Catalyst layers of membrane-electrode assemblies and methods of making same
Improved catalyst layers for use in fuel cell membrane electrode assemblies, and methods for making such catalyst layers, are provided. Catalyst layers can comprise structured units of catalyst, catalyst support, and ionomer. The structured units can provide for more efficient electrical energy production and/or increased lifespan of fuel cells utilizing such membrane electrode assemblies. Catalyst layers can be directly deposited on exchange membranes, such as proton exchange membranes.
1. A method of forming an electrode comprising a plurality of spherical structured units utilizing an electrospraying process, the method comprising:
providing to a first reservoir a first dispersion comprising a plurality of catalyst particles, an ionomer, a first solvent, and water;
providing to a second reservoir a second dispersion comprising the ionomer and a second solvent;
applying an electrical bias between a substrate and a first needle in fluid communication with the first reservoir and a second needle in fluid communication with the second reservoir;
pumping the first dispersion through the first needle towards a surface of the substrate and
pumping the second dispersion through the second needle towards the surface of the substrate to form the plurality of spherical structured units.
2. The method of claim 1 , wherein the second needle is positioned coaxially within the first needle.
3. The method of claim 1 , further comprising evaporating the first solvent prior to contacting the surface of the substrate.
4. The method of claim 1 , further comprising evaporating the second solvent prior to contacting the surface of the substrate.
5. The method of claim 1 , wherein the first dispersion further comprises an additive.
6. The method of claim 5 , wherein the additive a hydrophobic polymer, a radical scavenging ion, or a hydrophobic powder.
7. The method of claim 1 , wherein the second solvent comprises a polar solvent.
8. The method of claim 7 , wherein the second solvent comprises a mixture of water and an alcohol.
9. The method of claim 1 , wherein the ionomer comprises at least one of perfluorosulfonic acid (PFSA), perfluoro imide acids (PFIA), a quaternary polyphenylene oxide (QPPO), or a hydrocarbon-based ionomer.
10. The method of claim 1 , wherein the plurality of catalyst particles comprises particles of at least one of a platinum group metal catalyst or a transition-metal-based n4-macrocyclic metal complex catalyst.
11. The method of claim 1 , wherein the first dispersion further comprises a plurality of cerium oxide nanoparticles.
12. The method of claim 1 , further comprising varying the electrical bias between formation of a first layer of the plurality of spherical structural units and formation of a second layer of the plurality of spherical structural units.