Current reversal tolerant multilayer material, method of making the same, use as an electrode, and use in electrochemical processes
The invention provides an electrode comprising a substrate and a coating on the substrate. The coating comprises a plurality of layers, including the following layers in sequence moving outwardly from the substrate: a base layer comprising an oxide of a valve metal; a lower layer comprising an oxide of a platinum group metal and/or an oxide of a precious metal; and a mixed oxide primary layer comprising both: (i) an oxide of a platinum group metal and/or an oxide of a precious metal, and (ii) an oxide of a valve metal and/or an oxide of a group 15 metal. The base layer is devoid of any platinum group metal oxide, and the lower layer is devoid of any valve metal oxide. The present invention also provides methods of manufacturing such electrodes. Also provide are methods of using an electrochemical cell equipped with a certain multilayer coated electrode.
1. A method of using an electrochemical cell to perform an electrochemical process, the electrochemical cell comprising an electrode immersed in an electrolyte, the electrode comprising a substrate and a coating on the substrate, the method comprising operating the electrochemical cell so as to reverse a polarity of electrical current flow through the electrode during at least 10 current reversal cycles, and the electrode maintains an overpotential that does not change by more than 15%, and the coating does not lose any layers, the coating comprising a plurality of layers, the plurality of layers comprising the following in sequence moving outwardly from the substrate:
(a) a base layer comprising an oxide of a valve metal, the base layer being devoid of any platinum group metal oxide;
(b) a lower layer comprising an oxide of a platinum group metal and/or an oxide of a precious metal, the lower layer being devoid of any valve metal oxide;
(c) a mixed oxide primary layer comprising both: (i) an oxide of a platinum group metal and/or an oxide of a precious metal, and (ii) an oxide of a valve metal and/or an oxide of a group 15 metal;
(d) an intermediate layer comprising an oxide of a platinum group metal and/or an oxide of a precious metal, the intermediate layer being devoid of any valve metal oxide; and
(e) a mixed oxide upper layer comprising both: (i) an oxide of a platinum group metal and/or an oxide of a precious metal, and (ii) an oxide of a valve metal and/or an oxide of a group 15 metal;
wherein the base layer is in contact with the substrate, the lower layer is in contact with the base layer, and the mixed oxide primary layer is in contact with the lower layer.
2. The method of claim 1 , wherein the electrolyte comprises water containing calcium carbonate in a range of 61 to 120 mg/L or more, and the method involves operating the electrode while it is immersed in the water, said reversal of polarity of electrical current flow through the electrode removing scale buildup from the electrode.
3. The method of claim 1 , wherein the electrode maintains the overpotential so it does not change by more than 10%.
4. The method of claim 1 , wherein the electrochemical process generates an oxidant selected from the group consisting of ozone, peracetic acid, and persulfuric acid.
5. The method of claim 1 , wherein the coating has an exposed face that is defined by the mixed oxide upper layer.
6. The method of claim 1 , wherein the mixed oxide upper layer and the mixed oxide primary layer have the same composition.
7. The method of claim 1 , wherein the base layer comprises a plurality of sublayers that all have the same composition.
8. The method of claim 1 , wherein the base layer consists of 4-6 sublayers.
9. The method of claim 1 , wherein the lower layer comprises more than two, but has less than six, sublayers.
10. The method of claim 1 , wherein the base layer is formed by multiple sublayers, the lower layer is formed by multiple sublayers, and the mixed oxide upper layer is formed by multiple sublayers.
11. The method of claim 1 , wherein the mixed oxide primary layer consists of a single sublayer.
12. The method of claim 1 , wherein the intermediate layer comprises 1-5 sublayers.
13. The method of claim 1 , wherein the mixed oxide upper layer comprises a plurality of sublayers that all have the same composition.
14. The method of claim 1 , wherein the mixed oxide upper layer consists of 15-35 sublayers.
15. The method of claim 1 , wherein the mixed oxide upper layer includes the oxide of the group 15 metal and comprises bismuth, antimony, or a combination thereof.
16. The method of claim 1 , wherein the electrolyte comprises water containing calcium carbonate in a range of 121 to 180 mg/L or more.
17. The method of claim 1 wherein said operating the electrochemical cell includes reversing the polarity of electrical current flow through the electrode during at least 1,000 current reversal cycles.
18. The method of claim 1 , wherein the intermediate layer and the lower layer have the same composition.
19. A method of using an electrochemical cell to perform an electrochemical process, wherein the electrochemical process generates ozone, the electrochemical cell comprising an electrode immersed in an aqueous electrolyte, the aqueous electrolyte comprising water containing calcium carbonate in a range of 61 to 120 mg/L or more, and the method involves operating the electrode while it is immersed in the aqueous electrolyte, the electrode comprising a substrate and a coating on the substrate, the method comprising operating the electrochemical cell so as to reverse a polarity of electrical current flow through the electrode during at least 1,000 current reversal cycles, and the electrode maintains an overpotential that does not change by more than 15%, the coating does not lose any layers, and the electrochemical process continues generating ozone, the coating comprising a plurality of layers, the plurality of layers comprising the following in sequence moving outwardly from the substrate:
(a) a base layer comprising an oxide of a valve metal, the base layer being devoid of any platinum group metal oxide;
(b) a lower layer comprising an oxide of a platinum group metal and/or an oxide of a precious metal, the lower layer being devoid of any valve metal oxide;
(c) a mixed oxide primary layer comprising both: (i) an oxide of a platinum group metal and/or an oxide of a precious metal, and (ii) an oxide of a valve metal and/or an oxide of a group 15 metal;
(d) an intermediate layer comprising an oxide of a platinum group metal and/or an oxide of a precious metal, the intermediate layer being devoid of any valve metal oxide; and
(e) a mixed oxide upper layer comprising both: (i) an oxide of a platinum group metal and/or an oxide of a precious metal, and (ii) an oxide of a valve metal and/or an oxide of a group 15 metal;
wherein the base layer is in contact with the substrate, the lower layer is in contact with the base layer, and the mixed oxide primary layer is in contact with the lower layer.
20. The method of claim 19 , wherein the mixed oxide upper layer comprises a plurality of sublayers that all have the same composition.
21. The method of claim 19 , wherein the aqueous electrolyte comprises water containing calcium carbonate in a range of 121 to 180 mg/L or more.
22. The method of claim 19 wherein said operating the electrochemical cell includes reversing the polarity of electrical current flow through the electrode during at least 3,000 current reversal cycles.
23. The method of claim 19 , wherein the intermediate layer and the lower layer have the same composition.
24. A method of using an electrochemical cell to perform an electrochemical process, the electrochemical cell comprising an electrode immersed in an electrolyte, the electrode comprising a substrate and a coating on the substrate, the method comprising operating the electrochemical cell so as to reverse a polarity of electrical current flow through the electrode during at least 10 current reversal cycles, the coating comprising a plurality of layers, the plurality of layers comprising the following in sequence moving outwardly from the substrate:
(a) a base layer comprising an oxide of a valve metal, the base layer being devoid of any platinum group metal oxide;
(b) a lower layer comprising an oxide of a platinum group metal and/or an oxide of a precious metal, the lower layer being devoid of any valve metal oxide;
(c) a mixed oxide primary layer comprising both: (i) an oxide of a platinum group metal and/or an oxide of a precious metal, and (ii) an oxide of a valve metal and/or an oxide of a group 15 metal;
(d) an intermediate layer comprising an oxide of a platinum group metal and/or an oxide of a precious metal, the intermediate layer being devoid of any valve metal oxide; and
(e) a mixed oxide upper layer comprising both: (i) an oxide of a platinum group metal and/or an oxide of a precious metal, and (ii) an oxide of a valve metal and/or an oxide of a group 15 metal;
wherein the base layer is in contact with the substrate, the lower layer is in contact with the base layer, and the mixed oxide primary layer is in contact with the lower layer, and
wherein the intermediate layer and the lower layer have the same composition.
25. The method of claim 24 , wherein the electrode maintains an overpotential that does not change by more than 15%, and the coating does not lose any layers.