CN103474679A

CN103474679A - Anode catalyst for direct formic acid fuel cell and preparation method of anode catalyst

Info

Publication number: CN103474679A
Application number: CN2013103976745A
Authority: CN
Inventors: 吴冬霜; 曹荣
Original assignee: Fujian Institute of Research on the Structure of Matter of CAS
Current assignee: Fujian Institute of Research on the Structure of Matter of CAS
Priority date: 2013-09-04
Filing date: 2013-09-04
Publication date: 2013-12-25

Abstract

The invention discloses an anode catalyst for a direct formic acid fuel cell and a preparation method of the anode catalyst, belonging to the field of fuel-cell catalysts. The catalyst is composed of palladium (Pd) nano-particles protected by a compound formed by ruthenium bivalent ions and polyvinylpyrrolidone, wherein the effective active ingredient is Pd.

Description

A kind of direct methanoic acid fuel cell anode catalyst and preparation method thereof

Technical field

The present invention relates to utilize ruthenium compound and polyvinylpyrrolidone to prepare the method for palladium nano-particles as the direct methanoic acid fuel cell anode catalyst as pattern guiding agent and protective agent.Effectively regulate and control pattern and the decentralization of palladium nano-particles by the adjusting to kinetic factor, prepare there is high activity, the direct methanoic acid fuel cell anode catalyst of high stability, belong to the fuel-cell catalyst field.

Background technology

Direct methanoic acid fuel cell is directly to use liquid formic acid to act as a fuel to supply with source, belongs to a kind of in the proton exchange membrane low-temperature fuel cell.With direct methanol fuel cell and compare, this class battery has lot of advantages: 1) the electrochemistry oxygen voltinism of formic acid is better than methyl alcohol, and theoretical open circuit voltage is 1.45V, higher than methyl alcohol; 2) formic acid, by the little order of magnitude of permeability ratio methyl alcohol of proton exchange membrane, allows to use the formic acid of high concentration; 3) formic acid is a kind of electrolyte, is conducive to increase the proton conductivity of solution in anode chamber; 4) freezing point of formic acid is lower, and resistance to low temperature is good; 5) formic acid is substantially nontoxic; 6) formic acid is nonflammable, stores and transport safer.Therefore direct methanoic acid fuel cell development in recent years is swift and violent, is considered to most possibly obtain the earliest the fuel cell of commercial applications.In direct methanoic acid fuel cell, what anode catalyst was mainly used is that platinum (Pt) is catalyst based, but the oxidizing process of formic acid on Pt mainly can produce by a kind of that carbon monoxide intermediate product " non-direct way " carries out.This intermediate product carbon monoxide has very strong adsorption capacity to Pt, thereby makes rapid catalyst deactivation.And in the reserves rareness of occurring in nature Pt, expensive, further limited the business-like process of direct methanoic acid fuel cell.In recent years, palladium (Pd) had caused widely and had paid close attention to as a kind of desirable Pt substitute.Therefore a large amount of research shows that Pd mainly carrys out catalytic oxidation formic acid by " direct way ", does not produce the toxicity intermediate products such as CO, to the electro catalytic activity of Oxidation of Formic Acid far above Pt; And the earth's crust storage capacity of Pd is at least 50 times of Pt, thereby reduced the catalyst cost.Bibliographical information is for example arranged, and the peak power output of using the formic acid battery of Pd/C anode catalyst in the time of 25 ℃ is the twice of the Pt/C catalyst for preparing with same method, has still kept 1.5 times in the time of 50 ℃.But the Pd poor catalyst stability, easily oxidation, also become a large problem of direct methanoic acid fuel cell.Therefore the balance between catalytic activity and stability, Performance and Cost Modeling remains the key point of direct methanoic acid fuel cell Catalyst Design and preparation.And improve the catalyst based stability of Pd, realize that key active and that stability coexists is structure and the pattern of appropriate design catalyst.Because the process of catalytic oxidation formic acid is the process of a surface catalysis, structure and the pattern of its catalytic activity and stability and catalyst are closely bound up.

The research of the low index crystal face Single Crystalline Electrodes catalytic oxidation formic acid of relevant Pd shows, under the practical application potential range of battery, (being less than 0.5V) Pd (111) crystal face has the highest activity and stability.But for nanocrystal, except the crystal face exposed, the defect in crystal structure (twin plane, accumulation dislocation etc.), most advanced and sophisticated atom kink atom, surface charges etc. are also the key factors that affects electrocatalysis characteristic.Although for example research discovery Pd icosahedron and tetrahedron are all wrapped up in and formed by (111) bread, the icosahedral Formic Acid Catalytic Oxidation activity that contains five times of twin symmetry axis will be far above not containing the tetrahedron of twin plane.Therefore reasonably design pattern and the structure of Pd catalyst, make it have high activity and high stability concurrently, remain a great problem.The method of the catalyst based catalytic performance of anode Pd of current optimization direct methanoic acid fuel cell mostly is introduces the second metal, transition metal such as gold, nickel, ruthenium, cobalt and tin, and they and Pd form the structures such as shell-core, alloy or heterojunction.The second metal of introducing exists in catalyst system and catalyzing mainly with zeroth order, and these metal ingredients easily come off in the catalytic cycle process, leaks in electrolyte solution contaminated electrode and make the rapid catalysqt deactivation of catalyst.And in fact not all metal active component in the electro-catalysis process is the nano particle of zeroth order.The metal Ru (Ru) of take is example, and the research of many application shows, the active component of ruthenium in catalytic process is actually the hydrate (RuO of ruthenium _xh _y).Just contain large packaged RuO in business-like Pt-Ru catalyst _xh _y, to improve catalyst activity.Although the Pt-Ru catalyst is commercially produced, the bright rare report of Pd-Ru electro-catalysis system.This is that lattice height due to metal Pd and metal Ru does not mate, the reduction cell difference is larger, thereby its pattern and structure are difficult to obtain the control of rationality.But the compound of introducing Ru in the catalyst system and catalyzing of metal Pd is good undoubtedly.At first, the compound of Ru (RuO especially _xh _y) be the active component of electro-catalysis, improve catalytic activity.Secondly, RuO _xh _ybe generally to be present in system with unformed shape, can well disperse the Pd nano particle, prevent from reuniting, increase its stability.Again, RuO _xh _ycan modify the electronic structure on Pd surface, increase proton conductivity.In addition, Ru, in building-up process, can experience a series of redox reaction, can produce tremendous influence to the nucleation of Pd nano particle and the dynamical mechanism of growth.Thereby we can utilize this process, regulate and control cleverly reaction condition, thereby synthetic have specific morphology the compound-modified Pd nano particle of Ru, make these Pd nano particles show good activity and resisting CO poisoning ability to the catalytic oxidation of formic acid.

Summary of the invention

The object of the invention is to overcome existing technical problem in the production of above-mentioned direct methanoic acid fuel cell anode catalyst and use procedure, provide to prepare top layer with the compound of ruthenium and polyvinylpyrrolidone as pattern guiding agent and stabilizer and palladium nano-particles that ruthenium compound modifies is arranged for the direct methanoic acid fuel cell anode catalyst, and the control by the reduction process kinetic factor make nano particle be rendered as { 111 } crystal face parcel contain single twin plane go to hold the trigonal biyramid structure.

The present invention utilizes ruthenium trichloride and polyvinylpyrrolidone to prepare palladium nano-particles that ruthenium bivalent compound that particle diameter is less than 20 nanometers modifies for the direct methanoic acid fuel cell anode catalyst as pattern guiding agent and protective agent respectively.This nanoparticle catalyst be by { 111 } crystal face parcel contain single twin plane go to hold the trigonal biyramid structure.The present invention is by introducing ruthenium compound, realized the kinetic factor control of nucleation and the growth course of palladium nano-particles, thereby obtain the structure that contains single twin plane of all being wrapped up in by { 111 } bread, and synthetic palladium nano-particles skin is wrapped in the ruthenium bivalent compound with electro-chemical activity.With commercially available palladium black, compare, the prepared palladium nanocatalyst of the present invention shows good catalytic activity and stability and active regeneration ability to the catalytic oxidation of formic acid.Preparation technology of the present invention is simple, easy to operate, but industrialization production.

The invention provides a kind of direct methanoic acid fuel cell anode catalyst and preparation method thereof, comprise the following steps:

(1) take a certain amount of polyvinylpyrrolidone, stir it is dissolved in ethylene glycol fully, make solution A;

(2), at 90 ℃～110 ℃, the aqueous solution to adding a certain amount of ruthenium trichloride in solution A, obtain jade-green mixed liquid B after stirring;

(3) dropwise drip the potassium chloropalladate aqueous solution in mixed liquid B, obtain mixture C;

Wherein the mol ratio of polyvinylpyrrolidone and potassium chloropalladate is not higher than 36, and the mol ratio of ruthenium trichloride and potassium chloropalladate is not higher than 1;

(4) cooling naturally after mixture C slaking at a certain temperature; Curing temperature is not less than 110 ℃;

(5) after the product that step (4) obtains is centrifugal, with deionized water and acetone washing several, be distributed in a certain amount of ethanol, obtain described direct methanoic acid fuel cell anode catalyst.

The direct methanoic acid fuel cell anode catalyst that adopts preceding method to prepare, it consists of the palladium nano-particles (Ru of the compound protection of ruthenium divalent ion and polyvinylpyrrolidone formation ²⁺-PVP complex protected Pd nanoparticles), wherein the effective active composition is palladium.

The preparation method of direct methanoic acid fuel cell anode catalyst provided by the present invention has the following advantages:

(1) catalyst prepared is gone through evenly, good dispersion, structure is { 111 } crystal face parcel contain single twin plane go to hold the trigonal biyramid structure, { 111 } face of palladium is active under practical operation voltage and the best crystal face of stability, Twin Defects has increased activity, go to hold the trigonal biyramid structure be rich in edge and most advanced and sophisticated atom be beneficial to improve active;

(2) outer surface of palladium nano-particles wraps up the ruthenium bivalent compound of this amorphous state, can effectively prevent the reunion of palladium nano-particles, and improves the proton conductivity in the electro-catalysis process;

(3) catalyst prepared by the method, have advantages of that catalytic activity is high, long service life, renewable be strong.

The accompanying drawing explanation

Fig. 1. the large regional transmission electron microscope photo of prepared catalyst, scale is of a size of 200 nanometers;

Fig. 2. the zonule transmission electron microscope photo of prepared catalyst, scale is of a size of 20 nanometers;

Fig. 3. the high-resolution-ration transmission electric-lens photo of prepared catalyst, scale is of a size of 2 nanometers;

Fig. 4. prepared catalyst and commercially available palladium black catalyst in the 0.5mol/L sulfuric acid solution to 0.25mol/L formic acid catalytic oxidation cyclic voltammogram;

Fig. 5. the time current curve of catalyst.

Embodiment

Below in conjunction with embodiment and accompanying drawing, the present invention is made further to detailed speed time second, but do not limit the present invention.The transmission electron microscope that transmission electron microscope photo is used is: JEOL-2010, and using voltage is 200 kilovolts; The instrument that electro-chemical test is used is: Epsilon EC electrochemical work station(BASi, the U.S.).

Embodiment

(1) polyvinylpyrrolidone of 0.1g (PVP) joins in the ethylene glycol (EG) of 15ml, is uniformly mixed;

(2) under 110 ℃, add the 0.025mmmol ruthenium trichloride aqueous solution (0.08ml) in the mixed liquor A obtained to step (1), obtain mixture B;

(3) drip the 0.025mmol potassium chloropalladate aqueous solution (3ml), mixture C in the mixture B obtained to step (2);

(4) mixture C step (3) obtained is at least reacted 1 hour in the oil bath of 110 ℃, naturally cools to room temperature;

(5) product step (4) obtained is separated (7900 rev/mins) with acetone, the 5mL deionized water adds 30ml acetone cyclic washing at least 3 times, then is distributed in a certain amount of ethanol and obtains direct methanoic acid fuel cell anode catalyst of the present invention.

The transmission electron microscope photo of the catalyst that Fig. 1-3 provide for case study on implementation, can see that from Fig. 1-2 the catalyst particle size of synthesized is even, on average about 17 nanometers left and right.Can see in Fig. 2 that most of particle twin plane all is high-visible.The part particle may not manifest due to the reason of position phase its twin plane.Fig. 3 is the high-resolution-ration transmission electric-lens picture of a single particle, the twin plane of dotted line representative is high-visible, in the twin plane both sides, lattice symmetry distributes, and { 111 } face that to be all interplanar distance be 0.23 nanometer illustrates that the outer surface of this particle is wrapped up by { 111 } face.

The preparation of the glass-carbon electrode of surface catalyst layer: get nano particle and active carbon mixing that a certain amount of ethanol disperses, ultrasonic 4 hours, then under room temperature, stir 48 hours, centrifugal collection, drying, obtain activated carbon supported palladium nanocatalyst.This catalyst is distributed in ethanolic solution again, and the content that makes palladium is 1mg/ml.The loaded catalyst of getting 3 microlitres drips the glass-carbon electrode surface that is 3mm at diameter, natural drying under room temperature.

The mensuration of the cyclic voltammetry curve of catalyst: adopt three-electrode system to measure the chemical property of catalyst.With the glass-carbon electrode of the above-mentioned surface catalyst layer prepared, as work electrode, platinum filament is to electrode, and Ag/AgCl is reference electrode.In the aqueous solution that contains 0.25mol/L formic acid and 0.5mol/L sulfuric acid, measure cyclic voltammetry curve and time current curve under room temperature condition.

Fig. 4 is the cyclic voltammetry curve of the catalyst that provides of case study on implementation.As can be seen from the figure the catalyst of synthesized has stronger electro-chemical activity, and the peak current density of forward scan is almost 8 times of commercially available palladium blacks.Time current curve in Fig. 5 shows that prepared catalyst stability is also better, and after 2000 seconds, remaining electric current is greater than commercially available palladium black.

Above said content is the basic explanation under conceiving for the present invention only, and, according to any equivalent transformation that technical scheme of the present invention is done, all should belong to protection scope of the present invention.

Claims

1. the preparation method of a direct methanoic acid fuel cell anode catalyst comprises the following steps:

2. the direct methanoic acid fuel cell anode catalyst that adopts method claimed in claim 1 to prepare, it consists of the palladium nano-particles of the compound protection of ruthenium divalent ion and polyvinylpyrrolidone formation, and wherein the effective active composition is Pd.