Water-in-salt electrolyte for electrochemical redox reactions

1. A flow cell for reducing carbon dioxide, the flow cell comprising:

a first chamber having a gold coated gas diffusion layer working electrode, a reference electrode, and a water-in-salt electrolyte comprising a concentrated aqueous solution of lithium bis-(trifluoromethanesulfonyl)imide (LiTFSI);

a second chamber adjacent the first chamber and having gold coated gas diffusion layer counter electrode and the water-in-salt electrolyte, the second chamber being separated from the first chamber by a proton exchange membrane; and

a reservoir containing a volume of the water-in-salt electrolyte and a head space, the reservoir being coupled to each of the first and the second chambers with a pump.

2. The flow cell of claim 1 , wherein a volume ratio of the water-in-salt electrolyte to the head space in the reservoir is in a range from 3-5.

3. The flow cell of claim 1 , wherein the reference electrode comprises a lithium-iron-phosphate electrode.

4. The flow cell of claim 1 , wherein the proton exchange membrane comprises Nafion.

5. The flow cell of claim 1 , wherein LiTFSI is present in the water-in-salt electrolyte at a molality in a range from 15 mole/kg to 21 mole/kg.

6. The flow cell of claim 1 , wherein the water-in-salt electrolyte has a pH in a range from 5 to 7 as measured by a double-junction pH electrode.

7. The flow cell of claim 1 , wherein water is present in the water-in-salt electrolyte at a concentration in a range from 13 M to 18 M.

8. The flow cell of claim 1 , wherein the water-in-salt electrolyte from both the first and the second chambers is saturated with carbon dioxide.

9. A method of reducing carbon dioxide to carbon monoxide, the method comprising:

saturating a water-in-salt electrolyte in a flow cell with carbon dioxide; and

applying a potential across a working electrode and a counter electrode of the flow cell, wherein the flow cell comprises a first chamber having a gold coated gas diffusion layer as the working electrode, a reference electrode, and the water-in-salt electrolyte comprises a concentrated aqueous solution of lithium bis-(trifluoromethanesulfonyl)imide (LiTFSI), a second chamber adjacent the first chamber and having gold coated gas diffusion layer as the counter electrode and the water-in-salt electrolyte, the second chamber being separated from the first chamber by a proton exchange membrane, and a reservoir containing a volume of the water-in-salt electrolyte and a head space, the reservoir being coupled to each of the first and the second chambers with a pump.

10. The method of claim 9 , wherein the potential applied across the working electrode and the counter electrode is in a range from −0.8 V to −0.3 V measured relative to a reversible hydrogen electrode.

11. The method of claim 9 , wherein partial pressure of carbon dioxide in each of the first and second chambers of the flow cell is in a range from 0.2 atm to 1 atm.

12. The method of claim 9 , further comprising:

measuring a selectivity ratio of partial current density due to carbon monoxide to partial current density due to carbon monoxide and partial current density due to hydrogen; and

adjusting one or both of a partial pressure of carbon dioxide in the water-in-salt electrolyte and the applied potential so as to maximize selectivity ratio.

13. The method of claim 9 , wherein the water-in-salt electrolyte has a pH in a range from 5 to 7 as measured by a double-junction pH electrode.

14. The method of claim 9 , wherein LiTFSI is present in the water-in-salt electrolyte at a molality in a range from 15 mole/kg to 21 mole/kg.

15. The method of claim 9 , wherein water is present in the water-in-salt electrolyte at a concentration in a range from 13 M to 18 M.

16. The method of claim 9 , wherein the reference electrode comprises a lithium-iron-phosphate electrode.