JP2015534607A - Electrolytic electrode catalyst - Google Patents

Abstract

The present invention relates to electrolysis electrocatalysts and electrolysis processes, such as electrolysis of water, more particularly to produce hydrogen at the cathode of a water electrolysis cell or to produce oxygen at the anode of a water electrolysis cell. Use and to a water electrolyzer containing such an electrode catalyst. The electrode catalyst used in the present invention contains a combination of palladium and iridium. [Selection] Figure 1

Description

  The present invention relates to an electrocatalyst for use in an electrolysis process, such as electrolysis of water. In the context of water electrolysis, the present invention relates to the use of such an electrocatalyst to produce hydrogen at the cathode of the electrolyzer or to produce oxygen at the anode of the electrolyzer, as well as water electrolysis comprising such an electrocatalyst. Regarding the tank.

  A number of electrolysis processes have industrially useful applications. For example, electrolysis of water provides a source of hydrogen and oxygen. Alternatively, electrolysis of water containing sodium chloride provides a source of hydrogen, chlorine, and sodium hydroxide.

  The water electrolysis process basically involves breaking down water into its components, but other chemical reactions using water electrolysis are possible. In the water electrolyzer, water is decomposed into its constituent components: hydrogen (gas) and oxygen (gas). The electrolytic cell substantially includes a cathode, an anode, and an electrolyte. Hydrogen is produced by a hydrogen releasing reaction (HER) at the cathode. Oxygen is produced at the anode by an oxygen release reaction (OER).

In acidic media, the half-cell reaction and the total reaction are
Anode: 2H ₂ O (liquid) → O ₂ (gas) + 4H ⁺ + 4e ⁻
Cathode: 4H ⁺ + 4e ⁻ → 2H ₂
Overall: H ₂ O (liquid) → H ₂ (gas) + 1 / 2O ₂ (gas)
It is.

In an alkaline medium, the half-cell reaction and all reactions are
Anode: 2OH ⁻ → 1 / 2O ₂ (gas) + H ₂ O + 2e ⁻
Cathode: 2H ⁺ + 2e ⁻ → H ₂ (gas)
Overall: H ₂ O (liquid) → H ₂ (gas) + 1 / 2O ₂ (gas)
It is.

Other electrolysis chemical reactions include the chlor-alkali process, where the half-cell reaction and all reactions are
Anode: 2Cl ⁻ → Cl ₂ (gas) + 2e ⁻
Cathode: 2H ₂ O + 2e ⁻ → H ₂ + 2OH ⁻
Overall: 2H ₂ O (liquid) + 2NaCl (aqueous solution) → 2NaOH (aqueous solution) + H ₂ (gas) + Cl ₂ (gas)
It is.

  Usually, the anode in a chlor-alkali process is usually based on titanium coated with a rutile oxide catalyst such as a platinum group metal oxide. Chloralkali cathodes are often nickel-based and usually have some platinum group metal catalyst to greatly reduce overvoltage. Newer methods include oxygen gas diffusion electrodes that significantly reduce power consumption to produce sodium hydroxide, which also uses a catalyst to greatly reduce overvoltage.

  Anodization such as electrochlorination, chlorine release, Kolbe reaction, and other organic electrosynthesis, or other electrolysis chemistry such as cathodic reduction in electroplating, electrochemical nitro group reduction, and other organic electrosynthesis There is a reaction. For example, the Kolbe reaction involves the electrolytic decarboxylation of carboxylic acids in the presence of platinum and / or platinum alloys to produce free radicals that primarily cause dimerization of similar radicals. An overview of some electrosynthesis is Rautenbach, Daniel, "The Development of an Electrochemical Process for the Production of Para-Substituted Di-Hydroxy Benzenes", PhD Thesis, Nelson Mandela Metropolitan University, January 2005.

  An electrical bias is present between the cathode and anode to provide energy for this reaction, but this reaction is often on both electrodes to proceed with a lower energy consumption per unit of electrolysis product. Promoted by catalysis at For example, water electrolysers are seen as an attractive and efficient method for large-scale hydrogen production, but cracking water without using a catalyst is much less likely to produce the same amount of hydrogen and oxygen. Requires a lot of energy. Furthermore, the catalysts used in many electrolysis processes are expensive. Electrocatalysts that reduce the energy consumption of the electrolysis process are particularly desirable compared to currently used materials. It is desirable to have an electrocatalyst that is less expensive than current materials while maintaining the same efficiency as currently used materials. Electrocatalysts that reduce both energy consumption and material costs are highly desirable.

  A basic water electrolyzer includes an anode, a cathode, an electrolyte, and a power supply that supplies current. The power supply continues to flow electrons to the cathode where hydrogen ions consume it to form hydrogen gas. Usually, suitable diaphragms are used to hold the gas products separately so that they can be recovered for other uses. The cells of this basic electrolyzer unit can be arranged in series in either a monopolar or bipolar arrangement in order to produce a larger amount of chemical products, in particular product gas. In alkaline applications, the electrolyte is most often a solution of potassium hydroxide; for acidic applications, the electrolyte is a solid polymer membrane that often also functions as a diaphragm. An excellent review of alkaline water electrolysis is K. Zeng, D. Zhang, Progress in Energy and Combustion Science 36 (2010) 307-326; an excellent example of a conventional water electrolyzer is P. Millet et al., It is described in International Journal of Hydrogen Energy 34 (2009) 4974-4982.

  In the chlor-alkali industry, three different types of cells have been used in the past: mercury, membrane, and diaphragm cells. The nature of the reactions involved in the production of chlorine limits the choice of electrode material for the anode. Non-reactive metals such as titanium are often used as electrode substrates, and an electrode catalyst is deposited on the substrate. However, a wider range can be selected on the cathode side. Nickel is often used, which is often impregnated or otherwise impregnated with platinum or other platinum group metal catalysts to reduce the water electrolysis overvoltage and thus the required energy input.

Rautenbach, Daniel, "The Development of an Electrochemical Process for the Production of Para-Substituted Di-Hydroxy Benzenes", PhD Thesis, Nelson Mandela Metropolitan University, January 2005 K. Zeng, Progress in Energy and Combustion Science 36 (2010) 307-326 P. Millet et al., International Journal of Hydrogen Energy 34 (2009) 4974-4982

In a first aspect, the present invention provides the use of an electrocatalyst comprising palladium and iridium to catalyze an electrolysis process.
In one aspect, the electrolysis process is an electrosynthesis process. The electrocatalyst may be part of the anode, part of the cathode, or part of both electrodes.

In one aspect, the electrolysis process is water electrolysis.
In one aspect, the electrolysis process is a chlor-alkali process, also known as electrolysis of aqueous sodium chloride (brine). The electrocatalyst may be part of the anode, part of the cathode, or part of both electrodes. In a particular embodiment, the electrocatalyst is used at the cathode of a chloralkali process.

In one aspect, the electrolysis process is a Kolbe reaction electrolysis process.
In one aspect, the electrolysis process is an electroplating process.
In one aspect, the electrolysis process is an electrogalvanization process.

In one aspect, the electrolysis process is one in which the efficiency of the process is improved by an electrocatalyst.
In one aspect, the electrocatalyst is part of an electrode in an electrolysis system such as a water electrolyzer.

  In one embodiment, an electrocatalyst comprising palladium and iridium is used to catalyze the production of hydrogen at the cathode of the water electrolysis cell. At the cathode, the electrocatalyst of the present invention exhibits a dynamic performance comparable to or greater than that of platinum with respect to the hydrogen releasing reaction, and provides great cost savings. Hydrogen is produced at the cathode of the water electrolysis cell and can be recovered.

  In one aspect, an electrocatalyst comprising palladium and iridium is used to catalyze the production of oxygen at the anode of the water electrolysis cell. At the anode, the electrocatalyst of the present invention provides significant cost savings for oxygen release reactions without compromising dynamic performance compared to iridium oxide. Oxygen is produced at the anode of the water electrolyzer and can be recovered.

  In a further embodiment, an electrocatalyst comprising palladium and iridium is used to catalyze the production of hydrogen at the cathode of the water electrolyser and to catalyze the production of oxygen at the anode of the water electrolyser. Either or both of hydrogen produced at the cathode and oxygen produced at the anode can be recovered.

  In one embodiment, an electrocatalyst comprising palladium and iridium is used to catalyze the production of hydrogen at the cathode of an electrolysis system that produces hydrogen by electrolysis of an aqueous sodium chloride solution. Hydrogen is produced at the cathode of the electrolysis system and can be recovered.

In a second form, the present invention provides an electrolysis electrocatalyst comprising palladium and iridium. For example, the electrolytic cell may be a water electrolytic cell.
In a third aspect, the present invention provides an electrolysis system wherein the electrocatalyst comprises an electrocatalyst comprising palladium and iridium. For example, the electrolysis system may be a water electrolysis cell.

  In one aspect, the electrolysis system includes a cathode, an anode, and one or more electrolytes, and the cathode or anode, or both the cathode and anode, include an electrocatalyst that includes palladium and iridium.

In a fourth aspect, the present invention provides
(I) providing a water electrolyzer comprising an anode, a cathode, and one or more electrolytes, wherein at least one of the anode and cathode comprises an electrocatalyst comprising palladium and iridium;
(Ii) contacting the water electrolyzer with water; and (iii) producing hydrogen and / or oxygen;
A method of electrolyzing water comprising the steps is provided.

Alternatively, the present invention
(I) providing an electrolysis system comprising an anode, a cathode, and one or more electrolytes, wherein at least one of the anode and cathode comprises an electrocatalyst comprising palladium and iridium;
(Ii) contacting the cathode and anode with one or more electrolytes, wherein at least one of the electrolytes comprises an aqueous sodium chloride solution; and (iii) producing hydrogen and / or chlorine and / or sodium hydroxide;
A method is provided for electrolyzing an aqueous sodium chloride solution comprising a step.

For example, the anode can be contacted with a sodium chloride solution and the cathode can be contacted with concentrated sodium hydroxide.
In an optional aspect of the fourth aspect, the production of hydrogen and / or chlorine and / or sodium hydroxide is accomplished by an electrolysis process performed by creating an electrical bias between the cathode and the anode.

In a fourth aspect, the present invention provides:
(I) providing an electrolysis system comprising an anode, a cathode, and one or more electrolytes, wherein at least one of the anode and cathode comprises an electrocatalyst comprising palladium and iridium;
(Ii) contacting the cathode and anode with one or more electrolytes;
(Iii) passing an electric current through the electrolysis system; and (iv) generating a new state of the electrolysis product and / or material;
A method of electrolyzing any suitable input comprising the steps is provided.

In a fifth aspect, the present invention provides:
(I) providing a water electrolyzer comprising an anode, a cathode, and one or more electrolytes, wherein at least one of the anode and cathode comprises an electrocatalyst comprising palladium and iridium;
(Ii) contacting the water electrolyzer with water; and (iii) electrolyzing the water to produce hydrogen and / or oxygen;
A method for producing hydrogen and / or oxygen comprising the steps is provided.

Alternatively, the present invention
(I) providing an electrolysis system comprising an anode, a cathode, and one or more electrolytes, wherein at least one of the anode and cathode comprises an electrocatalyst comprising palladium and iridium;
(Ii) contacting the cathode and anode with one or more electrolytes, wherein at least one of the electrolytes is an aqueous sodium chloride solution; and (iii) electrolyzing the system to hydrogen and / or chlorine and / or water Producing sodium oxide;
A method for producing hydrogen and / or chlorine and / or sodium hydroxide comprising a step is provided.

For example, the above method can include contacting the anode with an aqueous sodium chloride solution and contacting the cathode with concentrated sodium hydroxide.
In one aspect, the electrolysis step is performed by generating an electrical bias between the cathode and the anode.

  In a sixth aspect, the present invention includes assembling a cathode, an anode, and one or more electrolytes, wherein the cathode, anode, or both cathode and anode include an electrocatalyst comprising palladium and iridium. A method of manufacturing an electrolysis system is provided.

  In a further aspect, the present invention provides the use of a cathode electrocatalyst comprising palladium and iridium for producing hydrogen by an electrolysis process. Such use can include electrolysis of water or electrolysis of aqueous sodium chloride.

In a further aspect, the present invention provides the use of an anode electrocatalyst comprising palladium and iridium for producing oxygen by electrolysis of water.
In a further aspect, the present invention provides an electrolysis cathode electrocatalyst comprising palladium and iridium.

In a further aspect, the present invention provides an electrolytic anode electrocatalyst comprising palladium and iridium.
In all aspects of the invention, the electrolysis system may be any electrolysis system such as a water electrolyzer.

  The electrolysis of the present invention can be used in numerous applications such as supply to natural gas infrastructure, refueling stations, energy depots, and the like.

FIG. 1 compares the present invention with platinum in an acidic half-cell device for HER. FIG. 2 shows the effectiveness of the present invention for an oxygen release reaction in an acidic atmosphere. FIG. 3 shows the effectiveness of using palladium rich catalyst species for the water electrolysis cell cathode in an acidic atmosphere. FIG. 4 shows that the platinum-iridium electrocatalyst can be used to generate hydrogen not only in an acidic atmosphere but also under alkaline conditions. FIG. 5 shows the effectiveness of the present invention for the oxygen evolution reaction in alkaline conditions.

  The electrode catalyst used in the present invention contains palladium and iridium. The concentration of iridium in the electrocatalyst may be any molar concentration, but in one embodiment, the atomic ratio of iridium and palladium may be any value from about 1:99 to about 99: 1. For example, palladium and iridium may be about 9: 1 to about 1: 1, about 5: 1 to about 1: 1, about 3: 1 to about 1: 1, about 5: 1 to about 3: 1, about 9: It can be present in the electrocatalyst at an atomic ratio of Pd: Ir of about 1, about 5: 1, about 3: 1, or about 1: 1.

  Iridium can be present as an alloy with palladium, as a surface modification component of palladium, as an amorphous material, as a structure similar to a core shell having a surface layer rich in palladium, or any combination thereof. Palladium can be present as an alloy with iridium, as a surface modifying component of iridium, as an amorphous material, as a structure similar to a core shell having a surface layer rich in iridium, or any combination thereof. The metal component of the catalyst may be a neat metal surface, may be in oxide form, or may be a mixed form of both oxide and neat metal surfaces.

  A person skilled in the art knows that electrocatalysts are not only present in trace amounts as impurities in other catalyst components, but also functionally significant amounts of palladium and iridium, palladium and / or iridium alloys, palladium or iridium. The material in a mixed amorphous state and / or surface modified palladium / iridium. For the purposes of the present invention, a “functionally significant” amount of palladium and iridium refers to the production of electrolysis products or a reduction in the energy required to produce an equivalent amount of electrolysis products. It means enough to cause a detectable increase in the measured electrolysis efficiency.

  In one embodiment, the electrocatalyst can further include other catalyst components such as other metals. The catalyst can include two metals, three metals, or even four or more different metals in any desired or convenient ratio.

In one embodiment, the electrode catalyst can include palladium oxide and iridium oxide, or a mixture of palladium oxide and iridium oxide and a pure metal.
Palladium and iridium can also be present in substantially pure form (at least 99.1% purity) or in a mixture with one or more additional elements. Palladium and iridium in the electrocatalyst are believed to be closely involved in the catalysis of the electrochemical reaction. However, other elements which can advantageously be included in the catalyst do not necessarily have to be actively involved in the catalysis. For example, these may be by improving or increasing the stability of palladium and / or iridium in any electrolysis medium, or by promoting side reactions useful for the long term durability of the system, Alternatively, beneficial effects can be provided in several other forms. Thus, references to these materials that form part of or are included in an electrocatalyst do not necessarily have catalytic activity with respect to the electrochemical reaction that the material under discussion is itself catalyzed by the electrocatalyst. This is not implied, but this may actually be the case.

Those skilled in the art will appreciate that palladium, iridium, and other catalyst components, if present, are preferably in a form having a large surface area, such as micronized or nanoparticulates.
Traditionally, platinum catalysts are the optimal catalyst for cathodes of electrolysis systems that exhibit much better mechanical properties and stability when compared to other materials, but platinum is expensive. However, the surprising discovery of the present invention makes it possible to use electrocatalysts containing low levels of platinum and even to use electrocatalysts that do not contain platinum. Platinum can be present in the electrode catalyst used in the present invention, but platinum is usually present in a trace amount (less than 0.05 atomic%, preferably less than 0.1 atomic%) when present. preferable. More preferably, the electrode catalyst used in the present invention does not contain platinum. That is, the electrode catalyst used in the present invention contains palladium and iridium in the absence of platinum.

  An electrolysis system, such as an electrolytic cell, typically includes an electrolyte and two electrodes (a cathode and an anode). The cathode and anode can be connected to a power supply for the purpose of generating an electrical bias between the two.

  As an example, a water electrolyzer is operational when the anode and cathode electrodes are in a suitable functional relationship with the electrolyte so that a useful amount of hydrogen and / or oxygen is produced from the electrolysis of water. For example, this occurs when a power supply is connected to two electrodes.

  A water electrolysis cell shows a typical example of the use of an electrode catalyst in an electrolysis application, and is a preferable application. The scope of the invention covers any electrolysis application (eg water electrolysis, chlor-alkali process, hydrogen production, chlorine gas production, sodium hydroxide production, electrogalvanization, electroplating, electrosynthesis, Kolbe reaction Etc.), in particular, the use of electrocatalysts in any electrolysis application using platinum, platinum group metal catalysts, platinum group metal alloys, or alloys or other combinations using platinum group metals and other elements that are not platinum group metals.

  The present invention covers the use of palladium-iridium electrocatalysts in electrolysis processes in all cases where this catalyst system increases the efficiency of electrolysis chemical reactions and / or reduces the overall cost of processing. Is intended. This is particularly true in electrolysis processes using platinum, iridium, or other platinum group metal catalysts, as well as their alloys, surface modified platinum group metal systems, and the like.

  In the present invention, the electrocatalyst of the present invention is included in one or both of the cathode and the anode. In one aspect, the anode includes an electrocatalyst comprising palladium and iridium. In one embodiment, the cathode includes an electrocatalyst comprising palladium and iridium. In one embodiment, both the cathode and the anode comprise an electrocatalyst comprising palladium and iridium.

  The electrode catalyst used in the present invention can contain one type of electrolyte, or more than one type of electrolyte. For example, the electrolyte used in the present invention may be a combination of a plurality of electrolytes.

  The electrolyte used in the context of the present invention is an ionically conductive medium in a water electrolyzer, electrolysis system, or other electrolysis process. The electrocatalyst of the present invention exhibits high catalytic efficiency over a wide range of pH. In one aspect of the invention, the electrolyte may be any suitable electrolyte system with an acidic, alkaline, or neutral pH.

  The acidic electrolyte can be any conventional acidic electrolyte. For example, the acidic electrolyte may be a polymer electrolyte or a liquid electrolyte. More specifically, the acidic electrolyte may be a cation exchange membrane, a free flowing liquid electrolyte, or a liquid electrolyte contained within a porous matrix.

  The alkaline electrolyte can be any conventional alkaline electrolyte. For example, the alkaline electrolyte may be a liquid electrolyte or even an anion conducting membrane. More specifically, the alkaline electrolyte is a free-flowing liquid electrolyte, a liquid electrolyte contained in a porous matrix, a cation exchange membrane, an anion exchange membrane, or an anion exchange membrane in functional contact with an alkaline electrolyte. Good.

  The electrolyte or electrolytes of the electrolysis system may also be a combination of both acidic and alkaline electrolytes. These composite electrolysis systems can be configured in any form in which the electrolyte has an appropriate functional relationship with the electrodes (cathode and anode). For example, some alkaline water electrolyzers can use cation exchange membranes (here cations are charge carriers), or use anion exchange membranes (here anions are charge carriers). it can. The use of a combination of electrolytes does not limit the scope of the present invention.

In the following, electrolytes suitable for use in the present invention are further described.
The electrolyte may be liquid, solid, or a combination of liquid and solid.
For liquid electrolyte applications, the electrolyte may be either an acidic solution, an alkaline solution, or even a suitably ion-conducting solution at neutral pH. Depending on the system and application, this solution can be either a concentrated or dilute solution. Examples of acidic liquid electrolytes include sulfuric acid or phosphoric acid solutions; examples of alkaline liquid electrolytes include potassium hydroxide or sodium hydroxide solutions. Several other possible liquid acidic solutions, liquid alkaline solutions, and neutral pH ionic solutions are possible, and the examples given are not intended to limit the invention.

  A suitable solid electrolyte includes an ionomer formed on an ion conductive membrane. For example, the solid electrolyte may be either a cation conducting ionomer or an anion conducting ionomer. In one aspect, the electrolyte is a cation exchange polymer membrane.

  Alternatively, the electrolyte may be a matrix, membrane or gel impregnated with a liquid electrolyte, ie a combination of liquid and solid. Examples include porous membranes impregnated with acid or similarly impregnated gels or other such matrices.

  Nafion® (E.I. DuPont De Nemours) is a suitable commercially available cation conducting exchange membrane and is used in several electrolysis applications such as water electrolyzer and chlor-alkali industries. There are also several other cation exchange ionomers such as Aquivion® (Solvay, Belgium) and Fumion® (Fumatech, Germany). The backbone of the acidic polymer need not be a polyfluorocarbon, and some hydrocarbon-based cation exchange membranes can also be utilized. A review of non-perfluorosulfonic acid ionomers is J. Perron et al., Energy Environ, Sci., 2011, 4, 1575-1591. A-006 (Tokuyama, Japan) is a suitable commercially available anion conducting (alkaline) polymer electrolyte. Varcoe et al., Solid State Ionics 176 (2005) 585-597, illustrate several anion exchange membrane technologies and chemical reactions that can be used for alkaline-based electrolysis. However, the overwhelming majority of alkaline-based electrolysis is currently performed by liquid electrolytes using a matrix or diaphragm to prevent product gas or product chemical crossover. The above examples of solid polymer electrolytes are given as detailed examples and are not intended to limit the scope of the present invention.

  To form an electrode for electrolysis applications, the electrocatalyst can be functionally contacted with a suitable conductive substrate for the application after coating on the substrate, on the conductive substrate. Or can be contacted with other conductors for any reason after direct coating on a conductive substrate. In the water cell anode embodiment, any conductive support or conductive substrate must tolerate high voltages. For solid polymer electrolytes, the electrocatalyst layer can be functionally contacted with a suitable conductive substrate and / or electrical conductor for the application after being deposited directly on the membrane by any suitable means. . Titanium mesh is an example of a conductive substrate suitable for use in a water electrolyzer. Nickel or nickel mesh is another example of a suitable conductor for this application. Other suitable conductive substrates or suitable electrical conductors are available, the choice of conductive substrate or electrical conductor, or how the catalyst functions with the conductive substrate, electrical conductor, and / or electrolyte It is not limited whether the contact is made.

  An electrocatalyst in the form of an ink can be coated on the electrical conductor and / or the conductive substrate. The ink can be coated on an electrical conductor or conductive substrate in various ways: brush coating, doctor blade coating, gravure, screen printing, roll-to-roll, or spray coating. Alternative methods of applying electrocatalysts: solution coating, dip coating, sputtering, electrospinning, vacuum deposition, etc. are fully available. The method of applying an electrode catalyst to form an electrode, such as any method of intermediate treatment or post-deposition treatment such as treatment with heat or reactive gas, does not limit the invention. Ideally, the electrode exhibits excellent mass transfer characteristics and can introduce water onto the catalyst surface while simultaneously releasing product gas at a rate commensurate with the turnover rate of the catalyst. Although the present invention is not intended to describe a patented method of manufacturing electrolytic cell electrodes, it is intended to protect the use of the electrocatalysts of the present invention in water electrolytic cells or any electrolysis application.

  The anode and cathode structures are advantageously very similar in general, but they may be different. Typically, both the anode and the cathode may be of substantially conventional structure, including: solid carbon, graphitic carbon, solid metal, metalized fabric, metalized polymer fiber, metal mesh, carbon cloth, carbon Conductive supports such as, but not limited to, paper and one of the carbon felts can be included. The conductive support may be a material such as stainless steel, nickel, mild steel, titanium, tungsten carbide, but is not necessarily limited to these materials. The conductive support may also be in the form of sintered powder, foam, powder compact, mesh (eg titanium, nickel), woven or non-woven material, perforated sheet, tube assembly, etc. The electrocatalyst can be deposited on or otherwise bonded.

The electrocatalyst may be unsupported as catalyst black or may be supported on any suitable support for any electrode. In some applications, one of the electrodes can be composed of an unsupported electrocatalyst while the other electrode catalyst is supported on the other electrode. For water electrolysers, which are examples of conventional electrolysis, the cathode support is a high surface area carbon such as Denka Black, Vulcan XC-72R, and Ketjen Black® EC-300JD, Nanocyl®. Such nanotubes, acetylene black, or furnace black. The cathode can also be supported on a metal or metal oxide such as nickel spheres, titanium oxide (eg, Ti ₄ O ₇ Ebonex®), tungsten carbide, and the like. Polymer supports such as polyaniline, polypyrrole, and polythiophene can also be used if appropriately modified for electrical conduction. Metal, metal oxide, and polymer supports are more suitable. The actual nature of the support (or the absence of support) does not limit the invention. These can be used in other electrolysis applications that have greater flexibility with respect to the support material capable of the anode. The above examples merely provide potential examples and methods by which electrocatalysts can be used in electrolysis applications, and the nature of the catalyst support and the absence of the catalyst support do not limit the invention.

  Electrocatalysts, whether supported or unsupported, must be in a functional relationship with the electrolyte once formed into the appropriate electrode for the application. The electrolyte can be either acidic, alkaline, or more neutral pH, and can be liquid or solid or a combination of liquid and solid (eg, a porous polymeric group impregnated with a liquid acidic or liquid alkaline solution). Material). Examples of possible solid polymer electrolytes are given above, and Nafion® is the most widely used cation exchange membrane for many electrolysis processes.

  In one aspect, the electrocatalyst used in the present invention is a chemical that contacts the palladium and iridium electrocatalysts on a conductive support or substrate, optionally with a suitable binder, while discharging the chemical product formed. Allowing chemicals (ie, water, salt water, electrolytes) to be close to the catalyst surface while allowing the electrocatalyst to be electrically connected to the conductive substrate: preferred using method comprising steps Formed on a simple electrode. The nature of the binder does not limit the invention. These binders are usually solvent dispersion variants of solid polymer membranes such as Nafion® and Tokuyama A-006®, but they are also PVDF or other suitable resins, epoxy It may be an inert polymer that still maintains the necessary mass transfer properties of the electrode, such as a resin, a thermosetting resin, or the like. The application of the electrocatalyst can vary, and the application and use of a flow modifier to apply the electrocatalyst does not limit the scope of the invention. Some examples of suitable methods of applying an electrocatalyst to an electrode are disclosed in US-5865968, EP-0944822, WO-200301077, US-4150076, US-6864204, and WO2001094668. These references describe the usual procedure for producing inks with electrocatalysts and applying them to a (carbon-based) substrate; different solvents, different binders, different application methods, or different substrate materials, or any combination thereof. It is intended to illustrate the method used, or actually excluding any of these does not limit the scope of the invention.

  A general method for producing the electrocatalyst described in this invention is to disperse (i) a palladium salt and / or iridium salt in an aqueous solution, usually (but not necessarily) in the presence of a conductive support. (The pH of the aqueous solution is usually maintained at this pH by adding a suitable material (sodium bicarbonate is one example) at this stage); (ii) palladium and iridium are chemically Precipitating either as a metal or a metal oxide on a conductive support with a catalytic reducing agent or by heat-activated reduction (eg in the presence of ethylene glycol); (iii) filtering and washing the resulting precipitate And (iv) subjecting to a final thermal reduction in the presence of hydrogen to clean the metal surface while preventing agglomeration.

Suitable palladium and iridium salts include palladium nitrate, palladium chloride, and iridium chloride. Suitable reducing agents include, but are not limited to, sodium hypophosphite (NaH ₂ PO ₂ ) and sodium borohydride (NaBH ₄ ). Also, heat activated reduction in the presence of a suitable agent can be used, an example being reduction in the presence of ethylene glycol at a temperature below 100 ° C. A suitable reducing atmosphere for step (iv) is 5% to 20% hydrogen in nitrogen or argon. An example of the thermal reduction condition is 150 ° C. for 1 hour. This heating process is advantageous for the present invention because it facilitates hydroxide / oxide removal from the surface of the catalyst without promoting sintering and loss of the surface area of the catalyst.

  In general, these techniques are summarized by forming a mixture of one or more active catalyst materials and optionally a suitable binder in the presence of a suitable solvent, and drying the mixture to form a suitable group in the construction of the electrode. A catalytic material is deposited and adhered to the material. The electrode is then placed into a functional relationship with the cell electrolyte. The opposing electrode may or may not contain the electrode catalyst of the present invention. This also has a functional relationship with the cell electrolyte. In a liquid electrolyte, the catalyst layer of an electrode should just contact with an electrode (it may be either a fluid state or a stagnation state). Usually in liquid electrolytes, the two electrodes are separated by a diaphragm or semi-permeable membrane. When using a solid polymer electrolyte, an electrode comprising one or more electrocatalyst layers can be bonded to the membrane using heat and pressure in any suitable lamination process suitable for the membrane material, Alternatively, the layer can simply be mechanically pressed against the membrane with any force suitable for the cell or system. Energy (electrons) for causing a chemical reaction is provided by direct current.

  Methods for forming and depositing catalysts are generally well known to those skilled in the art and do not require detailed description. The actual quality of the electrode layer (eg metal loading, support type, substrate, etc.) depends on several factors such as chemical inputs, electrolytes, system operating conditions, chemical products, etc., as well as the overall technology In general, it is unrelated to general general criteria for manufacturing known in the art. The electrocatalyst layer can be deposited on any suitable conductive material (eg, titanium, nickel, or carbon based), or directly on the electrolyte membrane for cells using polymer films or impregnated skeletons. Can be made.

  The electrolytic cell (cell) of the present invention includes at least one electrode comprising palladium and iridium as described herein. Other electrodes can include the same or different electrocatalysts. Moreover, an electrode catalyst can also be included in both electrodes.

FIG. 1 compares the present invention with platinum in an acidic half-cell configuration for HER. Data were captured using the thin film rotating disk electrode (TF-RDE) technique described in Gasteiger et al., Applied Catalysis B, 2005. The experiment was performed using thin film rotating disk electrode technology, and about 35 μg / cm ² of each metal was deposited on the glassy carbon electrode. The electrolyte was 0.1M perchloric acid. Perchloric acid was used instead of sulfuric acid to prevent ion absorption on platinum. In FIG. 1, the electrode catalyst used as the cathode electrode catalyst in the present invention exhibits improved efficiency (compared to platinum) in the production of hydrogen in the water electrolyzer. At a given current density, an electrode with the electrocatalyst of the present invention requires less energy to produce the same amount of hydrogen as platinum.

  FIG. 2 shows the effectiveness of the present invention for an oxygen release reaction in an acidic atmosphere. The electrocatalyst used in the present invention maintains effectiveness comparable to state-of-the-art iridium electrocatalysts, especially at low current densities. However, the lower cost of palladium provides an excellent cost / efficiency ratio over iridium. Apparently, the electrocatalyst used in the present invention exhibits greatly improved effectiveness compared to platinum. The data in FIG. 2 was generated using carbon-supported palladium-iridium subjected to a corrosion potential on the electrolytic cell anode half-cell.

  FIG. 3 shows the effectiveness of using a palladium rich species of catalyst for the water electrolysis cell cathode in an acidic atmosphere. In FIG. 3, a further embodiment rich in palladium of the present invention was compared with a platinum catalyst. In this example, all the catalyst was coated on a suitable electrode substrate (in this case graphitic carbon rods) and immersed in a 3 electrode cell filled with 1M-sulfuric acid. FIG. 3 shows that palladium and iridium catalysts with an atomic ratio of 3: 1 (palladium: iridium) are superior to similar platinum electrodes for hydrogen evolution reactions.

  FIG. 4 shows that the platinum-iridium electrocatalyst can be used to generate hydrogen not only in an acidic atmosphere but also under alkaline conditions. The electrode was 5M potassium hydroxide and the working electrode was a graphite plate coated in an electrode catalyst. FIG. 5 shows the effectiveness of the present invention for the oxygen evolution reaction in alkaline conditions. Here, the activity of the electrocatalyst over a wide pH range indicates the flexibility of the application that can be utilized by the present invention.

  All data in FIGS. 1, 2, 4, and 5 were generated using a 1: 1 atomic ratio of palladium to iridium. The catalyst system was supported on Ketjen carbon to constitute about 40% of the mass of catalyst from which the metal was obtained. FIG. 3 was performed using a 3: 1 palladium to iridium atomic ratio. These catalyst systems were also supported on Ketjen carbon to constitute about 40% of the mass of catalyst from which the metal was obtained.

  The example of platinum in FIGS. 1-3 is a commercially available catalyst (Alfa Aesar). Platinum was supported on Vulcan carbon (XC72R) to constitute about 40% of the mass of catalyst from which the metal was obtained.

  A method for producing the catalyst is disclosed in British patent application GB1110045.0 (published as GB2481309A), the contents of which are incorporated herein by reference.

Example 1: Palladium / Iridium [PdIr (1: 1 atomic%)] catalyst on carbon, 150 ° C .:
In a round bottom flask, carbon black (Ketjen Black EC300JD, 0.8 g) was added to 1 liter of water and heated to 80 ° C. Carbon was dispersed for 12 hours using a top stirrer and paddle.

  In a second vessel, palladium nitrate (0.475 g, 42.0 wt% (analytical) Pd) was carefully weighed and dissolved in 50 mL of deionized (DI) water. In a third vessel, iridium chloride (0.660 g, 54.4 wt% (analytical) Ir) was carefully weighed and dissolved in 50 mL of DI water. The salt was then carefully introduced into a vessel containing a carbon slurry that was being stirred at 80 ° C.

Once the metal salt was transferred to the larger container, the residual contents of the addition funnel were washed away into the larger container. The pH of the stirring slurry was then carefully raised to 7.0 by adding a saturated solution of sodium bicarbonate (NaHCO ₃ ). The pH of the slurry was maintained at 7.0-7.5 for 1 hour by further controlled addition of sodium bicarbonate.

A solution of sodium hypophosphite (NaH ₂ PO ₂ , 0.495 g, diluted in 50 mL of DI water) was prepared. 2.5 times the molar amount of palladium in the catalyst is the preferred usage of sodium hypophosphite. Half of this solution was introduced into a reaction vessel containing a carbon-salt slurry. The slurry was maintained at 80 ° C. for an additional hour with continuous stirring.

After cooling the slurry to room temperature, the filtrate was collected on a microporous filter and washed until the conductivity of the filtrate was 2.42 mS. The catalyst was dried in an oven at 80 ° C. for 10 hours. The dried catalyst was then ground in a pestle and mortar to give a fine powder, which was carefully placed in a ceramic boat to a maximum depth of 5 mm. The boat was placed in a tube furnace and heated at 150 ° C. for 1 hour in a 20% H ₂ /80% N ₂ atmosphere. The yield for 1.4 g with respect to 40 wt% metal was 1.23 g.

Claims (38)

  Use of an electrocatalyst comprising palladium and iridium to catalyze an electrolysis process.   Use according to claim 1, wherein the electrolysis process is an electrosynthesis process.   Use according to claim 1, wherein the electrolysis process is electrolysis of water.   Use according to claim 1, wherein the electrolysis process is electrolysis of an aqueous sodium chloride solution.   The use according to any of claims 1 to 4, wherein the electrocatalyst comprises palladium and iridium in an atomic ratio of about 9: 1, about 5: 1, about 3: 1, or about 1: 1.   Use according to any of the preceding claims, wherein the electrocatalyst is part of a cathode and / or anode in an electrolysis system, the electrolysis system comprising a cathode, an anode and one or more electrolytes.   Use according to claim 6, wherein the electrolysis system is a water electrolyser.   Use according to claim 6, wherein the electrolysis system is an aqueous sodium chloride electrolysis system.   Use according to any of claims 6 to 8, wherein the electrode is a cathode.   The use according to claim 9, wherein an electrocatalyst is used to catalyze the production of hydrogen at the cathode.   Use according to any of claims 6 to 8, wherein the electrode is an anode.   12. Use according to claim 11, wherein an electrocatalyst is used to catalyze the production of oxygen, chlorine or sodium hydroxide at the anode.   Use according to any of claims 6 to 12, wherein the electrolyte is acidic, alkaline or neutral pH.   Use according to any of claims 6 to 13, wherein the electrolyte is a liquid, a solid, or a combination of a liquid and a solid.   15. Use according to claim 14, wherein the electrolyte is a cation conducting polymer membrane.   An electrolysis system comprising an electrocatalyst, wherein the electrocatalyst comprises palladium and iridium.   An electrolysis system comprising a cathode, an anode, and one or more electrolytes, wherein the cathode, anode, or both cathode and anode comprise an electrocatalyst comprising palladium and iridium.   The electrolysis system according to claim 17, wherein the electrolysis system is a water electrolysis tank or a sodium chloride aqueous solution electrolysis system.   19. An electrolysis system according to claim 17 or claim 18, wherein the cathode comprises an electrocatalyst comprising palladium and iridium.   20. An electrolysis system according to any of claims 17 to 19, wherein the anode comprises an electrocatalyst comprising palladium and iridium.   The electrolysis system according to any one of claims 17 to 19, wherein the electrolyte has an acidic, alkaline, or neutral pH.   The electrolysis system according to any one of claims 17 to 21, wherein the electrolyte is a liquid, a solid, or a combination of a liquid and a solid.   The electrolysis system according to any one of claims 17 to 22, wherein the electrolyte is a cation conductive polymer membrane. (I) providing a water electrolyzer comprising an anode, a cathode, and one or more electrolytes, wherein at least one of the anode and cathode comprises an electrocatalyst comprising palladium and iridium;
(Ii) contacting the water electrolyzer with water; and (iii) producing hydrogen and / or oxygen;
A method for electrolyzing water, comprising a step.   25. The method of claim 24, wherein hydrogen and oxygen are generated by generating an electrical bias between the cathode and anode. (I) providing an electrolysis system comprising an anode, a cathode, and one or more electrolytes, wherein at least one of the anode and cathode comprises an electrocatalyst comprising palladium and iridium;
(Ii) contacting the cathode and anode of the electrolysis system with one or more electrolytes, wherein one of the electrolytes is an aqueous sodium chloride solution; and (iii) hydrogen and / or chlorine and / or sodium hydroxide Generate;
A method for electrolyzing an aqueous sodium chloride solution comprising a step.   27. The method of claim 26, wherein hydrogen and chlorine are generated by generating an electrical bias between the cathode and anode. (I) providing a water electrolyzer comprising an anode, a cathode, and one or more electrolytes, wherein at least one of the anode and cathode comprises an electrocatalyst comprising palladium and iridium;
(Ii) contacting the water electrolyzer with water; and (iii) electrolyzing the water to produce hydrogen and / or oxygen;
A method for producing hydrogen and / or oxygen, comprising a step.   29. The method of claim 28, wherein water electrolysis is performed by creating an electrical bias between the cathode and anode. (I) providing an electrolysis system comprising an anode, a cathode, and one or more electrolytes, wherein at least one of the anode and cathode comprises an electrocatalyst comprising palladium and iridium;
(Ii) contacting the electrolysis system with one or more electrolytes, wherein one of the electrolytes is an aqueous sodium chloride solution; and (iii) electrolyzing the aqueous sodium chloride solution to hydrogen and / or chlorine and / or Producing sodium hydroxide;
A method for producing hydrogen and / or chlorine and / or sodium hydroxide, comprising a step.   29. The method of claim 28, wherein the aqueous sodium chloride solution is electrolyzed by creating an electrical bias between the cathode and anode.   24. The method of any of claims 17-23, comprising assembling a cathode, an anode, and one or more electrolytes, wherein the cathode, anode, or both cathode and anode comprise an electrocatalyst comprising palladium and iridium. A method of manufacturing an electrolysis system.   Use of a cathode electrocatalyst comprising palladium and iridium to produce hydrogen by an electrolysis process.   Use according to claim 32, wherein the electrolysis process is electrolysis of water or electrolysis of aqueous sodium chloride solution.   Use of an anode electrocatalyst comprising palladium and iridium to produce oxygen by electrolysis of water.   An electrolytic cell electrode catalyst containing palladium and iridium.   An electrolytic cell cathode electrode catalyst containing palladium and iridium.   An electrolytic cell anode electrode catalyst containing palladium and iridium.

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