CN100536215C - Fuel cells and fuel cells catalysts - Google Patents

Fuel cells and fuel cells catalysts Download PDF

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CN100536215C
CN100536215C CNB038127989A CN03812798A CN100536215C CN 100536215 C CN100536215 C CN 100536215C CN B038127989 A CNB038127989 A CN B038127989A CN 03812798 A CN03812798 A CN 03812798A CN 100536215 C CN100536215 C CN 100536215C
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fuel cell
anode
catalyst
formic acid
fuel
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CN1659732A (en
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理查德·I·马塞尔
辛西娅·A·赖斯
皮奥特尔·瓦茨祖克
安德尔泽吉·威科夫斯基
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Illinois Trust Management Committee, University of
University of Arkansas
University of Illinois
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/88—Processes of manufacture
    • H01M4/8803—Supports for the deposition of the catalytic active composition
    • H01M4/881—Electrolytic membranes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B01J23/40—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals of the platinum group metals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/8605—Porous electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/88—Processes of manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/88—Processes of manufacture
    • H01M4/8825—Methods for deposition of the catalytic active composition
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/88—Processes of manufacture
    • H01M4/8878—Treatment steps after deposition of the catalytic active composition or after shaping of the electrode being free-standing body
    • H01M4/8882—Heat treatment, e.g. drying, baking
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/90—Selection of catalytic material
    • H01M4/92—Metals of platinum group
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/96—Carbon-based electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M8/1004—Fuel cells with solid electrolytes characterised by membrane-electrode assemblies [MEA]
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M8/1009—Fuel cells with solid electrolytes with one of the reactants being liquid, solid or liquid-charged
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells

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Abstract

A direct organic fuel cell (10) includes an anode (12) within an anode enclosure (18), solid polymer electrolyte (14), and gas diffusion cathode (16) within a cathode enclosure (20). An electrical load is connected between the anode (12) and cathode (16) via electrical linkage (22). A liquid fuel comprising between about 10 % and 95 % by weight formic acid is supplied to the anode enclosure. Oxidant is supplied to the cathode enclosure. Gas removal ports (24 and 26) are provided to remove carbon dioxide and water from the fuel cell.

Description

Fuel cell and fuel-cell catalyst
Technical field
Put it briefly, the present invention relates to the catalyst of fuel cell and fuel cell.
Background technology
Fuel cell is an electrochemical cell, and wherein the free energy that produces because of fuel oxidation reaction is converted to electric energy.The application of fuel cell comprises the battery replacement, mini and microelectric technique, car engine, power station and a lot of other fields.One of advantage of fuel cell is its essentially no pollution.
In hydrogen fuel cell, the oxidized generation water of hydrogen as the accessory substance of oxidation reaction, produces utilizable electric current.The solid polymer membrane electrolyte layer can be used for isolating hydrogen fuel and oxygen.Anode and cathode arrangement are on two facing surfaces of film.The anode and the electron stream between cathode layer of membrane electrode assembly can be used to provide electric power.Yet hydrogen fuel cell is unpractical in a lot of practical applications, because store and handle the difficulty of hydrogen.
As the substitute of hydrogen fuel cell, organic fuel cell is proved to be and can be applied to a lot of applications.In organic fuel cell, organic-fuel such as methyl alcohol are oxidized to carbon dioxide at anode, and air or oxygen are reduced into water at negative electrode simultaneously.It is that the former can utilize the liquid organic-fuel to come work that organic/air-fuel battery is better than one of advantage of hydrogen fuel cell.This has eliminated with hydrogen treat and has stored relevant problem.Some organic fuel cell need carry out initial conversion by converter, and organic-fuel is changed into hydrogen.These batteries are referred to as " " fuel cell indirectly.Required converter has increased volume of battery, cost, complexity and start-up time.The organic fuel cell of other type is referred to as " directly " organic fuel cell has been eliminated these shortcomings, need not to change into hydrogen by the direct oxidation organic-fuel.Up to now, the exploitation of direct organic fuel cell mainly concentrates on the use of methyl alcohol and other Aalcohols fuel.
Conventional direct methanol fuel cell has the problem that wait solve relevant with himself.For example, methyl alcohol and other alcohols have high infiltration and diffusion leap rate (crossover rate) to commercial polymer membrane electrode assembly.The fuel of crossing over has been avoided electrode reaction, thereby can not be used to produce electric energy.This has limited battery efficiency.With crossing over another relevant problem is that anode is poisoned.Along with methyl alcohol or other Aalcohols fuel are crossed over polymer film arrival cathode side, thereby methyl alcohol or other Aalcohols fuel are adsorbed on blocking reaction position on the cathod catalyst.Thereby reduction battery efficiency.A solution that just addresses this problem proposition provides extra catalyst.But, can increase expense like this, especially consider normally used when being very expensive noble metal such as platinum or accurate noble metal catalyst.
Because this serious leap, methyl alcohol and other alcohol fuel battery are usually to be not more than about 3～8% fuel concentration work.Yet, use this dilution can bring other problem again.This low fuel concentration needs relatively large ultra-pure water, normally provides by the recirculating system that comprises pump and filter.In addition, the concentration of fuel be need critically monitor and control, thereby transducer and controller needed.All these ancillary equipment all increase cost, complexity, weight and the size of direct organic fuel cell.
In addition, this required outer water tube reason equipment has greatly limited the validity of direct methanol fuel cell in the application that size and weight is had strict demand.For example, with regard to portable, mini and microelectronic applications,, make that the application of direct methanol fuel cell is unrealistic to the requirement of ancillary equipment size, weight and complexity.
And the dilution in the fuel cell is at a lot of fuel cells, and for example the portable set of outdoor application can freeze and expand under the temperature that may run into.Expansion can make equipment malfunction.People's such as Conduit United States Patent (USP) U.S.6,528,194 point out, when fuel cell is not worked, can avoid freezing through tanks by the circulation of fluid that makes heating.Yet, can waste energy like this and increase complexity.
The other problem of existing direct methanol fuel cell is relevant with the electro-oxidation reaction that anode causes.For example, in a lot of direct methanol fuel cell, the intermediate product that is produced by methyl alcohol during oxidation/reduction reaction is poisonous carbon monoxide (CO) gas, thereby dangerous.In addition, people know that CO can make platinum catalyst poisonings such as (Pt), thereby reduce battery efficiency.
In the prior art, these and other problem is still unresolved.
The present invention's general introduction
One embodiment of the invention relate to a kind of direct organic fuel cell, and it comprises the anode that links to each other with negative electrode, anode chamber, and cathode chamber.Fuel cell also comprises the liquid fuel solutions that comprises 10% weight organic-fuel at least.In a preferred embodiment of the invention, organic-fuel is formic acid and has anode catalyst that anode catalyst comprises platinum (Pt) and palladium (Pd).
Another embodiment of the present invention relates to a kind of membrane electrode assembly, and it comprises solid polymer electrolyte, and is positioned at lip-deep anode of solid polymer electrolyte and another lip-deep negative electrode.Anode is made into certain shape to promote that organic-fuel directly decomposes, and does not form the CO intermediate.
Another embodiment of the present invention relates to a kind of method for preparing anode catalyst, and this method comprises the steps: to prepare the suspension of nano particle; This suspension is coated on the carrier; Dry suspension is to form film on carrier; Then with carrier impregnation in a kind of metallic solution, with plated metal island (metal island) spontaneously on the Pt nano particle.
An embodiment more of the present invention relates to a kind of anode catalyst that is used for direct aminic acid fuel battery.Exemplary anode catalyst comprises the metal nanoparticle that scribbles second kind of metal on it at least, and this catalyst can promote formic acid along not comprising that the response path dehydrogenation that forms the CO intermediate forms CO effectively 2And H +
Another embodiment of the present invention relates to the fuel cell of low freezing point.
Description of drawings
Fig. 1 is the schematic diagram of example fuel cell of the present invention;
Fig. 2 is the flow chart of the illustrative methods of preparation catalyst of the present invention;
Fig. 3 (a) and (b) be respectively the data and curves of the active and power of the battery of the first exemplary aminic acid fuel battery of the present invention with respect to formic acid concn;
Fig. 4 is the data and curves of formic acid concn to the influence of the open circuit voltage of the present invention's first exemplary aminic acid fuel battery;
Fig. 5 is that formic acid concn is to the data and curves of first example fuel cell in the influence of the current density of 0.4V;
Fig. 6 is the data and curves of formic acid concn to the influence of the resistance of first example fuel cell;
Fig. 7 is the data and curves of anode polarization of first example fuel cell of 12M formic acid;
Fig. 8 is the cyclic voltammetric data and curves of a kind of exemplary catalyst of the present invention in being equivalent to the example fuel cell of electrochemical cell;
Fig. 9 is the reactivity data and curves of exemplary catalyst in being equivalent to the example fuel cell of electrochemical cell;
Figure 10 is the CO stripping voltammetry data and curves of exemplary catalyst of the present invention;
Figure 11 (a) and 11 (b) are exemplary catalyst of the present invention and the performance data curve of 5M formic acid in the 3rd example fuel cell of the present invention;
Figure 12 is exemplary catalyst of the present invention and the performance data curve of 5M formic acid in the 3rd example fuel cell of the present invention;
Figure 13 is the time dependent data and curves of the performance of exemplary catalyst of the present invention under 0.6V;
Figure 14 is the time dependent data and curves of the performance of exemplary catalyst of the present invention under 0.5V;
Figure 15 is the time dependent data and curves of the performance of exemplary catalyst of the present invention under 0.4V; And
Figure 16 is the time dependent data and curves of the performance of exemplary catalyst of the present invention under 0.3V.
The present invention describes in detail
The schematic diagram of Fig. 1 shows exemplary direct organic fuel cell of the present invention synoptically and is represented with 10.Fuel cell 10 comprises anode 12, solid polymer protonically conducting electrolyte 14, gas diffusion cathode 16.Anode 12 is encapsulated in the anode chamber 18, and negative electrode 16 is encapsulated in the cathode chamber 20.When electric load (not shown) by being electrically connected 22 when being connected between anode 12 and the negative electrode 16, the electroxidation of organic-fuels takes place at anode 12, the electroreduction of oxidants takes place at negative electrode 16.
With negative electrode 16 different reactions taking place at anode 12, causes producing voltage difference between two electrodes.Conduct via being electrically connected 22 by the electronics that electroxidation produces at anode 12, finally be captured at negative electrode 16.The hydrogen ion or the proton that result from anode 12 pass through film electrolyte 14, migrate to negative electrode 16.Thereby, by keeping electric current via the ion flow of battery with via the electron stream that is electrically connected 22.This electric current can be used for driving electric equipment.
Anode 12, solid polymer electrolyte 14, and negative electrode 16 be single multi-layer compound structure in a preferred version, it can be called membrane electrode assembly (" MEA ").Preferred solid polymer electrolyte 14 is the cation-exchange membrane of proton conduction, and it comprises sulfate anion, for example fluoridized sulfonic acid polymer film, and commercial can obtaining from the chemicals Co., Ltd of Du Pont of the Delaware State, registered trade mark is NAFION.NAFION is the copolymer of tetrafluoroethene and perfluorovinyl sulfide ether sulfonic acid.Also can use other membrane material,, gather the hydrocarbon sulfonate film, comprise the film of other acid aglucon such as the perfluorinated sulfonic acid polymer film of modification, and the compound of two or more proton exchange membrane.
Anode 12 and negative electrode 16 can each self-contained catalyst layers, and the example is the meticulous Pt particle that has carrier or do not have carrier.If use preferred single MEA, then anode 12 and negative electrode 16 can comprise the catalyst layer of directly coating NAFION film both sides.Can obtain the NAFION of 0.002 inch and 0.007 inch standard thickness on the market.Single MEA can be by directly " coating " anode and cathod catalyst printing ink prepare on two surfaces of film 14.When catalyst ink was dry, solid catalyst particle formed anode 12 and negative electrode 16 attached on the film 14.
If catalyst has carrier, then Shi Yi carrier comprises meticulous carbon granule or makes it and high surface area carbon thin slice that electrocatalyst particles electrically contacts.As instantiation, anode 12 can so prepare: electrocatalyst materials such as metal and binding agent such as NAFION are mixed, and with about 0.5～5mg/cm 2Exemplary heap(ed) capacity coat on the carbon backing paper (backing paper).Then, can be with on the surface of this backing paper attached to NAFION film 14.Electrocatalyst for cathode alloy and carbon-fiber backed can comprise the TEFLON of about 10～50% (weight), and then hydrophobicity is provided, to set up three-phase boundary and to remove the electroreduction of deoxidation effectively and the water that produces.With the cathod catalyst backing attached to NAFION dielectric film 14 with anode 12 facing surfaces on.
Example fuel cell 10 is utilized formic acid (formic acid, " FA "), and fuel solution comes work, although other fuel also may be utilized.Formic acid fuel solution is offered anode chamber 18, simultaneously with the O of oxidant such as air or higher concentration 2Offer cathode chamber 20.At anode 12, formic acid fuel is oxidized:
HCOOH → 2H ++ CO 2+ 2e -(reaction 1)
CO 2Product flows out the anode chamber via exhaust outlet 24.Have been found that a general tubulose exhaust outlet, its internal diameter is less than about 1/32 inch, be preferably about 1/32 inch or littler, and length allows CO at least about 1/32 inch 2Gas passes through, but prevents that fully formic acid from passing through simultaneously.The length/diameter ratio of preferred exhaust outlet 24 is at least about 0.5.In addition, also preferred exhaust outlet 24 is to be made by hydrophobic material, and exemplary material comprises fluorocarbon-based polymers, can obtain from Minnesotan 3M company in market, and its registered trade mark is KEL-F.
The H of reaction 1 +Product arrives negative electrode 16 via polyelectrolyte floor 14, and the free electron product is flowed through by being electrically connected 22 arrival negative electrodes 16.At negative electrode 16, following reduction reaction takes place:
O 2+ 2e -+ 2H +→ 2H 2O (reaction 2)
H 2The O product flows out cathode chamber 20 via exhaust outlet 26.Can provide pump or other device, to drive flowing and air/O of formic acid fuel solution 2Flow.
Have been found that utilizing formic acid fuel solution to carry out oxidation at anode 12 can provide lot of advantages.Formic acid is stronger electrolyte, thereby promotes good protolysis in the anode chamber 18.It has lower vapour pressure, and at room temperature keeps liquid.In addition, formic acid/oxygen fuel cell of the present invention has high theoretical open circuit potential or the emf of about 1.45V.
Find that also formic acid has the diffusion and the towing leap rate (drag crossover rate) of low-down leap solid polymer dielectric film 14.This provides another valuable advantage for aminic acid fuel battery of the present invention.When formic acid was dissolved in the water, part was dissociated into anion.It is believed that this anion is attracted by anode 12, and repelled, pull and diffusion thereby stop via the infiltration of dielectric film 14 by the sulfate anion in the preferred polymer dielectric film 14.This greatly reduces or has eliminated the leap (crossover) of fuel via dielectric film 14.
The reason that the low leap of fuel is useful is a lot.For example, the low leap allows fuel cell 10 to move with high fuel concentration.It is believed that from about 10% formic acid concn rational performance can be provided to about 95% weight.High fuel concentration can provide the high current density and the high power output of per unit area, and can reduce or eliminate the water management of prior art.Low fuel leap rate also reduces or eliminates the poisoning of negative electrode 16 widely.This improves the performance of fuel cell 10 equally significantly.Another advantage of formic acid fuel solution is, it is believed that when 25～140 ℃ platinum catalyst is exposed to gaseous state formic acid, only produce can the amount of ignoring CO gas.On the other hand,, methyl alcohol it is believed that under conditions of similarity can produce a large amount of carbon monoxide products.
The present invention is not limited to aminic acid fuel battery.Other embodiments of the present invention comprise the direct organic fuel cell that utilizes organic-fuel solution and effectively realize the dielectric film of low fuel solution leap rate, described organic-fuel solution comprises at least about 10% weight, the organic-fuel that preferably is greater than about 25% weight.Represent that with current unit the dielectric film of example fuel cell of the present invention can be effectively be limited in the leap amount of fuel solution less than producing about 30mA/cm down at about 25 ℃ 2The amount that dielectric film is required.Although formic acid is preferred organic-fuel, other organic-fuel can comprise methyl alcohol and other alcohols, formaldehyde and other aldehydes, ketone, two and trimethoxy-methane and other oxygenate (oxygenate).
Have been found that by careful design electrolyte, make it to have very little or do not have fuel to cross over, can utilize the organic-fuel outside the formic acid to realize high fuel concentration.For example, have been found that electrolytic polymer film thickness, can keep fuel to cross over and be lower than a certain critical value j by selecting to suit f c, below the critical value, fuel cell can be worked constantly at this.As reasonably approximate, fuel leap rate j fCan provide by following formula:
Figure C0381279800101
(equation 1)
In the formula, C fBe the fuel concentration on described anode, D fBe the effective diffusion cofficient of fuel in membrane electrode assembly, K fThe equilibrium constant of the distribution coefficient that is fuel in the dielectric film, t is a film thickness,
Figure C0381279800102
Be Faraday constant, n fBe that the electron number that discharged when oxidized of 1 mole fuel is (for formic acid n f=2, for methyl alcohol n f=6).Reset equation 1, just can calculate the film thickness that obtains the required minimum of enough low leap rate:
Figure C0381279800111
(equation 2)
With methyl alcohol and aminic acid fuel battery is example, it is believed that to work as
Figure C0381279800112
Fuel cell performance reduces widely, works as j f cBe about 30mA/cm 2Or more hour, best operation appears.Should be appreciated that and rule of thumb to determine j for any required organic-fuel solution f cValue.Utilize in the document about 10M formic acid and the methyl alcohol permeation data through the NAFION film of 1100 equivalents, the minimum MEA thickness that can calculate formic acid is about 30 microns, and the minimum MEA thickness of methyl alcohol is about 600 microns.
On the other hand, the present invention relates to be used for the anode catalyst of direct organic fuel cell.Catalyst of the present invention comprises the nano particle of metal, and its surface scribbles at least a other metal coating.This coating can be about 2nm of thickness or littler continuous film, also can be formation thing or the island that disperses.Used term " discrete formation thing " and " island " among the present invention refers to be positioned at the group (grouping) of first metal surface and discontinuous basically second metal widely.It is thick that preferred discrete formation thing or island are not more than 3nm, and be individual layer or bilayer.
In catalyst of the present invention, the metal that can be used for metallic particles and coating thereof or island comprises platinum (Pt), palladium (Pd), ruthenium (Ru), rhenium (Re), iridium (Ir), gold (Au), silver (Ag), cobalt (Co), iron (Fe), nickel (Ni), yttrium (Y), and manganese (Mn).A preferred examples comprises the Pt particle, scribbles among Pd or the Ru one or more on it, and a most preferred example choosing scribbles the Pt of Pd.In addition, the material that is used for metallic particles and is used for coating can exchange mutually.As an example, the Pt island can be coated on the Pd particle.In a preferred exemplary Pt/Pd catalyst, about 10% to about 90% catalyst surface is covered by Pd.About 60% catalyst surface is covered by Pd in a most preferred exemplary Pt/Pd catalyst.Equally, the island of Pt can be coated on Pd or the Ru particle.Find that in addition when surface composition was different from the body composition, catalyst of the present invention provided best beneficial effect.This can pass through, and for example, prepares catalyst of the present invention by means of spontaneous deposition and realizes.The applicant believes, catalyst of the present invention can be used among several direct organic fuel cells any, and the example comprises the direct organic fuel cell that utilizes formaldehyde and comprise the alcohols of methyl alcohol.
When being used for aminic acid fuel battery of the present invention, the heap(ed) capacity of exemplary catalyst of the present invention is about 0.1mg/cm 2To about 12mg/cm 2When utilizing the air feed, preferred heap(ed) capacity is about 4mg/cm 2Increase heap(ed) capacity and as if do not change the electric current output basically.Be higher than about 12gm/m 2Heap(ed) capacity can seriousness slow down electric current output.Generally need more a spot of catalyst on the anode of the battery of breathe air.The applicant believes, can use to be low to moderate about 0.1mg/cm 2Heap(ed) capacity.
Have been found that advantageous particularly when catalyst of the present invention is used for aminic acid fuel battery of the present invention, although also be favourable when being used for other organic fuel cell.For example, have been found that the catalyst of the application of the invention, the electric current and the power density of aminic acid fuel battery 10 significantly strengthen.Have been found that preferred Pt/Pd catalyst is 80 times of Pt catalyst aspect raising aminic acid fuel battery current density.
Another advantage that it is believed that preferred Pt/Pd catalyst is to promote the formic acid oxidation reaction mechanism.The electro-oxidation reaction that it is believed that formic acid mainly is in the presence of metallic catalyst such as Pt, is undertaken by two parallel reaction paths.One of reaction path is via the dehydration mechanism that forms the CO intermediate:
HCOOH+Pt → Pt-CO+H 2O (reaction 3)
H 2O+Pt → Pt-OH+H ++ e -(reaction 4)
Pt-CO+Pt-OH → 2Pt+CO 2+ H ++ e -(reaction 5)
Formic acid is adsorbed on the Pt surface, forms the CO intermediate species (reaction 3) of absorption.Then, the OH group that need adsorb (being formed at reaction 4) further is oxidized to the CO intermediate of absorption the CO of gaseous state 2(reaction 5).
Second reaction path is more direct, and follows dehydrogenation mechanism:
HCOOH+M → CO 2+ M+2H ++ 2e -(reaction 6)
This reaction path directly forms CO 2Product, and the generation of the CO intermediate poisoning step of prevention absorption, the result forms the CO intermediate hardly.Directly the advantage of reaction path is seldom to have catalyst to poison because of CO, thus in fuel cell 10, need less platinum, and can obtain high current density.This direct reaction path also strengthens overall reaction rate, and is particularly lower and make and do not have surperficial OH on the Pt at sun level electromotive force -Situation under.At last, except making catalyst poisoning, because its poisonous person's character does not generally wish to form CO.It is believed that preferred its surface has the Pt nanoparticle catalyst promotion reaction 6 of Pd island, and do not promote to react 3.Thereby, utilize this preferred catalyst can solve in the prior art and much form relevant problem with CO.
Again on the one hand, the present invention relates to the preparation method of anode catalyst.The flow chart of Fig. 2 shows the step of an illustrative methods 50 of preparation catalyst of the present invention.The Pt nano particle is suspended in (square frame 52) in the liquid.Then suspension is coated on such as on the carriers such as carbon backing, gold dish (square frame 54).Follow dry suspension, on carrier, form the film (square frame 56) of Pt nano particle.At last, carrier is dipped in a kind of ionic metallic solution, spontaneously to deposit the island (square frame 58) of this kind metal at the Pt nano grain surface.
Another aspect the present invention relates to fuel cell, and the fuel solution of this fuel cell has and is lower than about 0 ℃, preferably is lower than-5 ℃ approximately, more preferably less than-10 ℃ freezing point approximately.The fuel cell that the present invention has enough high organic-fuel concentration can provide these advantages.For example, concentration of the present invention will have the freezing point that is lower than-10 ℃ of pacts at least about the aminic acid fuel battery of 20% weight.As more example, table 1 shows to the freezing point of water-fuel mixture being reduced to pact below-10 ℃, is used for the required minimum fuel concentration of various exemplary organic-fuel of fuel cell of the present invention.
Table 1
In another aspect of this invention, antifreezing agent can be added in the fuel solution of fuel cell, to reduce the solidification point of solution.Exemplary antifreezing agent comprises inorganic acid such as sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, and perchloric acid.These antifreezing agents can add or mix adding separately, be reduced to solidification point fuel solution about below 0 ℃, preferred approximately below-5 ℃, more preferably from about-10 ℃ below.Table 2 has provided exemplary antifreezing agent, and reduces the extremely about concentration required below-10 ℃ of solidification point of 1% methanol fuel solution.
Table 2
Figure C0381279800132
Should be noted that fuel and acid in table 1 and 2 only are that a series of fuel and inorganic acid can use in the present invention for example.In addition, should be appreciated that the advantage relevant with the low freezing point fuel solution all having the value of utilization in the fuel cell widely, and be not restricted to organic fuel cell.As special case, also recognize and antifreezing agent can be added in the hydrogen fuel cell such as the present invention.
For various aspects of the present invention are described better, some example fuel cell of the present invention adopt different fuel concentrations to come work with different catalyst of the present invention.The performance of these exemplary battery and catalyst is discussed below.
Example fuel cell 1:
First example fuel cell is consistent with fuel cell 10 shown in Figure 1 generally.For convenience, will under suitable situation, use the element numbers that comes from this fuel cell.The membrane electrode assembly of this example fuel cell (MEA) comprises anode 12, NAFION dielectric film 14 and negative electrode 16, and utilizes direct coating technique that catalyst layer 12 and 16 is coated on the NAFION film 14 and prepare.The NAFION film that is used for each example fuel cell has about 0.007 inch thickness.The active cell zone is 5cm 2Catalyst ink be by the dispersed catalyst nano particle in an amount of Millipore pure water and 5% double teeming NAFION solution (1100EW, Solution Technology, Inc.) in and preparation.Anode and cathod catalyst printing ink directly are coated on the both sides of NAFION 117 films respectively.Gained multilayer MEA constitutes anode 12, dielectric film 14 and negative electrode 16.
Used cathod catalyst is the platinum black (27m that is not with carrier 2/ g, Johnson Matthey), the loaded with standard amount is about 7mg/cm 2For anode, use preferred Pt/Pd catalyst, heap(ed) capacity is about 4mg/cm 2This catalyst prepares by Johnson Matthey Hispec 1000 palladium blacks are added on the golden ship.Then golden ship is dipped in palladium nitrate (II) solution (5mM Pd (NO 3) 2+ 0.1M H 2SO 4) in about 5 minutes.Catalyst Millipore water rinse removes denitrification with cyclic voltammetry then.Once more golden ship is dipped in palladium nitrate (II) solution (5mM Pd (NO 3) 2+ 0.1M H 2SO 4) in about 5 minutes.Catalyst Millipore water rinse removes denitrification with cyclic voltammetry then.Dry catalyst particles then.
First example fuel cell 10 comprises anode chamber 18 and the cathode chamber 20 that is machined to the electrically conductive graphite piece.Carbon cloth diffusion layer (can be from E-Tek on the market, Somerset, NJ acquisition) is placed the top of negative electrode and anode catalyst layer.Formic acid fuel solution enters anode chamber 20 via the Swagelock accessory of plastics.Cambium layer 12,14 and 16 MEA and carbon cloth are clipped between two electrode chambers 18 and 20, and by 35 scleroscopic silicon (Si) packing seals.Graphite block electrode chamber 18 and 20 is contained between two piece of stainless steel that are heated.Place the one-sided PC plate between piece of stainless steel and the machine work graphite block back to serve as collector body.
At first, with MEA layer 12,14 and 16 under 60 ℃ temperature in fuel cell with H 2/ O 2(anode/cathode) fuel cell pattern is regulated 1～2 hour, and (Fuel CellTechnologies, Inc.) keeping cell voltage potential is 0.6V to utilize the fuel cell experiments station simultaneously.H 2Flow velocity was set to 200scc/ minute, and air-flow enters before the battery humidification to 75 ℃, and applied the counter-pressure (backpressure) of 30psig.O 2Flow velocity is 100scc/ minute, air-flow humidification to 70 ℃, and apply the counter-pressure of 30psig.Stand-by H 2/ O 2After the adjusting, under 60 ℃, obtain the battery polarization curve.With regard to the measurement of battery polarization, used anode fuel is formic acid (Aldrich, a 96%A.C.S. grade).On negative electrode, O 2The flow velocity with 100scc/ minute provides under the situation of counter-pressure and humidification to 70 ℃ not having.
Anode 12 polarization curves are by using H 2Replace the O of negative electrode 16 2Air-flow obtains.Under the sweep speed of 1mV/s, with constant current device/potentiostat (273 types, EG﹠amp; G) electromotive force of control anode 12.Be positioned at the platinum/H of the cathode side of fuel cell anchor clamps 2Dynamic hydrogen reference electrode (DHE) is served as in combination, and the counterelectrode of high surface.H 2Humidification to 75 ℃ before entering battery, and under the constant counter-pressure of 10psig, keeping flow velocity is 100scc/ minute.Formic acid offers the anode-side of fuel cell MEA with 1mL/ minute flow velocity, to serve as the work electrode of electrochemical cell.
Fig. 3 (a) shows the battery polarization curve of this example fuel cell when adopting certain limit formic acid fuel solution concentration.The comprehensive battery activity of battery polarization curved measurement under various anode fuel feed concentration.The battery polarization curve of Fig. 3 (a) is to obtain in the scope of about 2M to 20M in the formic acid fuel solution concentration.
Should be noted that can be molar concentration and/or weight percent concentration here formic acid concn unit.It will be understood by those of skill in the art that the conversion between these two kinds of concentration is quite easy.For convenience, provide the present invention the transfer ratio of interested approximate concentration scope in the following table 3:
Table 3
Molar concentration The approximate weight percent concentration
1 5
2 9
4 18
5 22
9 39
11 46
13 54
15 61
17 69
20 79
Shown in Fig. 3 (a), the battery activity increases with feed concentration.The activity of 2M formic acid is very little.At 10M and being lower than under the fuel feed concentration of 10M, the applicant believes, supplies with formic acid and limits to the mass transportation of anode 12, limited the battery activity.Utilize the formic acid concn of about 10M, can obtain better result to about 20M.Battery that should be exemplary when formic acid is 12M, observes maximum current, and its value under 60 ℃ is about 134mA/cm 2When formic acid concn is 20M and 20M when above, the battery polarization curve descends.
As shown in Fig. 3 (a), this exemplary aminic acid fuel battery has the higher open circuit potential (OCP) of about 0.72V, and this is beyond thought and useful result.For example, the OCP of direct methanol fuel cell (DMFC) under conditions of similarity only is about 0.6V usually.The higher OCP of fuel cell of the present invention changes into high power density and can strengthen battery efficiency under lower application load.When in the best feed concentration range of formic acid concn at 10M to 20M, the battery under the high cell voltage potential (0.72V to 0.50V) is significantly active, and is different with the situation that observes in DMFC.
In Fig. 3 (b), the data among Fig. 3 (a) are further handled, and, be that unit maps to current density with power density at various formic acid concns.For the concentration below the 10M, the power density curve shows that power density increases with current density during beginning, reaches maximum, sharply descends then.It is believed that this decline is caused by the mass transportation restriction, this mass transportation restriction causes supply of fuel to reduce.Along with formic acid feed concentration increases to 12M from 2M, before supply of fuel reduced, initial power density slope was followed identical general trend.For 2M formic acid feed concentration, can obtain about 5mW/cm 2Power density.When the formic acid fuel solution concentration is about 12M, maximum power density appears among Fig. 3 (b), and it is about 48.8mW/cm 2The power density curve display of 20M formic acid goes out the overall loss of battery performance, because overall power density has reduced with respect to current density.
Should be noted that for the formic acid of 12M its maximum power density that records is about 48.8mW/cm under about 0.4V 2, this DMFC that safely challenges comparison with is at conditions of similarity (1M methyl alcohol, 60 ℃, Pt is catalyst based) measured maximum power density under about 0.27V: about 51.2mW/cm 2Comparative example fuel under 0.4V, the aminic acid fuel battery of 12M surpasses common 1M methanol fuel cell, and their maximum power density is respectively 48.8mW/cm 2To 32.0mW/cm 2
Fig. 3 (a) and 3 (b) show that in order to obtain rational current density, higher formic acid fuel solution concentration is preferred.It is believed that this is because the mass transportation restriction.Stoping formic acid may be interior NAFION and/or carbon cloth of catalyst layer to two kinds of anode mass transportation possible obstacles.At high-end (20M and more than the 20M) of the concentration studied spectrum, example fuel cell big electromotive force occurs and reduces, and causes the battery activity to move to disadvantageous direction.It is believed that and cause this result's reason to be that when in the fuel solution during water concentration step-down, NAFION dielectric film 14 takes place dry, and correspondingly causes its ionic conductivity to reduce.Therefore, required high formic acid concn should be considered with the overall balance that requires that keeps reasonable water concentration.
It is believed that when fuel used solution to have about 5% to the formic acid concn of about 95% weight and about 5% during to the water concentration of about 95% weight, fuel cell of the present invention is practical.General more preferably from about 25% to the formic acid concn of about 65% weight with at least about the water concentration of 30% weight.It is believed that this water concentration can keep the good ionic conductivity of passing through dielectric film 14.Fuel cell is to move the most favourable concentration that can influence formic acid fuel with the air of drying or with the air of humidification.For example, when the air with humidification moved, the formic acid concn that it is believed that about 50% to 70% weight was best.When the air with drying moves, and when the reagent of water confining force of any promotion negative electrode was not provided, the applicant believed that the concentration of about 20% to 40% weight is best.
About 1% alcohols to about 15% weight, the alcohols of preferred about 5% to 15% weight, for example ethylene glycol also can exist in fuel cell of the present invention.Except that other reason, also because alcohols can work fuel cell 10 as the media that disperses reaction heat under lower temperature.
Fig. 4 shows the influence of formic acid concn to the open circuit potential (OCP) of this example fuel cell.The feed concentration range of being studied is extremely about 22M formic acid of about 2M, and its flow velocity is about 1mL/ minute.Under lower fuel cell feed concentration, observe the maximum OCP that this example fuel cell has about 0.72V.Along with fuel feed concentration increases to about 10M formic acid from 2M, it is constant that OCP relatively keeps.More than about 10M, the OCP of example fuel cell begins to reduce.
In Fig. 5, show the influence of formic acid concn to the current density of this example fuel cell under the 0.4V cell voltage potential.The formic acid fuel solution concentration scope of being studied is extremely about 22M of about 1M, and flow velocity is about 1mL/ minute.Obtain current density under the 0.4V from the battery polarization curve.Under lower fuel feed concentration, has very little activity.Active increase with formic acid concn increases, and when fuel solution is about 10M extremely during about 20M, observes maximum activity.When fuel solution is about 15M, observes dielectric film and have about 120mA/cm 2Maximum current.When feed concentration during greater than about 15M, the battery activity begins to reduce, and sharply descends for about 20M or when higher in concentration.Should be noted that the area of anode and negative electrode is substantially the same in the application described first and the 3rd example fuel cell, and be substantially equal to the area of dielectric film.In addition, except as otherwise noted, electric current described in the application and power density will be represented with the unit are of dielectric film for example fuel cell 1 and 3; For exemplary battery 2, electric current and power density values will be represented with the unit are on Pt surface.
Fig. 6 shows the influence of formic acid concn to the high frequency battery resistance of example fuel cell.In the process that obtains the battery polarization curve, measure high frequency battery resistance.Resistance increases with formic acid feed concentration stabilize ground, i.e. about 0.43 Ω/cm under the 2M 2Increase to the about 0.675 Ω/cm under the 22M 2It is believed that this main under high formic acid concn, become dry (dry out) with the NAFION film and conductivity decline due to relevant than low electric conductivity.
Trend among Fig. 3 to Fig. 5 can be summarized as: (1) is higher than under the situation of about 10M in the formic acid fuel solution concentration, OCP reduces, (2) in the formic acid fuel solution concentration for about 20M or when above, the polarized current density of battery reduces, and the resistance of (3) fuel cell is with the concentration approximately linear ground increase of formic acid fuel solution.The applicant believes that a common phenomenon is arranged after all these trend.Especially, the applicant believes that polymer dielectric film 14 dewaters with the reduction of water concentration in the formic acid fuel solution, has caused these trend.The applicant believes, comprises about 40～65% weight formic acid and at least about the preferred fuel solution concentration scope of 30% weight water, can bring comparatively perfect performance.
Fig. 7 has drawn the anodic polarization curves of 12M formic acid.The difference of the battery polarization data of the data of Fig. 7 and Fig. 2 is: the electromotive force of Fig. 7 is directly with reference to dynamic hydrogen reference electrode (DHE).This has removed the influence of negative electrode, thereby helps illustrating quantitatively the result of catalyst/fuel performance.Fig. 7 shows that for this example fuel cell, initial formic acid oxidation reaction starts from about 0.15V (with respect to DHE).This compares with the electromotive force of methyl alcohol when beginning oxidation among the DMFC is favourable.
Example fuel cell equivalent 2:
Operate an exemplary formic acid battery of equal value and make its work, to further specify the performance of catalyst of the present invention.In this equivalence battery, catalyst of the present invention comprises the Pt nano particle, is furnished with deposit or the island of second metal such as Pd or Ru on it.Other catalyst of the present invention comprises the Pt nano particle, has the deposit (" Pt/Pd/Ru ") of Ru and Pd on it.By the 3rd example fuel cell this two kinds of catalyst are described.
Use three-electrode electro Chemical cell, wherein Pan Rao platinum plating Pt lead is a counterelectrode, is dipped in Ag/AgCl among the 3MNaCl as reference electrode.All electromotive forces are all by the electromotive force record with respect to reversible hydrogen electrode (RHE).(Johnson-Matthey) make, and it is fixed on the surface of gold dish (diameter 12mm, height 7mm) by physical action by platinum black by the Pt nanoparticle catalyst for work electrode.With the concentrated sulfuric acid (obtaining GFS Chemicals) and Millipore water with the quartz glass second distillation, the H of preparation 0.1M 2SO 4 Support electrolyte.Use 88% aqueous formic acid (second distillation, DFS Chemicals), and use ultra-pure argon gas to remove the air in all used in this experiment electrochemical cells.Adopt the CO (SJ Smith/Matheson) of ultra-high purity to carry out the measurement of CO adsorption/desorption.Employing is connected with the EG﹠amp of computer and CorrWare software (Scribner Associates); G Instruments PAR 283 barostats/galvanostat is as the power supply of battery.
According to the method for preparing catalyst that comprises spontaneous deposition of the present invention, prepare exemplary Pt/Pd catalyst of the present invention.The black nano particle of Pt-of known quantity is suspended in (catalyst of 4mg/ml) in the Millipore water.Term " nano particle " general reference diameter used among the present invention is the particle of a tens of/nanometer to tens nanometer.The 100-μ l aliquot of suspension is coated clean golden panel surface and made it air-dry in air, form the uniform catalyst film.This Au dish is nonactive to formic acid, and serves as the conductive carrier easily of catalyst.Owing to do not use organic polymer that catalyst is bonded in the Au dish, make pure catalyst surface can be exposed to the electrolyte media.
Clean the golden disc electrode that this has been coated with Pt, the end of extent (EOE) that electromotive force begins about platinum oxidation by cyclic voltammetry then.Next step, with electrode at palladium nitrate (II) solution (5mM Pd (NO 3) 2+ 0.1MH 2SO 4) the middle dipping about 5 minutes.After the deposition, electrode is washed with Millipore water, and handle the residue of removing nitrate anion from the surface, and reduce any palladium oxide that may between depositional stage, be formed at the surface by cyclic voltammetry.
Except Pd or as the substitute of Pd, can adopt ruthenium, by similar method, prepare exemplary ternary Pt/Pd/Ru of the present invention and exemplary Pt/Ru catalyst.In other words, clean the electrode of making by the gold dish of the top Pt/Pd of being coated with nano particle (as above preparing) or Pt nano particle by voltammetry once more, and make it at ruthenic chloride (III) solution (5mM RuCl 3+ 0.1M HClO 4) the middle dipping about 5 minutes.After the deposition, wash electrode, and remove the residue of cl anion, and reduce ru oxide with voltammetry.The final cyclic voltammogram (CV) of Pt/Pd/Ru electrode is shown among Fig. 8 with dashdotted form.
Have been found that in preparation during catalyst of the present invention that repeated deposition step 2～3 time may be favourable.It is believed that it is about sedimentary deposit of 0.3 to about 3nm that this repetition can produce thickness.Have been found that this thickness can improve the useful life of catalyst.It is believed that and repeat to cause the formation thing of deposit thickness more than this step 3 time greater than about 3nm.The sedimentary deposit that has been found that this thickness can be because of the oxidation reaction deterioration.
Actual electrode surface area is measured by the hydrogen adsorption/desorption amount of Pt surface before deposition Pd and/or Ru.Although the CV feature between pure, that deposit Pd, as to deposit Pd and the Ru Pt nano particle is completely different, the total hydrogen adsorption/desorption amount on Pt/Pd and the Pt/Pd/Ru but with pure Pt on equate.This shows, under all situations of being studied, all has about 1: 1 correlation between the number of hydrogen atoms of absorption and the number of sites of metal, and this helps long-pending the determining of real surface.
Block curve among Fig. 8 is represented the voltage-current characteristic of exemplary Pt/Pd catalyst of the present invention.Compare with the peak on the pure Pt, the electric current in hydrogen adsorption/desorption district-electromotive force peak is wideer and still less be restricted.Compare these new voltage-current characteristics more remarkable on exemplary Pt/Pd/Ru catalyst (chain-dotted line among Fig. 8) with Pt.Beyond thoughtly be that the formation of the oxide on surface on the exemplary Pt/Pd catalyst starts from the electromotive force of the about 50mV lower than pure Pt, obviously, has formed oxide on surface still less in the oxide scope of routine.In addition, for exemplary Pt/Pd and Pt/Pd/Ru catalyst, (double-layer charging current) is littler for double-deck charging current.
Fig. 9 shows the reactivity of exemplary catalyst in formic acid battery of equal value.Particularly, Fig. 9 comprises the timing ampere analytic curve that adopts exemplary catalyst electroxidation formic acid.In order to ensure stable state (steady state) state, timing ampere analysis experiment was carried out under about 0.27V 18 hours.Reach stable state after about 6 hours, in Fig. 9, only provided initial 8 hours that experiment is carried out.As shown in the figure, have been found that Pt/Pd catalyst of the present invention has more significant activity when using than catalyst to Pt with formic acid under this electromotive force.Find that also Pt/Pd/Ru catalyst of the present invention is more favourable than Pt catalyst.The current density of Pt and Pt/Pd catalyst is respectively about 0.011 μ A/cm 2With 0.84 μ A/cm 2Should be noted that this exemplary battery electric current and power density are to represent with the Pt surface of the cm of unit.Thereby Pt/PD catalyst of the present invention has been realized the enhancing than high about two orders of magnitude of Pt catalyst (about 80 times) aspect reactivity.This is unexpected and useful effect.
Should also be noted that to have been found that when preferred Pt/Pd catalyst uses with aminic acid fuel battery of the present invention, can be under the much lower electromotive force of the desired electromotive force of oxidation methyl alcohol than known direct methanol fuel cell, promote the oxidation of formic acid.For example, for the oxidation of formic acid on Pt/Pd, the current density that records under the 0.27V is about 0.84 μ A/cm 2Pt, and the current density of methyl alcohol under 0.4V (with respect to RHE) of the employing Pt/Ru catalyst of having reported is about 0.94 μ A/cm 2Pt.
Be the intoxication of test CO, the CO of ultra-high purity was imported in the example fuel cell 40 minutes, utilize high-purity argon from battery, to remove CO (under 0.13V, carrying out 20 minutes) then.Figure 10 shows the stripping voltammogram (dotted line) of the electrode with Pt catalyst, stripping voltammogram (solid line) with electrode of Pt/Pd catalyst of the present invention, have the stripping voltammogram (chain-dotted line) of the electrode of Pt/Pd/Ru catalyst of the present invention, and have the stripping voltammogram (imaginary point line) of the electrode of Pt/Ru catalyst of the present invention.
For pure Pt nanoparticle electrode, observe " prewave (pre-wave) " that onset potential is low to moderate about 0.3V, at 0.66V main peak appears then.For Pt/Pd catalyst of the present invention, observe same pattern, just prewave is little and flat, and main peak is bigger and more sharp-pointed than Pt simultaneously.The prewave of Pt/Pd starts from the electromotive force of the about 0.05V more positive than Pt, and the electromotive force at the main CO stripping peak of Pt and Pt/Pd nano particle is increased to the 0.69V of Pt/Pd by the 0.66V of Pt.For Pt and Pt/Pd, the total electrical charge of CO stripping is identical, is about 330 μ C/cm 2Ru is added in the Pt/Pd nano particle, and the peak position produces the displacement of about 0.15V, and surface C O oxidation current peak changes to about 0.55V.This peak is a broad peak, and has fine structure clearly, seems (chain-dotted line among Figure 10) be made up of a plurality of overlap peaks.For the Pt/Ru nano particle, CO stripping peak occurs under lower electromotive force.It is believed that in this case, peak division clearly occurs, because the oxidation of CO comes from two kinds of different surperficial phases: the Pt/Ru island, and unmodified in the surface (" pure ") the Pt part.In a word, the data suggest of Figure 10, stripping has higher electromotive force to Pt/Pd catalyst of the present invention to CO, and this can be interpreted as the tolerance of CO is lower than Pt.
Seem, when using with formic acid fuel solution of the present invention, Pt/Pd catalyst advantageous particularly of the present invention.For example, Fig. 9 shows that the Pt/Pd surface has higher steady-state current, and Figure 10 shows that then the Pt/Pd catalyst has lower CO tolerance, as higher CO stripping electromotive force confirms.This is another beyond thought beneficial effect of preferred Pt/Pd catalyst.It is believed that it is because the Pt/Pd catalyst promotes the formic acid direct dehydrogenation response path of reaction 6 rather than reacts 3～5 dehydrogenation reaction path that these and other beneficial effect can be realized.
Example fuel cell 3:
Prepare the direct fuel cell of the 3rd exemplary formic acid, to further specify fuel cell of the present invention and catalyst of the present invention.The 3rd example fuel cell is consistent with the fuel cell 10 that schematically provides among Fig. 1 generally.For convenience's sake, use consistent element number.By following method, preparation comprises the monobasic membrane electrode assembly (MEA) of anode 12, polymer dielectric 14 and negative electrode 16: directly catalyst ink is coated on the relative both sides of NAFION film.The active cell district is about 5cm 2
Catalyst ink be by with the catalyst nano Dispersion of Particles the double teeming NAFION of an amount of Millipore water and 5% solution (1100EW, Solution Technology, Inc.) in and the preparation.For all prepared exemplary MEA, negative electrode 16 comprises platinum black nano particle (the about 27m that is not with carrier 2/ g, Johnson Matthey), the loaded with standard amount is about 7mg/cm 2Two kinds of different exemplary male electrode catalysts are compared with the black catalyst (Johnson Matthey) of Pt of standard.These two kinds of exemplary catalyst are: the Pt of modification black (" Pt/Ru ") by spontaneous deposition Ru submono, and the Pt of the modification by spontaneous deposition Pd submono black (" Pt/Pd ").But exemplary catalyst, with reference to the electrochemical cell of described example fuel cell equivalence is not coated on suspension on the carrier by being similar to above-mentioned method preparation, and also moist suspension is to form film on carrier.On the contrary, use the catalyst of catalyst fines, and make it to be exposed to the solution of slaine, with plated metal island spontaneously as self-supporting.The heap(ed) capacity of all three kinds of catalyst is 4mg/cm 2Carbon cloth diffusion layer (E-Tek) is placed on the top of negative electrode and anode catalyst layer, and the two sides is all with the TEFLON coating, to carry out water management.
At room temperature in test cell, regulate earlier MEA, use the H of methyl alcohol/humidification 2(more than 10 ℃ battery temperature) (anode of fuel cell/negative electrode) moves some anodic polarization curves, is increased to 80 ℃ final battery temperature simultaneously lentamente.The negative electrode of fuel cell serves as dynamic hydrogen reference electrode (DHE), and serves as the high surface counterelectrode in this adjustment process.H 2Flow velocity is 100scc/ minute under the 10psig counter-pressure, and the air-flow humidification is to being higher than 10 ℃ of battery temperatures.Methyl alcohol (1M) is offered the anode-side of fuel cell MEA, and flow velocity is 0.5mL/ minute, and serves as the work electrode of electrochemical cell.With power supply (Hewlett Packard, 6033A type) control anode potential, electromotive force increased with 5 seconds the time interval and the stride of 10mV.
In fuel cell mode, under 80 ℃, Yi Bian H is provided 2/ O 2(anode/cathode), further regulate MEA on one side, simultaneously cell voltage potential was kept under 0.6V 1～2 hour.With fuel cell experiments station (Fuel Cell Technologies, Inc) control cell voltage potential.H 2Flow velocity is set at 200scc/ minute, and air-flow enters before the battery humidification to 95 ℃, and applies the counter-pressure of 30psig.O 2Flow velocity is 100scc/ minute, air-flow humidification to 90 ℃, and apply the counter-pressure of 30psig.Stand-by H 2/ O 2After the adjusting, battery temperature is reduced to 30 ℃.As final regulating step, with 4M methyl alcohol (0.5mL/ minute)/O 2(100scc/ minute, 40 ℃) obtains the battery polarization curve.
Under 30 ℃, utilize the formic acid (Aldrich, 96%A.C.S. level) of 5M, with 0.5mL/ minute flow velocity, obtain three kinds of anode catalyst MEA battery polarization curve separately.With O 2Under the situation of the counter-pressure of 30psi and humidification to 40 ℃, offer negative electrode with 100scc/ minute flow velocity.With flow velocity is 0.2mL/ minute 5M formic acid, obtains the life test result under 0.6V, 0.5V, 0.4V and 0.3V.With O 2Under the situation of the counter-pressure of 30psi and humidification to 40 ℃, offer negative electrode with 100scc/ minute flow velocity.Apply electromotive force load earlier, step to 0.1V, step to required actual potential then by open circuit potential.
Under 30 ℃, obtain the stripping cyclic voltammogram of carbon monoxide (CO).In the measurement, anode serves as work electrode; Electromotive force is controlled with barostat/galvanostat (Solartron, SI 1287 types), and sweep speed is 1mV/ second.H 2Feed is in fuel battery negative pole chamber, platinum/H 2Dynamic reference electrode (DHE) and counterelectrode are served as in combination.H 2Flow velocity is 100scc/ minute under the situation of the counter-pressure of 10psig and humidification to 40 ℃.Between the CO adsorption cycle, anode potential remains 0.15V (with respect to DHE).Originally, be the argon gas (Ar) of 30psig and humidification to 40 ℃ with counter-pressure, offer anode of fuel cell with 400scc/ minute flow velocity.The CO that comes from 0.1% among the Ar (flow velocity 400scc/ minute, counter-pressure 30psig, humidification to 40 ℃) was adsorbed 30 minutes from the teeth outwards.Washed the anode chamber 10 minutes with Ar then.Measure the surface area of each anode by CO stripping peak, suppose that loading density (packing density) is 1.0.
Figure 11 shows the influence of anode catalyst composition to the battery polarization curved profile, and three kinds of catalyst being tested are Pt, Pt/Ru and the Pt/Pd that are used for this example fuel cell, and this example fuel cell adopts the formic acid fuel solution of 5M.Data show that exemplary catalyst Pt/Ru of the present invention and Pt/Pd are influential to the OCP of example fuel cell.The OCP of platinum anode is about 0.71V, and the OCP of Pt/Ru catalyst is about 0.59V, and the OCP of Pt/Pd catalyst is about 0.91V.The data of Figure 11 show that also the current density output of Pt/Pd catalyst reality is lower than 0.8V, is different from Pt and Pt/Ru anode catalyst, for the latter two, do not observe current density output yet when the voltage that is applied is lower than 0.6V.It should be noted that the exemplary aminic acid fuel battery that adopts catalyst of the present invention under identical condition, provides the OCP than the high about 0.2V of DMFC.For the reverse scan battery polarization curve of Pt and Pt/Pd, observe bigger current density.For the Pt/Ru catalyst, forward scan and reverse scan are substantially the same.Provide following electric current by reverse scan.Under 0.5V, three kinds of catalyst based current densities of oxygen are output as: Pt (33mA/cm 2), Pt/Ru (38mA/cm 2), and Pt/Pd (62mA/cm 2).Pt/Ru has the highest current density (lower apply electromotive force) under the highest heap(ed) capacity.Under 0.2V, current density is output as: Pt (187mA/cm 2), Pt/Ru (346mA/cm 2), and Pt/Pd (186mA/cm 2).Should be noted that electric current and power density are with every cm 2The anode of the 3rd example fuel cell of unit is represented.
In Figure 11 (b),, the data among Figure 11 (a) are further handled according to the relation of the power density under the room temperature (25 ℃) to the cell voltage potential that applied.For three kinds of catalyst, the maximum power density of gained is respectively: Pt-43mW/cm 2(0.26V), Pt/Ru-70mW/cm 2(0.26V), reach Pt/Pd-41mW/cm 2(0.27V).Exemplary Pt/Pd catalyst near its maximum power density, makes fuel cell (～0.5V) operation more than cell voltage potential under the required electromotive force that applies.Pt/Ru has the highest power density output, but only under low cell voltage potential (0.27V).Should also be noted that the performance of this example fuel cell and catalyst of the present invention is compared with DMFC under the substantially the same condition that the measured maximum power density of the latter only is about 12mW/cm 2
Figure 12 shows the Pt anode catalyst of employing 5M formic acid fuel solution and the anodic polarization curves of exemplary Pt/Pd of the present invention and Pt/Ru catalyst.The difference of anodic polarization curves figure and battery polarization curve chart is that the electromotive force of anode of fuel cell chamber is directly with reference to dynamic reference electrode.This has removed the influence of negative electrode, thereby helps explaining quantitatively the anode catalyst performance.
The anode polarization result truly reflects the result that can observe generally in the battery polarization curve of Figure 11 (a).Compare with the Pt catalyst, when formic acid begins oxidation on exemplary Pt/Pd catalyst, have OCP difference greater than 0.1V, this part explained the OCP difference of existing 0.2V.When electromotive force is lower than 0.4V (with respect to DHE), there is not current density on the Pt/Ru anode catalyst basically, then more than 0.45V, activity sharply increases.Table 4 has been listed the current density of exemplary catalyst under several anode potential:
Table 4
Anode potential with respect to DHE Pt(mA/cm 2) Pt/Ru(mA/cm 2) Pt/Pd(mA/cm 2)
0.2V 3 1.6 12
0.3V 7.6 1.6 18
0.4V 19.6 3 31.6
0.49V 43.6 111.36 48
Under low potential, Pt/Pd catalyst of the present invention obtains than Pt or the high electric current of Pt/Ru catalyst.
With regard to Figure 12 and table 4 (in the original specification in English, it reads " Table 2; " which should be a typo), should be noted that preferred Pt/Pd catalyst realizes that under the electromotive force of about 0.2V about 4 times increase to the Pt activity of such catalysts.Although this growth is obvious and useful,, measured approximate 80 times growth when this growth is different from top described employing second example fuel cell significantly is referring to Fig. 9.It is believed that the reason that causes this species diversity is the cathode structure difference in these two experiments.Particularly, it is believed that second exemplary battery is anode restrictive (reaction speed is subject to anode reaction).Therefore, anode improves and directly is reflected in the battery output.On the other hand, it is believed that the 3rd exemplary battery is negative electrode overriding (reaction speed is subject to cathode reaction), so the improvement of antianode reaction not as in second exemplary battery, directly is not reflected in the battery output.In addition, utilize this exemplary aminic acid fuel battery to carry out life test, this battery drives with oxygen, adopt exemplary catalyst, and the cell voltage potential that is applied is 0.6V to 0.3V.The results are summarized among Figure 12 to Figure 15.In Figure 13, the cell voltage potential that is applied is 0.6V.Have only Pt and Pt/Pd catalyst under this electromotive force that is applied, to demonstrate tangible current density.Figure 14 shows the testing data of life-span under the 0.5V cell voltage potential.Pt/Pd of the present invention and Pt/Ru catalyst all bring the performance than Pt catalyst excellence, and the Pt/Pd catalyst is the most desirable under this electromotive force.When cell voltage potential kept 2 hours under 0.5V after, final approximation steady state current density was: Pt-22.02mA/cm 2(10.30mW/cm 2), Pt/Ru-35.14mA/cm 2(16.44mW/cm 2), Pt/Pd-46.39mA/cm 2(21.71mW/cm 2).
Figure 15 has provided the data of the life test of being carried out under the electromotive force of 0.4V.Pt/Pd and Pt/Ru catalyst are better than the Pt catalyst again.When cell voltage potential kept 2 hours under 0.4V after, final approximation steady state current density was: Pt-37.44mA/cm 2(15.69mW/cm 2), Pt/Ru-60.61mA/cm 2(25.40mW/cm 2), and Pt/Pd-67.32mA/cm 2(28.24mW/cm 2).
Final life test is to obtain under the cell voltage potential of 0.3V, the results are shown among Figure 16.Reconfirm that catalyst of the present invention is better than Pt.Under this applied electromotive force, the Pt/Ru catalyst was better than Pt/Pd.When cell voltage potential kept 2 hours under 0.3V after, final approximation steady state current density was: Pt-62.53mA/cm 2(19.36mW/cm 2), Pt/Ru-166.72mA/cm 2(51.35mW/cm), Pt/Pd-125.98mA/cm 2(39.14mW/cm 2).
The results of property of example fuel cell shows that formic acid fuel solution of the present invention and catalyst have huge future in application of power.It provides the advantage that much is better than DMFC of the prior art and other organic fuel cell.These advantages may be particularly useful in mini electronic equipment or microelectronic device.For example, because the aminic acid fuel battery that drives with high fuel concentration does not have the water management of DMFC, so do not need to comprise the big and complicated water management system of volume of pump, transducer etc.Thereby aminic acid fuel battery advantageously of the present invention can provide the size compacter than DMFC.In addition, the high 0.2V of open-circuit cell voltage ratio DMFC of aminic acid fuel battery is so power adjustments is easier.Adopt some exemplary application of aminic acid fuel battery of the present invention to comprise portable battery, portable electric appts such as transducer, communication apparatus, control device etc.Should be appreciated that these and other can comprise the fuel cell of a plurality of series connection such as the fuel cell 10 of series in using because the electromotive force of single aminic acid fuel battery is lower.
Specific embodiments disclosed herein and structure are used to illustrate implements preferred and best mode of the present invention, is restriction to the defined scope of the present invention of appended claims and it should be construed to.

Claims (22)

1. direct organic fuel cell comprises:
Liquid fuel solutions, it comprises the formic acid of water and 25% to 95% weight;
Anode, it is included in the anode chamber, also comprises described liquid fuel solutions in this anode chamber;
Negative electrode, it is electrically connected and is included in the cathode chamber with described anode, also comprises oxidant in this cathode chamber; And
Electrolyte, it is with described anode and described cathode isolation.
2. according to the direct organic fuel cell of claim 1, wherein said electrolyte comprises solid polymer proton exchange membrane, and described anode and described cathode arrangement are on two of this solid polymer proton exchange membrane relative sides.
3. according to the direct organic fuel cell of claim 2, wherein said solid polymer proton exchange membrane comprises the perfluorinated sulfonic acid ionomer.
4. according to the direct organic fuel cell of claim 2, wherein said electrolyte can not permeated by described liquid fuel solutions basically.
5. according to the direct organic fuel cell of claim 1, wherein said fuel solution comprises the formic acid of 25% to 70% weight.
6. according to the direct organic fuel cell of claim 1, wherein said fuel solution comprises the formic acid of 25% to 65% weight.
7. according to the direct organic fuel cell of claim 1, wherein said oxidant comprises the air of humidification, and the concentration of described formic acid is 50% to 70% weight.
8. according to the direct organic fuel cell of claim 1, wherein said oxidant comprises dry air, and the concentration of described formic acid is 25% to 40% weight.
9. according to the direct organic fuel cell of claim 1, also comprise the anode catalyst of the Pt nano particle that scribbles the Pd island, the configuration of wherein said anode promotes that formic acid reacts by the directapath of avoiding forming the CO intermediate product.
10. according to the direct organic fuel cell of claim 9, when wherein this battery is worked, can effectively produce 20 under 25 ℃ temperature to 60mW/cm 2Power density.
11., when wherein this battery is worked, can effectively produce 20 under 25 ℃ temperature to 60mW/cm according to the direct organic fuel cell of claim 1 2Power density.
12. according to the direct organic fuel cell of claim 1, wherein said anode chamber has at least one CO 2Exhaust outlet.
13. according to the direct organic fuel cell of claim 12, wherein said exhaust outlet be tubulose and make by hydrophobic material.
14. direct organic fuel cell according to claim 1, also comprise containing Pt Pd, Ru, Re, Ir, Au, Ag, Co, Fe, the anode catalyst of the metal nanoparticle of one or more among Ni or the Mn wherein also comprises the coating of the discrete island of one of Pt, Pd or Ru on described metal nanoparticle.
15. according to the direct organic fuel cell of claim 14, wherein said metal nanoparticle is Pt, and described coating is among Pd or the Ru one or more.
16. according to the direct organic fuel cell of claim 15, the useful load of wherein said anode catalyst is 0.5 to 12gm/cm 2
17. according to the direct organic fuel cell of claim 15, wherein said anode catalyst has different surface compositions and body phase composition.
18. according to the direct organic fuel cell of claim 1, also comprise the anode catalyst of the Pt nano particle of the discrete island that scribbles Pd, the configuration of wherein said anode promotes the formic acid dehydrogenation to CO 2And H +, do not form the CO intermediate.
19. according to the direct fuel cell of claim 1, wherein:
Described electrolyte comprises polymer dielectric film, and it has opposite first and second surface;
Described anode arrangement is on the first surface of described dielectric film;
Described liquid fuel solutions comprises the formic acid of 25% to 65% weight,
Described anode comprises effective promotion formic acid fuel solution direct dehydrogenation and does not form the catalyst of CO intermediate;
Described cathode arrangement is at the second surface of described dielectric film, and comprises O in the described cathode chamber 2And
This direct fuel cell further comprises described anode is connected to electrical connection on the described negative electrode.
20. direct organic fuel cell according to claim 1, wherein said electrolyte comprises the solid polymer electrolyte with first and second surfaces, described anode is positioned on the described first surface, described negative electrode is positioned on the described second surface, and described solid polymer electrolyte has the thickness t that satisfies following formula:
Figure C038127980003C1
In the formula, C fBe the fuel concentration on described anode, D fBe the effective diffusion cofficient of fuel in described solid polymer electrolyte, K fThe equilibrium constant of the distribution coefficient that is fuel in the described solid polymer dielectric film,
Figure C038127980004C1
Be Faraday constant, n fBe the electron number that 1 mole fuel is discharged when oxidized, j f cBe the leap rate critical value that can keep fuel to cross over, fuel cell can be worked below the leap rate constantly at this.
21. according to the direct organic fuel cell of claim 20, wherein said solid polymer electrolyte is the leap amount of fuel limitation effectively, makes it less than producing 30mA/cm down at 25 ℃ 2Required amount.
22. according to the direct organic fuel cell of claim 1, wherein said liquid fuel solutions comprises the formic acid of 40% to 95% weight.
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