Porous electrolessly deposited coatings
A new electroless plating approach to generate a porous metallic coating is described in which a metal is electrolessly deposited on a surface. Microparticles in the metal are removed to leave pores in the metal coating. Another method of forming electroless coatings is described in which a blocking ligand is attached to the surface, followed by a second coating step. The invention includes coatings and coated apparatus formed by methods of the invention. The invention also includes catalyst structures comprising a dense substrate and a porous metal adhered to the dense substrate, which is further characterized by one or more of the specified features.
1. A catalyst structure, comprising:
a dense substrate, and
a porous metal adhered to the dense substrate,
particles of metal oxides disposed in the porous metal; and
a bi-modal distribution of pore sizes in the porous metal.
2. The structure of claim 1 wherein the dense substrate comprises a wall of the microchannel apparatus.
3. The catalyst structure of claim 2 wherein the microchannel apparatus comprises a chemical reactor.
4. The catalyst structure of claim 2 wherein the microchannel apparatus comprises reactive distillation apparatus.
5. The catalyst structure of claim 2 wherein the wall is an iron based alloy or a Ni-, Co- or Fe-based superalloy.
6. The catalyst structure of claim 1 comprising a bi-modal distribution of pore sizes in the porous metal wherein the large pores are in the size range of 0.1 to 10 micrometers (μm) and the small pores are in the range from 1 to 10 nm.
7. The catalyst structure of claim 6 wherein at least 90% of total pore volume is within the two ranges that define the bimodal distribution.
8. The catalyst structure of claim 1 wherein the porous metal is a post-assembly coating.
9. The catalyst structure of claim 8 wherein the post-assembly fills gaps or cracks in the microchannel apparatus.
10. The catalyst structure of claim 1 wherein metal oxide particles are exposed within the pores of the porous metal.
11. The catalyst structure of claim 1 wherein a metal oxide coating is disposed between the substrate and the porous metal.
12. The catalyst structure of claim 10 wherein porous metal is made method of forming a metal coating on a substrate, comprising:
providing a liquid composition comprising a metal complex;
contacting the substrate with microparticles;
wherein the microparticles comprise a removable material and a non-removable metal oxide;
contacting the substrate with the liquid composition;
reacting the metal complex with a reducing agent; and
removing the removable material to form the porous metal coating on the substrate.
13. A fuel cell comprising a catalyst structure, the catalyst structure, comprising:
a dense substrate, and
a porous metal adhered to the dense substrate,
particles of metal oxides disposed in the porous metal; and
one or more of the following features:
an average pore size of at least 1 micron in the porous metal; or
a bi-modal distribution of pore sizes in the porous metal.
14. The fuel cell of claim 13 wherein the porous metal comprises Pt, Pd, Rh, Ag, Cu, Au, Fe, Co, Re, and their alloys.
15. The fuel cell of claim 14 wherein the porous metal comprises Pt—Rh, Pt—Pd, Pt—Au, Pt—Pd—Au, Pt—Cu and Pt—Ag.