Electroless process for depositing refractory metals
The invention provides an inexpensive, scalable process for coating materials with a film of a refractory metal. As an example, the immersion process can comprise the deposition of a sacrificial zinc coating which is galvanically displaced by the ether-mediated reduction of oxophilic WCl 6 to form a complex WO x Cl y film, and subsequently annealed to crystalline, metallic tungsten. The efficacy of this process was demonstrated on a carbon foam electrode, showing a 50% decrease in electrode resistance and significant gains in electrochemical performance. This process enables voltage efficiency gains for electrodes in batteries, redox flow batteries, and industrial processes where high conductivity and chemical stability are paramount.
1. An electroless process for depositing a refractory metal, comprising:
depositing a sacrificial coating having an electrochemical reduction potential lower than the refractory metal on a surface of a substrate; and
immersing the coated substrate in a nonaqueous solution containing dissolved refractory metal ions, whereby atoms of the sacrificial coating are oxidized into the nonaqueous solution and the dissolved refractory metal ions are reduced onto the surface of the substrate by galvanic exchange with the atoms of the sacrificial coating to provide a refractory metal-containing coating on the surface.
2. The process of claim 1 , wherein the refractory metal comprises tungsten.
3. The process of claim 1 , wherein the refractory metal comprises molybdenum, niobium, or tantalum.
4. The process of claim 1 , wherein the sacrificial coating comprises zinc.
5. The process of claim 1 , wherein the sacrificial coating comprises lithium, sodium, potassium, magnesium, or manganese.
6. The process of claim 1 , wherein the nonaqueous solution comprises ether.
7. The process of claim 6 , wherein the ether comprises diethyl ether.
8. The process of claim 6 , wherein the ether comprises a polyether, cyclic either, glycol ether, tetrahydrofuran, or dioxane.
9. The process of claim 2 , wherein a salt providing the dissolved tungsten ions comprises tungsten hexachloride.
10. The process of claim 2 , wherein a salt providing the dissolved tungsten ions comprises WF 6 , WCl 4 , WBr 6 , WBr 5 , WOCl 4 , or a tungsten metallocene.
11. The process of claim 1 , wherein the substrate comprises graphite.
12. The process of claim 1 , wherein the substrate comprises a carbon foam.
13. The process of claim 1 , wherein the substrate comprises carbon powder, glassy carbon, vitreous carbon, or a carbon felt.
14. The process of claim 1 , wherein the substrate comprises a glass, ceramic, metal, or plastic.
15. The process of claim 1 , further comprising annealing the refractory metal-containing coating in a reducing atmosphere at a sufficiently high annealing temperature to convert the refractory metal-containing coating to the refractory metal.
16. The process of claim 15 , wherein the reducing atmosphere has an oxygen partial pressure low enough to reduce any refractory metal oxide to the refractory metal.
17. The process of claim 15 , wherein the reducing atmosphere comprises a forming gas.
18. The process of claim 5 , wherein the sufficiently high annealing temperature is greater than 300° C.
19. The process of claim 1 , wherein the refractory metal-containing coating comprises a refractory metal oxide or refractory metal oxyhalide.