Search

US-12620601-B2 - Catalyst

US12620601B2US 12620601 B2US12620601 B2US 12620601B2US-12620601-B2

Abstract

Catalyst material comprising nanoparticles dispersed within a metal oxide layer, the metal oxide layer comprises metal oxide comprising at least one metal cation, wherein the nanoparticles comprise Pt, wherein the nanoparticles comprise less than 10 atom % of oxygen, and wherein the metal oxide layer has an average thickness not greater than 50 nanometers. The catalyst material comprising nanoparticles dispersed within a metal oxide layer can be converted, for example, to nanoporous catalyst layer comprising nanoparticles fused together, wherein the nanoparticles comprise Pt, wherein the nanoparticles comprise less than 10 atom % of oxygen, and wherein the layer has an average thickness not greater than 50 nanometers. The nanoporous catalyst layer is useful, for example, in fuel cell membrane electrode assemblies.

Inventors

  • Andrew J. L. Steinbach
  • Amy E. Hester
  • Sean M. Luopa
  • Andrew T. Haug
  • Krzysztof A. Lewinski
  • Grant M. Thoma

Assignees

  • 3M INNOVATIVE PROPERTIES COMPANY

Dates

Publication Date
20260505
Application Date
20191028

Claims (7)

  1. 1 . A catalyst material comprising: a metal oxide layer comprising at least one metal cation; and nanoparticles dispersed within the metal oxide layer, the nanoparticles comprising Pt, wherein the nanoparticles comprise less than 10 atom % of oxygen, and wherein the metal oxide layer has an average thickness not greater than 50 nanometers.
  2. 2 . The catalyst material of claim 1 , wherein the nanoparticles further comprise metal of the metal cation.
  3. 3 . The catalyst material of claim 1 , wherein the catalyst material further comprises at least one of the following transition metals: Cu, Ni, Co, or Fe, and wherein at least 50 atom % of the transition metal is present within the catalyst in the 0 oxidation state.
  4. 4 . A catalyst comprising nanostructured elements comprising microstructured support whiskers having an outer surface at least partially covered by the catalyst material of claim 1 .
  5. 5 . A method of making the catalyst material of claim 1 , the method comprising depositing one or more alternating layers of Pt and an oxophilic metal using physical vapor deposition with a source of reactive oxygen with a partial pressure of at least 1×10 −6 Torr.
  6. 6 . A method of making a nanoporous catalyst layer, the method comprising: providing a catalyst material comprising nanoparticles dispersed within a metal oxide layer of claim 1 ; and leaching the catalyst material to remove at least a portion of the oxophilic metal from the catalyst.
  7. 7 . A nanoporous catalyst layer made by the method of claim 6 .

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application is a national stage filing under 35 U.S.C. 371 of PCT/IB2019/059222, filed Oct. 28, 2019, which claims the benefit of Provisional Patent Application No. 62/779,126, filed Dec. 13, 2018, the disclosures of which are incorporated by reference in their entirety herein. This invention was made with Government support under Contract No. DE-EE0007270 awarded by DOE. The Government has certain rights in this invention. BACKGROUND Fuel cells produce electricity via electrochemical oxidation of a fuel and reduction of an oxidant. Fuel cells are generally classified by the type of electrolyte and the type of fuel and oxidant reactants. One type of fuel cell is a polymer electrolyte membrane fuel cell (PEMFC), where the electrolyte is a polymeric ion conductor and the reactants are hydrogen fuel and oxygen as the oxidant. The oxygen is often provided from the ambient air. PEMFCs typically require the use of electrocatalysts to improve the reaction rate of the hydrogen oxidation reaction (HOR) and oxygen reduction reactions (ORR), which improve the PEMFC performance. PEMFC electrocatalysts often comprise platinum, a relatively expensive precious metal. It is typically desirable to minimize the platinum content in PEMFC devices to minimize cost. Sufficient platinum content, however, is needed to provide sufficient catalytic activity and PEMFC device performance. As such, there is a desire to increase the catalyst activity per unit catalyst mass (mass activity). There are two general approaches to increase the mass activity, namely increasing the catalyst activity per unit catalyst surface area (specific activity) and increasing the catalyst surface area per catalyst mass (specific surface area or specific area). The HOR and ORR occur on the catalyst surface, so increasing the specific surface area and/or the specific activity can reduce the amount of catalyst needed to achieve a desired absolute performance, reducing cost. To maximize specific area, PEMFC electrocatalysts are often in the form of nanometer-scale thin films or particles on support materials. An exemplary support material for nanoparticle PEMFC electrocatalysts is carbon black, and an exemplary support material for thin film electrocatalysts is whiskers. To increase the specific activity, PEMFC Pt ORR electrocatalysts often also comprise certain transition metals such as cobalt or nickel. Without being bound by theory, incorporation of certain transition metals into the Pt lattice is believed to induce contraction of the Pt atoms at the catalyst surface, which increases the kinetic reaction rate by modification of the molecular oxygen binding and dissociation energies and the binding energies of reaction intermediates and/or spectator species. PEMFC electrocatalysts may incorporate other precious metals. For example, HOR PEMFC Pt electrocatalysts can be alloyed with ruthenium to improve tolerance to carbon monoxide, a known Pt catalyst poison. HOR and ORR PEMFC electrocatalysts may also incorporate iridium to facilitate improved activity for the oxygen evolution reaction (OER). Improved OER activity may improve the durability of the PEMFC under inadvertent operation in the absence of fuel and during PEMFC system startup and shutdown. Incorporation of iridium into the PEMFC ORR electrocatalyst, however, may result in decreased mass activity and higher catalyst cost. Iridium has relatively lower specific activity for ORR than platinum, potentially resulting in decreased mass activity. Iridium is also a precious metal, and thereby its incorporation can increase cost. PEMFC Pt electrocatalysts may also incorporate gold, which is also a precious metal and can increase cost. Gold is known to be relatively inactive for HOR and ORR in acidic electrolytes. Incorporation of gold can result in substantial deactivation for HOR and ORR due to the propensity for gold to preferentially segregate to the electrocatalyst surface, blocking active catalytic sites. PEMFC electrocatalysts may have different structural and compositional morphologies. The structural and compositional morphologies are often tailored through specific processing methods during the electrocatalyst fabrication, such as variations in the electrocatalyst deposition method and annealing methods. PEMFC electrocatalysts can be compositionally homogenous, compositionally layered, or may contain composition gradients throughout the electrocatalyst. Tailoring of composition profiles within the electrocatalyst may improve the activity and durability of electrocatalysts. PEMFC electrocatalyst particles or nanometer-scale films may have substantially smooth surfaces or have atomic or nanometer scale roughness. PEMFC electrocatalysts may be structurally homogenous or may be nanoporous, being comprised of nanometer-scale pores and solid catalyst ligaments. As compared to structurally homogenous electrocatalysts, nanoporous PEMFC electrocatalysts may have hi