Electrochemical devices comprising novel catalyst mixtures
Electrochemical devices comprising electrocatalyst mixtures include at least one Catalytically Active Element and, as a separate constituent, one Helper Catalyst. The electrocatalysts can be used to increase the rate, modify the selectivity or lower the overpotential of chemical reactions. These electrocatalysts are useful for a variety of chemical reactions including, in particular, the electrochemical conversion of CO 2 . Chemical processes employing these catalysts produce CO, HCO − , H 2 CO, (HCOO) − , HCOOH, 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 , or (COO − ) 2 . Devices using the electrocatalysts include, for example, a CO 2 sensor and a CO 2 electrolyzer.
1. An electrochemical device comprising:
an anode and a cathode, the cathode comprising at least one Catalytically Active Element, the at least one Catalytically Active Element contacting both a Positively Charged Cyclic Amine and carbon dioxide (CO 2 ), wherein said Positively Charged Cyclic Amine comprises a polymer and wherein, when electrical energy is applied to create a cell voltage between the anode and the cathode, the electrochemical device is capable of converting at least a portion of the CO 2 to a carbonaceous product when the cell voltage is equal to 2.8 V, the conversion effectuated electrochemically with electrical energy as the primary energy source, said carbonaceous product consisting of one of CO, HCO − , H 2 CO, (HCOO) − , HCOOH, CH 4 , C 2 H 4 , CH 3 CH 2 OH, CH 3 OH, CH 3 COO − , CH 3 COOH, C 2 H 6 , (COOH) 2 and (COO − ) 2 .
2. The electrochemical device of claim 1 wherein said Positively Charged Cyclic Amine comprises a five-member or a six-member aromatic ring, wherein all ring nitrogen atoms are attached only to non-hydrogen atoms.
3. The electrochemical device of claim 1 , wherein the predominant carbonaceous product consists of one of carbon monoxide (CO), formic acid (HCOOH) or formate ions (HCOO) − ).
4. The electrochemical device of claim 1 , wherein the predominant carbonaceous product is one of formic acid (HCOOH) or formate ions (HCOO) − ), and wherein the Positively Charged Cyclic Amine comprises an imidazolium or a pyridinium.
5. The electrochemical device of claim 1 , wherein the Catalytically Active Element is selected from the group consisting of V, Cr, Mn, Fe, Co, Ni, Cu, Sn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Ir, Pt, Au, Hg, Al, Si, C, In, Tl, Pb, Bi, Sb, Te, U, Sm, Tb, La, Ce and Nd.
6. The electrochemical device of claim 5 , wherein the Catalytically Active Element comprises at least one of Ag, Au, Zn, Cd, Pd, Ga and Ni.
7. The electrochemical device of claim 5 , wherein the Positively Charged Cyclic Amine comprises an imidazolium or a pyridinium.
8. The electrochemical device of claim 1 , wherein the cathode has a cathode potential, and wherein the predominant carbonaceous product is carbon monoxide (CO) and at least a portion of the CO 2 is convertible to CO when the cathode potential is equal to or less negative than −0.75 V versus the Standard Hydrogen Electrode (SHE).
9. The electrochemical device of claim 1 , wherein the cathode has a cathode potential, and wherein the electrochemical device is capable of converting at least a portion of the CO 2 to the predominant carbonaceous product when the cathode potential is equal to or less negative than −0.75 V versus the Standard Hydrogen Electrode (SHE).
10. The electrochemical device of claim 1 , wherein the cathode has a cathode potential, and wherein at least a portion of the CO 2 is convertible to the predominant carbonaceous product when the cathode potential is equal to or less negative than −0.6 V versus the Standard Hydrogen Electrode (SHE).
11. The electrochemical device of claim 1 , wherein the cathode has a cathode potential, and wherein at least a portion of the CO 2 is convertible to the predominant carbonaceous product when the cathode potential is equal to or less negative than −0.4 V versus the Standard Hydrogen Electrode (SHE).
12. The electrochemical device of claim 1 comprising a CO 2 sensor or a fuel cell.
13. The electrochemical device of claim 12 , wherein the device is a CO 2 sensor and the Catalytically Active Element is Au.
14. The electrochemical device of claim 12 wherein the device shows a response to CO 2 when there is a potential difference of from 2.7 to 4.3 volts between the anode and cathode.
15. The electrochemical device of claim 13 , wherein the Positively Charged Cyclic Amine comprises an imidazolium.
16. The electrochemical device of claim 1 wherein the Positively Charged Cyclic Amine is a Helper Catalyst, wherein said Positively Charged Cyclic Amine comprises a polymer and wherein a substance S is identifiable as a Helper Catalyst for an electrochemical reaction R that is catalyzed by a Catalytically Active Element M by applying a test comprising:
filling a three-electrode electrochemical cell with an electrolyte E suitable for effectuating reaction R, said electrochemical cell comprising a working electrode, a counter electrode and a reference electrode;
electrically connecting said Catalytically Active Element M to said working electrode and electrically connecting said working electrode to said counter electrode and to a source of electrical energy, thereby forming an electrical circuit;
employing said reference electrode to measure a reversible hydrogen electrode (RHE) potential in said electrolyte E;
loading at least one reactant for reaction R into said cell;
measuring a cyclic voltammogram for reaction R to identify a potential of a peak associated with reaction R;
calculating a difference V1 between RHE and an onset potential of said peak associated with reaction R;
calculating a difference V1A between RHE and a maximum potential of said peak associated with reaction R;
adding to said electrolyte E between 0.0001% and 99.9999% by weight of said Helper Catalyst;
measuring an RHE potential in electrolyte E with said added Helper Catalyst;
measuring a cyclic voltammogram of reaction R with said added Helper Catalyst;
calculating a difference V2 between RHE and an onset potential of said peak associated with reaction R;
calculating a difference V2A between RHE and a maximum potential of said peak associated with reaction R;
determining whether V2<V1 or V2A<V1A at any concentration of said Helper Catalyst between 0.0001% and 99.9999%; and
identifying substance S as said Helper Catalyst for reaction R at concentrations at which V2<V1 or V2A<V1A.