JP2013543056A - Electrolytic cell - Google Patents

Abstract

The anode region and the cathode region are an electrolytic cell including an anode in the anode region, a cathode in the cathode region, and an anolyte in a flowing fluid communicating with the anode, which are separated by an ion-selective polymer electrolyte membrane. And
The anolyte comprises water and a redox mediator pair that is at least partially oxidized at the anode during operation of the electrolyzer and is at least partially reduced by reaction with water after such oxidation at the anode. Including electrolytic cell.
[Selection] Figure 1

Description

  The present invention relates to an electrolytic cell, and relates to a component of the electrolytic cell, a composition for using the electrolytic cell, and a component for a reagent.

  The most commonly used technology for mass production of hydrogen gas, such as the reforming process, uses fossil fuel as a feedstock. In recent years, concerns about environmental costs associated with the acquisition and use of fossil fuels have increased, and therefore industrial processes that utilize alternative feedstocks are desired.

  A further problem with hydrogen gas production from hydrocarbon feedstock is that the resulting hydrogen gas is not suitable for use in applications where high purity hydrogen gas is required.

  Higher purity hydrogen is obtained by electrolyzing water. It has been known for hundreds of years to electrolyze water, that is, to separate water into its constituent hydrogen and oxygen using electric current.

In its simplest form, water electrolysis is performed by inserting an anode and a cathode connected to a power source into the water. Oxygen (O ₂ ) gas is released at the anode and hydrogen (H ₂ ) gas is released at the cathode. There are many factors that affect the volume of oxygen and hydrogen gas released.

In order to increase the volume of hydrogen gas produced, an electrolyte may be added to the water. It is preferred to select an electrolyte with a cation with a lower electrode potential than H ⁺ , and thus generally alkaline electrolytes containing cations such as Li ⁺ , Na ⁺ , K ⁺ and Cs ⁺ are preferred.

  An electrocatalyst may be used to further enhance the production of hydrogen gas. One system for performing electrolysis using such a catalyst is a polymer electrolyte membrane system. In such systems, a semi-permeable membrane separates one or more anodes and cathodes, allowing passage of protons other than hydrogen or oxygen gas. The anode and cathode may be comprised of an electrocatalyst, most commonly a noble metal electrocatalyst, or they may be applied. In addition or alternatively, the electrocatalyst may be applied to the polymer electrolyte membrane itself.

  Although the use of electrocatalysts greatly improves the purity of the resulting hydrogen gas, these catalysts are generally expensive.

  Conventional polymer electrolyte membrane systems maximize the speed of a number of operations, such as pumping water to the catalyst surface, removing oxygen, removing protons to the anode, and removing electrodes to the external circuit. Since the electrode / membrane / electrode assembly has to be formed, it is complicated.

  Also, the dimensions of the electrolyzer are currently limited, partly because it is necessary to remove gaseous products from the electrolyzer during operation.

  It is desirable to improve the efficiency of producing hydrogen gas by electrolysis of water, and the cost of doing so is comparable to the cost of producing hydrogen gas by a more environmentally harmful process, such as hydrocarbon reforming Or seems to be below it. This can be achieved by one or more of increasing the yield of hydrogen gas, increasing the purity of the hydrogen gas, reducing or eliminating the need for the use of catalysts formed from noble or semi-noble metals. I will.

It is a figure which shows the anode area | region of the electrolytic cell of this invention.

  Thus, according to the first aspect of the invention, the anode region and the cathode region are separated by an ion-selective polymer electrolyte membrane, the anode in the anode region, the cathode in the cathode region, and the fluid in communication with the anode. An electrolyzer comprising an anolyte in a fluid, said anolyte being at least partially oxidized at the anode during operation of the electrolyzer and reacting with water after such oxidation at the anode And an electrolyzer is provided wherein the reaction is driven by a catalyst contained in the anode region.

The redox mediator pair (RMC) is at least partially oxidized at the anode according to the following formula:
RMC _red → RMC _ox + e ⁻

This reaction rate in terms of current density is at least 0.5 A / cm ² , more preferably at least about 1 A / cm ² , and most preferably about 1-2 A / cm ² .

Upon contact with water, the oxidized redox mediator pair is at least partially reduced to obtain oxygen gas and protons according to the following formula (hereinafter referred to as the generation reaction).
RMC _ox + 2H ₂ O → RMC _red + O ₂ + 4H ⁺

  This reaction does not occur at all at the anode. By allowing the generation reaction to take place away from the anode, simpler and less costly anode assemblies can be used. It is also envisioned that gas generation can occur completely away from the main cell assembly.

  Protons formed by the generation reaction are sent to the cathode through the polymer electrolyte membrane to form hydrogen gas.

  A further advantage of the present invention is that the amount of noble metal or semi-noble metal catalyst required to generate hydrogen is substantially reduced or even eliminated compared to conventional electrolysis reactions.

  In order to drive the generation reaction, a catalyst is used in the anode region of the electrolytic cell. The catalyst may be dissolved or suspended in the anolyte. In addition or alternatively, the catalyst may be dissolved at one or more fixed locations along the anolyte flow path, for example, in the form of a fixed bed type arrangement.

Examples of particularly preferred catalysts that may be used in the anode region of the fuel cell of the present invention include transition metals, especially those belonging to Groups 6-9, such as manganese, osmium, rhodium, ruthenium, tungsten and / or iridium. Is mentioned. Polyoxometalate catalysts are particularly preferred. Especially preferred catalysts are ruthenium oxide ^{_{iridium-doped, [Ru III 2 Zn 2 (}} H 2 O) 2 (ZnW 9 O 34) 2] 14-, Cs 10 [Ru 4 (μ-O) 4 (μ- OH) ₂ (H ₂ O) ₄ (γ-SiW ₁₀ O ₃₆ ) ₂ ], Na ₁₄ [Ru ₂ Zn ₂ (H ₂ O) ₂ (ZnW ₉ O ₃₄ ) ₂ ] and / or Li ₁₀ [Ru ₄ ( μ-O) ₄ (μ-OH) ₂ (H ₂ O) ₄ (γ-SiW ₁₀ O ₃₆ ) ₂ ].

Other preferred catalysts include Yagi et al., Photochem. Photobiol. Sci. , 2009, 8, 139-147, especially di-μ-oxodimanganese complexes, such as [(terpy) (H ₂ O) Mn (μ-O) Mn (terpy) (H ₂ O)] ³⁺ , [Mn ₂ (mcbpen) ₂ (H ₂ O) ₂ ] ²⁺ , Mn ₄ O ₄ Cuban complex, Mn porphyrin dimer; dinuclear ruthenium complex such as [(bpy) ₂ (H ₂ O) Ru ( ^{_{μ-O) Ru (H 2}} O) (bpy) 2] 4+, [(terpy) 2 (H 2 O) Ru (bpp) Ru (H 2 O) (terpy) 2] 3+, [(tBu 2 qui) (OH) Ru (btpyan) Ru (OH) (tBu ₂ qui)] ²⁺ and [Ru ₂ (macroN ₆ ) (Rpy) ₄ Cl] ³⁺ ; mononuclear ruthenium complexes, eg, [Ru (tBudnpp ) (Rpy) ₂ OH ₂ ] ²⁺ complex, [Ru (Rterpy) (bpy) OH ₂ ] ²⁺ complex; and ([Ir ^III (R ₁ R ₂ ppy) ₂ (OH ₂ ) ₂ ] ⁺ ), R ₁ is hydrogen or alkyl, in particular methyl, and R ₂ is hydrogen, phenyl or halogen such as F or Cl), and iridium complexes, including cyclometalated iridium aco complexes. .

  One factor that affects the choice of catalyst to be used is the nature of the redox mediator pair to be used in the anolyte. The redox potential of the redox mediator pair should ideally exceed 1.23 V (oxygen reduction potential). However, redox mediator pairs that exhibit a redox potential significantly above 1.23 V are generally undesirable because they reduce reaction efficiency. A redox mediator pair having a redox potential in the range of about 1.25 to about 2.0V is preferred. In particularly preferred combinations, the redox mediator pair exhibits a redox potential of about 1.3V to about 1.8V, about 1.3V to about 1.7V, and most preferably about 1.4V to about 1.6V. Indicates.

The redox mediator pair that may be used in the anolyte present in the electrolytic cell of the present invention is preferably a lanthanum metal atom, most preferably cerium ^{3 + / 4 +} having a redox potential (Nernst) of 1.4V. Can be mentioned. Additional materials, such as acids, may be used to improve the solubility of the redox mediator pair. An example of an acid that can improve the solubility of cerium is methanesulfonic acid.

  The oxidation-reduction potential of the catalyst preferably exceeds the oxidation-reduction potential of oxygen, ideally is similar to or less than 200 mV of the redox potential of the mediator, and about 50-100 mV below the mediator redox potential. More preferably, it is low.

  The anolyte preferably flows through the anode region in the anolyte flow path, which is preferably circulatory.

  As the generation reaction proceeds, the amount of oxygen gas present in the anolyte stream increases.

  In order to prevent an excessive increase in pressure in the anode region of the electrolytic cell, it is preferable to provide means for escaping oxygen from the anode region. That is, in a preferred embodiment, the anolyte is flowed to a separation zone that separates at least a portion of the oxygen gas formed by the generation reaction from the anolyte.

  Separation of oxygen gas from the anolyte is accomplished in a number of ways. For example, bubbles are formed when oxygen gas enters the anolyte. The foamed mixture may flow to the separation chamber. The flow rate in the separation chamber is preferably slower than the anolyte flow rate everywhere in the anolyte region residue. The foamed anolyte is passed through the separation chamber by the natural collapse of the foam bubbles. In order to increase the collapse rate, a cavity forming means may be provided. The cavity forming means may include a cyclone separator that provides rapid separation of the gas and liquid phases.

  The separation zone preferably includes one or more separation chambers in which the anolyte and oxygen gas are separated, a first inlet that receives the anolyte and oxygen gas, and a first that supplies the anolyte to the anode region of the electrolytic cell. An outlet, a second inlet receiving a supply of water and / or redox mediator pair and / or catalyst, and a second outlet for escaping oxygen from the chamber.

  One or more demisters may be provided upstream, downstream or in the second outlet of the second outlet to reduce and possibly eliminate any loss in the anolyte solution.

  In addition, a capacitor may be provided upstream, downstream or in the second outlet to prevent excessive evaporation of water from the anolyte. When a capacitor is used in the electrolytic cell of the present invention, it is preferably arranged to return a predetermined amount of agglomerates back to the system. Prior to returning to the anolyte, the agglomerates are preferably passed through a demister (s).

  In certain arrangements of the present invention, it is preferred that the anolyte channels increase in cross-sectional area in the direction of anolyte flow. This is to increase the volume of the anolyte and oxygen gas, thereby preventing the acceleration of the flow rate. The increase in the cross-sectional area can be performed by a flow path having a branch taper. When the formation of oxygen gas is expected to occur at the same point in the anolyte flow path, for example, when the flowing anolyte is exposed to a packed bed of catalyst (in a fixed position) or a catalyst provided on the anode The use of a channel portion with an increased cross section is particularly useful.

  One or more pumps may be provided at any convenient location within the anolyte flow path to circulate the anolyte solution. Preferably, at least one pump is installed between the downstream end of the separation zone and the upstream end of the anode.

  One skilled in the art will be familiar with materials that may be used to produce the polymer electrolyte membrane.

  The polymer electrolyte membrane is preferably adapted so that protons pass from the anode side to the cathode side through the membrane during operation of the electrolytic cell. The membrane is preferably selective for protons over other cations.

  The membrane may be formed of any appropriate material, but preferably contains a polymer substance having a cation exchange ability. Suitable examples include fluororesin type ion exchange resins and non-fluororesin type ion exchange resins. Examples of the fluororesin type ion exchange resin include perfluorocarboxylic acid resin and perfluorosulfonic acid resin. Perfluorocarboxylic acid resins such as “Nafion” (registered trademark) (DuPont), “Flemion” (registered trademark) (Asahi Glass Co., Ltd.), “Aciplex” (Asahi Kasei Corporation) and the like are preferable. Examples of the non-fluorine resin type ion exchange resin include polyvinyl alcohol, polyalkylene oxide, styrene-divinylbenzene ion exchange resin, and metal salts thereof. Preferable non-fluororesin type ion exchange resins include polyalkylene oxide-alkali metal salt complexes. These are obtained, for example, by polymerizing ethylene oxide oligomers in the presence of lithium chlorate or other alkali metal salts. Other examples include phenol sulfonic acid, polystyrene sulfonic acid, polytrifluorostyrene sulfonic acid, sulfonated trifluorostyrene, sulfonated copolymers based on α, β, β trifluorostyrene monomers, and radiation graft membranes. As non-fluorinated membranes, sulfonated poly (phenylquinoxaline), poly (2,6-diphenyl-4-phenylene oxide), poly (aryl ether sulfone), poly (2,6-diphenylenol); acid doped Polybenzimidazoles, sulfonated polyimides; styrene / ethylene-butadiene / styrene triblock copolymers; partially sulfonated polyarylene ether sulfones; partially sulfonated polyether ether ketones (PEEK); polybenzyl sulfonate siloxanes (PBSS).

  The electrode of the electrolytic cell and the polymer electrolyte membrane are preferably arranged in a sandwich type structure in the electrolytic cell, and the cell includes an anode chamber on the anode side of the sandwich structure, and a cathode chamber on the cathode side of the sandwich structure. including.

  The range of materials that may be used to manufacture the anode is known to those skilled in the art. The anode in the electrolytic cell of the present invention may comprise a metal material such as carbon or platinum, nickel and / or metal oxide species. However, it is preferred to avoid expensive anode materials and therefore preferred anode materials include carbon, nickel metal oxides. The anode material may be composed of a fine dispersion of particulate anode material, the dispersion being bound by a suitable adhesive. The anode may be porous, partially porous or non-porous. The anode is designed so that a maximum flow of anolyte is created on the anode surface. Thus, it may consist of a flow regulator or a three-dimensional electrode formed, the liquid flow having a liquid flow path adjacent to the electrode, or in the case of a three-dimensional electrode, the liquid is forced to flow through the electrode. It may be managed in an array. The surface of the electrode may also be formed with an electrocatalyst, or it may be advantageous for the electrocatalyst to adhere in the form of particulates deposited on the surface of the electrode.

  The anode may be a composite electrode primarily comprising an anode material of the type discussed above, further reinforced with particulates of a material such as zirconium oxide, kaolin or zeolite.

  In a preferred embodiment of the present invention, the anode takes the form of an anode assembly that includes an anolyte inlet channel and one or more channels in fluid in communication with the anolyte inlet channel, the channel comprising: The channel wall is defined by a channel wall including one or more anode regions, and at least one channel is not connected to the anolyte inlet channel.

  “Anolyte inlet channel” means a channel that not only directs the anolyte towards the assembly, but also carries the anolyte to the anode. Thus, the inlet provided outside the anode assembly chamber wall, where the anolyte goes to the assembly, is not considered to be an anolyte inlet flow path by itself. However, the flow path supplied by such an inlet is considered to be an anolyte inlet flow path even though it is not connected to the inlet that carries the anolyte to the assembly.

  During operation of the electrolytic cell, the anolyte provides a flow in the fluid that communicates with the anode through the anode assembly of the electrolytic cell. The redox mediator pair is at least partially oxidized at the anode during operation of the electrolytic cell and is at least partially reduced by reaction with water.

  In a preferred embodiment, the anode includes one or more regions that are porous. In such embodiments, the electrolyser is positioned such that the anolyte passes through the porous region (s) of the anode and the redox mediator pair is at least partially oxidized. In arrangements where a porous anode region is used, the partially defined flow path is such that the anolyte is forced to flow through the least resistive path, i.e. the porous area (s) of the anode, to the flow path. In addition, one end may be closed. If the flow path is closed, the porous anode region is provided at least at the closed end of the flow path, but may additionally extend along the entire wall defining the flow path.

  Despite the porosity of the anode region, in some embodiments, substantially all of the channel walls may be formed of an anode material that may or may not be porous. .

  The use of one or more channels that are not connected to the anolyte inlet channel effectively creates a plurality of short channels for the anolyte through the anode. As the anolyte passes through the non-linear flow path, a loss of anolyte velocity is observed. This loss of anolyte velocity advantageously reduces any drop in fluid pressure observed when anolyte passes through the anode assembly without loss. By minimizing the pressure drop, the interaction between the anolyte and the anode region is maximized. In addition, a reduction in flow distance cancels out the flow velocity loss, so that a high total anolyte flow rate through the electrolytic cell can be maintained.

  Minimizing the anolyte pressure drop through the anode assembly is particularly advantageous in assemblies applied to direct the flow of anolyte through the porous anode. If there is a pressure drop in the anolyte flow, the anolyte fluid resistance through the anode (s) will increase. This will have the effect of reducing the total fluid velocity of the anolyte through the anode assembly. Since the viability of the electrolytic cell depends on the high flow rate of the anolyte therethrough, the speed of the anolyte flowing through the porous anode, and thus the pressure of the fluid, is important.

  The linear flow path can be effectively used in an anode assembly that can be used in the electrolytic cell of the present invention. However, in other embodiments, the flow path is non-linear and includes one or more corners and / or angles.

  In the most preferred embodiment, the highest possible ratio of channels is not connected to the anolyte inlet channel.

  The anode is preferably designed to create a maximum flow of anolyte solution on the anode surface. Thus, it may consist of a flow regulator or a three-dimensional electrode formed, the liquid flow having a liquid flow path adjacent to the electrode, or in the case of a three-dimensional electrode, the liquid is forced to flow through the electrode. It may be managed in an array.

  Also, although the electrode surface is intended to be an electrocatalyst, it may be advantageous for the electrocatalyst to be deposited in the form of particulates deposited on the electrode surface.

  In one embodiment, the one or more channels extend from the anolyte inlet channel. It will be understood that one or more of the unconnected channels extend from the anolyte inlet channel at an angle. It is the angle that draws the anolyte inlet channel and channel (s). In a preferred embodiment, the one or more channels extend from the anolyte inlet channel at an angle of 135 or less, 120 ° C. or less, and most preferably 90 ° C. or less. To avoid misunderstandings, the projection angle of one or more flow paths is measured from the vertical axis of the anolyte inlet tube just before the flow path (ie upstream).

  In other arrangements, the anolyte inlet channel may end at the anolyte deposition zone rather than having a channel extending therefrom. In such an arrangement, one or more flow paths may extend from the anolyte deposition zone.

  It is preferable that the flow paths are generally parallel. In a particularly preferred embodiment of the present invention, the plurality of parallel channels extends vertically from the anolyte inlet channel.

  In order to avoid any misunderstandings, it is considered that the channel is not connected to the anolyte inlet channel only if it is parallel to the channel.

  The anode assembly preferably includes an anolyte collection zone. At least a portion of the anolyte collection zone is defined by the outer wall of one or more flow paths. The wall defining the anolyte collection zone may include the anode region (s). The anolyte will accumulate in the anolyte collection zone after exiting one or more flow paths.

  The anolyte collection zone may include a collection channel preferably formed by the outer wall of the channel. In a preferred embodiment, the collection channel will be provided between a plurality of parallel channels and will provide a combined structure. The anode region may be provided in a wall that defines a collection flow path.

  The anode assembly is preferably housed in the chamber. The chamber wall may partially define one or more anolyte inlet channels, one or more channels, one or more collection channels, and an anolyte collection zone.

  The anode assembly is preferably provided with an anolyte outlet channel. In arrangements where an anolyte collection zone is present, the anolyte outlet channel is preferably in fluid communication with the collection zone. In an arrangement where there is no anolyte collection zone, the anolyte outlet channel is preferably in fluid communication with at least one channel.

According to a second aspect of the present invention, a method for operating an electrolytic cell,
a) providing an anode in the anode region of the electrolytic cell and a cathode in the cathode region, wherein the anode region and the cathode region are separated by an ion selective polymer electrolyte membrane;
b) providing an anolyte comprising water and a redox mediator pair;
c) contacting the anolyte with the anode, wherein the anolyte is at least partially oxidized at the anode and, after such oxidation at the anode, is at least partially reduced by reaction with water comprising the steps of: And a step wherein the reaction is driven by a catalyst contained in the anode region.

  To avoid misunderstanding, when describing various aspects of the first aspect of the invention, specifically the characteristics of the electrolyzer, and its constituents and reagents, those characteristics are the same as those of the second aspect of the invention. The same applies to the components and reagents.

  The invention will be described more specifically with reference to the following examples.

Example 1
FIG. 1 illustrates the anode region of the electrolytic cell (10) of the present invention. The electrolyzer (10) includes a series of cathodes (12) and anodes (14) separated by a membrane (16). The anolyte flows through a circulating anolyte channel (20) around the anolyte region. In the illustrated embodiment, the anolyte contains a catalyst dissolved therein. Thereby, the generated reaction is allowed to proceed constantly regardless of the position of the anolyte in the anolyte region. It will be appreciated that in other arrangements where the fixed bed of catalyst is in or adjacent to the anolyte flow path, the rate of the generation reaction depends on the proximity of the anolyte to the catalyst bed.

  As the evolutionary reaction proceeds, protons are produced, which are carried in the anolyte flow path to the anode where they pass through the membrane to the cathode where hydrogen gas is formed. This is obtained via line 18.

  In addition to the production of protons, oxygen gas is also produced by the generation reaction. This is carried to the separation zone 24 in the form of a liquid with entrained bubbles 22.

  The separation zone 24 includes a separation chamber through which the anolyte passes. Decreasing the anolyte flow rate in the separation chamber causes oxygen bubble cavities to form inside the anolyte. To facilitate this process, cavitation means are provided in the form of a cyclone separator (not shown).

  The separation zone is provided with an oxygen outlet 26 that allows oxygen to escape from the separation chamber. A demister and / or condenser that returns any captured water to the anolyte may be provided in or downstream of the oxygen outlet 26. If there is water loss from the anolyte system, additional water can be provided via line 28.

Claims (16)

  An anode region and a cathode region are separated by an ion-selective polymer electrolyte membrane, and an electrolysis comprising an anode in the anode region, a cathode in the cathode region, and an anolyte in a flowing fluid communicating with the anode. A bath wherein the anolyte is at least partially oxidized at the anode during operation of the electrolyzer and is at least partially reduced by reaction with water after such oxidation at the anode. An electrolytic cell wherein the reaction is driven by a catalyst contained in the anode region.   The electrolytic cell according to claim 1, wherein the catalyst is provided on a surface of the anode and / or the membrane.   The electrolytic cell according to claim 1, wherein the catalyst is provided on a fixed bed in the anolyte flow path.   The electrolytic cell according to claim 1, wherein the catalyst is dissolved or suspended in the anolyte.   5. The electrolytic cell according to claim 1, wherein the catalyst contains one or more atoms of Group 6 to 9 transition metals.   6. The electrolytic cell according to claim 5, wherein the Group 6-9 transition metal is manganese, osmium, rhodium, ruthenium, tungsten and / or iridium.   The electrolytic cell according to claim 1, wherein the redox mediator pair has a redox potential exceeding 1.25V.   The electrolytic cell according to claim 1, wherein the redox mediator pair has a redox potential of 1.3 V to 1.8 V.   The electrolytic cell according to any one of claims 1 to 8, wherein the redox mediator pair includes cerium.   10. The electrolytic cell according to any one of claims 1 to 9, wherein the anode region is provided with a separation zone and removes at least some oxygen gas from the anolyte.   The electrolytic cell according to claim 10, wherein the separation zone includes a cavity forming means for separating a gas and a liquid phase.   The electrolytic cell according to claim 10 or 11, wherein the separation zone further includes an oxygen gas outlet.   The electrolytic cell according to claim 12, further comprising a capacitor and / or a demister, which may be provided upstream, downstream or in the oxygen gas outlet of the oxygen gas outlet.   The electrolytic cell according to any one of claims 1 to 13, wherein the anode is non-porous, partially porous or porous.   The electrolytic cell according to claim 1, wherein the anode is a composite electrode. A method of operating an electrolytic cell,
a) providing an anode in the anode region of the electrolytic cell and a cathode in the cathode region, wherein the anode region and the cathode region are separated by an ion selective polymer electrolyte membrane;
b) providing an anolyte comprising water and a redox mediator pair;
c) contacting the anolyte with the anode, oxidizing the anolyte at least partially at the anode, and after such oxidation at the anode, at least partially reducing by reaction with water. Wherein the reaction is driven by a catalyst contained in the anode region.

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