[go: up one dir, main page]

US20180069207A1 - Core-Shell Fuel Cell Electrodes - Google Patents

Core-Shell Fuel Cell Electrodes Download PDF

Info

Publication number
US20180069207A1
US20180069207A1 US15/811,892 US201715811892A US2018069207A1 US 20180069207 A1 US20180069207 A1 US 20180069207A1 US 201715811892 A US201715811892 A US 201715811892A US 2018069207 A1 US2018069207 A1 US 2018069207A1
Authority
US
United States
Prior art keywords
electrocatalyst
core
catalytically active
particle
thin layer
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Abandoned
Application number
US15/811,892
Inventor
Radoslav R. Adzic
Stoyan Bliznakov
Miomir Vukmirovic
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Brookhaven Science Associates LLC
Original Assignee
Brookhaven Science Associates LLC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Brookhaven Science Associates LLC filed Critical Brookhaven Science Associates LLC
Priority to US15/811,892 priority Critical patent/US20180069207A1/en
Publication of US20180069207A1 publication Critical patent/US20180069207A1/en
Assigned to UNITED STATES DEPARTMENT OF ENERGY reassignment UNITED STATES DEPARTMENT OF ENERGY CONFIRMATORY LICENSE (SEE DOCUMENT FOR DETAILS). Assignors: BROOKHAVEN SCIENCE ASSOC-BROOKHAVEN LAB
Abandoned legal-status Critical Current

Links

Images

Classifications

    • H01M2/10—
    • 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
    • H01M4/8647—Inert electrodes with catalytic activity, e.g. for fuel cells consisting of more than one material, e.g. consisting of composites
    • H01M4/8657—Inert electrodes with catalytic activity, e.g. for fuel cells consisting of more than one material, e.g. consisting of composites layered
    • 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
    • H01M4/8807—Gas diffusion layers
    • 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
    • H01M4/8817—Treatment of supports before application 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
    • H01M4/90—Selection of catalytic material
    • H01M4/9041—Metals or alloys
    • 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
    • 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
    • H01M4/921—Alloys or mixtures with metallic elements
    • 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
    • H01M2008/1095—Fuel cells with polymeric electrolytes
    • 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
    • Y02E60/10—Energy storage using batteries
    • 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

Definitions

  • This disclosure relates generally to electrocatalysts, more specifically to electrocatalysts for use in polymer electrolyte membrane fuel cells.
  • a fuel cell is an electrochemical device capable of converting the chemical energy of a fuel and an oxidant into electrical energy.
  • a standard fuel cell is comprised of an anode and cathode separated by a conducting electrolyte which electrically insulates the electrodes yet permits the flow of ions between them.
  • the fuel cell operates by separating electrons and ions from the fuel at the anode and transporting the electrons through an external circuit to the cathode.
  • the ions are concurrently transported through the electrolyte to the cathode where the oxidant is combined with the ions and electrons to form a waste product.
  • An electrical circuit is completed by the concomitant flow of ions from the anode to cathode via the conducting electrolyte and the flow of electrons from the anode to the cathode via the external circuit.
  • PEMFCs polymer electrolyte membrane fuel cells
  • PEMFCs may eliminate electrolyte leakage, lower corrosion, simplify stack design and increase ruggedness.
  • Producing PEMFCs may require complex procedures, such as powder catalyst production, ink preparation from catalyst powder, and spreading the ink on a gas diffusion layer.
  • Pt platinum
  • Embodiments of the invention provide for electrocatalysts that have increased reaction sites in the catalytic layer while at the same time have reduced the catalytic metal loading. These electrocatalysts may be used in polymer electrolyte membrane fuel cells (PEMFC).
  • PEMFC polymer electrolyte membrane fuel cells
  • An embodiment provides for an electrocatalyst which includes at least one gas-diffusion layer having a first side and a second side and particle cores adhered to at least the first side of the at least one gas-diffusion layer.
  • the particle cores include a first surface area adhered to the first side of the at least one gas-diffusion layer and a second surface area not in contact with the at least one gas-diffusion layer.
  • a thin layer of catalytically active metal atoms is adhered to the second surface area of the particle cores not in contact with the at least one gas-diffusion layer.
  • An embodiment provides for a membrane electrode assembly which includes at least one gas-diffusion layer having a first side and a second side and particle cores adhered to at least the first side of the at least one gas-diffusion layer.
  • the particle cores include a first surface area adhered to the first side of the at least one gas-diffusion layer and a second surface area not in contact with the at least one gas-diffusion layer.
  • a thin layer of catalytically active metal atoms is adhered to the second surface area of the particle cores not in contact with the at least one gas-diffusion layer.
  • At least one proton exchange membrane is attached to at least the first side of the at least one gas-diffusion layer.
  • Another embodiment provides for a method of forming a membrane electrode assembly.
  • the method includes treating at least one gas-diffusion layer to at least partially oxidize at least one surface of the least one gas-diffusion layer, depositing core particles on the at least one surface of the least one gas-diffusion layer, and depositing a thin layer of catalytically active metal atoms on a surface area of the core particles not in contact with the at least one surface of the least one gas-diffusion layer.
  • FIG. 1 is a diagram of a polymer electrolyte membrane fuel cell (PEMFC);
  • FIG. 2A is an illustration of a Pt-encapsulated nanoparticle attached to a carbon surface with Pt atoms in contact with carbon that are not accessible to protons
  • FIG. 2B is an illustration of a Pt-encapsulated nanoparticle attached to a carbon surface with all Pt atoms accessible to protons;
  • FIG. 3 is a plot of the pulse deposition protocol for PdAu alloy core deposition on GDL
  • FIG. 4 shows polarization curves of Example 1B (Pt ML PdAu, 25 cm 2 ) in a single H 2 /O 2 cell;
  • FIG. 5 shows polarization curves of Example 1A (Pt ML PdAu, 5 cm 2 ) in air or oxygen, and after 1000 and 2000 cycles;
  • FIG. 6 shows the polarization curve of Example 1C (Pt ML PdAu, 450 cm 2 );
  • FIG. 7 shows the polarization curve of Example 4A (Pt ML PdWNi 5 cm 2 ).
  • FIG. 8 shows the polarization curve of Example 4B (Pt ML PdWNi 25 cm 2 ).
  • Embodiments described in this disclosure include electrocatalysts that have increased reaction sites in the catalytic layer while at the same time have reduced the catalytic metal loading. These electrocatalysts may be used in polymer electrolyte membrane fuel cells (PEMFC)
  • FIG. 1 is a diagram of PEMFC.
  • a proton exchange membrane fuel cell transforms the chemical energy liberated during the electrochemical reaction of hydrogen and oxygen to electrical energy, as opposed to the direct combustion of hydrogen and oxygen gases to produce thermal energy.
  • a stream of hydrogen is delivered to the anode side of the membrane electrode assembly (MEA). At the anode side it is catalytically split into protons and electrons. (http://en.wikipedia.org/wiki/Proton_exchange_membrane_fuel_cell, last accessed May 15, 2013)
  • This oxidation half-cell reaction or Hydrogen Oxidation Reaction (HOR) is represented by:
  • the reversible reaction is expressed in the equation and shows the reincorporation of the hydrogen protons and electrons together with the oxygen molecule and the formation of one water molecule.
  • the MEA may be formed with an increase in reaction sites in the catalytic layer while at the same time reducing the catalytic metal loading.
  • the MEA may be formed by first providing a gas diffusion layer (GDL).
  • GDL gas diffusion layer
  • the gas diffusion layer may be constructed of known materials. They may be formed of a porous material including a conducting material such as carbon. For example, porous carbon woven fabric provides efficient transport of fuel gas or oxidant gas into the catalyst layers.
  • At least one surface of the GDL may be treated to at least partially oxide the carbon surface of the GDL.
  • the GDL may be treated with an acid. Any suitable acid may be used, such as nitric acid or sulfuric acid.
  • Core particles may be formed on the partially oxidized GDL surface. Any suitable method of forming core particles may be deployed. For example the methods of forming core nanoparticles described in U.S. Patent Publication Nos. US 20100197490 A1, 20100216632 A1, US 20110155579 A1, and in U.S. Pat. No. 7,691,780 B2, U.S. Pat. No. 7,704,918 B2, and U.S. Pat. No. 7,855,021 B2, all incorporated herein by reference in their entirety, may be used. Furthermore, core nanoparticles may be formed as described in U.S. patent application Ser. No. 13/860,316, filed Apr. 10, 2013, titled Synthesis of Nanoparticles Using Ethanol, U.S. Publication No. 2013/0264198, the contents of which is incorporated herein in its entirety.
  • the core particles may, for example, be deposited using electrodeposition of metal salt solutions of the metals to be deposited directly on the GDL.
  • metal salt solutions may be used.
  • metal salts of at least one noble metal such as ruthenium, rhodium, palladium, silver, rhenium, osmium, iridium, platinum, gold may be used.
  • metal salts of non-noble metals such as Ti, Hf, Zr, W, Ta, Nb, V, Re, Cr, Mo, Tc, and Mn, may also be used. Combinations of noble metal salts and non-noble metal salts may also be used.
  • the metal salts may be chlorides, carbonates, acetates, citrates, fluorides, nitrates, nitrites, phosphates, sulfates, or combinations thereof, of the metal ions.
  • FIG. 3 shows a pulse deposition protocol for PdAu alloy core deposition on GDL, 0.5 seconds at ⁇ 500 mV, 4.5 seconds at ⁇ 350 mV, 3 seconds at open circuit potential.
  • the electrolyte composition can include 1 mM PdCl 2 +0.1 M NaCl+0.1 mM NaAuCl.
  • the core particle may include at least one noble metal, such as ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), and gold (Au).
  • the core particle may include at least one non-noble metal.
  • the core particle includes Ti, Hf, Zr, W, Ta, Nb, V, Re, Cr, Mo, Tc, and Mn.
  • the core particle may include at least an alloy of at least two noble metals, or at least one noble metal and at least one non-noble metal.
  • the core particle comprises an alloy selected from the group consisting of Pd 1-x Au x , Pd 1-x Ti x , Pd 1-x W x , Pd 1-x Nb x , Pd 1-x Ta x , Pd 1-x Re x , Pd 1-x Ir x , Ir 1-x Ti x , Ir 1-x Ta x , Ir 1-x Nb x , Ir 1-x Re x , Au 1-x Ta x , Au 1-x Ir x , and Au 1-x Re x and x represents the concentration of the alloying element, being adjustable over the range 0 ⁇ x ⁇ 1.
  • the alloy is PdAu.
  • the particles disclosed and described in this specification are not limited to any particular shape or size, but in some embodiments may be nanoparticles with sizes ranging from 1 to 100 nm in one more dimensions. However, the size is not so limited and may extend into the micrometer and millimeter size range.
  • the shape may be spherical or spheroidal, but again is not so limited.
  • the particles will be primarily disclosed and described as essentially spherical nanoparticles. It is to be understood, however, that the particles may take on any shape, size, and structure as is well-known in the art. This includes, but is not limited to branching, conical, pyramidal, cubical, mesh, fiber, cuboctahedral, and tubular nanoparticles.
  • the nanoparticles may be agglomerated or dispersed, formed into ordered arrays, fabricated into an interconnected mesh structure, either formed on a supporting medium or suspended in a solution, and may have even or uneven size distributions.
  • the particle shape and size is preferably configured so that the bonding configuration of surface atoms is such that their reactivity and, hence, their ability to function as a catalyst is increased.
  • Core particle formation is followed by the deposition of a catalytically active surface layer (or shell) having thicknesses in the monolayer-to-multilayer range.
  • a catalytically active surface layer or shell having thicknesses in the monolayer-to-multilayer range.
  • FIG. 2A illustrates core particles that have a thin layer of a catalytically active metal wholly surrounding the particle.
  • FIG. 2B illustrates an embodiment of the present disclosure. It can be seen that the core particle is encapsulated by the GDL and the catalytically active surface layer, and all the catalytically active metal atoms of the shell is available to interact with the protons (i.e., active).
  • a monolayer is formed when the surface of a substrate (or core), not in contact with the GDL, is fully covered by a single, closely packed layer comprising adatoms of a second material which farms a chemical or physical bond with atoms at the surface of the substrate.
  • the surface is considered fully covered when substantially all available surface sites, not in contact with the GDL, are occupied by an adatom of the second material. If the surface of the substrate is not completely covered by a single layer of the adsorbing material, then the surface coverage is considered to be submonolayer. However, if a second or subsequent layers of the adsorbant are deposited onto the first layer, then multilayer surface coverages (e.g., bilayer, trilayer, etc.) result.
  • multilayer surface coverages e.g., bilayer, trilayer, etc.
  • the catalytically active surface layer may be deposited using any of a wide variety of thin film deposition processes which are well-known in the art.
  • catalytically active surface layer may be deposited as described in U.S. Publication No. 2013/0264198.
  • the deposition process is a series of electrochemical reactions which, when performed sequentially result in a film with the targeted coverage and composition.
  • the procedure involves the initial formation of an adlayer of a metal onto a substrate by underpotential deposition (UPD). This is followed by the galvanic displacement of the adlayer by a more noble metal, resulting in the conformal deposition of a ML of the more noble metal on the substrate.
  • the overall process includes the irreversible and spontaneous redox displacement of an adlayer of a non-noble metal by a more noble metal. This enables the controlled deposition of a thin, continuous layer of a desired metal.
  • the substrate metal is more noble than the metal undergoing deposition in order to avoid becoming oxidized.
  • the redox reaction can be described by the following equation
  • M UPD 0 represents a UPD metal adatom on the electrode surface and L z+ is a noble metal cation with positive charge z+ and valence z.
  • the M m+ represents the metal cation in the solution obtained after the UPD adatom was oxidized, and L 0 is a noble atom deposited in the redox process.
  • the catalytically active surface layer is not limited to any particular material, it is preferably Pt due to its excellent catalytic properties. Consequently, an example in which a monolayer of Pt is formed on nanoparticles using the processes described by Brankovic and Adzic will now be described in detail. It is to be understood, however, that the process is not limited to Pt and other noble metals may be utilized.
  • the method involves the initial formation of a monolayer of a metal such as copper (Cu) by underpotential deposition (UPD) in a solution comprised of 50 mM CuSO 4 in a 50 mM H 2 SO 4 solution. The Cu-coated nanoparticles are then immersed from solution and rinsed with deionized water to remove Cu 2+ ions from the surface.
  • a metal such as copper (Cu) by underpotential deposition (UPD)
  • UPD underpotential deposition
  • the above process results in the conformal deposition of a ML of Pt on high-surface-area core particles.
  • the deposition cycle comprising UPD of Cu followed by galvanic displacement with Pt may be repeated as needed to produce two or more layers of Pt in order to ensure complete coverage of the nanoparticle surface.
  • the UPD of Cu may be controllably limited such that submonolayer coverages of Cu and, hence, Pt are obtained.
  • Deposition of an initial adlayer by UPD may also be accomplished using metals other than Cu such as, for example, lead (Pb), bismuth (Bi), tin (Sn), cadmium (Cd), silver (Ag), antimony (Sb), and thallium (Tl).
  • the choice of metal used for UPD will influence the final Pt surface coverage obtained for a given UPD adlayer. This occurs due to variations in the size and valency among the different metals.
  • the metal overlayer used is not limited to Pt, but may be formed from other noble metals as long as the desired metal is more noble than the UPD adlayer. This may be accomplished by contacting the copper-coated particles with their corresponding salts. For example, monolayers of iridium, ruthenium, osmium, and rhenium can be deposited by displacement of a ML of a less noble metal such as copper using IrCl 3 , RuCl 3 , OsCl 3 , or ReCl 3 , respectively.
  • the metal overlayer may be formed as an alloy with any number of constituents such as binary, ternary, quaternary, or quinary alloys with experimentally optimized stoichiometry ratios.
  • the process offers unprecedented control over film growth and is advantageous in terms of its versatility, reproducibility, and efficient utilization of source material. Since a costly precious metal such as Pt can be utilized as a thin film instead of in bulk form, significant cost savings can be attained.
  • the utilization of a noble metal/substrate nanoparticle may also provide unexpectedly heightened catalytic activity due to synergistic effects between the nanoparticles and the catalytic overlayer. The unexpected increase in catalytic activity may arise due to electronic and geometric effects which arise from the formation of surface metal-metal bonds and the differing lattice constants of the catalytic overlayer and underlying substrate.
  • the catalytic properties of the surface overlayer may also be engineered by use of a suitable core particle.
  • a core of a non-noble metal such as Ni, Co, Fe, Ti, W, Nb, V, or Ta may be coated with a more noble metal such as Au, Pd, or Pt.
  • the catalytic activity of the final coated nanoparticle may be controlled by engineering the electronic properties and lattice parameter of the underlying core-shell nanoparticles with respect to those of the metal overlayer.
  • the GDL with the cores having atomically thin surface layers deposited thereon in situ may then be contacted with a proton exchange membrane (PEM) such that the cores having atomically thin surface layers are sandwiched between the GDL and the PEM.
  • PEM proton exchange membrane
  • Any suitable PEM may be used, such as for example Nafion membranes.
  • An anode layer may be contacted with the second surface (the surface not in contact with the core particles and PEM). This assembly may then be hot-pressed together to form the membrane electrode assembly (MEA).
  • the methods described herein amounts to in situ catalyst deposition directly onto the GDL and fabrication of the MEA can be performed in mere minutes (e.g., several minutes), and without the need to prepare catalyst ink and paint the catalyst ink onto the GDL. Furthermore, as the particles are formed in-situ and on the GDL, there is less opportunity for exposure to free nanoparticles or for nanoparticles to be released into the environment.
  • MEA Membrane Electrode Assembly
  • MEAs were prepared by first cutting gas diffusion layers (GDLs) into 5 cm 2 , 25 cm 2 , or 450 cm 2 pieces. The GDLs were then functionalized by pretreatment in hot (70° C.) concentrated nitric acid for 1 hour followed by thorough rinsing with nanopure water, boiling in water for 1 hour, and rinsing again with nanopure water. Nanoparticles were then deposited or sprayed onto the treated GDLs, and the nanoparticles coated with a Pt layer according to the methods described below. The GDLs with the Pt coated nanoparticles was rinsed with nanopure water and dried. A Nafion 211 membrane was then hot-pressed to the GDL together with an anode electrode to complete the MEA fabrication.
  • GDLs gas diffusion layers
  • PdAu Core deposition Elongated Pd 0.9 Au 0.1 nanoparticles with an average particle size of 6 nm were electrodeposited directly on the GDL (Example 1A: 5 cm 2 , Example 1B: 25 cm 2 , Example 1C: 450 cm 2 ) at constant potential ( ⁇ 330 mV vs. Ag/AgC/Cl ⁇ (3M KCl)).
  • the electrolyte composition was 1 mM PdCl 2 +0.1 M NaCl+0.1 mM NaAuCl 4 and the loading of the Pd 0.9 Au 0.1 nanoparticles was controlled by the charge and was limited to 30 ⁇ g/cm 2 .
  • Pt monolayer coating Pt monolayer shell deposition on the Pd 0.9 Au 0.1 nanoparticle cores was performed as described in U.S. Pat. No. 7,691,780. First a Cu underpotentially deposited (UPD) monolayer was deposited at underpotentials from 50 mM CuSO 4 +50 mM H 2 SO 4 solution. Then the electrolyte was replaced with 1 mM KPtCl 4 +50 mM H 2 SO 4 solution and the pre-deposited Cu ML was galvanically displaced by Pt for less than a minute. There were no changes observed in the shape and the particle size distribution of the resulting Pt ML Pd 0.9 Au 0.1 electrocatalysts. The shape and the average particle size distribution remained the same as of the Pd 0.9 Au 0.1 nanoparticles core.
  • UPD Cu underpotentially deposited
  • Pd hollow core deposition Hollow palladium nanoparticles made using a micro-emulsion method were combined with Vulcan XC-72R carbon black and water to obtain a palladium catalyst ink loading of about 30 wt % total palladium. The ink was then sprayed onto the GDL (5 cm 2 ) and dried.
  • Pt monolayer coating Pt monolayer shell deposition on the Pd hollow nanoparticle cores was performed as described for Examples 1A-1C. There were no changes observed in the shape and the particle size distribution of the resulting Pt ML Pd hollow electrocatalysts. The shape and the average particle size distribution remained the same as of the Pd hollow nanoparticles core.
  • Pd nanowires Core deposition Pd nanowires with diameter of 3-4 nm and length of 50-60 nm were electrodeposited directly on functionalized GDL (Example 3A: 5 cm 2 , Example 3B: 25 cm 2 ) at constant potential ( ⁇ 330 mV vs. Ag/AgC/Cl ⁇ (3M KCl)).
  • the electrolyte composition was 1 mM PdCl 2 +0.1 M NaCl and the loading of the Pd nanowires was controlled by the charge and was limited to 30 ⁇ g/cm 2 .
  • Pt monolayer coating Pt monolayer shell deposition on the Pd nanowires nanoparticle cores was performed as described for Examples 1A-1C. There were no changes observed in the shape and the particle size distribution of the resulting Pt ML Pd nanowires electrocatalysts. The shape and the average particle size distribution remained the same as of the Pt ML Pd nanowires nanoparticles core.
  • the electrolyte was replaced by 1 mM PdCl 2 +50 mM H 2 SO 4 solution, and parts of the Ni atoms from the alloy were galvanically displaced by Pd. As a result a Pd reach shell was formed on the WNi core, and the particle size distribution remained unchanged.
  • Pt monolayer coating Pt monolayer shell deposition on the PdWNi nanoparticle cores was performed as described for Examples 1A-1C. There were no changes observed in the shape and the particle size distribution of the resulting Pt ML PdWNi electrocatalysts. The shape and the average particle size distribution remained the same as of the Pt ML Pd nanowires nanoparticles core.
  • Pd core deposition Palladium nanoparticles made in ethanol using the method as described in U.S. Publication No. 2013/0264198, were combined with Vulcan XC-72R carbon black and water to obtain a palladium catalyst ink loading of about 30 wt % total palladium. The ink was then sprayed onto the GDL (5 cm 2 ) and dried.
  • Pt monolayer coating Pt monolayer shell deposition on the Pd nanoparticle cores was performed as described for Examples 1A-1C. There were no changes observed in the shape and the particle size distribution of the resulting Pt ML Pd electrocatalysts. The shape and the average particle size distribution remained the same as of the Pd nanoparticles core.
  • FIG. 4 shows polarization curves of Example 1B in a single H 2 /O 2 cell with only 50 ⁇ g/cm 2 of all platinum-group metals on the cathode as compared to 400 ⁇ g/cm 2 in commercial Pt catalysts.
  • the PGM mass activity is 0.4 A/mg
  • the specific activity is 0.2 mA/cm 2
  • the Pt mass activity is 1.1 A/mg Pt .
  • FIG. 5 shows polarization curves of Example 1A in air or oxygen, and after 1000 and 2000 cycles. After 2000 potential cycles it can be seen that the activity increased.
  • the PGM mass activity is 0.5 A/mg
  • the specific activity is 0.4 mA/cm 2
  • the Pt mass activity is 1.2 A/mg Pt .
  • FIG. 6 shows the polarization curve of Example 1C. It can be seen that Examples 1A and 1B (5 and 25 cm 2 electrodes, respectively) show a similar activity, while Example 1A (450 cm 2 electrode) shows a lower activity. This may be caused by the ambient pressure applied and low open circuit potential which may be due to the state of the surface. However, this may be corrected.
  • Example 1C has a PGM mass activity is 0.4 A/mg and a Pt mass activity of 1 A/mg Pt .
  • FIG. 7 shows the polarization curve of Example 4A
  • FIG. 8 shows the polarization curve of Example 4B. It can be seen that the performance increased after 5000 cycles for Example 4A (5 cm 2 ) and after 15,000 cycles for Example 4B (25 cm 2 ),
  • Table 1 shows a summary of the results for the 5 cm 2 MEA examples herein compared to a MEA made using commercially available Pt/C materials. It can be seen that all the example Pt catalysts have a PGM activity 3-5 times higher than the commercially available catalyst, and their Pt mass activity is one order of magnitude higher than that of the commercially available catalyst. The only exception is lower PGM activity for the Pt ML Pd nanowire catalyst caused by the mass of Pd wire.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Composite Materials (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Sustainable Development (AREA)
  • Sustainable Energy (AREA)
  • Inert Electrodes (AREA)
  • Catalysts (AREA)

Abstract

Embodiments of the disclosure relate to membrane electrode assemblies. The membrane electrode assembly may include at least one gas-diffusion layer having a first side and a second side, and particle cores adhered to at least one of the first and second sides of the at least one gas-diffusion layer. The particle cores includes surfaces adhered to the at least one of the first and second sides of the at least one gas-diffusion layer and surfaces not in contact with the at least one gas-diffusion layer. Furthermore, a thin layer of catalytically atoms may be adhered to the surfaces of the particle cores not in contact with the at least one gas-diffusion layer.

Description

    CROSS-REFERENCE TO A RELATED APPLICATION
  • This application is a continuation application of application Ser. No. 15/627,882 filed Jun. 20, 2017, which is a divisional application of application Ser. No. 14/279,012 filed, May 15, 2014, issued as U.S. Pat. No. 9,716,279, which claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional Application No. 61/823,845 filed on May 15, 2013, the contents of which are incorporated herein in its entirety.
  • This invention was made with Government support under contract number DE-AC02-98CH10886 awarded by the U.S. Department of Energy. The Government has certain rights in the invention.
    • FIELD OF THE INVENTION
  • This disclosure relates generally to electrocatalysts, more specifically to electrocatalysts for use in polymer electrolyte membrane fuel cells.
    • BACKGROUND
  • A fuel cell is an electrochemical device capable of converting the chemical energy of a fuel and an oxidant into electrical energy. A standard fuel cell is comprised of an anode and cathode separated by a conducting electrolyte which electrically insulates the electrodes yet permits the flow of ions between them. The fuel cell operates by separating electrons and ions from the fuel at the anode and transporting the electrons through an external circuit to the cathode. The ions are concurrently transported through the electrolyte to the cathode where the oxidant is combined with the ions and electrons to form a waste product. An electrical circuit is completed by the concomitant flow of ions from the anode to cathode via the conducting electrolyte and the flow of electrons from the anode to the cathode via the external circuit.
  • In particular, polymer electrolyte membrane fuel cells (PEMFCs) may be of interest. PEMFCs may eliminate electrolyte leakage, lower corrosion, simplify stack design and increase ruggedness. Producing PEMFCs may require complex procedures, such as powder catalyst production, ink preparation from catalyst powder, and spreading the ink on a gas diffusion layer. Furthermore, as PEMFCs may require platinum (Pt) catalyst as an active material of electrodes, it may be beneficial to increase the reaction sites in the catalytic layer and, thus, to improve electrode performance and reduce Pt loading. Therefore there is a need to develop methods that increase the reaction sites in the catalytic layer while at the same time reduce the Pt loading.
    • SUMMARY OF THE INVENTION
  • Embodiments of the invention provide for electrocatalysts that have increased reaction sites in the catalytic layer while at the same time have reduced the catalytic metal loading. These electrocatalysts may be used in polymer electrolyte membrane fuel cells (PEMFC).
  • An embodiment provides for an electrocatalyst which includes at least one gas-diffusion layer having a first side and a second side and particle cores adhered to at least the first side of the at least one gas-diffusion layer. The particle cores include a first surface area adhered to the first side of the at least one gas-diffusion layer and a second surface area not in contact with the at least one gas-diffusion layer. A thin layer of catalytically active metal atoms is adhered to the second surface area of the particle cores not in contact with the at least one gas-diffusion layer.
  • An embodiment provides for a membrane electrode assembly which includes at least one gas-diffusion layer having a first side and a second side and particle cores adhered to at least the first side of the at least one gas-diffusion layer. The particle cores include a first surface area adhered to the first side of the at least one gas-diffusion layer and a second surface area not in contact with the at least one gas-diffusion layer. A thin layer of catalytically active metal atoms is adhered to the second surface area of the particle cores not in contact with the at least one gas-diffusion layer. At least one proton exchange membrane is attached to at least the first side of the at least one gas-diffusion layer.
  • Another embodiment provides for a method of forming a membrane electrode assembly. The method includes treating at least one gas-diffusion layer to at least partially oxidize at least one surface of the least one gas-diffusion layer, depositing core particles on the at least one surface of the least one gas-diffusion layer, and depositing a thin layer of catalytically active metal atoms on a surface area of the core particles not in contact with the at least one surface of the least one gas-diffusion layer.
    • BRIEF DESCRIPTION OF THE DRAWINGS
  • FIG. 1 is a diagram of a polymer electrolyte membrane fuel cell (PEMFC);
  • FIG. 2A is an illustration of a Pt-encapsulated nanoparticle attached to a carbon surface with Pt atoms in contact with carbon that are not accessible to protons
  • FIG. 2B is an illustration of a Pt-encapsulated nanoparticle attached to a carbon surface with all Pt atoms accessible to protons;
  • FIG. 3 is a plot of the pulse deposition protocol for PdAu alloy core deposition on GDL;
  • FIG. 4 shows polarization curves of Example 1B (PtMLPdAu, 25 cm2) in a single H2/O2 cell;
  • FIG. 5 shows polarization curves of Example 1A (PtMLPdAu, 5 cm2) in air or oxygen, and after 1000 and 2000 cycles;
  • FIG. 6 shows the polarization curve of Example 1C (PtMLPdAu, 450 cm2);
  • FIG. 7 shows the polarization curve of Example 4A (PtMLPdWNi 5 cm2); and
  • FIG. 8 shows the polarization curve of Example 4B (PtMLPdWNi 25 cm2).
    •  DETAILED DESCRIPTION
  • Embodiments described in this disclosure include electrocatalysts that have increased reaction sites in the catalytic layer while at the same time have reduced the catalytic metal loading. These electrocatalysts may be used in polymer electrolyte membrane fuel cells (PEMFC)
  • FIG. 1 is a diagram of PEMFC. A proton exchange membrane fuel cell transforms the chemical energy liberated during the electrochemical reaction of hydrogen and oxygen to electrical energy, as opposed to the direct combustion of hydrogen and oxygen gases to produce thermal energy.
  • A stream of hydrogen is delivered to the anode side of the membrane electrode assembly (MEA). At the anode side it is catalytically split into protons and electrons. (http://en.wikipedia.org/wiki/Proton_exchange_membrane_fuel_cell, last accessed May 15, 2013) This oxidation half-cell reaction or Hydrogen Oxidation Reaction (HOR) is represented by:
    • At the Anode:

  • H2→2H++2e − E°=0V   (1)
  • The newly formed protons permeate through the polymer electrolyte membrane to the cathode side. The electrons travel along an external load circuit to the cathode side of the MEA, thus creating the current output of the fuel cell. Meanwhile, a stream of oxygen is delivered to the cathode side of the MEA. At the cathode side oxygen molecules react with the protons permeating through the polymer electrolyte membrane and the electrons arriving through the external circuit to form water molecules. This reduction half-cell reaction or oxygen reduction reaction (ORR) is represented by:
    • At the Cathode:

  • 1/2O2+2H++2e −→H2O E°=1.220V   (2)
    • Overall Reaction:

  • H2+1/2O2→H2O E°=1.229V   (3)
  • The reversible reaction is expressed in the equation and shows the reincorporation of the hydrogen protons and electrons together with the oxygen molecule and the formation of one water molecule.
  • Disclosed herein is a MEA that may be formed with an increase in reaction sites in the catalytic layer while at the same time reducing the catalytic metal loading. The MEA may be formed by first providing a gas diffusion layer (GDL). The gas diffusion layer may be constructed of known materials. They may be formed of a porous material including a conducting material such as carbon. For example, porous carbon woven fabric provides efficient transport of fuel gas or oxidant gas into the catalyst layers.
  • At least one surface of the GDL may be treated to at least partially oxide the carbon surface of the GDL. The GDL may be treated with an acid. Any suitable acid may be used, such as nitric acid or sulfuric acid.
  • Core particles may be formed on the partially oxidized GDL surface. Any suitable method of forming core particles may be deployed. For example the methods of forming core nanoparticles described in U.S. Patent Publication Nos. US 20100197490 A1, 20100216632 A1, US 20110155579 A1, and in U.S. Pat. No. 7,691,780 B2, U.S. Pat. No. 7,704,918 B2, and U.S. Pat. No. 7,855,021 B2, all incorporated herein by reference in their entirety, may be used. Furthermore, core nanoparticles may be formed as described in U.S. patent application Ser. No. 13/860,316, filed Apr. 10, 2013, titled Synthesis of Nanoparticles Using Ethanol, U.S. Publication No. 2013/0264198, the contents of which is incorporated herein in its entirety.
  • The core particles may, for example, be deposited using electrodeposition of metal salt solutions of the metals to be deposited directly on the GDL. Any suitable metal salt solutions may be used. For example metal salts of at least one noble metal such as ruthenium, rhodium, palladium, silver, rhenium, osmium, iridium, platinum, gold may be used. Furthermore, metal salts of non-noble metals, such as Ti, Hf, Zr, W, Ta, Nb, V, Re, Cr, Mo, Tc, and Mn, may also be used. Combinations of noble metal salts and non-noble metal salts may also be used. The metal salts may be chlorides, carbonates, acetates, citrates, fluorides, nitrates, nitrites, phosphates, sulfates, or combinations thereof, of the metal ions. FIG. 3 shows a pulse deposition protocol for PdAu alloy core deposition on GDL, 0.5 seconds at −500 mV, 4.5 seconds at −350 mV, 3 seconds at open circuit potential. In certain embodiments the electrolyte composition can include 1 mM PdCl2+0.1 M NaCl+0.1 mM NaAuCl.
  • The core particle may include at least one noble metal, such as ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), and gold (Au). In other embodiments the core particle may include at least one non-noble metal. In certain embodiments the core particle includes Ti, Hf, Zr, W, Ta, Nb, V, Re, Cr, Mo, Tc, and Mn. Alternatively, the core particle may include at least an alloy of at least two noble metals, or at least one noble metal and at least one non-noble metal.
  • In certain embodiments the core particle comprises an alloy selected from the group consisting of Pd1-xAux, Pd1-xTix, Pd1-xWx, Pd1-xNbx, Pd1-xTax, Pd1-xRex, Pd1-xIrx, Ir1-xTix, Ir1-xTax, Ir1-xNbx, Ir1-xRex, Au1-xTax, Au1-xIrx, and Au1-xRex and x represents the concentration of the alloying element, being adjustable over the range 0<x<1. In one embodiment the alloy is PdAu.
  • The particles disclosed and described in this specification are not limited to any particular shape or size, but in some embodiments may be nanoparticles with sizes ranging from 1 to 100 nm in one more dimensions. However, the size is not so limited and may extend into the micrometer and millimeter size range. The shape may be spherical or spheroidal, but again is not so limited. Throughout this specification, the particles will be primarily disclosed and described as essentially spherical nanoparticles. It is to be understood, however, that the particles may take on any shape, size, and structure as is well-known in the art. This includes, but is not limited to branching, conical, pyramidal, cubical, mesh, fiber, cuboctahedral, and tubular nanoparticles. The nanoparticles may be agglomerated or dispersed, formed into ordered arrays, fabricated into an interconnected mesh structure, either formed on a supporting medium or suspended in a solution, and may have even or uneven size distributions. The particle shape and size is preferably configured so that the bonding configuration of surface atoms is such that their reactivity and, hence, their ability to function as a catalyst is increased.
  • Core particle formation is followed by the deposition of a catalytically active surface layer (or shell) having thicknesses in the monolayer-to-multilayer range.
  • The deposition of a catalytically active surface layer takes place on the surface areas of the core particle that are not adhered or attached to the GDL. FIG. 2A illustrates core particles that have a thin layer of a catalytically active metal wholly surrounding the particle. Thus, there are catalytically active metal atoms sandwiched between the core particles and the GDL that are not accessible to protons and therefore are “inactive” atoms. However, FIG. 2B, illustrates an embodiment of the present disclosure. It can be seen that the core particle is encapsulated by the GDL and the catalytically active surface layer, and all the catalytically active metal atoms of the shell is available to interact with the protons (i.e., active).
  • For purposes of this specification, a monolayer (ML) is formed when the surface of a substrate (or core), not in contact with the GDL, is fully covered by a single, closely packed layer comprising adatoms of a second material which farms a chemical or physical bond with atoms at the surface of the substrate. The surface is considered fully covered when substantially all available surface sites, not in contact with the GDL, are occupied by an adatom of the second material. If the surface of the substrate is not completely covered by a single layer of the adsorbing material, then the surface coverage is considered to be submonolayer. However, if a second or subsequent layers of the adsorbant are deposited onto the first layer, then multilayer surface coverages (e.g., bilayer, trilayer, etc.) result.
  • The catalytically active surface layer may be deposited using any of a wide variety of thin film deposition processes which are well-known in the art.
  • For example catalytically active surface layer may be deposited as described in U.S. Publication No. 2013/0264198.
  • A synthetic procedure which employs the principles of electrodeposition and galvanic displacement has been utilized by Brankovic, et al. (hereinafter “Brankovic”) to deposit a monolayer of Pt onto Au(111) substrates and by Adzic, et al. (hereinafter “Adzic”) to deposit Pt monolayers onto Pd(111) and carbon-supported Pd nanoparticles. These procedures are described, for example, in “Metal Monolayer Deposition By Replacement Of Metal Adlayers On Electrode Surfaces,” Surf. Sci., 474, L173 (2001) and U.S. Pat. No. 7,691,780, respectively. This process has also been described in detail by J. Zhang, et al. in “Platinum Monolayer Electrocatalysts for O2 Reduction: Pt Monolayer On Pd(111) And On Carbon-Supported Pd Nanoparticles,” J. Phys. Chem. B 108, 10955 (2004). Each of the aforementioned references is incorporated by reference as if fully set forth in this specification.
  • The deposition process is a series of electrochemical reactions which, when performed sequentially result in a film with the targeted coverage and composition. The procedure involves the initial formation of an adlayer of a metal onto a substrate by underpotential deposition (UPD). This is followed by the galvanic displacement of the adlayer by a more noble metal, resulting in the conformal deposition of a ML of the more noble metal on the substrate. The overall process includes the irreversible and spontaneous redox displacement of an adlayer of a non-noble metal by a more noble metal. This enables the controlled deposition of a thin, continuous layer of a desired metal. In the process the substrate metal is more noble than the metal undergoing deposition in order to avoid becoming oxidized. The redox reaction can be described by the following equation

  • MUPD 0+(m/z)Lz+
    Figure US20180069207A1-20180308-P00001
    Mm++(m/z)L0   (1)
  • where MUPD 0 represents a UPD metal adatom on the electrode surface and Lz+ is a noble metal cation with positive charge z+ and valence z. The Mm+ represents the metal cation in the solution obtained after the UPD adatom was oxidized, and L0 is a noble atom deposited in the redox process.
  • Although the catalytically active surface layer is not limited to any particular material, it is preferably Pt due to its excellent catalytic properties. Consequently, an example in which a monolayer of Pt is formed on nanoparticles using the processes described by Brankovic and Adzic will now be described in detail. It is to be understood, however, that the process is not limited to Pt and other noble metals may be utilized. The method involves the initial formation of a monolayer of a metal such as copper (Cu) by underpotential deposition (UPD) in a solution comprised of 50 mM CuSO4 in a 50 mM H2SO4 solution. The Cu-coated nanoparticles are then immersed from solution and rinsed with deionized water to remove Cu2+ ions from the surface. This is followed by immersion in a solution comprised of 1.0 mM K2PtCl4 in 50 mM H2SO4 under a N2 atmosphere for approximately two minutes to replace all Cu atoms with Pt atoms. The Pt-coated nanoparticle substrate is again rinsed with deionized water. The above processes are carried out in a multi-compartment cell under a N2 atmosphere in order to prevent Cu oxidation by O2 during sample transfer.
  • The above process results in the conformal deposition of a ML of Pt on high-surface-area core particles. The deposition cycle comprising UPD of Cu followed by galvanic displacement with Pt may be repeated as needed to produce two or more layers of Pt in order to ensure complete coverage of the nanoparticle surface. Conversely, the UPD of Cu may be controllably limited such that submonolayer coverages of Cu and, hence, Pt are obtained. Deposition of an initial adlayer by UPD may also be accomplished using metals other than Cu such as, for example, lead (Pb), bismuth (Bi), tin (Sn), cadmium (Cd), silver (Ag), antimony (Sb), and thallium (Tl). The choice of metal used for UPD will influence the final Pt surface coverage obtained for a given UPD adlayer. This occurs due to variations in the size and valency among the different metals. The metal overlayer used is not limited to Pt, but may be formed from other noble metals as long as the desired metal is more noble than the UPD adlayer. This may be accomplished by contacting the copper-coated particles with their corresponding salts. For example, monolayers of iridium, ruthenium, osmium, and rhenium can be deposited by displacement of a ML of a less noble metal such as copper using IrCl3, RuCl3, OsCl3, or ReCl3, respectively. Furthermore, the metal overlayer may be formed as an alloy with any number of constituents such as binary, ternary, quaternary, or quinary alloys with experimentally optimized stoichiometry ratios.
  • The process offers unprecedented control over film growth and is advantageous in terms of its versatility, reproducibility, and efficient utilization of source material. Since a costly precious metal such as Pt can be utilized as a thin film instead of in bulk form, significant cost savings can be attained. The utilization of a noble metal/substrate nanoparticle may also provide unexpectedly heightened catalytic activity due to synergistic effects between the nanoparticles and the catalytic overlayer. The unexpected increase in catalytic activity may arise due to electronic and geometric effects which arise from the formation of surface metal-metal bonds and the differing lattice constants of the catalytic overlayer and underlying substrate.
  • The catalytic properties of the surface overlayer may also be engineered by use of a suitable core particle. A core of a non-noble metal such as Ni, Co, Fe, Ti, W, Nb, V, or Ta may be coated with a more noble metal such as Au, Pd, or Pt. The catalytic activity of the final coated nanoparticle may be controlled by engineering the electronic properties and lattice parameter of the underlying core-shell nanoparticles with respect to those of the metal overlayer.
  • The GDL with the cores having atomically thin surface layers deposited thereon in situ, may then be contacted with a proton exchange membrane (PEM) such that the cores having atomically thin surface layers are sandwiched between the GDL and the PEM. Any suitable PEM may be used, such as for example Nafion membranes. An anode layer may be contacted with the second surface (the surface not in contact with the core particles and PEM). This assembly may then be hot-pressed together to form the membrane electrode assembly (MEA).
  • By electrodeposition of cores onto the GDL and then adding the atomic layers (such as for example a Pt monolayer) to form the shell, there are no shell atoms trapped by other atoms or trapped between the core and the GDL, and they are thus accessible to reactant gas, electrons, and protons. Thus, 100% utilization of the shell atoms can be achieved. Furthermore, the methods described herein amounts to in situ catalyst deposition directly onto the GDL and fabrication of the MEA can be performed in mere minutes (e.g., several minutes), and without the need to prepare catalyst ink and paint the catalyst ink onto the GDL. Furthermore, as the particles are formed in-situ and on the GDL, there is less opportunity for exposure to free nanoparticles or for nanoparticles to be released into the environment.
    • EXAMPLES
  • Membrane Electrode Assembly (MEA)
  • MEAs were prepared by first cutting gas diffusion layers (GDLs) into 5 cm2, 25 cm2, or 450 cm2 pieces. The GDLs were then functionalized by pretreatment in hot (70° C.) concentrated nitric acid for 1 hour followed by thorough rinsing with nanopure water, boiling in water for 1 hour, and rinsing again with nanopure water. Nanoparticles were then deposited or sprayed onto the treated GDLs, and the nanoparticles coated with a Pt layer according to the methods described below. The GDLs with the Pt coated nanoparticles was rinsed with nanopure water and dried. A Nafion 211 membrane was then hot-pressed to the GDL together with an anode electrode to complete the MEA fabrication.
    • Examples 1A-1C PtMLPdAu, 5 cm2, 25 cm2, or 450 cm2
  • PdAu Core deposition: Elongated Pd0.9Au0.1 nanoparticles with an average particle size of 6 nm were electrodeposited directly on the GDL (Example 1A: 5 cm2, Example 1B: 25 cm2, Example 1C: 450 cm2) at constant potential (−330 mV vs. Ag/AgC/Cl− (3M KCl)). The electrolyte composition was 1 mM PdCl2+0.1 M NaCl+0.1 mM NaAuCl4 and the loading of the Pd0.9Au0.1 nanoparticles was controlled by the charge and was limited to 30 μg/cm2.
  • Pt monolayer coating: Pt monolayer shell deposition on the Pd0.9Au0.1 nanoparticle cores was performed as described in U.S. Pat. No. 7,691,780. First a Cu underpotentially deposited (UPD) monolayer was deposited at underpotentials from 50 mM CuSO4+50 mM H2SO4 solution. Then the electrolyte was replaced with 1 mM KPtCl4+50 mM H2SO4 solution and the pre-deposited Cu ML was galvanically displaced by Pt for less than a minute. There were no changes observed in the shape and the particle size distribution of the resulting PtMLPd0.9Au0.1 electrocatalysts. The shape and the average particle size distribution remained the same as of the Pd0.9Au0.1 nanoparticles core.
    • Example 2 PtMLPdhollow 5 cm2
  • Pdhollow core deposition: Hollow palladium nanoparticles made using a micro-emulsion method were combined with Vulcan XC-72R carbon black and water to obtain a palladium catalyst ink loading of about 30 wt % total palladium. The ink was then sprayed onto the GDL (5 cm2) and dried.
  • Pt monolayer coating: Pt monolayer shell deposition on the Pdhollow nanoparticle cores was performed as described for Examples 1A-1C. There were no changes observed in the shape and the particle size distribution of the resulting PtMLPdhollow electrocatalysts. The shape and the average particle size distribution remained the same as of the Pdhollow nanoparticles core.
    • Examples 3A and 3B PtMLPdnanowires 5 cm2 and 25 cm2
  • Pdnanowires Core deposition: Pdnanowires with diameter of 3-4 nm and length of 50-60 nm were electrodeposited directly on functionalized GDL (Example 3A: 5 cm2, Example 3B: 25 cm2) at constant potential (−330 mV vs. Ag/AgC/Cl− (3M KCl)). The electrolyte composition was 1 mM PdCl2+0.1 M NaCl and the loading of the Pdnanowires was controlled by the charge and was limited to 30 μg/cm2.
  • Pt monolayer coating: Pt monolayer shell deposition on the Pdnanowires nanoparticle cores was performed as described for Examples 1A-1C. There were no changes observed in the shape and the particle size distribution of the resulting PtMLPdnanowires electrocatalysts. The shape and the average particle size distribution remained the same as of the PtMLPdnanowires nanoparticles core.
    • Examples 4A and 4B PtMLPdWNi 5 cm2 and 25 cm2
  • PdWNi Core deposition: The deposition of the PdWNi nanocrystalline core was performed directly on functionalized GDL (Example 4A: 5 cm2, Example 4B: 25 cm2) in two steps. In the first step refractory WNi alloy were co-electrodeposited in a solution of 0.05 M NiSO4+0.4 M Na2WO4+0.6 M trisodium citrate (pH=7.5) at constant current density of 15 mA/cm2. The obtained deposits were very fine composite amorphous-nanocrystilline microstructure with an average particle size distribution of 3 nm and 1:1 atomic ratio between W and Ni. After finishing the deposition step, the electrolyte was replaced by 1 mM PdCl2+50 mM H2SO4 solution, and parts of the Ni atoms from the alloy were galvanically displaced by Pd. As a result a Pd reach shell was formed on the WNi core, and the particle size distribution remained unchanged.
  • Pt monolayer coating: Pt monolayer shell deposition on the PdWNi nanoparticle cores was performed as described for Examples 1A-1C. There were no changes observed in the shape and the particle size distribution of the resulting PtMLPdWNi electrocatalysts. The shape and the average particle size distribution remained the same as of the PtMLPdnanowires nanoparticles core.
    • Example 5 PtMLPd 5 cm2
  • Pd core deposition: Palladium nanoparticles made in ethanol using the method as described in U.S. Publication No. 2013/0264198, were combined with Vulcan XC-72R carbon black and water to obtain a palladium catalyst ink loading of about 30 wt % total palladium. The ink was then sprayed onto the GDL (5 cm2) and dried.
  • Pt monolayer coating: Pt monolayer shell deposition on the Pd nanoparticle cores was performed as described for Examples 1A-1C. There were no changes observed in the shape and the particle size distribution of the resulting PtMLPd electrocatalysts. The shape and the average particle size distribution remained the same as of the Pd nanoparticles core.
    • Results
  • FIG. 4 shows polarization curves of Example 1B in a single H2/O2 cell with only 50 μg/cm2 of all platinum-group metals on the cathode as compared to 400 μg/cm2 in commercial Pt catalysts. The PGM mass activity is 0.4 A/mg, the specific activity is 0.2 mA/cm2, and the Pt mass activity is 1.1 A/mgPt.
  • FIG. 5 shows polarization curves of Example 1A in air or oxygen, and after 1000 and 2000 cycles. After 2000 potential cycles it can be seen that the activity increased. The PGM mass activity is 0.5 A/mg, the specific activity is 0.4 mA/cm2, and the Pt mass activity is 1.2 A/mgPt.
  • FIG. 6 shows the polarization curve of Example 1C. It can be seen that Examples 1A and 1B (5 and 25 cm2 electrodes, respectively) show a similar activity, while Example 1A (450 cm2 electrode) shows a lower activity. This may be caused by the ambient pressure applied and low open circuit potential which may be due to the state of the surface. However, this may be corrected. Example 1C has a PGM mass activity is 0.4 A/mg and a Pt mass activity of 1 A/mgPt.
  • FIG. 7 shows the polarization curve of Example 4A and FIG. 8 shows the polarization curve of Example 4B. It can be seen that the performance increased after 5000 cycles for Example 4A (5 cm2) and after 15,000 cycles for Example 4B (25 cm2),
  • Table 1 shows a summary of the results for the 5 cm2 MEA examples herein compared to a MEA made using commercially available Pt/C materials. It can be seen that all the example Pt catalysts have a PGM activity 3-5 times higher than the commercially available catalyst, and their Pt mass activity is one order of magnitude higher than that of the commercially available catalyst. The only exception is lower PGM activity for the PtMLPdnanowire catalyst caused by the mass of Pd wire.
  • TABLE 1
    Specific Pt mass PGM mass
    activity activity activity,
    mA/cm2 A/mgPt a/mgpgm
    (at 0.9 v) (at 0.9 v) (at 0.9 v)
    Example 1A 0.4 1.2 0.5
    Example 2 1.4 1.2 0.5
    Example 3A 0.7 1.7 0.1
    Example 4A 0.3 1.3 0.5
    Example 5 1.3 0.9 0.4
    Commercial Pt/C 0.15-0.2 0.1-0.12 0.1-0.12
  • The description has not attempted to exhaustively enumerate all possible variations. The alternate embodiments may not have been presented for a specific portion of the invention, and may result from a different combination of described portions, or that other undescribed alternate embodiments may be available for a portion, is not to be considered a disclaimer of those alternate embodiments. It will be appreciated that many of those undescribed embodiments are within the literal scope of the following claims, and others are equivalent. Furthermore, all references, publications, U.S. Patents, and U.S. Patent Application Publications cited throughout this specification are incorporated by reference as if fully set forth in this specification.

Claims (14)

1. An electrocatalyst comprising:
particle cores directly adhered to a carbon surface, wherein the particle cores include a first surface area adhered to the carbon surface and a second surface area not in contact with the carbon surface; and
a thin layer of catalytically active metal atoms adhered to the second surface area of the particle cores not in contact with the carbon surface, and not adhered in-between the first surface area of the particle cores and carbon surface.
2. The electrocatalyst of claim 1, wherein the particle core comprises a noble metal selected from at least one of ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), and gold (Au).
3. The electrocatalyst of claim 2, wherein the particle core further comprises a non-noble metal.
4. The electrocatalyst of claim 1, wherein the thin layer of catalytically active metal atoms comprises noble metals.
5. The electrocatalyst of claim 4, wherein the thin layer of catalytically active metal atoms is one to three monolayers thick.
6. The electrocatalyst of claim 5, wherein the thin layer of catalytically active metal atoms comprises platinum (Pt).
7. The electrocatalyst of claim 1 wherein the particle core is a nanoparticle having dimensions of 1 to 100 nm along three orthogonal directions.
8. The electrocatalyst of claim 1, wherein the particle core comprises an alloy.
9. The electrocatalyst of claim 2, wherein the particle core comprises at least two different noble metals selected from ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), and gold (Au).
10. The electrocatalyst of claim 1, wherein the particle core comprises an element selected from the group consisting of Ti, Hf, Zr, W, Ta, Nb, V, Re, Cr, Mo, Tc, and Mn.
11. The electrocatalyst of claim 1, wherein the particle core comprises at least one metal selected from the group comprising tungsten (W), molybdenum (Mo), and rhenium (Re), and at least one metal selected from group comprising nickel (Ni), iron (Fe), and cobalt (Co).
12. The electrocatalyst of claim 11, wherein the thin layer of catalytically active metal atoms comprises palladium (Pd), gold (Au), or platinum (Pt).
13. The electrocatalyst of claim 11, further comprising a shell layer between the second surface area of the particle core not in contact with the carbon surface and the thin layer of catalytically active metal atoms, wherein the shell comprises at least one metal selected from the group comprising palladium (Pd) and gold (Au), and wherein the thin layer of catalytically active metal atoms comprises platinum (Pt).
14. The electrocatalyst of claim 13, wherein the core comprises tungsten (W) and nickel (Ni), and the shell comprises palladium (Pd).
US15/811,892 2013-05-15 2017-11-14 Core-Shell Fuel Cell Electrodes Abandoned US20180069207A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
US15/811,892 US20180069207A1 (en) 2013-05-15 2017-11-14 Core-Shell Fuel Cell Electrodes

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
US201361823845P 2013-05-15 2013-05-15
US14/279,012 US9716279B2 (en) 2013-05-15 2014-05-15 Core-shell fuel cell electrodes
US15/627,882 US9853255B2 (en) 2013-05-15 2017-06-20 Core-shell fuel cell electrodes
US15/811,892 US20180069207A1 (en) 2013-05-15 2017-11-14 Core-Shell Fuel Cell Electrodes

Related Parent Applications (1)

Application Number Title Priority Date Filing Date
US15/627,882 Continuation US9853255B2 (en) 2013-05-15 2017-06-20 Core-shell fuel cell electrodes

Publications (1)

Publication Number Publication Date
US20180069207A1 true US20180069207A1 (en) 2018-03-08

Family

ID=52277341

Family Applications (3)

Application Number Title Priority Date Filing Date
US14/279,012 Active 2035-01-04 US9716279B2 (en) 2013-05-15 2014-05-15 Core-shell fuel cell electrodes
US15/627,882 Active US9853255B2 (en) 2013-05-15 2017-06-20 Core-shell fuel cell electrodes
US15/811,892 Abandoned US20180069207A1 (en) 2013-05-15 2017-11-14 Core-Shell Fuel Cell Electrodes

Family Applications Before (2)

Application Number Title Priority Date Filing Date
US14/279,012 Active 2035-01-04 US9716279B2 (en) 2013-05-15 2014-05-15 Core-shell fuel cell electrodes
US15/627,882 Active US9853255B2 (en) 2013-05-15 2017-06-20 Core-shell fuel cell electrodes

Country Status (1)

Country Link
US (3) US9716279B2 (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20180047993A1 (en) * 2015-03-10 2018-02-15 The Doshisha Method for Manufacturing Platinum Catalyst, and Fuel Cell Including the Same

Families Citing this family (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9716279B2 (en) * 2013-05-15 2017-07-25 Brookhaven Science Associates, Llc Core-shell fuel cell electrodes
US9976199B2 (en) 2014-04-22 2018-05-22 Brookhaven Science Associates, Llc Synthesis of Au-induced structurally ordered AuPdCo intermetallic core-shell nanoparticles and their use as oxygen reduction catalysts
JP6308090B2 (en) * 2014-10-02 2018-04-11 トヨタ自動車株式会社 Method for producing core-shell catalyst
US10675681B2 (en) * 2017-02-02 2020-06-09 Honda Motor Co., Ltd. Core shell
CN107863557A (en) * 2017-10-31 2018-03-30 桂林市漓江机电制造有限公司 Electrolyte of lithium-ion secondary battery additive
JP2019141809A (en) * 2018-02-22 2019-08-29 国立大学法人信州大学 Manufacturing method of core-shell structure type catalyst layer
US12005391B2 (en) 2019-12-11 2024-06-11 Brookhaven Science Associates, Llc Method for trapping noble gas atoms and molecules in oxide nanocages

Family Cites Families (37)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6344272B1 (en) 1997-03-12 2002-02-05 Wm. Marsh Rice University Metal nanoshells
US20030135971A1 (en) 1997-11-12 2003-07-24 Michael Liberman Bundle draw based processing of nanofibers and method of making
US6346189B1 (en) 1998-08-14 2002-02-12 The Board Of Trustees Of The Leland Stanford Junior University Carbon nanotube structures made using catalyst islands
US6749892B2 (en) 2000-03-22 2004-06-15 Samsung Electronics Co., Ltd. Method for fabricating membrane-electrode assembly and fuel cell adopting the membrane-electrode assembly
US20040055419A1 (en) 2001-01-19 2004-03-25 Kurihara Lynn K. Method for making metal coated powders
US6670301B2 (en) 2001-03-19 2003-12-30 Brookhaven Science Associates Llc Carbon monoxide tolerant electrocatalyst with low platinum loading and a process for its preparation
US6843902B1 (en) 2001-07-20 2005-01-18 The Regents Of The University Of California Methods for fabricating metal nanowires
KR100438408B1 (en) 2001-08-16 2004-07-02 한국과학기술원 Method for Synthesis of Core-Shell type and Solid Solution type Metallic Alloy Nanoparticles via Transmetalation Reactions and Their Applications
CN1165092C (en) 2002-04-30 2004-09-01 中国科学院长春应用化学研究所 Preparation method of nano-platinum/carbon electrocatalyst for polymer electrolyte membrane fuel cell cathode
FR2849267B1 (en) 2002-12-20 2005-03-25 St Microelectronics Sa MANUFACTURE OF A HIGH CAPACITOR CAPACITOR
US7001669B2 (en) 2002-12-23 2006-02-21 The Administration Of The Tulane Educational Fund Process for the preparation of metal-containing nanostructured films
US7029514B1 (en) 2003-03-17 2006-04-18 University Of Rochester Core-shell magnetic nanoparticles and nanocomposite materials formed therefrom
JP5082187B2 (en) 2003-10-06 2012-11-28 日産自動車株式会社 Method for producing electrode catalyst particles for polymer electrolyte fuel cell
US9005331B2 (en) * 2004-12-22 2015-04-14 Brookhaven Science Associates, Llc Platinum-coated non-noble metal-noble metal core-shell electrocatalysts
US7855021B2 (en) 2004-12-22 2010-12-21 Brookhaven Science Associates, Llc Electrocatalysts having platium monolayers on palladium, palladium alloy, and gold alloy core-shell nanoparticles, and uses thereof
US7691780B2 (en) 2004-12-22 2010-04-06 Brookhaven Science Associates, Llc Platinum- and platinum alloy-coated palladium and palladium alloy particles and uses thereof
US7507495B2 (en) 2004-12-22 2009-03-24 Brookhaven Science Associates, Llc Hydrogen absorption induced metal deposition on palladium and palladium-alloy particles
US7632601B2 (en) 2005-02-10 2009-12-15 Brookhaven Science Associates, Llc Palladium-cobalt particles as oxygen-reduction electrocatalysts
US8062552B2 (en) 2005-05-19 2011-11-22 Brookhaven Science Associates, Llc Electrocatalyst for oxygen reduction with reduced platinum oxidation and dissolution rates
US7704919B2 (en) 2005-08-01 2010-04-27 Brookhaven Science Associates, Llc Electrocatalysts having gold monolayers on platinum nanoparticle cores, and uses thereof
US8048548B2 (en) 2007-09-11 2011-11-01 Brookhaven ScienceAssociates, LLC Electrocatalyst for alcohol oxidation at fuel cell anodes
EP2303452B1 (en) 2008-06-23 2016-02-24 Brookhaven Science Associates LLC Underpotential deposition-mediated layer-by-layer growth of thin films
US20100099012A1 (en) 2008-10-17 2010-04-22 Brookhaven Science Associates, Llc Electrocatalyst Synthesized by Depositing a Contiguous Metal Adlayer on Transition Metal Nanostructures
US9099253B2 (en) 2008-10-21 2015-08-04 Brookhaven Science Associates, Llc Electrochemical synthesis of elongated noble metal nanoparticles, such as nanowires and nanorods, on high-surface area carbon supports
US8404613B2 (en) 2008-10-21 2013-03-26 Brookhaven Science Associates, Llc Platinum-based electrocatalysts synthesized by depositing contiguous adlayers on carbon nanostructures
US8699207B2 (en) 2008-10-21 2014-04-15 Brookhaven Science Associates, Llc Electrodes synthesized from carbon nanostructures coated with a smooth and conformal metal adlayer
US20100216632A1 (en) 2009-02-25 2010-08-26 Brookhaven Science Associates, Llc High Stability, Self-Protecting Electrocatalyst Particles
US8815465B2 (en) * 2010-02-02 2014-08-26 Honda Motor Co., Ltd. Membrane electrode assembly for polymer electrolyte fuel cell and polymer electrolyte fuel cell
WO2011119818A1 (en) 2010-03-24 2011-09-29 Brookhaven Science Associates Apparatus and method for the synthesis and treatment of metal monolayer electrocatalyst particles in batch or continuous fashion
US20120251926A1 (en) * 2010-04-29 2012-10-04 Ford Global Technologies, Llc Thin Film Catalyst With Heat-Extendable Wires
US20130177838A1 (en) 2010-07-14 2013-07-11 Brookhaven Science Associates, Llc Hollow nanoparticles as active and durable catalysts and methods for manufacturing the same
US20120245019A1 (en) 2011-03-23 2012-09-27 Brookhaven Science Associates, Llc Method and Electrochemical Cell for Synthesis of Electrocatalysts by Growing Metal Monolayers, or Bilayers and Treatment of Metal, Carbon, Oxide and Core-Shell Nanoparticles
US9017530B2 (en) 2011-03-23 2015-04-28 Brookhaven Science Associates, Llc Method and electrochemical cell for synthesis and treatment of metal monolayer electrocatalysts metal, carbon, and oxide nanoparticles ion batch, or in continuous fashion
US9490486B2 (en) 2012-01-05 2016-11-08 Brookhaven Science Associates, Llc Method for removing strongly adsorbed surfactants and capping agents from metal to facilitate their catalytic applications
US9550170B2 (en) 2012-04-10 2017-01-24 Brookhaven Sciecne Associates, LLC Synthesis of nanoparticles using ethanol
US8927453B2 (en) 2012-04-20 2015-01-06 Brookhaven Science Associates, Llc Molybdenum and tungsten nanostructures and methods for making and using same
US9716279B2 (en) * 2013-05-15 2017-07-25 Brookhaven Science Associates, Llc Core-shell fuel cell electrodes

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20180047993A1 (en) * 2015-03-10 2018-02-15 The Doshisha Method for Manufacturing Platinum Catalyst, and Fuel Cell Including the Same
US10749186B2 (en) * 2015-03-10 2020-08-18 The Doshisha Method for manufacturing platinum catalyst, and fuel cell including the same

Also Published As

Publication number Publication date
US20150017565A1 (en) 2015-01-15
US20170331117A1 (en) 2017-11-16
US9716279B2 (en) 2017-07-25
US9853255B2 (en) 2017-12-26

Similar Documents

Publication Publication Date Title
US9853255B2 (en) Core-shell fuel cell electrodes
US9005331B2 (en) Platinum-coated non-noble metal-noble metal core-shell electrocatalysts
US9689085B2 (en) Underpotential deposition-mediated layer-by-layer growth of thin films
CN101332425B (en) Nanoporous gold-supported ultra-thin platinum-group metal film catalyst and preparation method thereof
JP7105941B2 (en) Method for producing core-shell particles using carbon monoxide
Habibi et al. Carbon–ceramic supported bimetallic Pt–Ni nanoparticles as an electrocatalyst for oxidation of formic acid
KR101857338B1 (en) Production method for catalyst microparticles, and fuel cell containing catalyst microparticles produced by said production method
JP2014512252A (en) Method for making a complete platinum monolayer on palladium-based core nanoparticles
JP5768848B2 (en) Core-shell catalyst and method for producing core-shell catalyst
Zhu et al. Au nanowires with high aspect ratio and atomic shell of Pt-Ru alloy for enhanced methanol oxidation reaction
Wang et al. Carbon-free nanoporous gold based membrane electrocatalysts for fuel cells
US9755246B2 (en) Hollow platinum nanoparticles for fuel cells
Kazemi et al. Deposition of palladium submonolayer on nanoporous gold film and investigation of its performance for the methanol electrooxidation reaction
JP5477463B2 (en) Fuel cell
CN103079696A (en) Fine catalyst particles and method for producing fine catalyst particles
JP3684570B2 (en) Fuel cell electrode and method of manufacturing the same
KR20190069400A (en) Tin-based catalyst, its preparation, and fuel cell using the catalyst
US10038198B2 (en) Platinum nanoparticles having hollow skeletal structures and methods of making
WO2012102714A1 (en) A catalyst for a fuel cell and a method for making the same
EP3161889B1 (en) Method for producing gas diffusion electrodes for a fuel cell, gas diffusion electrode, and fuel cell
US20190221856A1 (en) Electrocatalyst for the Oxygen Reduction Reaction
Kamyabi et al. Efficient methanol electrooxidation on activated pencil graphite electrode modified with PtCu catalyst
Ding et al. Nanoporous metals for fuel cell applications
JP2014117652A (en) Method for producing catalyst fine particle, and fuel battery including catalyst fine particle produced by the same method
Vukmirovic et al. New Metal Deposition Methods for Electrocatalysts Syntheses

Legal Events

Date Code Title Description
AS Assignment

Owner name: UNITED STATES DEPARTMENT OF ENERGY, DISTRICT OF CO

Free format text: CONFIRMATORY LICENSE;ASSIGNOR:BROOKHAVEN SCIENCE ASSOC-BROOKHAVEN LAB;REEL/FRAME:045303/0317

Effective date: 20180216

STCB Information on status: application discontinuation

Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION