Electrochemical device for converting carbon dioxide to a reaction product
An electrochemical device converts carbon dioxide to a reaction product. The device includes an anode and a cathode, each comprising a quantity of catalyst. The anode and cathode each has reactant introduced thereto. A polymer electrolyte membrane is interposed between the anode and the cathode. At least a portion of the cathode catalyst is directly exposed to gaseous carbon dioxide during electrolysis. The average current density at the membrane is at least 20 mA/cm 2 , measured as the area of the cathode gas diffusion layer that is covered by catalyst, and CO selectivity is at least 50% at a cell potential of 3.0 V. In some embodiments, the polymer electrolyte membrane comprises a polymer in which a constituent monomer is (p-vinylbenzyl)-R, where R is selected from the group consisting of imidazoliums, pyridiniums and phosphoniums. In some embodiments, the polymer electrolyte membrane is a Helper Membrane comprising a polymer containing an imidazolium ligand, a pyridinium ligand, or a phosphonium ligand.
1. An electrochemical device for converting CO 2 to a reaction product, the device comprising:
(a) an anode comprising a quantity of anode catalyst, said anode having an anode reactant introduced thereto via at least one anode reactant flow channel;
(b) an electrolyzer cathode comprising a quantity of an electrolyzer cathode catalyst, said cathode having a cathode reactant introduced thereto via at least one cathode reactant flow channel;
(c) a polymer electrolyte membrane interposed between said anode and said cathode;
(d) a source of potential which applies a potential difference across the anode and the cathode;
wherein said cathode is encased in a cathode chamber and at least a portion of the cathode catalyst is directly exposed to gaseous CO 2 during electrolysis, and wherein the device satisfies a test comprising:
(1) with said anode open to atmospheric air, introducing a stream of CO 2 humidified at 50° C. into the cathode chamber while the device is at room temperature and atmospheric pressure;
(2) applying a cell potential of 3.0 V via an electrical connection between said anode and said cathode with the device at room temperature;
(3) measuring the current across the cell and the concentration of CO and H 2 at the exit of said cathode chamber;
(4) calculating the CO selectivity as follows:
Selectivity
=
(
CO
production
rate
)
(
CO
production
rate
+
H
2
production
rate
)
;
(5) performing steps (1)-(4) with room temperature water being directed to said anode; and
(6) determining that the device has satisfied the test if the average current density at the membrane is at least 20 mA/cm 2 , where the cm 2 is measured as the area of the cathode gas diffusion layer on which the catalyst is disposed, and CO selectivity is at least 50% at a cell potential of 3.0 V in at least one of step (4) and step (5).
2. The electrochemical device in claim 1 , wherein at least 50% by mass of the cathode catalyst is directly exposed to gaseous CO 2 during electrolysis.
3. The electrochemical device of claim 2 , wherein the gaseous CO 2 is directed within 2 mm of the catalyst or the gas diffusion layer on which the catalyst is disposed.
4. The electrochemical device in claim 2 , wherein at least 90% by mass of the cathode catalyst is directly exposed to gaseous CO 2 during electrolysis.
5. The electrochemical device of claim 4 , wherein the gaseous CO 2 is directed within 2 mm of the catalyst or the gas diffusion layer on which the catalyst is disposed.
6. The electrochemical device in claim 4 , wherein the polymer electrolyte membrane is an anionic exchange membrane.
7. The electrochemical device in claim 6 , wherein at least a portion of said polymer electrolyte membrane is a Helper Membrane identifiable by applying a test comprising:
(1) preparing a cathode comprising 6 mg/cm 2 of silver nanoparticles on a carbon fiber paper gas diffusion layer;
(2) preparing an anode comprising 3 mg/cm 2 of RuO 2 on a carbon fiber paper gas diffusion paper;
(3) preparing a polymer electrolyte membrane test material;
(4) interposing the membrane test material between the anode and the cathode, the side of cathode having the silver nanoparticles disposed thereon facing one side of the membrane and the side of the anode having RuO 2 disposed thereon facing the other side of the membrane, thereby forming a membrane electrode assembly;
(5) mounting the membrane electrode assembly in a fuel cell hardware assembly;
(6) directing a stream of CO 2 humidified at 50° C. into the cathode reactant flow channels while the fuel cell hardware assembly is at room temperature and atmospheric pressure, with the anode reactant flow channels left open to the atmosphere at room temperature and pressure;
(7) applying a cell potential of 3.0 V via an electrical connection between the anode and the cathode;
(8) measuring the current across the cell and the concentration of CO and H 2 at the exit of the cathode flow channel;
(9) calculating the CO selectivity as follows:
Selectivity
=
(
CO
production
rate
)
(
CO
production
rate
+
H
2
production
rate
)
;
and
(10) identifying the membrane as a Helper Membrane if the average current density at the membrane is at least 20 mA/cm 2 , measured as the area of the cathode gas diffusion layer that is covered by catalyst, and CO selectivity is at least 50% at a cell potential of 3.0 V.
8. The electrochemical device of claim 7 , wherein the polymer electrolyte membrane is entirely a Helper Membrane.
9. The electrochemical device of claim 1 , wherein said polymer electrolyte membrane is a Helper Membrane comprising a polymer containing at least one of an imidazolium ligand, a pyridinium ligand and a phosphonium ligand.
10. The electrochemical device of claim 1 , wherein said anode catalyst is applied as a coating facing said membrane and the cathode catalyst is applied as a coating facing said membrane.
11. The electrochemical device of claim 1 , wherein said polymer electrolyte membrane is essentially immiscible in water.
12. The electrochemical device of claim 1 , wherein the reaction product is selected from the group consisting of CO, HCO − , H 2 CO, (HCO 2 ) − , H 2 CO 2 , CH 3 OH, CH 4 , C 2 H 4 , CH 3 CH 2 OH, CH 3 COO − , CH 3 COOH, C 2 H 6 , (COOH) 2 , (COO − ) 2 , H 2 C═CHCOOH, and CF 3 COOH.
13. The electrochemical device of claim 1 , further comprising a Catalytically Active Element.
14. The electrochemical device of claim 13 , wherein said Catalytically Active Element is selected from the group consisting of Au, Ag, Cu, Sn, Sb, Bi, Zn and In.