System and method for methane production
Provided herein are systems and methods for operating carbon oxide (CO x ) reduction reactors (CRRs) for producing methane (CH 4 ). Embodiments of the systems and methods may also be used for producing other organic compounds including alcohols, carboxylic acids, and other hydrocarbons such as ethylene (CH 2 CH 2 ). According to various embodiments, the systems and methods may be characterized by one or more of the following features. In some embodiments, a membrane electrode assembly (MEA) includes a cathode catalyst layer with a relatively low catalyst loading. In some embodiments, a bipolar MEA includes a thin cation-conducting layer and a thin anion-conducting layer, with the cation-conducting layer being thicker than the anion-conducting layer. In other embodiments a pure anion exchange polymer only membrane may be used to bridge the cathode catalyst and the anode catalyst. These and other features are described further below.
1. A membrane electrode assembly (MEA) comprising:
a cathode catalyst layer comprising a carbon oxide reduction catalyst that selectively promotes production of a product selected from a hydrocarbon, a carboxylic acid, or an alcohol, wherein the carbon oxide reduction catalyst comprises copper,
wherein the roughness factor of the cathode catalyst layer is below 0.25;
an anode catalyst layer comprising a catalyst that promotes oxidation of water; and
a polymer electrolyte membrane (PEM) layer disposed between, and in contact with, the cathode catalyst layer and the anode catalyst layer, wherein the cathode catalyst layer is characterized by a catalyst loading of less than 1 mg/cm 2 and wherein the PEM layer comprises an anion conducting polymer layer in contact with the cathode catalyst layer.
2. The MEA of claim 1 , wherein the catalyst loading is less than 0.5 mg/cm 2 .
3. The MEA of claim 1 , wherein the catalyst loading is less than 0.25 mg/cm 2 .
4. The MEA of claim 1 , wherein the catalyst loading is less than 0.15 mg/cm 2 .
5. The MEA of claim 1 , wherein the copper is pure copper.
6. The MEA of claim 1 , wherein the copper is in a mixture of nanoparticles, the mixture comprising copper nanoparticles and further comprising nanoparticles comprising one or more of silver, gold, and nickel.
7. The MEA of claim 1 , wherein the copper is a copper alloy.
8. The MEA of claim 1 , further comprising salt ions from a salt solution that contacts the MEA, wherein the salt ions in the salt solution have a concentration of at least about 10 μM.
9. The MEA of claim 1 , further comprising salt ions from a salt solution that contacts the MEA, wherein the salt ions in the salt solution have a concentration of at least about 10 mM.
10. The MEA of claim 8 , wherein the product is methane and the salt ions are sodium ions.
11. The MEA of claim 8 , wherein the product has two or more carbon atoms and the salt ions comprise ions of potassium, cesium, rubidium, or any combination thereof.
12. The MEA of claim 1 , wherein the MEA is bipolar, and wherein the MEA further comprises at least one layer of a cation conducting polymer.
13. The MEA of claim 1 , wherein the PEM layer comprises a polymer electrolyte layer and a cathode buffer layer.
14. The MEA of claim 13 , wherein the polymer electrolyte layer comprises a cation conducting polymer and the cathode buffer layer comprises the anion conducting polymer layer.
15. The MEA of claim 14 , wherein the polymer electrolyte layer is between 20 and 60 microns thick.
16. The MEA of claim 14 , wherein the ratio of the thickness of the polymer electrolyte layer to the thickness of the cathode buffer layer is at least 3:1.
17. The MEA of claim 14 , wherein the cathode buffer layer is no more than 20 microns thick.
18. The MEA of claim 1 , wherein the MEA is an anion-exchange membrane (AEM)-only MEA and the AEM comprises the anion conducting polymer layer.
19. The MEA of claim 18 , wherein the AEM is between 10 and 75 microns thick.
20. The MEA of claim 1 , wherein the carbon oxide reduction catalyst is supported on a support structure.
21. The MEA of claim 20 , wherein the support structure comprises carbon.
22. The MEA of claim 1 , wherein the carbon oxide reduction catalyst is in the form of metal particles.
23. The MEA of claim 1 , wherein the carbon oxide reduction catalyst is in the form of metal nanoparticles.
24. The MEA of claim 1 , wherein the catalyst loading is less than 0.1 mg/cm 2 .
25. The MEA of claim 1 , wherein the MEA is capable of producing methane from carbon dioxide at a selectivity of at least 25% as measured by Faradaic yield under an applied current density of 200 mA/cm 2 .
26. A membrane electrode assembly (MEA) comprising:
a cathode catalyst layer comprising a carbon oxide reduction catalyst that selectively promotes production of a product selected from a hydrocarbon, a carboxylic acid, or an alcohol,
wherein the roughness factor of the cathode catalyst layer is below 0.25;
an anode catalyst layer comprising a catalyst that promotes oxidation of water; and
a polymer electrolyte membrane (PEM) layer disposed between, and in contact with, the cathode catalyst layer and the anode catalyst layer, wherein the cathode catalyst layer is characterized by a copper loading of less than 0.1 mg/cm 2 and wherein the PEM layer comprises an anion conducting polymer layer in contact with the cathode catalyst layer.
27. A CO 2 electrolyzer comprising:
a cell comprising:
a cathode catalyst layer comprising a carbon oxide reduction catalyst that selectively promotes production of a product selected from a hydrocarbon, a carboxylic acid, or an alcohol, wherein the carbon oxide reduction catalyst comprises copper, and
wherein the roughness factor of the cathode catalyst layer is below 0.25;
an anode catalyst layer comprising a catalyst that promotes oxidation of water;
a polymer electrolyte membrane (PEM) layer disposed between, and in contact with, the cathode catalyst layer and the anode catalyst layer, wherein the cathode catalyst layer is characterized by a copper catalyst loading of less than 0.6 mg/cm 2 and wherein the PEM layer comprises an anion conducting polymer layer in contact with the cathode catalyst layer; and
a power source controller configured to apply a current to the cell at a current density of at least 400 mA/cm 2 .
28. The CO 2 electrolyzer of claim 27 , wherein the power source controller is configured to apply the current to the cell at the current density of at least 500 mA/cm 2 and wherein the copper loading is less than 0.25 mg/cm 2 .
29. The CO 2 electrolyzer of claim 27 , wherein the copper loading is less than 0.14 mg/cm 2 .