Making electrocatalyst supports for fuel cells
View Patent ↗Titanium oxide (usually titanium dioxide) catalyst support particles are doped for electronic conductivity and formed with surface area-enhancing pores for use, for example, in electro-catalyzed electrodes on proton exchange membrane electrodes in hydrogen/oxygen fuel cells. Suitable compounds of titanium and a dopant are dispersed with pore-forming particles in a liquid medium. The compounds are deposited as a precipitate or sol on the pore-forming particles and heated to transform the deposit into crystals of dopant-containing titanium dioxide. If the heating has not decomposed the pore-forming particles, they are chemically removed from the, now pore-enhanced, the titanium dioxide particles.
1. A method of making catalyst support particles comprising:
co-dispersing compounds of titanium and a salt or alkoxide of a dopant element as solutes or a sol in a liquid alcohol or water/alcohol_medium, the dopant element being selected to enhance the electrical conductivity of the catalyst support particles;
dispersing insoluble pore-forming particles in the liquid alcohol or water/alcohol medium using ultrasonic vibration of the medium, the pore-forming particles being no larger than about twenty nanometers in largest dimension;
precipitating the dispersed compounds of titanium and dopant element on the pore-forming particles;
separating the precipitate from the liquid alcohol or water/alcohol medium;
heating the precipitate in a controlled atmosphere to form crystalline, dopant element-containing titanium dioxide particles; and
removing the embedded pore-forming particles from the crystalline, dopant element-containing titanium dioxide particles to leave surface-area increasing internal and external pores in the crystalline, dopant element-containing titanium dioxide particles.
2. A method as recited in claim 1 in which removing the embedded pore-forming particles comprises chemically etching the embedded pore-forming particles.
3. A method as recited in claim 2 in which the chemically etching is performed with aqueous sodium hydroxide or hydrogen fluoride.
4. A method as recited in claim 1 in which removing the embedded pore-forming particles comprises heating the embedded pore-forming particles.
5. A method as recited in claim 1 in which heating the precipitate in a controlled atmosphere comprises heating to about 1000° C.
6. A method as recited in claim 1 in which the titanium compound is a titanium (IV) alkoxide compound.
7. A method as recited in claim 6 in which the titanium compound is titanium (IV) isopropoxide or titanium (IV) 2-ethylhexyloxide.
8. A method as recited in claim 1 in which the insoluble pore-forming particles are at least one of silica particles, polymer particles, nylon particles, or vinyl chloride particles.
9. A method as recited in claim 8 in which the insoluble pore-forming particles are silica particles, and in which the silica particles are dispersed in the liquid alcohol or water/alcohol medium in an amount to provide about 1.2 parts by weight of silicon per part of titanium.
10. A method as recited in claim 1 in which the insoluble pore-forming particles are 10-15 nanometers in largest dimension.
11. A method as recited in claim 1 in which the electrical conductivity-enhancing dopant element comprises one or more elements selected from the group consisting of lanthanum, manganese, molybdenum, niobium, tantalum, tungsten, strontium, vanadium, and yttrium.
12. A method as recited in claim 11 in which the electrical conductivity-enhancing dopant element is niobium.
13. A method as recited in claim 1 in which the controlled atmosphere comprises hydrogen or ammonia.
14. A method as recited in claim 1 in which the dopant electrical conductivity-enhancing element is niobium, the catalyst support particles contain Ti/Nb in an atomic ratio of 2, and the catalyst support particles have a BET surface area of 125 m 2 /g.
15. A method of making a catalyst for an electrode for a fuel cell comprising:
co-dispersing compounds of titanium and a salt or alkoxide of a dopant element as solutes or a sol in a liquid alcohol or water/alcohol_medium, the dopant element being selected to enhance the electrical conductivity of the catalyst;
dispersing insoluble pore-forming particles in the liquid alcohol or water/alcohol medium using ultrasonic vibration of the medium, the pore-forming particles being no larger than about twenty nanometers in largest dimension;
precipitating the dispersed compounds of titanium and dopant element on the pore-forming particles;
separating the precipitate from the liquid alcohol or water/alcohol medium;
heating the precipitate in a controlled atmosphere to form crystalline, dopant element-containing titanium dioxide particles;
removing the embedded pore-forming particles from the crystalline, dopant element-containing titanium dioxide particles to leave surface-area increasing internal and external pores in the crystalline, dopant element-containing titanium dioxide particles; and
depositing catalyst particles on the crystalline, dopant element-containing titanium dioxide particles to form the catalyst for an electrode for a fuel cell.
16. A method as recited in claim 15 in which the catalyst particles are a noble metal.
17. A method as recited in claim 15 in which the catalyst particles are platinum.