WO2015085363A1

WO2015085363A1 - Electrochemical cell without an electrolyte-impermeable barrier

Info

Publication number: WO2015085363A1
Application number: PCT/AU2014/050408
Authority: WO
Inventors: Gerhard Frederick Swiegers; Michael Leigh ANGLISS
Original assignee: Aquahydrex Pty Ltd
Priority date: 2013-12-10
Filing date: 2014-12-10
Publication date: 2015-06-18
Also published as: US20160312370A1

Abstract

In one aspect there is provided an electrochemical cell without an electrolyte- impermeable barrier. In another aspect there is provided an electrochemical cell comprising a liquid electrolyte, a cathode and at least one cathode product able to be produced at the cathode, and an anode and at least one anode product able to be produced at the anode. The at least one anode product and the at least one cathode product are substantially separated, and the cell is without an electrolyte-impermeable barrier positioned between the cathode and the anode.. There is a relatively low ratio of electrolyte volume to electrode geometric surface area of the cathode or the anode (electrolyte volume (m³) / electrode surface area (m²)). The cell can be operated at a relatively low current density. Optionally, an electrolyte-permeable separator may be employed.

Description

ELECTROCHEMICAL CELL WITHOUT AN ELECTROLYTE.

IMPERMEABLE BARRIER TECHNICAL FIELD iOOl.^'j The present invention relates to electrochemical ceils. In one form, the present invention more specifically relates to the elimination of the need for an electrolyte- impermeable barrier in electrochemical cells, where in a conventional, electrochemical cell an electrolyte dmpenneable barrier would be needed to ensure products from the anode and cathode are kepi separate while allowing ion transport through the eleetroly e-impemieabie barrier, for example as is the case- in commercial water eiecirolysers. BACKGROUND

[002] In. many electrochemical processes different products are generated at the anode and the cathode electrodes. Because the electrodes are most advantageously located in the closest possible proximity to each ther, the products (e.g. gases, in the form of hubbies) may mix, contaminating each other. The product generated at one electrode may also be converted back to its reaetant or destroyed if it contacts the opposite, electrode. To avoid this possibility, electrochemical cells of this type typically employ an electroiyte-impermeable barrier. The eleetrolyte-impemieabie barrier is a physical barrier that lies betwee the electrodes, either partially or fully, Being impermeable to liquid electrolyte, the electrolyte-impermeable barrier stops or hinders the products of the anode from, mixing with the product of the cathode immediately after their formation {e.g. the mixing of dissimilar gas- supersaturated electrolyte solutions generated at the anode and the cathode). The ekctroiyte-iinpermeable barrier is, neve heless_!, also designed so as to allow for electrical communication between the anode and cathode. This usually occurs in the form of an ion current between, the electrodes. Thus, for example-, the electrolyte- impermeable barrier may be a polymeric, ίόη-exchange membrane that allows ions to move from one side of the electrolyte- impermeable barrier acros the electrolyte-impermeable barrier to the other side of the eiecli olyte-jmperraeable .barrier (thereby closing the electrical circuit between the anode and the cathode), but not liquid electrolyte nor associated reaction products of the ions. An electrolyte-impermeable barrier of this type- is sometimes referred to as a "diaphragm-'. Alternatively, the electrolyte-impermeable barrier may be an impermeable solid material which partially but not completely partitions the anode from the cathode, and around whose side's ions may migrate between the electrodes to thereb close th electrical circuit. An electrolyte-impermeable barrier of this type is sometimes referred to as a "skirt", a "partition waif , or a "chamber divider". [003] To illustrate the need for and role of an electfolyte-inipemieabie barrier, one may consider the representative ease of water electrolysis., in this process, water is electrochemieally split into oxygen gas at the anode and hydrogen gas at the cathode as per the half-reactions below

At the anode: 2 ¾0 -»⁽¾ + 4 H* + 4 e^" = 1.23 V

At the cathode: 4 H* + 4 e^~-*2 ¾ E°_red ^ 0.00 V

Overall reaction: 2 H₂0^™ 0₂ -* 2 ¾ E% »^· 1.23 V [004] As can be seen, hydr.oni.um ions (H⁺ also called 'protons'} are generated at the anode and must, migrate to the cathode in order to close the electrical circuit. Thus, the electrolyte-impermeable barrier i a water eleetro-lyser must allow H* ions to move from the anode to the cathode but stop the water electrolyte and associated gas bubbles from movin between the anode and cathode compartments.

[005] In modern-day water eleciroiysers, the electrolyte-impermeable barrier used is most typically a diaphragm comprising sulfonated tetrafiuoroethylene based iIiK ropolymer-copolyniei' material, sold under the trade n me Nation ' which is a "proton-exchange membrane" (or "PEM"), Protons (H^†) are readily able to migrate across such a PEM and thereby move from one electrode to the other. Liquid water electrolyte and associated gas bubble / molecules are, however, blocked from passing through the PEM polymer. In lkaline eleetrolysers, asbestos woven cloths have traditionally been used as electrolyte-impermeable diaphragms in the past. [006] According to an authoritative scientific review of water electrolysis issued by the Danish government lab, Riso, entitled "Pre-lnvestigation of Water Electrolysis" (PSO-F&U; (2008), Pre-Investigation of Water electrolysis, NEI-DK-5057, p. 39-49). the electrolyte -impermeable diaphragm in such an electrolysis eel! must fulfil multiple roles, including the following:

(1) The electrolyte-impermeable barrier must prevent mixing of gas-filled electrolyte from the cathode with gas-filled electrolyte from the anode. Gas evolution at an electrode in an electrochemical cell typically generate a two- phase mixture of liquid electrolyte with dispersed bubbles. Mixing of the anode and cathode electrolyte will result in mixing of the gases, precluding the attainment of high ga purities and electrical efficiencies,

(2) The electrolyte-impermeable barrier must form an effective diffusion barrier for the gas molecules formed at each of the anode and cathode, so as to thereby avoid contamination of the gases by molecular diffusion across the d^'eetroly e-impermeable barrier.

(3) In the ease of an elastic elec rolyte-iinpermeabie barrier, the electrolyte- impermeable barrier may also be useful in preventing the formation of an electrically insulating gas bubble curtain at the front side of the electrodes. This is achieved by locating the electrodes physically close to the electrolyte- iinpenneabie barrier, such that the bubbles are rapidly swept off the face of the electrode.

(4) Most importantly, in order to avoid an uncontrolled increase in the electrical resistance of the electrolysis cell, it i critical that the poles of the electroiyte- impenneable barrier should not become clogged with gas. bubbles. This may occur when mechanical forces dri ve gas bubbles into the mouths of the pores, or when a gas-supersaturated electrolyte solution spontaneousl forms new bubbles inside the pores. In such cases, bubbles may onl form, in small caviti.es of radius r if a certain degree of supersaturation is established according to the equation:

At 30— 60 bar, the simersamration pressures of hydrogen and oxygen are believed to be no more than a few bars. Thus, for electrolyte surface tensions of ca. 200 dyn era^"1, pore diameters of 1-2 micrometers will reliably avoid gas clogging of the electrolyte-impermeable barrier.

(5) The electrolyte-impermeable barrier must also provide a sufficiently high hydrodynamie resistance, of more than ca. 5 cm^'1 eentipoises (cn bar s)^~ so as to avoid mixing of oxygen saturated electrolyte from the anode with hydrogen saturated electrolyte from the cathode due to occasional, operational pressure differences between the cathodic and anodic compartments.

(6) The electrolyte-impermeable barrier must display a low electrical surface specific resistance when immersed in the electrolyte, ideally not exceeding 0.2 cm² so as to avoid high ohmic potential drops within the electrolyte- impermeable barrier at current densities around 1 A cm^"2.

[007] Thus, there is a conventional understanding that electrolyte-impermeable barriers are required in electrochemical cells, A key challenge experienced in the water electrolyse* industry, b way of example, is the high, cost of the most widel used etectrolyte~imperme.ab.le barrier material, Nafion™, which ma routinely retail for prices of U$$5O0-$ 1.500 per square meter at the present time. The excessive, cos of the eieelrolyte-h¾permeable barrier is. beaten, in many wate eieeirolysers only b the still, higher c st of the precious metal, catalysts that must be used; for exam le,: platinum, which is used in electrolysexs with acidic electrolytes, currently trades for around US$1,300 per ounce on world markets, in water eiectr.olyse.rs employing basic electrolyte, the electrolyte-imperaieable barrier is often the highest cost component. [008] Complicating ibis challenge is the fact thai alternative elecirol.yte-im.perrneahle barrier n tte.rials, which may be less costly, generally displa higher resistance to ion (H⁺) transport when used in a cell. This means that such alternative electrolyte- impermeable barrier materials increase the energy requirement to drive the .electrochemical process. i009^'3 The key limitation at the present time in respect of water electrolyser electrolyte- impermeable barriers, is that many commercial water electrolysers operate most efficiently ax current' densities of 1500-3000 niAfe.ro² at voltages of <3 V. At the presen ime however, only expensive electrolyte-impermeable barrier materials like Nation* ¹ membranes are capable of facilitating such current densities at these voltages.

[01.0] It is for these reasons that the US Department of Energy (DOE) have, over many years, instituted well- funded and wide-ranging program seeking to identify suitable, low-cost, low-energy, alternative materials for use. as eiectrolyte-imrjermeable barriers In water electrolyser cells.

[011] The DOE has also funded extensive programs aimed at reducing the high cost of the catalysts used water electrol sers, most particularly the platinum employed in acidic electrolysers and the iridium oxide rased in alkaline electrolysers. These two components- comprise, by far, the major and overwhelming cost, of water electrolyser stacks.

[012] Very similar challenges exist in a wide range of other industrial electrochemical processes, including, for example, the ehior-alkali process for manufacturing chlorine, which is one of the most widel used electrochemical reactions in the world. The obvious way to reduce the capital cost of the cells in. such cases, is to use a simpler, less expensive eleetrolyte-imperrHeahie barrier. [013] In summary, the challenge of findin cheaper and more, energy efficient: alternatives to the electrolyte-impermeable barriers -used in. current electrochemical cells remains a problem, for which a solution is still needed. [014] The reference in this specification to any prior publication for information derived from it), or to any matter which is knovvn, is not, and should not be take as an acknowledgment or admission or any form of suggestion that the prior publication (or information derived from it.) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

SUMMARY

[01.5] This Summary is provided to introduce a selection of concepts in a simplified form that, are further described below in the Examples. This Summary is not intended to identify all of the key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

[016] In. one form., the present invention provides an electrochemical cell without an eleclT lyte-i permeabie barrier positioned between the electrodes (i.e. between the anodeCs) and the ca hodeis}) of the electrochemical cel.!. This is contrasted to a conventional electrochemical cell, where an eiectroiyte-impermeable barrier is required to be present to ensure products, from the anode( s) and (he calhode(s) are kept separate while allowing ion transport through or around the electrolyte-impermeable barrier.

[017] In another form, there- is provided: an electrochemical cell comprising a. liquid electrolyte, cathode and at least, one cathode product able to be produced at the cathode, and an anode and at. least one anode product able to be produced at the anode. ^'The at least one anode product -and the at. least one cathode product are substantially separated, and the cell is without an clectrolyte-imperaieable- barrier positioned between the cathode and the anode.

[01.8] The inventors have discovered that re-configuration of the components and/or their operating; conditions within electrochemical cells, like exemplar water electrolyser cells, provides for the advantageous elimination of any need for an eiectroiyte- impermeable barrier between electrodes. This may be achieved without incurrin a substantial energy and/or a cost penalty. Indeed_* an overall energy and/or cost benefit may instead be realised. [019] Contrary to current practice, the inventors have recognised that at lower current densities, arid preferably with appropriate, improved or ideal electrolytes, there may be a relatively small energy penalty associated with increasing the inter-electrode gap, That is, with use of a strongly ion-conductive electrolyte, the anode and cathode may be located relatively far apart from each other i a cell, without creating an excessive ion- eonduclion resistance and thereby incurring a large energy penalty to operating the cell.

[020] Moreover, at lower current densities, each of the anode and cathode will typically generate a relatively small stream of products {e.g. gas bubbles) per unit area. In die specific ease of product streams comprising gas bubbles that rise to the surface of a Liquid electrolyte, two such well separated and small product streams cm, additionally, be collected in different parts of the cell, thereb avoiding mixing of the gases. Cells may be specifically designed to separately collect the small and distinct streams of gas hubbies.

[0213 Alternatively and optionally, two such well, separated and small. roduct, streams can be directed to different locations within a cell for collection, by ensuring that electrolyte which flows or is pumped^' through the ceil, sweeps the products (e.g. gas bubble streams) away from each other, or otherwise maintains a separation ^'between the product gas bubble streams, and. to different compartments within the cell where they are separately collected,

[022] This need not involve an additional cost, since virtually all such electrochemical cells already require circulating pumps. The onl additional cost , in this non-limiting example, is then incurred in designing the cell so as to ensure that the electrolyte is pumped or flows along pathways that sweep the product streams to different locations for collection. Collection may involve: (i) in cases where the products, are gases: coalescence of the gas bubbles: and drawing off of the gas through a suitable gas outlet or valve; or (ii) in cases where the products are in the liquid phase; physical removal of the electrolyte stream containing the products through a suitable outlet or valve, for isolation or use of the products elsewhere. Various other means of collection may also be used. [023] In effect, and referring to an example only, the inventors have unexpectedly realised that in the case where:

i. a small product stream is generated at the anode and/or the cathode-, and ii. at least one of the product streams involves the generation of gas babbles. and

iii. the anode and cathode are well separated,

then the physical features noted above that, are associated with the optimum electrolyte- impermeable barrier (e.g. maximum pore diameter, supersaturatkm pressure, hydrodyna k resistance and surface specific electrical resistance) are such, that the electrolyte-impefmeabie barrier is not required or may be replaced with a barrier or structure that .is electrolyte-permeable. That is, there is no substantive need for an electrolyte-impermeable barrier ^'between the electrodes at all. Alternatively, an electrolyte-permeable separator, or structure, mat is wholly or substantially permeable (e.g. porous) to the liquid electrolyte may be located between the electrodes in place of an electrolyte-impermeable bamer. For example, a porous plastic sheet, that allows: free .movement of the liquid electrolyte through the porous plastic sheet, provides an electrolyte-permeable separator and may be used instead of an electrolyte-impermeable barrier in electrochemical cells of the present invention. ( 024] The distinction between an eiectrol te-itnpemieabk barrier, that still allows ion transport, and an electrolyte-permeable separator can be very significant when considered from the viewpoint of cost There are a very wide variety of available electrolyte-permeable separators thai are porous to liquids; many of these are commodity materials -that, are already ^'manufactured in. high volume and. at low cost. By contrast, there is a much more limited number of electrolyte -impermeable barrier materials available and only a .relatively small fraction of those have ion-exchange- or other properties that make them suitable as an electrolyte -impermeable barrier in an electrochemical cell. Thus, there generally will be a substantial cost advantage to using an electmlyte-pemieable separator in an electrochemical cell, if a separator is used at all, rather than an electrolyte-impermeable- barrier. Still more inexpensive would be to not have an electroiyte-permeahie separator between the electrodes. [025] Thus, in an example embodiment there is provided an electrochemical cell without m electrolyte-impermeable barrier and with an ekctrolyie-perraeable separator between the electrodes. In another example embodiment there is provided an electrochemical ceil without an elecfirolyfe-impermeable barrier and without an .electrolyte-permeable separator between the electrodes. Preferably, the electrochemical ceil, is an electro-synthetic cell (i.e. a commercial ceil having industrial application) or an electro-energy cell {e.g. a fuel ceil). In another example, the cell utilizes abiologicai manufactured components. [026] In nesting the above, tile inventors recognised that, there is., of course, a larger trade-off in cost, in that a cell of the above alternative design needs electrodes with a substantially greater surface area than does a conventional cell, in order to generate the same overall quantity of products. For example, a cell based on the above alternative approach and operating at a low current density of 10 mA/cnr would, in one example, have to emplo about ISO-times mom electrode surf ce area than, a conventional cell operating at 1.800 mA/cm , in order to generate the same overall, quantity of products (assuming no changes- in microscopic pore structure of the electrode material).

[027] Furthermore, the inventors have recognized that another benefit of operating at low current density is that, at low current densities, one may make use of inexpensive catalysts and electrodes, and still facilitate the electrochemical transformation with high energy efficiency. For example, in the case of water electrolysis, one may avoid using very expensive precioas metal catalysts, like platinum, or iridium ruthenium oxide, which are essential to achieving high energy efficiencies at high current densities. Instead, one may instead use cheaper, Earth- bundant materials, like nickel or manganese / cobalt oxides. At low current densities, the cheaper catalysts ma readil achieve or even surpass the energy efficiencies achieved by the expensive catalysis at high current densities, [028] Alternatively, one may still mate use of precioas metal catalysts but at: low current density operation, one would typically require orders of magnitude less of the precious metal catalysts per unit area than is conventionally required. Low current densit operation may, in thi way, also result in lower overall costs. [029] Thus, e ample cells of the a!teraative designs and operation, may, n fact, achieve better overall cost and energy efficiencies than existing, conventional electrochemical cell technology,

[0.30] The inventors have farther recognised that a cell having a large geometric electrode surface area can only be operated viably, i.e. commercially, at a low current density if the ratio of the electrolyte volume (unit; m^J) to the electrode surface area (unit: m²) of either the cathode or the anode, is relatively low. The electrode surface area, of either the cathode(s) or the anode(s) separately, refers to the geometric surface area of the cathode(s) or the anode(s). The geometric surface area is the macroscopic surface area of the cathode(s) or the anode(s) (i.e. not including microscopic pores that might provide a higher elecirochemically active surface area). For example, if the ratio of electrolyte volume to the geometric surface area of one of the electrodes (electrolyte volume : electrode surface area) is 1 : 1, or in fractional notation electrolyte volume / electrode surface area is 1 m. (unit: metres), then a conventional cell operating at 1800 mA/cm² with an electrode surface area of 1 m² and an electrolyte volume of 1 m³ cannot he adapted to low current density operation at 10 mA/cm² to achieve the same overall output, since increasing the electrode surface area by 180-fold will require an increase in the electrolyte volume to 180 n.v\ which would be impractical and unviable. For (his reason, a cell operating at a low current density can only do so practically if it- has- relatively low ratio of electrolyte volume to electrode surface area expressed in ^•fractional notation (unit: in), i.e. a relatively low ratio of electrolyte volume : electrode surface area. If there is an array of cathodes, then, the electrode surface area is the geometric surface area of the cathodes in the array of cathodes. If there is an array of anodes, then the electrode surface area is the geometric surface area of the anodes in the array of anodes.

10313 In one example, the ratio of electrolyte volume to electrode surface are is less than or about 0.1 m (or 100 mm) (i.e. 1 m^J : 1 m"). In another example, the ratio is less than, or about 0.01 m (or 10 mm). In another example, the ratio is less than or about 0 001 m (or 1 mm). In another example, the ratio is less than or about 0.0001 m (or 100 μτη). In another example, the ratio is les than or about 0.00001 m (or 10 urn). In another example, the ratio is less than or about 0.000001 m (or 1 μιτι). hi another example, the ratio is less than of about.0.0000001 m (or 0.1 μηι). In another example, the ratio is less than or about 0.00000001 m (or 0.0 ί μπι). I another example, th ratio is less than or about 0.000000001 m (or 0.001 μιη).

[032] In another example form, there is provided an electrochemical cell, comprising a cathode located in a cathode compartment and an anode located in a physically separated anode compartment, and at least two fluid passages allowing an electrolyte to flow between the cathode compartment and the anode compartment,

[033] In another example form, there is provided an electrochemical cell, comprising a cathode that in operation may produce a cathode product, and an anode that in operation may produce an anode product. The cell also includes an electrolyte, and the cathode and the anode are separated within the cell. Preferably,, at least one product from the cathode, if any are produced, and/or at. least one product from the anode, if any are produced, are directed to different locations ,

[034] In another example fomi, there is provided for the partial or complete elimination of a. need for an electrolyte-impermeable barrier between the electrodes in electrochemical cells, .in which dissimilar products are generated at the anode and the cathode. In one form., this can be achieved by:

locating the anode(s) and. the cathode(s) in substantiall separate locations within the cell, whereby;

a product stream from the anode(s), if present, and a product stream from the cathode(s), if present, are directed to different locations; and,

wherein the cell is operated at a relatively low current density,

[035] Optionally, but not essentially, the cell ma be so configured that circulating electrolyte separately sweeps the product stream(s) and/or intermediate ion(s) from the ea.thode(s and/or the anode(s) to different locations within, the cell, from where the products may be separatel collected in pure or near-pure form. [036] Optionally, but not essentially, an electrolyte- ermeable separator through which liquid electrolyte is able to move freely, may be positioned between or partially between the electrodes, such as being located in the inter-electrode gap between the anode and cathode to assist with the complete .separation of the product, streams originating from the anode and the cathode. The electrolyte-permeable separator is. distinguished from an dectrol te-impernieable barrier in that the electrolyte-permeable separator permits free liquid electrolyte, movement across the thickness of the electrolyte-permeable separator, whereas a electrolyte-impermeabie barrier does not. An example of an electrolyte-permeable separator is a plastic sheet that is .freely permeable by a liquid electrolyte. Examples of such sheets include, for example, woven polymer or natural fabrics having large, liquid-permeable holes / pores through: the Mi thickness of the sheets.

[037] Preferably, but not exclusively, the cell employs an electrolyte that has a high ionic conductivity to thereb ensure a. low overall resistance to the electrical current.

[038] Preferably, but not excl sively, the cell operates a a low current density, This is preferably,, but not exclusively, less than or about. 1 niA/ena'\ In an alternative embodiment, this is preferably, but not exclusively, less than or about 20 mA/cffi^*. in an. alternative -embodiment, this is preferably, but not exclusively: less than or about 70 niA/cnr. In a still further alternative embodiment, this is preferably, but not exclusively, less than or about. 250 mA/cm-². in additional embodiments, this is preferably, but not exclusively,, less than or about 500 mA c.nrⁱ, or less than or about 1000 mA/em².

BRIEF DESCRIPTIO OF THE DRAWINGS

[039] Illustrative embodiments will now be described solely by way of non-!in iting examples and with, reference to the accompanying figures. Various example embodiments will be apparent from the following description, given by way of example only, of at least one preferred but non-limiting embodiment, described in connection with the accompanying figures. [040] Figures 1(a) and 1(b) illustrate example tank electrochemical cells (e.g. eleelrolysers) without, an. electro.1 yte-itn.pernj.eabk· barrier between the anode(s) and eathode(s). [041] Figure 2 schematically illustrates an example electrochemical cell (e.g., eleeirolyser) without an electrolyte-impermeable barrier between the anode(s) and eathode(s) and having circulating electrolyte.

EXAMPLES

[042] The following modes, features or aspects, given by way of example only, are described in order to provide a more precise understanding of the subject matter of a preferred embodiment or embodiments. [043] In one example there is provided an electrochemical cell, comprising cathode that in operation produces a cathode product, and an anode that in operation produces an anode product. The electrochemical cell, comprising the cathode, the anode and. an electrolyte, is without an electrolyte-impermeable barrier positioned between the cathode and the anode. The cell also includes an electrolyte, and the cathode and the anode are separated within the ceil, and fee cathode product and. the anode product are directed to different locations. The ceil can be operated at a low current density, due to the ratio of a relatively small electrolyte volume to a relatively large electrode geometric surface area. The ratio of electrolyte- volume to electrode geometric surface area can.be expressed as electrolyte volume (ni ) : electrode surface area (m"), or preferably the ratio can be expressed in fractional notation as electrolyte volume ( f / electrode surface area (nf ). To be clear, reference to the electrode surface area refer to either: the macroscopic geometric surface area of the cathode if there is one cathode; the macroscopic geometric surface area of the cathode if there^' i more than one cathode; the macroscopic geometric surface area of the anode if there is one anode; or the macroscopic geometric surface area of the anodes if there is more than one anode. Hence, a relatively low ratio may apply to the cathode(s) and no the anode-(s), to the anode(s) and not the cathode(s), or to both the cafhode(s) and the anode(s). [044] For example, th ratio is less than or about 0,1 m, less than or about 0.0.1 or, les than or .about 0.001, less that! or about 0,0001., less than, or about. 0,00001 , less than or about 0.000001. less than or about 0.0000001 m, less than or abou 0.00000001 m, or less than or about 0.000000001 m. The electrochemical cell is without an electrolyte- impermeable barrier. That .is, the electrochemical cell does not require or include a partial or full electrolyte-intpemteable barrier between the cathode and the anode. In another form, the cell may incorporate a partial or full electrolyte-permeable separator between the anode and the cathode. [045] In a general example, there is provided an electrochemical cell, comprising a liquid electrolyte, a cathode and an .anode. At the cathode at least one cathode product is able to be produced. At the anode at least one anode product is able to be produced. The at least one anode product and the at least one cathode product are substantially separated,, or most preferably separated, after being produced. The ceil is without an eleetfolyte-impewaeable barrier positioned between the cathode and the anode. By between, is also meant partially between, i.e. ther i no electrolyte-impermeable barrier positioned between, wholly or in part, the cathode and the anode, or between part of the cathode and anode (or cafhode(s) and anode(s.) is electrode arrays are used). [046] In an example, the electrolyte flows past either the cathode or the anode, and/or the electrolyte exits the cell after flowing past the cathode or the anode. In another example the electrolyte circulates between the cathode and the anode. The electrolyte can sweep an ion species away from the cathode or the anode. This means the cell does not require or include an electrolyte-impermeable barrier between the cathode and the anode,

[047] In another example, the cathode and or the anode have some degree of porosity to enable electrol te to pass through the cathode and/or the anode. For example, the cathode and/or the anode can be a series of ribbons of thin metallic foil, and the thin metallic foil can be of the orde of about 0.025 mm thick. A spacing between the ribbons can be in the range of about 1 mm to about 20 mm. A spacing between the cathode and the anode can be greater than 10 mm, greater than 35 mm, or greater than 90 mm. In other examples, the ribbon are coated with nano-particiilates of a metal and a binder; the cathode and/or the anode are made at least; partly from nickel; the cathode and/or the anode are made at least partly from titanium; or the cathode and/or the anode are made at least partly from manganese or cobalt oxides. In further examples, the cathode is located in a cathode compartment and the anode is located in an anode compartment, and the cathode compartment and the anode compartment are physically separated,

|048] Preferably, but not exclusively, the cell can be configured and operated in a manner that maximises the energy and cost savings tha can be achieved. Alternatively, the cell .can. preferably, but not exclusively, be configured and operated in a. manner that achieves some energy and cos savings, Alternatively, the cell can preferably, but not. exclusivel , be configured and. operated in a manner that, is suitable in respect, of the energ and cost savings that can be achieved. Preferably, but not. exclusively, the separation of the anode(s) and cathodeis) is limited to the minimum required for a reliable and complete separation of the products in more than 99.99% purity each.

}049] n the representative case of a water e!eetrolyser, where the products are streams of hydrogen or oxygen bubbles, the anode s) and caihode(s) can preferably, but not exclusively, be separated by more than 10 mm. In an alternative embodiment, the anode(s) and cathodeis) can preferably but not exclusively, be separated by more than. .35 mm. In a. still .further alternative, embodiment, the anodets) and cathodeis) can preferably_^ but not exclusively, be separated by more than 90 mm. Preferably, but not exclusively, the bubble streams from each of the anode and cathode can be collected in separate compartments within the cell, within which the gas babbles can be allowed to coalesce to form, a bulk ga phase that will then be collected, dried and stored.

[050] Preferably, but not exclusively, low-cost, Earth-abundant catalysts and conductors cars be used at the anodefs) and cathodeis). For example, in the example case of a water electrolysis cell,, cheap, Earth-abundant materials, like manganese or cobalt oxides can be used for the anode catalyst and nickel used for the cathode catalyst, Preferably, but not exclusively, the cell can be fabricated out of low-cost materials. For example, in the case of a water electrolysis cell, the cell may be fabricated out. of low- cost polymeric materials which may be manufactured using low-cost manufacturing techniques, such as injection moulding or extrusion. [0513 Iti -one, fion-limitiug example emhodmient, ihe ceil is a water electrolyser of a tank design, containing near its base, at least one water inlet regulated by a suitable valve, and containing near its top, at least two gas outlets regulated by suitable gas valves. In this example embodiment, the tank is separated at a defined height, for example about two thirds of the way up, into two physically-di stinct compartments, each of which acts as the gas collection receptacle for gas bubbles from either the cathode or the anode electrodes of the electrolyser, respectively. Each compartment is open at its base to the electrolyte in the cell. Each compartment contains- near its top, a gas outlet regulated by a suitable gas valve. Directly below each compartment, are located closely-packed arrays of electrically-connected, conductive sheets or foils, coated with suitable, inexpensive catalysts that serve as either the anodes or the cathodes of the cell (depending on which compartment they lie beneath). The purpose of having in each array, large numbers of very closely packed conductive sheets or foils coated with suitable catalysts, is to maximize the surface area of that particular electrode at the lowest possible cost.

[052] Preferably but not exclusively, the cathode and anode arrays are, at their closest, physically separated by about 35 mm, or greater, this being the minimum separation that ensures that bubble streams created at each of the arrays only rise into the compartments for whic they are designated:.

[053] Preferably, hut not exclusively, the electrodes have a large surface are and, even more preferably, the electrode have some degree of porosity so that the electrolyte is made to pass through the electrodes (to thereby ensure near- to complete reaction of a chemical specie at the electrode before the electrolyte is circulated back to the other electrode),

[054] In particular examples, the cell has a relatively small volume of electrolyte, giving rise to a relatively low ratio of electrolyte volume to electrode geometric surface area, ^'For example, the ratio of electrolyte volume to electrode surface area, expressed in fractional notation as electrolyte volume (n ) / electrode surface area (nf), is less than or about 0.1 m (or 100 mm). In one example, the ratio i less than or about 0.01 m (or 10 mm). In another example, the ratio is less than or about 0.001 ra (or 1 mm). In another example, the ratio is less than o about 0,0001 m (or 1.00 μηι). In another example, the ratio is less tha or about 0.00001 m (or 1 μηι). In another e mples the ratio is less than or about 0.000001 m (or 1 μηι). In. another example, the ratio is less than or about 0.0000001 m (or 0.1 μηι). In another example, the ratio is less than or about 0.00000001 m (or 0.01 μπι). hi another example, the ratio is less than or about 0.000000001 m (or 0,001 μιη)

[055] In other examples, the ratio of electrolyte volume to electrode surface area, expressed in fractional notation as electrolyte volume (nt ) / electrode surface are (m^*),_: is in the range of, inclusively, from .about 0.001 μχο to about 0.1 rn, or from about 0.001 μιη to about 0,01 m. or from, about 0,00.1 μηι to about 1 mm, or from about 0.001 μω. t about 100 μηι, or from about 0.001 μπϊ to about 10 μπΐ, or from about 0.001 μτη to about μιη, or from about 0.001 μτη to about 0, 1 μτη, or from about 0.001 μαι to about 0.0 ⁾ um.

[056] Preferably, there is no ion- conductive electrolyte-impermeable barrier, .between the electrodes / electrode arrays, either fully or in part. Optionally, but not. essentially, there may be an eiectrolyte-permea le separator located, either fully or in part, between the electrodes / electrode arrays. An example of such an electrolyte-permeable separator includes a polymer or natural fabric that allows free transport of the electrolyte -through the electrolyte-permeable separator.

[057] In one example, the electrode arrays are configured to not completely fill the compartment above them, but to. leave a headspaee near the top of the chamber for the collection of gases, Preferably, the. tank and the supports for the conductive sheets or foils in each array, are made of durable, economic polymers. The polymers may, optionally, be transparent. (0583 Optionally, there may he a water circulation system in the tank that is configured to separately sweep the bubble streams off each of the cathode and anode arrays in such, a way as to ensure that the bubbles end up in. their correct, designated compartment. In such a case, the minimum separation between the anode and cathode arrays may be smaller than 35 oun.

[059] Optionally, the anode array and the cathode array may be i separate tanks, connected by suitable piping such that there may be additional means to facilitate the removal of gaseous reaction product from the electrolyte in one tank before the electrolyte is circulated back to the following tank. Such additional means includes the use of reduced pressure, use of a media to facilitate the formation of gas bubbles, or the use of a gas-liquid contactor.

[060] Other eoafiguratkms, involving other reactions, can be provided without an electrolyte-impermeable barrier. For example, flat-sheet plate and frame configurations involving: circulating electrolyte that separately sweeps bubbles off multiple,, distinct cathode or anode electrodes and directs them into channels that are exclusively plumbed for hydrogen or oxygen bubble stream collection respectively,

[061] In. a particular example, the anode and/or cathode could be constructed according to the electrode examples, discussed in International Patent Publication No. WO 2012/075546 for "Multi-Layer Water- Splitting Devices", the disclosures of which are incorporated herein .

[062] The following examples provide a more detailed discussion of particular embodiments. The examples are intended to be merely illustrative and not limiting to the scope of the present invention.

Ex m le 1; ta k el ctrolyse? without an electrolyte-impermeable barrier which separates aseous product*

[063] Figure 1(a) schematically depicts an example tank electrolyser 5 without an electrolyte-impermeabie barrier. The electrolyser 5 includes a polymer tank containing a water inlet 10 near the base of electrolyser 5 , and two gas outlets - a first gas outlet 20 (for hydrogen coileetion) and a second gas outlet 30 (for oxygen collection) at the top of the electrolyser 5. The gas outlets 20, 30 sit atop a cathode compartment 200 and an anode compartment 300, respectively. For a top region, for example the top one third of the tank electrolyser 5, the compartments 200, 300 are separated by a solid polymer wall 40, as shown in Figure 1. Note that, in this example, the wall 40 does not extend to any point that is directly between the anode and cathode.

[064] Immediatel below the cathode compartment 200 is located the cathode electrode array 50. Immediately below the anode compartment 300 is located the anode electrode array 60, The arrays 50, 60 are placed so that gas bubbles emanating from them rise into the respective compartment 200, 300 immediately above the electrode array 50, 60 and not into the neighbouring compartment.

[065] Each of the anode and cathode arrays 50, 60 include a series of closely-spaced ribbons of thin metallic foil. The foil is typically titanium or nickel, which is optimally around 0.025 mm thick. The ribbons are typically coated with nano -particulate metal, such as nickel, arid a binder, for example a polymer such, as a f hloro oiymer-copoiymer <e,g, Nafion/¹*¹) (typically 5% of the coating by weight). The ribbons are physically and electrically attached at one or both ends to a metallic, 3D mounting bracket comprising numerous thin arms. The metal of the mounting bracket may be titanium, nickel, or metal-coated stainless steel. Various types of mounting brackets may be used. For example, the mounting bracket may be a series of closely-spaced, parallel, thin, rails from which the ribbons are made to hang in haphazard arrangements (much like clothing on hangers may hang from the racks of a clothing store). The spacing between ribbons may fall in the range of about 1 mm to about 20 mm. Ideally, but not necessarily, the ribbons are able to move during the formation, release and buoyant rise of generated gas bubbles, to thereby ensure that bubbles do not become blocked in the narrow spaces between the ribbons.

[066] The minimum spacing between the cathode and anode array 50, 60 i preferably about 35 mm at their nearest separation, this being as close as they can be located in this configuration without bubbles of hydrogen ending up in the anode compartment and bubbles of oxygen in the cathode compartment. [067] Each mounting bracket and thereby also all of the ribbons which are attached in each electrode array 50, .60, are electrically connected to an external terminal. The cathode array 50 k attached to the external electrical terminal 500. The anode array 60 is attached to the external electrical terminal. 600. The cathode and the anode each extend in a substantially vertical direction. The cathode and the anode are also Substantially parallel to each other,

[068] In order to operate the electrolyser 5, the tank is- filled from water inle 10 with an electrolyte solution. The tank is filled up to the fill-line 70. The electrolyte solution can be 6 M KGB in the case of an alkaline electrolyser, where the electrode arrays 50, 60 comprise of nickel strips. Alternatively, the electrolyte solution may be a strongly acidic electrolyte in the case of an acid electrolyser, where, the electrode arrays 50, 60 compri se of titanium or stainless steel strips. [069] A direc electrical current is now applied over the external terminals 500 and 600. A voltage of 1.8 V would typically be applied such that a low current density of between, inclusively, from about 2 to about. 20 rnA/cm~ is achieved. The ratio of electrolyte volume to electrode surface area is, in this example, less than 0.027 m. The ceil can also be operated at other low current density values, for example less than or about .1000 ffiA/cm^", less than or about 500 A/em², less than or about

less than or about 70 mA co . less than or about 20 mA em^*', or less than or about 10 in A/cm².

[070] As a result of the applied electrical current, bubble streams of hydrogen rise from the cathode array 50 into, exclusively, the cathode compartment 200. In the cathode compartment 200, the bubble coalesce and pure hydrogen gas is collected at the gas outlet or valve 20. At the same time, bubble streams of oxygen rise from the anode array 60 into,, exclusively, the anode compartment 300. In the anode compartment 300, the bubbles coalesce and pure oxygen gas is collected at the gas outlet or valve 30.

[071] During operation, hydronium ions (H⁺; pfotons) freed by the oxidation of water molecules migrate from the anode array 60 to the cathode array 50. This migration is unimpeded in any way by the presence of any sort of ion-permeable and electrolyte- impermeable barrier (e.g. diaphragm) between the anode array 60 and the cathode array 50. Electrons released from the oxidation of water molecules on the catalytic surface of the anode array 60 tra vel through the external electrical, circuit to the cathode array 50.

[072] Thus there is provided an electrochemical cell 5, comprising a cathode 50. an. anode 60 and an electrolyte, without an electrolyte•impermeable barrier positioned between the cathod 50 and the anode 60. [073] Hence, in this example embodiment, the tank eleetrolyser operates as follows. o Using the water valve(s), the tank is fed with water containing suitable ion-conductive electrolyte up to the level of the headspace in each chamber. A sensor may be used to detect and maintain the water level in the eleetrolyser. o The water in the tank fills the spaces between the closely packed conductive sheets or foil coated with catalysts that make up each of the anode and/or cathode arrays. o A suitable current is passed through the anode and cathode arrays, suc that, while the overall current may be large, only a relatively small current density is created at any one point on the conductive sheets or foils coated with catalysts that make up the arrays. o The dissimilar gases thereb generated at each of the arrays (hydrogen at the cathode array and oxyge at the anode array), form bubbles that rise in streams between the closely packed sheets or foils coated with catalyst, to thereby fill the headspace directly above the water in each compartment. o The gas collected in the anode compartment will then be pure oxygen, while the gas collected in the cathode compartment will then be pure hydrogen. o The accumulated gas bubbles in the headspaces atop each array are separately allowed to coalesce and the pure gases are collected by being drawn through the gas valves in each compartment in the tank. [074] Figure 1(b) illustrates an alternative embodiment of the electrolyser in Figure 1(a). The only difference with Figure 1(a) is thai an electrolyte-pertneable separator 4-5 is present between the anode and the cathode in Figure 1(b). The eieetrolyte-pernieabie separator 45 may be a fine metal mesh (eg. a 150 LPI stainless steel mesh), a porous plastic sheet, or a fine polymer net or fabric (e.g. a polypropylene mesh fabric). The eleetrolyre-penneable separator 45 is porous and readily allow transport of the electrolyte through^' its thickness. In so doing, the eleetrolyte-pemieabie separator 45 does not impede electrolyte movement, or block the movement of ions from the anode to the cathode, or vice versa. However, the presence of the electrolyte-permeable separator 45 acts to diminish turbulence in the liquid electroiyte. In so doing, the electT<>lyte-permeable separator 45 helps ensure that the bubbles of gas from each of the anode and cathode rise correctly into their respective collection areas or collection chambers. The tank electrolyser 5, providing an electrochemical cell, can be used an electro-synthetic cell (i.e. a commercial cell having industrial application) or an electro- energy cell (e.g. a fuel cell). The tank electrolyser 5 utilizes abiologieal manufactured components.

Example 2: A tank electrolyser without an eteclrolyie-tmperaieaWe barrier in which circulating electrolyte is used to separately collect gaseous products [075] Figure 2 depicts in a schematic form, another example tank electrolyser 15 of similar design to the electrolyser 5 shown in Figure L except that the cathode and anode compartments have been physically separated into two distinct chambers - an anode chamber 310 (i.e. anode compartment) and a cathode chamber 210 (i.e. cathode compartment). The cathode arra 50 has also been moved t the front of its chamber, while the anode array 60 ha been moved to the rear of its chamber. The two chambers are connected by passages, pipes, conduits or channels which allow the liquid electrolyte to circulate- from one chamber to the other - via a first or front pipe 80 and a second or rear pipe 90. [076] The operation of the electrolyser 15 shown in Figure 2 differs from that in Example 1 only in that the electrolyte is pumped between the two chamber 210, 310 in such a way that the electrolyte circulates from the anode chamber 310 along pipe 80 to the cathode chamber 210, and then back again along pipe 90. In so doing, the electrolyte sweeps hydroniu ions (H*; protons) that are generated at the anode array 60, to the cathode array 50, thereby facilitating and improving the necessary ion- conduction between the electrodes 50, 60. Indeed, if the anode array 60 and cathode arra 50 were located the same distance apart in a single tank filled with electrolyte, then the rate of ion migration between them would be slower than the case where the pump was running and driving the electrolyte through pipes 80 and 90. That is, all else being equal, pipes 80 and 90 represent the shortest pathway for ion migration by the protons between the anode array 60 and cathode array 50 when the pump is running. One effect of the circulating electrolyte is, arguably, to facilitate and speed up ion transport between the electrodes.

[077] That sweeping motion of the circulating electrolyte also acts to facilitate bubble formation and dislodgement at each of the anode array 60 and the cathode array 50. Because these arrays are relocated in their respective chambers toward the inlet for the circulating electrolyte and awa from the outlet for the circulating, electrolyte, any bubbles swept off each array have no option but. to rise into the collection area directly above their respective electrode array. That is, the action of pumping the circulating electrolyte around the cell acts to direct or release the bubbles into their correct collection area, thereby facilitating complete separation of the gases. This is done without need for an electrolyte-impermeable barrier between the electrodes. Indeed, the shortest pathway for ion-conduction between the electrode when the pump is running, along pipe 80 or 90. is entirely free of any eleetiOlyte-impemieable barrie - that is, there is no electroiyte-impermeable barrier present or e uir d, [078] Thus there is provided an electrochemical cell 15 comprising a cathode 50 located in a cathode compartment 21.0 and an anode 60 located in a physically separated anode compartment 310, and at least two fluid passages 80, 90 allowing an electrolyte to flow between the cathode compartment 210 and the anode compartment 310. [079] The schematic illustration of the ekctrolyser 15 in Figure 2 is intended to illustrate how circulating electrolyte may he harnessed and directed with the intention of eliminating the need for an elecfralyte-impermeable barrier in device like an eiectrolyser. As such, the separation that may be needed between the anode chamber 310 and the cathode chamber 210 is exaggerated and is not to scale. This has been done purely for the purpose of illustration. In fact, with the assistance of carefully directed circulating electrolyte, it is possible to locate the cathode and anode arrays in very close proximity to each other.

[080] In another example, the electrode arrays need not be located in physically distinct chambers. The electrode, arrays could be positioned apart in an integrated single compartment or chamber that allows liquid electrol te to flow or be pumped between or past the electrode arrays. For example the integrated single compartment or chamber could be torus or doughnut-shaped, and could have a variety of cross-sectional geometries such as circular, square or rectangular. The electrode arrays can be located to be diametrically opposite, and their respective gas collection areas, sections or chambers can be located above the electrode arrays. The electrolyte can be caused to flow in one direction around the integrated single eompartment or chamber. A variation in cross-section may be provided at different locations about the integrated single compartment or chamber, for example in regions between the electrode arrays the cross- sectional, area may be smaller.

[08.1] In a still further example, electrolyte -permeable separators, such as fine metal meshes (e.g. a 150 LPI stainless steel mesh) or fine polymer nets or fabrics (e.g. a polypropylene mes fabric) may be placed at the entrance to pipe 90 (in the cathode chamber) and/or at the entrance t pipe SO (in the anode chamber). The electrolyte- permeable separators allow free movement of the circulating electrolyte through them, but act to facilitate the bubbles from each of the anode and cathode rising in thei correct respective chambers for collection. Exaiwple 3; An electrochemical cell without an eiectrdiyte-impenneable barrier in which a C03iiiiiii»s flow of electrolyte Is used to separate .and collect products m the liquid phase [082] In strongly alkaline (caustic) environments (e.g. 1 M NaOH), hydrogen peroxide may be manufactured electrochernicafly. The process- uses a gas-diffusion electrode as the .- cathode and a conventional solid-state electrode as the anode. Oxygen i typically fed into the gas-diffusion cathode_* thereby inducing the following half reactions whe a suitable voltage and current are applied (with suitable peroxide-farming catalysis):

Cathode: 2Q» + 2Ho:0 + 4 e^" 2H0>^*+ 20Ή ...(1)

Anode: 4 OH -» < + 2 ¾0 + 4 e^" ...{2}

OVERALL: 0₂ + 2 GH^'-> 2 HG≥^" Ε 0..476 V .,,{3}

-~~ — — —

[083] As can be seen, this overall reaction .consumes base-, OH^', and oxygen, (¼, to produce the h dropero ide ion, HO ^", which is the natural form of hydrogen peroxide under basic conditions.

[084] A critical feature of this electrochemical process- is that the hydroperoxide ion thus formed, is not allowed, to contact the anode, if it does contact the anode, then the anode half -reaction changes to that shown below; Cathode: 0₂ + ¾0 + 2 e ->H(¾ + OH^' ...(.1)

Anode: H0₂ ^" + OH - 0₂ (pure) + I O + 2 e^" ....(4)

OVERALL: 0₂ (air) -» Q₂ (pure) ...(5)

[085 ] that is, a -suitable mechanism, is needed in such a cell, to keep the- hydroperoxide ion formed at the cathode away from the anode, whilst still allowing OH^' ions formed at. the cathode to migrate to the anode, where they are consumed. [0863 In other words, if the hydroperoxide km genera led at the cathode migrates to the anode, the cell will effectively waste the applied electrical energy to simply convert oxygen pumped in at the cathode into oxygen generated at the anode (equation (5) above),

[0873 solution to this problem is to separate the anodes and the cathodes as discrete arrays similar to those described in Example 1, with a continuous stream of 1 M KOH electrolyte pumped over and or through one or both of the electrode arrays. As a result the hydroperoxide ions generated at the cathode are swept away with the electrolyte and. do not have the possibility of contacting the anode. The four equivalents of hydroxide ion (OH^") consumed at the anode (in equation (2)) are provided by the continuous stream of 1 M NaOH, while the two equivalents of Off produced at the cathode (equation {!)) are swept away with the hydroperoxy ions to thereby replace two of the four equi valents consumed at the anode.

[088] Thus, before being passed over the electrode arrays, the electrolyte solution contains only 1 M KOH. After having been swept over the electrode arrays, the electrolyte solution now also contains hydrogen peroxide. The resulting solution may, typically fee used directly in a pulp and paper mill. That is, the electrolyte is not. circulated. Instead, the- electrolyte solution is manufactured as a 1 M NaOH solution,, which is then treated by being passed through a electrochemical cell which imparts the electrolyte solution with high concentrations of hydrogen peroxide. The resulting solution is used directly for pulp and paper treatment.

[089] This example therefore describes a situation in which a product in. the liquid phase in an electrochemical cell is swept away from one electrode fey a continuous stream of electrolyte to prevent the electrolyte from reaching the other electrode. For example, this may be achieved by appropriatel positioning a inlet area and an outlet area for the electrolyte in the cell, suc as near one of the electrodes,

[090] The cathode array in this example is preferably a set of closely packed, high surface area, gas-diffusion electrodes, while the anode array preferabl comprises of conductive ribbons of the type .described in Example I , A cell voltage of 1.6 V is preferably applied, resulting in a. low current density of from about 2 to about 10 mA/cm^*.

[0 1 J Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps bu not the exclusion of any other integer or step or group of integers or steps,

[092] Optional embodiments may also be said to broadly consist in the parts, elements and features referred to or indicated herein, individually or collectively, in any or ail combinations of two or more of -the parts, elements or features, and wherein specific integers are mentioned herein which have known equivalents in the art to which the invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

[093] Although a preferred embodiment has been described in detail, it should be understood that many modifications, changes, substitution or alterations will be apparent to those skilled in. the art wiihout departing from the scope of the present invention.

Claims

The claims.

1. An electrochemical cell comprising:

a liquid^■electrolyte;

a cathode, at least one cathode product able to he produced at the cathode; and

an anode, at least one anode product able to be produced at the anode: wherein, the at least one anode, product and the at least one cathode product are substantially separated, and without an electrolyte-impermeable barrier positioned between the cathode and the anode.

2. The. cell of claim. 1, where the cell is an electro-synthetic or an electro-energy cell,

3. The cell of claim 1 or 2, wherein the cell utilizes analogical manufactured components.

4. The ceil of any one of claims 1 to 3, wherein the ratio of electrolyte volume to electrode geometric surface area of the cathode or the anode (electrolyte volume (ni ) / electrode surface area (m )) is in the range of, inclusively, from about 0,001 μηι to about. 0,1 m.

5. The cell of any one of claims 1 to 3, wherein the ratio of electrolyte volume to electrode geometric surface area of the cathode or the anode (electrolyte volume fm^'' j / electrode surface area (n }) is less than or about 0.1 m (or 100 ram).

6. The ceil of any one of claims 1. to 3, wherein the ratio of electrolyte volume to electrode geometric surface area of the cathode or the anode (electrolyte volume: f??f J / electrode surface are (m^*)) is selected from, the group of:

less than or about 0.01 m (or 10 mm);

less than or about 0.001 m (or 1 mm);

less than or about 0.0001 m (or 100 μηι); less than or about 0,00001 m (or 10 μηι);

less than or about.0.000001 m (or 1 ttnV):

less than or about 0.0000001 m (or 0.1 μνη);

less than or about 0.00000001 m (or 0.01. μ.ηι); and less than or about 0.000000001 m (or 0.001 μιη),

7. Th cell of any one of claims 1 to 6, wherein in operation the cell has a low current density of less than or about 1000 mA/em".

8. The cell of any one of claims 1 to 6, wherein in operation the cell as a low current density of less than or about 500 raA/cra².

9. The cell of any one of claims 1 t 6„ wherein in operation the cell has a. low current density of less than or about 250 mA/enr.

10. The cell of any one of claims I to 6, wherein in. operation the cell has a low current density of less than or abou 70 mA/enr,

11. The cell of any one of claims i to 6. wherein in operation the cell has a low current density of less than or about 20 mA/cm^"'.

12. The cell of any one of claims 1 t 6, wherein in operation the cell has a low current density of less than or about 10 mA/enr.

13. The cell of any one of claims ί to 6, wherein in operation the cell has a low current density of between, inclusively, about 2 to about 20 mA/enr.

14. The cel.] of an one of claims 1 to 13, wherein an electrolyte-perrneable separator is positioned at least partially between the cathode and the anode.

15. The cell of any one of claims 1. to 1.3, wherein an electrolyte-permeable separator is positioned on the shortest pathway for ion-conduction, between the cathode and the anode.

16. The cell of any one of claims 1 to 1.5, wherein the electrolyte flows past the cathode or the anode.

17. The cell of claim 16, wherein the electrolyte exits the ceil after flowing past the cathode or the anode.

18. The cell of any one of claims 1 to 16, wherein the electrolyte circulates between the cathode and the anode.

1 . The cell of any one of claims 1 to 18, wherein the cathode and the anode are separated within the cell, and wherein the cathode product produced at the cathode and the anode product produced at the anode are directed to different collection areas,

20. The cell of any one of claims 1 to 19, wherein the cathode and the anode each extend in a. substantially, vertical direction.

21. The cell of any one of claims 1 to 20, wherein, the cathode and the anode are substantially parallel to each other.

22. The cell of any one of claims 1 to 21, wherein the cathode and/or the anode are an array of electrodes.

23. The ceil of any one of claims 1 to 22, wherein the cathode and/or the anode haye some degree of porosity to enable electrolyte to pass through the cathode and/or the anode.

24. The cell of any one of claims 1 to 23, wherein the cathode and/or the anode are a series of ribbons of thin metallic foil.

25. The cell of claim 24, wherei the thin metallic foil is of the order of about 0.025 mm. thick.

26. The cell of claim 24, wherein a spacing between the ribbons is in the range of about 1 mm to about 20 mm.

27. The cell of claim 24 or 26, wherein the ribbons are coated with nano-particulates of a metal and a binder.

28. The cell of any one of claims 1 to 27, wherein a spacing between the cathode and the anode is greater than 10 mm.

29. The cell of any one of claims 1 to 27, wherein a spacing between the cathode and the anode is greater than 35 mm.

30. The cell of any one of claims 1 to 27, wherei a spacing between the cathode and the anode is greater than 90 mm.

31. The cell of any one of claims 1 to 30, wherein the cathode and/or the anode are made- at least partly from nickel.

32. The cell of any one of claims 1 to 30, wherein the cathode and/or the anode ar made at least partly from titanium.

33. The cell of any one of claims 1 to 30, wherein the cathode and/or the anode axe made at least partly from manganese or cobalt oxides.

34. The cell. -of any one of claims 1 to 33, wherein the cathode is located in a cathode compartment and the anode is located in an anode compartment,

.

35. The cell of claim 34, wherein the cathode compartment and the anode compartment are physically separated.

36. The ceil of claim 34 or 35, wherein the cathode compartment has an associated cathode product outlet or valve,

37. The cell of a y one of claims 34 to 36, wherein the anode compartment ha an associated anode product outlet or valve.

38. The cell of any one of claims 1 to 37, wherein the cell is a water elcctrolyser and the cathode product is hydrogen gas and the anode product is oxygen gas,

39. The cell of any one of claims 1 to 37, wherein the ceil is used to manufacture hydrogen peroxide and the electrolyte flows past the cathode and sweeps hydroperoxide ions formed ar the cathode so that the hydroperoxide ions exit the cell,

40. An electrochemical cell, comprising a cathode, a anode and an electrolyte, wherein the ratio of electrolyte yolume to electrode geometric surface area of the cathode or the anode (electrolyt volume (W) / electrode surface area (m^~)) is in the range of, inclusively, from about.0.001 μοι to about 0.1. m.

41. An electrochemical cell, comprising a cathode located i a cathode compartment and an anode located in a physically separated anode compartment and at least two fluid passages allowing an .electrolyte to flow between the cathode compartment and the anode compartment.