further includes reservoirs  114  and  116  for cathode fluid layer  108 . During operation of the battery, cathode fluid may flow from reservoir  114  to reservoir  116  along support  106  (which may be a substantially smooth support), replenishing electrochemical species which may be depleted in the cathode fluid (note that “depleted” may include species that are reduced in concentration, rather than totally exhausted). In some embodiments, reservoirs  114  and  116  may be connected, allowing recirculation of cathode fluid. The cathode fluid may be composed primarily of the species that will participate in the electrochemical reaction, or it may include a carrier fluid (which may be electrochemically inert). A complementary half-reaction occurs at anode  102 . Electrolyte  104  supports transfer of at least one ionic species between cathode  100  and anode  102 , while preventing transfer of electrons. The differing chemical potentials of the two half-reactions thus generate an electrical potential across the battery between cathode  100  and anode  102 . 
     For example, in some embodiments, the cathode fluid may be substantially composed of a carrier fluid that is liquid at the desired working temperature (e.g., mercury, gallium, or a gallium alloy such as GALINSTAN™, a near-eutectic alloy of gallium, indium, and tin), doped with a lithium-containing compound such as LiFePO 4 . As lithium ions are converted to neutral lithium in the cathode fluid, depleted fluid flows into reservoir  116 , while fresh lithium ions flow from reservoir  114  into fluid layer  108 . Solid support  106  may be any of the very wide variety of materials wetted by the cathode fluid. In an embodiment including a fluid-surfaced anode as described above, the anode fluid may be a sodium-potassium alloy (e.g., the eutectic NaK 2 ) doped with lithium metal (e.g., at a concentration of about 10 atom-%). Electrolyte  104  may include any of a wide varieties of porous solid supports (e.g., polytetrafluoroethylene or polyethylene terephthalate), infiltrated with an organic solvent (e.g., diethyl ether) containing a dissolved lithium salt such as lithium perchlorate. In some embodiments, it may be possible to dispense with the porous solid support, using an electrolyte layer composed of the fluid organic solvent and (if necessary) a dissolved salt, as long as surface tension or other forces prevent anode  100  and cathode  102  from contacting one another to create an internal short (for example, anode and cathode fluids may wet the electrolyte fluid more than they wet one another, tending to reduce the possibility of a short, or some or all of the fluids may be immiscible). In other embodiments, the electrolyte layer may be a solid having sufficient ion transport properties, such as beta-alumina, a sulfide glass or another ion-conducting glass such as Li super-ion conducting glass (LISICON), a lithium-zinc-germanium oxide glass. Other suitable electrolyte materials are described, for example, in Patel, et al., “Plastic-polymer composite electrolytes: Novel soft matter electrolytes for recharegable lithium batteries,”  Electrochem. Comm.  10(12):1912-1915 (2008); MacFarlane, et al., “Lithium-doped plastic crystal electrolytes exhibiting fast ion conduction for secondary batteries,”  Nature  402:792-794 (1999); and U.S. Pat. No. 4,237,196, “Sodium ion-conducting glass electrolyte for sodium-sulfur batteries” (1980), all of which are incorporated by reference herein. In the illustrated embodiment, the electrolyte layer is connected to reservoirs  118 ,  120  which may be used to refresh the electrolyte fluid in an analogous manner to the refreshment of the cathode fluid using reservoirs  114 ,  116 . 
     The electrolyte layer may be partially or fully composed of a reaction product of the anode and cathode fluids (e.g., the anode and cathode fluids may include monomers that participate in interfacial polymerization). For some such embodiments, it may even be possible to withdraw depleted electrode fluids by continuously removing a solid or liquid reaction product during battery operation. In some embodiments, reaction products may also be found in either the anode or the cathode fluids, in which case they may optionally be removed by flow of the cathode or anode fluids. In some embodiments, reaction products may cling to solid support  106  (or an analogous structure of the anode) by a surface energy effect, thus potentially clearing them from the electrode-electrolyte interface. The solid support may also include one or more fluid-directing structures that facilitate flow of a reaction product. 
     In some embodiments, it is preferable to have as thin an electrolyte as possible while still avoiding arcing between electrodes. An electrode may be as thick as 1 cm or more, but may also be as thin as 1 mm, 100 μm, 10 μm, 1 μm, 100 nm, or even 10 nm. 
     In another embodiment, an electrochemical device such as that shown in  FIG. 1  may be used to recharge a depleted electrochemically active fluid. In such an embodiment, rather than drawing electrical current from the potential difference between the anode and the cathode, a voltage is applied to drive the reaction in reverse, returning the electrochemically active fluid to a higher chemical energy state for later use in the same or another device. 
     In some embodiments, solid support  106  may include one or more fluid-directing features (not shown). For example, solid support  106  may include ripples or channels that direct fluid flow, or areas of variable surface energy that influence wetting behavior of the fluid. In some embodiments, surface energy may be dynamically adjusted, for example using techniques described in Lahann, et al., “A Reversibly Switching Surface,”  Science  299:5605, pp. 371-374 (2003), which is incorporated by reference herein. These fluid-directing features may be selected, for example, to facilitate a flow pattern that optimizes an electrical property (e.g., global or local current, voltage, current density, amount or composition of electrochemically active fluid, or amount or composition of reaction products) of the device. For example, a flow pattern may be chosen that equalizes current flow transverse to the electrode-electrolyte interface by presenting a larger surface area of electrode fluid to the electrolyte as the fluid becomes depleted of charge carriers. In some embodiments, fluid-directing features may be responsive to pressure and/or applied fields, and may adjust flow rate, presented area of fluid, flow direction, or wetting behavior, for example by dynamically changing surface energy, shape, and/or temperature. 
       FIG. 2  is a schematic of an electrode for use with an electrochemical device. The electrode includes an active surface  130  which may be substantially smooth, or may have a shaped or textured surface. In the illustrated embodiment, the device includes a plurality of conduits  132 ,  134 ,  136 ,  138  through the thickness of the electrode (in the illustrated embodiment, perpendicular to the illustrated face of the electrode), which are connected by surface channels  140 ,  142  on the electrode surface. In use, cathodic fluids are flowed from a reservoir (not shown) up through conduits  132 , along surface channels  140 , down through conduits  136 , and into the same or another reservoir (not shown). Anodic fluids are similarly flowed up through conduits  134 , along surface channels  142 , and down through conduits  138 . In the illustrated embodiment, for each set of surface channels, the channels widen as flow proceeds along the surface, which may create a pressure drop to facilitate flow. In some embodiments, the conduits or surface channels may wet their respective fluids or retain fluids via surface tension. Channels or conduits may also be connected, either at the surface or within the electrode. The illustrated face of the electrode is placed in contact with an electrolyte (not shown) as described above. The electrolyte may be fluid, solid, or a combination such as a porous solid infiltrated with a fluid. 
     When the electrolyte is placed in contact with the fluids in surface channels  140 ,  142 , an ionic current from the cathode to the anode is produced in the electrolyte. In some embodiments, surface channels  140 ,  142  are small and/or closely spaced (e.g., on the order of millimeters or microns), allowing a high current density through the electrolyte and a high specific power output for a battery using the illustrated electrode. In some embodiments, the illustrated electrode and the electrolyte may be flexible. Electrodes and electrolyte may be stacked or arranged in other configurations to achieve a desired form factor (for instance, a “jellyroll” configuration of a rolled sheet of electrode and electrolyte, which may be flexible or rigid). 
     The illustrated electrode may be produced by micromachining, lithography, molding (including extrusion), printing, stamping, replica-printing, or other known processes for constructing MEMS and other microscale or nanoscale devices. Other electrode configurations that direct fluid according to a predetermined pattern may also be used—the arrangement illustrated in  FIG. 2  is merely exemplary. In some such embodiments, two electrodes positioned on opposing surfaces of the electrolyte (like the configuration of  FIG. 1 ) may be used. 
       FIG. 3  is a schematic of another electrode surface for an electrochemical device. Electrode plate  150  may be smooth or textured. The surface is treated to produce areas with differing wetting properties (e.g., hydrophilic, hydrophobic, oleophilic, or oleophobic surfaces). Surface treatment may be accomplished, for example, by binding different functional groups to different sites (for example, using soft lithography), by etching (e.g., to change physical properties or to expose a material overcoated with another material), by chemical or physical vapor deposition, by laser processing (e.g., by ablation or surface restructuring, such as by femtosecond laser pulses) by roughening or otherwise physically modifying the surfaces, or by a combination of these techniques. 
     In the illustrated embodiment, the surface is treated at areas  152  and  154  with two different surface treatments. Areas  152  are treated so that they will be wetted by a cathodic fluid, and areas  154  are treated so that they will be wetted by an anodic fluid. In one embodiment, a carrier fluid for a cathodic species is aqueous in nature, while a carrier fluid for an anodic species is nonaqueous, and areas  152  and  154  are each treated to be wetted by aqueous and nonaqueous species, respectively. In use, the fluids may be washed over the surface of electrode plate  150 , and will selectively cling to their respective areas. The electrode may then be placed in contact with an electrolyte (not shown) to produce the electrochemical reaction. Contacts (not shown) placed at the surface treated areas (e.g., connected via the back of electrode plate  150 ) may extract electrical energy from the electrochemical reaction. In some embodiments, the cathodic and anodic fluids will have a greater affinity for the electrolyte than they will for one another, thereby reducing chances for cathodic and anodic fluids to make direct electrical contact. As fluids become depleted in regions  152  and  154 , new fluids may be washed over the surface to replenish them, optionally after first wiping the surface clean of fluid. In some embodiments, this washing may be done at a temperature that prevents excessive reaction of the fluids during the washing process, either by slowing reaction kinetics or by placing at least one of the fluids in a nonreactive (e.g., solid) phase during a portion of the process. 
     Alternatively, fluids may be placed more selectively upon their respective areas (e.g., via channels from the back of electrode plate  150 ), and are retained in position by the differing surface energies of the different regions of electrode plate  150 . In another embodiment, two electrode plates are used, each with retaining areas for a single species of electrode fluid. In the illustrated embodiment, it will be noted that there are twice as many regions for anode fluids as for cathode fluids. In other embodiments, these proportions may be reversed or the proportions of areas may be equal (or any other appropriate ratio, taking into account the quantities, chemical activities, and availabilities of the electrode species). 
     In another embodiment, local surface energy regions  152 ,  154  may be placed directly on the surface of a solid electrolyte. The electrolyte may then be washed with the electrode fluids to deposit them in the appropriate regions. The regions of differing surface energy may all be placed on one common surface of the electrolyte, or they may be on opposing surfaces. 
       FIG. 4  is a schematic of another electrochemical device. Cathode  170  and anode  172  each include a sheet of substantially parallel fibers that may be infiltrated with an electrochemically active fluid as described above. These fibers are separated by electrolyte  174 . In use, the fibers function to guide flow of electrochemically active fluid along the surface of the electrolyte as shown by the arrows. In the illustrated embodiment, the fibers are of substantially uniform thickness, but tapered fibers may also be used to present differing surface areas of fluid to the electrolyte, or the fibers may be curved to define a curved flow path. In some embodiments, the fibers may be affixed to one another or to the electrolyte  174 . 
     In another embodiment, rather than parallel fibers, fluid may be guided along a known path by other structures such as particulates or a porous medium. In any of these cases, capillary flow may draw fluid through the fibers, particulates, or other medium. 
     In general, in order to extract or to store electrical energy in any of the previously described electrochemical devices, contacts will be used to connect the device to an electrical load or an electrical generator. These contacts may be placed at any convenient location in electrical contact with the electrode fluids. In cases where the fluids themselves are conductive, contacts may simply be immersed or otherwise placed in contact with the fluids. In some embodiments, the electrochemically active fluids may be nonconductive or have a relatively low conductivity. In these cases, if there is a support structure supporting the fluids, it may be convenient for the support structure to serve as an electrical connection. 
     Any of the electrochemical devices described herein may generate a certain amount of waste heat, and may be provided with a cooling system. In some embodiments, the flow of electrode or electrolyte fluids may provide cooling. 
     In some embodiments, electrochemical devices may further include circuitry or other mechanisms for monitoring depletion level of the various fluids of the electrodes or electrolyte. In some embodiments, these devices may monitor electrical output in order to infer depletion levels, or may directly measure chemical concentrations or activities. These monitored depletion levels may be used, for example, to determine remaining battery life, or to identify an economic value for depleted fluid (for example when recharging a battery by replacing depleted fluid with fresh fluid). 
     A wide variety of chemical reactions may be used in the electrochemical devices described herein. In principle, any pair of the half-reactions described in a standard electrode potential table may be used at the cathode and anode, although reactions that are substantially separated on the table are preferred for some embodiments as they will yield a higher device voltage. (An example table of standard electrode potentials is appended as Appendix A; however, reactions not listed in Appendix A may also be used in the devices described herein.) In some embodiments, reactants that are liquid at operating temperature (e.g., liquid metals and liquid metal alloys) may be preferred. Exemplary anode materials include lithium, sodium, mercury, tin, cesium, rubidium, potassium, and compounds containing any of these, while exemplary cathode materials include gallium, iron, mercury, tin, chlorine, and compounds containing any of these. Suitable electrolyte materials will generally include salts compatible with the chosen anode and cathode materials. Any of the above materials may include dissolved gases (e.g., oxygen), which may in some embodiments participate in the electrochemical reaction. 
     Various embodiments of electrochemical devices and methods have been described herein. In general, features that have been described in connection with one particular embodiment may be used in other embodiments, unless context dictates otherwise. For example, the electrodes described in connection with  FIG. 3  may be employed in the devices described in connection with  FIG. 1 , or with any of the embodiments described herein. For the sake of brevity, descriptions of such features have not been repeated, but will be understood to be included in the different aspects and embodiments described herein. 
     It will be understood that, in general, terms used herein, and especially in the appended claims, are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of introductory phrases such as “at least one” or “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim  1 ncludes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “an electrode” should typically be interpreted to mean “at least one electrode”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, it will be recognized that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two fluid-directing structures,” or “a plurality of fluid-directing structures,” without other modifiers, typically means at least two fluid-directing structures). Furthermore, in those instances where a phrase such as “at least one of A, B, and C,” “at least one of A, B, or C,” or “an [item] selected from the group consisting of A, B, and C,” is used, in general such a construction is intended to be disjunctive (e.g., any of these phrases would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, or A, B, and C together, and may further include more than one of A, B, or C, such as A 1 , A 2 , and C together, A, B 1 , B 2 , C 1 , and C 2  together, or B 1  and B 2  together). It will be further understood that virtually any disjunctive word or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.” 
     While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims. 
     
       
         
           
               
               
             
               
                 APPENDIX A 
               
               
                   
               
               
                 Half-reaction     
                 E° (V)     
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                  3/2N 2 (g) + H +  + e −      HN 3 (aq) 
                 −3.09 
               
               
                 Li +  + e −      Li(s) 
                 −3.0401 
               
               
                 N 2 (g) + 4H 2 O + 2e −      2NH 2 OH(aq) + 2OH −   
                 −3.04 
               
               
                 Cs +  + e −      Cs(s) 
                 −3.026 
               
               
                 Rb +  + e −      Rb(s) 
                 −2.98 
               
               
                 K +  + e −      K(s) 
                 −2.931 
               
               
                 Ba 2+  + 2e −      Ba(s) 
                 −2.912 
               
               
                 La(OH) 3 (s) + 3e −      La(s) + 3OH −   
                 −2.90 
               
               
                 Sr 2+  + 2e −      Sr(s) 
                 −2.899 
               
               
                 Ca 2+  + 2e −      Ca(s) 
                 −2.868 
               
               
                 Eu 2+  + 2e −      Eu(s) 
                 −2.812 
               
               
                 Ra 2+  + 2e −      Ra(s) 
                 −2.8 
               
               
                 Na +  + e −      Na(s) 
                 −2.71 
               
               
                 La 3+  + 3e −      La(s) 
                 −2.379 
               
               
                 Y 3+  + 3e −      Y(s) 
                 −2.372 
               
               
                 Mg 2+  + 2e −      Mg(s) 
                 −2.372 
               
               
                 ZrO(OH) 2 (s) + H 2 O + 4e −      Zr(s) + 4OH −   
                 −2.36 
               
               
                 Al(OH) 4   −  + 3e −      Al(s) + 4OH −   
                 −2.33 
               
               
                 Al(OH) 3 (s) + 3e −      Al(s) + 3OH −   
                 −2.31 
               
               
                 H 2 (g) + 2e −      2H −   
                 −2.25 
               
               
                 Ac 3+  + 3e −      Ac(s) 
                 −2.20 
               
               
                 Be 2+  + 2e −      Be(s) 
                 −1.85 
               
               
                 U 3+  + 3e −      U(s) 
                 −1.66 
               
               
                 Al 3+  + 3e −      Al(s) 
                 −1.66 
               
               
                 Ti 2+  + 2e −      Ti(s) 
                 −1.63 
               
               
                 ZrO 2 (s) + 4H +  + 4e −      Zr(s) + 2H 2 O 
                 −1.553 
               
               
                 Zr 4+  + 4e −      Zr(s) 
                 −1.45 
               
               
                 TiO(s) + 2H +  + 2e −      Ti(s) + H 2 O 
                 −1.31 
               
               
                 Ti 2 O 3 (s) + 2H +  + 2e −      2TiO(s) + H 2 O 
                 −1.23 
               
               
                 Ti 3+  + 3e −      Ti(s) 
                 −1.21 
               
               
                 Mn 2+  + 2e −      Mn(s) 
                 −1.185 
               
               
                 Te(s) + 2e −      Te 2−   
                 −1.143 
               
               
                 V 2+  + 2e −      V(s) 
                 −1.13 
               
               
                 Nb 3+  + 3e −      Nb(s) 
                 −1.099 
               
               
                 Sn(s) + 4H +  + 4e −      SnH 4 (g) 
                 −1.07 
               
               
                 SiO 2 (s) + 4H +  + 4e −      Si(s) + 2H 2 O 
                 −0.91 
               
               
                 B(OH) 3 (aq) + 3H +  + 3e −      B(s) + 3H 2 O 
                 −0.89 
               
               
                 TiO 2+  + 2H +  + 4e −      Ti(s) + H 2 O 
                 −0.86 
               
               
                 Bi(s) + 3H +  + 3e −      BiH 3   
                 −0.8 
               
               
                 H 2 O + 2e −      H 2 (g) + 2OH −   
                 −0.8277 
               
               
                 Zn 2+  + 2e −      Zn(Hg) 
                 −0.7628 
               
               
                 Zn 2+  + 2e −      Zn(s) 
                 −0.7618 
               
               
                 Ta 2 O 5 (s) + 10H +  + 10e −      2Ta(s) + 5H 2 O 
                 −0.75 
               
               
                 Cr 3+  + 3e −      Cr(s) 
                 −0.74 
               
               
                 [Au(CN) 2 ] −  + e −      Au(s) + 2CN −   
                 −0.60 
               
               
                 Ta 3+  + 3e −      Ta(s) 
                 −0.6 
               
               
                 PbO(s) + H 2 O + 2e −      Pb(s) + 2OH −   
                 −0.58 
               
               
                 2TiO 2 (s) + 2H +  + 2e −      Ti 2 O 3 (s) + H 2 O 
                 −0.56 
               
               
                 Ga 3+  + 3e −      Ga(s) 
                 −0.53 
               
               
                 AgI(s) + e −      Ag(s) + I −   
                 −0.15224 
               
               
                 U 4+  + e −      U 3+   
                 −0.52 
               
               
                 H 3 PO 2 (aq) + H +  + e −      P(white) + 2H 2 O 
                 −0.508 
               
               
                 H 3 PO 3 (aq) + 2H +  + 2e −      H 3 PO 2 (aq) + H 2 O 
                 −0.499 
               
               
                 H 3 PO 3 (aq) + 3H +  + 3e −      P(red) + 3H 2 O 
                 −0.454 
               
               
                 Fe 2+  + 2e −      Fe(s) 
                 −0.44 
               
               
                 2CO 2 (g) + 2H +  + 2e −      HOOCCOOH(aq) 
                 −0.43 
               
               
                 Cr 3+  + e −      Cr 2+   
                 −0.42 
               
               
                 Cd 2+  + 2e −      Cd(s) 
                 −0.40 
               
               
                 GeO 2 (s) + 2H +  + 2e −      GeO(s) + H 2 O 
                 −0.37 
               
               
                 Cu 2 O(s) + H 2 O + 2e −      2Cu(s) + 2OH −   
                 −0.360 
               
               
                 PbSO 4 (s) + 2e −      Pb(s) + SO 4   2−   
                 −0.3588 
               
               
                 PbSO 4 (s) + 2e −      Pb(Hg) + SO 4   2−   
                 −0.3505 
               
               
                 Eu 3+  + e −      Eu 2+   
                 −0.35 
               
               
                 In 3+  + 3e −      In(s) 
                 −0.34 
               
               
                 Tl +  + e −      Tl(s) 
                 −0.34 
               
               
                 Ge(s) + 4H +  + 4e −      GeH 4 (g) 
                 −0.29 
               
               
                 Co 2+  + 2e −      Co(s) 
                 −0.28 
               
               
                 H 3 PO 4 (aq) + 2H +  + 2e −      H 3 PO 3 (aq) + H 2 O 
                 −0.276 
               
               
                 V 3+  + e −      V 2+   
                 −0.26 
               
               
                 Ni 2+  + 2e −      Ni(s) 
                 −0.25 
               
               
                 As(s) + 3H +  + 3e −      AsH 3 (g) 
                 −0.23 
               
               
                 MoO 2 (s) + 4H +  + 4e −      Mo(s) + 2H 2 O 
                 −0.15 
               
               
                 Si(s) + 4H +  + 4e −      SiH 4 (g) 
                 −0.14 
               
               
                 Sn 2+  + 2e −      Sn(s) 
                 −0.13 
               
               
                 O 2 (g) + H +  e −      HO 2 •(aq) 
                 −0.13 
               
               
                 Pb 2+  + 2e −      Pb(s) 
                 −0.13 
               
               
                 WO 2 (s) + 4H +  + 4e −      W(s) + 2H 2 O 
                 −0.12 
               
               
                 P(red) + 3H +  + 3e −      PH 3 (g) 
                 −0.111 
               
               
                 CO 2 (g) + 2H +  + 2e −      HCOOH(aq) 
                 −0.11 
               
               
                 Se(s) + 2H +  + 2e −      H 2 Se(g) 
                 −0.11 
               
               
                 CO 2 (g) + 2H +  + 2e −      CO(g) + H 2 O 
                 −0.11 
               
               
                 SnO(s) + 2H +  + 2e −      Sn(s) + H 2 O 
                 −0.10 
               
               
                 SnO 2 (s) + 2H +  + 2e −      SnO(s) + H 2 O 
                 −0.09 
               
               
                 WO 3 (aq) + 6H +  + 6e −      W(s) + 3H 2 O 
                 −0.09 
               
               
                 P(white) + 3H +  + 3e −      PH 3 (g) 
                 −0.063 
               
               
                 HCOOH(aq) + 2H +  + 2e −      HCHO(aq) + H 2 O 
                 −0.03 
               
               
                 2H +  + 2e −      H 2 (g) 
                 0.0000 
               
               
                 AgBr(s) + e −      Ag(s) + Br −   
                 +0.07133 
               
               
                 S 4 O 6   2−  + 2e −      2S 2 O 3   2−   
                 +0.08 
               
               
                 Fe 3 O 4 (s) + 8H +  + 8e −      3Fe(s) + 4H 2 O 
                 +0.085 
               
               
                 N 2 (g) + 2H 2 O + 6H +  + 6e −      2NH 4 OH(aq) 
                 +0.092 
               
               
                 HgO(s) + H 2 O + 2e −      Hg(l) + 2OH −   
                 +0.0977 
               
               
                 Cu(NH 3 ) 4   2+  + e −      Cu(NH 3 ) 2   +  + 2NH 3   
                 +0.10 
               
               
                 Ru(NH 3 ) 6   3+  + e −      Ru(NH 3 ) 6   2+   
                 +0.10 
               
               
                 N 2 H 4 (aq) + 4H 2 O + 2e −      2NH 4+  + 4OH −   
                 +0.11 
               
               
                 H 2 MoO 4 (aq) + 6H +  + 6e −      Mo(s) + 4H 2 O 
                 +0.11 
               
               
                 Ge 4+  + 4e −      Ge(s) 
                 +0.12 
               
               
                 C(s) + 4H +  + 4e −      CH 4 (g) 
                 +0.13 
               
               
                 HCHO(aq) + 2H +  + 2e −      CH 3 OH(aq) 
                 +0.13 
               
               
                 S(s) + 2H +  + 2e −      H 2 S(g) 
                 +0.14 
               
               
                 Sn 4+  + 2e −      Sn 2+   
                 +0.15 
               
               
                 Cu 2+  + e −      Cu +   
                 +0.159 
               
               
                 HSO 4   −  + 3H +  + 2e −      SO 2 (aq) + 2H 2 O 
                 +0.16 
               
               
                 UO 2   2+  + e −      UO 2   +   
                 +0.163 
               
               
                 SO 4   2−  + 4H +  + 2e −      SO 2 (aq) + 2H 2 O 
                 +0.17 
               
               
                 TiO 2+  + 2H +  + e −      Ti 3+  + H 2 O 
                 +0.19 
               
               
                 Bi 3+  + 2e −      Bi +   
                 +0.2 
               
               
                 SbO +  + 2H +  + 3e −      Sb(s) + H 2 O 
                 +0.20 
               
               
                 AgCl(s) + e −      Ag(s) + Cl −   
                 +0.22233 
               
               
                 H 3 AsO 3 (aq) + 3H +  + 3e −      As(s) + 3H 2 O 
                 +0.24 
               
               
                 GeO(s) + 2H +  + 2e −      Ge(s) + H 2 O 
                 +0.26 
               
               
                 UO 2   +  + 4H +  + e −      U 4+  + 2H 2 O 
                 +0.273 
               
               
                 Re 3+  + 3e −      Re(s) 
                 +0.300 
               
               
                 Bi 3+  + 3e −      Bi(s) 
                 +0.32 
               
               
                 VO 2+  + 2H +  + e −      V 3+  + H 2 O 
                 +0.34 
               
               
                 Cu 2+  + 2e −      Cu(s) 
                 +0.340 
               
               
                 [Fe(CN) 6 ] 3−  + e −      [Fe(CN) 6 ] 4−   
                 +0.36 
               
               
                 O 2 (g) + 2H 2 O + 4e −      4OH − (aq) 
                 +0.40 
               
               
                 H 2 MoO 4  + 6H +  + 3e −      Mo 3+  + 2H 2 O 
                 +0.43 
               
               
                 Bi +  + e −     Bi(s) 
                 +0.50 
               
               
                 CH 3 OH(aq) + 2H +  + 2e −      CH 4 (g) + H 2 O 
                 +0.50 
               
               
                 SO 2 (aq) + 4H +  + 4e −      S(s) + 2H 2 O 
                 +0.50 
               
               
                 Cu +  + e −      Cu(s) 
                 +0.520 
               
               
                 CO(g) + 2H +  + 2e −      C(s) + H 2 O 
                 +0.52 
               
               
                 I 2 (s) + 2e −      2I −   
                 +0.54 
               
               
                 I 3   −  + 2e −      3I −   
                 +0.53 
               
               
                 [AuI 4 ] −  + 3e −      Au(s) + 4I −   
                 +0.56 
               
               
                 H 3 AsO 4 (aq) + 2H +  + 2e −      H 3 AsO 3 (aq) + H 2 O 
                 +0.56 
               
               
                 [AuI 2 ] −  + e −      Au(s) + 2I −   
                 +0.58 
               
               
                 MnO 4   −  + 2H 2 O + 3e −      MnO 2 (s) + 4OH −   
                 +0.59 
               
               
                 S 2 O 3   2−  + 6H +  + 4e −      2S(s) + 3H 2 O 
                 +0.60 
               
               
                 H 2 MoO 4 (aq) + 2H +  + 2e −      MoO 2 (s) + 2H 2 O 
                 +0.65 
               
               
                 O 2 (g) + 2H +  + 2e −      H 2 O 2 (aq) 
                 +0.70 
               
               
                 Tl 3+  + 3e −      Tl(s) 
                 +0.72 
               
               
                 PtCl 6   2−  + 2e −      PtCl 4   2−  + 2Cl −   
                 +0.726 
               
               
                 H 2 SeO 3 (aq) + 4H +  + 4e −      Se(s) + 3H 2 O 
                 +0.74 
               
               
                 PtCl 4   2−  + 2e −      Pt(s) + 4Cl −   
                 +0.758 
               
               
                 Fe 3+  + e −      Fe 2+   
                 +0.77 
               
               
                 Ag +  + e −      Ag(s) 
                 +0.7996 
               
               
                 Hg 2   2+  + 2e −      2Hg(l) 
                 +0.80 
               
               
                 NO 3   − (aq) + 2H +  + e −      NO 2 (g) + H 2 O 
                 +0.80 
               
               
                 [AuBr 4 ] −  + 3e −      Au(s) + 4Br −   
                 +0.85 
               
               
                 Hg 2+  + 2e −      Hg(l) 
                 +0.85 
               
               
                 MnO 4   −  + H +  + e −      HMnO 4   −   
                 +0.90 
               
               
                 2Hg 2+  + 2e −      Hg 2   2+   
                 +0.91 
               
               
                 Pd 2+  + 2e −      Pd(s) 
                 +0.915 
               
               
                 [AuCl 4 ] −  + 3e −      Au(s) + 4Cl −   
                 +0.93 
               
               
                 MnO 2 (s) + 4H +  + e −      Mn 3+  + 2H 2 O 
                 +0.95 
               
               
                 [AuBr 2 ] −  + e −      Au(s) + 2Br −   
                 +0.96 
               
               
                 Br 2 (l) + 2e −      2Br −   
                 +1.066 
               
               
                 Br 2 (aq) + 2e −      2Br −   
                 +1.0873 
               
               
                 IO 3   −  + 5H +  + 4e −      HIO(aq) + 2H 2 O 
                 +1.13 
               
               
                 [AuCl 2 ] −  + e −      Au(s) + 2Cl −   
                 +1.15 
               
               
                 HSeO 4   −  + 3H +  + 2e −      H 2 SeO 3 (aq) + H 2 O 
                 +1.15 
               
               
                 Ag 2 O(s) + 2H +  + 2e −      2Ag(s) + H 2 O 
                 +1.17 
               
               
                 ClO 3   −  + 2H +  + e −      ClO 2 (g) + H 2 O 
                 +1.18 
               
               
                 Pt 2+  + 2e −      Pt(s) 
                 +1.188 
               
               
                 ClO 2 (g) + H +  + e −      HClO 2 (aq) 
                 +1.19 
               
               
                 2IO 3   −  + 12H +  + 10e −      I 2 (s) + 6H 2 O 
                 +1.20 
               
               
                 ClO 4   −  + 2H +  + 2e −      ClO 3   −  + H 2 O 
                 +1.20 
               
               
                 O 2 (g) + 4H +  + 4e −      2H 2 O 
                 +1.23 
               
               
                 MnO 2 (s) + 4H +  + 2e −      Mn 2+  + 2H 2 O 
                 +1.23 
               
               
                 Tl 3+  + 2e −      Tl +   
                 +1.25 
               
               
                 Cl 2 (g) + 2e −      2Cl −   
                 +1.36 
               
               
                 Cr 2 O 7   −−  + 14H +  + 6e −      2Cr 3+  + 7H 2 O 
                 +1.33 
               
               
                 CoO 2 (s) + 4H +  + e −      Co 3+  + 2H 2 O 
                 +1.42 
               
               
                 2NH 3 OH +  + H +  + 2e −      N 2 H 5   +  + 2H 2 O 
                 +1.42 
               
               
                 2HIO(aq) + 2H +  + 2e −      I 2 (s) + 2H 2 O 
                 +1.44 
               
               
                 Ce 4+  + e −      Ce 3+   
                 +1.44 
               
               
                 BrO 3   −  + 5H +  + 4e −      HBrO(aq) + 2H 2 O 
                 +1.45 
               
               
                 β-PbO 2 (s) + 4H +  + 2e −      Pb 2+  + 2H 2 O 
                 +1.460 
               
               
                 α-PbO 2 (s) + 4H +  + 2e −      Pb 2+  + 2H 2 O 
                 +1.468 
               
               
                 2BrO 3   −  + 12H +  + 10e −      Br 2 (l) + 6H 2 O 
                 +1.48 
               
               
                 2ClO 3   −  + 12H +  + 10e −      Cl 2 (g) + 6H 2 O 
                 +1.49 
               
               
                 MnO 4   −  + 8H +  + 5e −      Mn 2+  + 4H 2 O 
                 +1.51 
               
               
                 HO 2   •  + H +  + e −      H 2 O 2 (aq) 
                 +1.51 
               
               
                 Au 3+  + 3e −      Au(s) 
                 +1.52 
               
               
                 NiO 2 (s) + 4H +  + 2e −      Ni 2+  + 2OH −   
                 +1.59 
               
               
                 2HClO(aq) + 2H +  + 2e −      Cl 2 (g) + 2H 2 O 
                 +1.63 
               
               
                 Ag 2 O 3 (s) + 6H +  + 4e −      2Ag +  + 3H 2 O 
                 +1.67 
               
               
                 HClO 2 (aq) + 2H +  + 2e −      HClO(aq) + H 2 O 
                 +1.67 
               
               
                 Pb 4+  + 2e −      Pb 2+   
                 +1.69 
               
               
                 MnO 4   −  + 4H +  + 3e −      MnO 2 (s) + 2H 2 O 
                 +1.70 
               
               
                 H 2 O 2 (aq) + 2H +  + 2e −      2H 2 O 
                 +1.78 
               
               
                 AgO(s) + 2H +  + e −      Ag +  + H 2 O 
                 +1.77 
               
               
                 Co 3+  + e −      Co 2+   
                 +1.82 
               
               
                 Au +  + e −      Au(s) 
                 +1.83 
               
               
                 BrO 4   −  + 2H +  + 2e −      BrO 3   −  + H 2 O 
                 +1.85 
               
               
                 Ag 2+  + e −      Ag +   
                 +1.98 
               
               
                 S 2 O 8   2−  + 2e −      2SO 4   2−   
                 +2.010 
               
               
                 O 3 (g) + 2H +  + 2e −      O 2 (g) + H 2 O 
                 +2.075 
               
               
                 HMnO 4   −  + 3H +  + 2e −      MnO 2 (s) + 2H 2 O 
                 +2.09 
               
               
                 F 2 (g) + 2e −      2F −   
                 +2.87 
               
               
                 F 2 (g) + 2H +  + 2e −      2HF(aq) 
                 +3.05