Metal-air cell with performance enhancing additive
View Patent ↗Systems and methods drawn to an electrochemical cell comprising a low temperature ionic liquid comprising positive ions and negative ions and a performance enhancing additive added to the low temperature ionic liquid. The additive dissolves in the ionic liquid to form cations, which are coordinated with one or more negative ions forming ion complexes. The electrochemical cell also includes an air electrode configured to absorb and reduce oxygen. The ion complexes improve oxygen reduction thermodynamics and/or kinetics relative to the ionic liquid without the additive.
1. A method comprising:
mixing a protic ionic liquid with an aprotic ionic liquid to create an ionically conductive medium comprising negative ions and positive ions, wherein at least one of the positive ions is a proton;
exposing the ionically conductive medium to oxygen; and electrochemically reducing the oxygen,
wherein the ionically conductive medium further comprises an additive selected from one or more of the group consisting of triflic acid, benzonitrile: HTf, acetophenone: HTf, methanesulfonic acid, hydronium triflate, pyridazinium triflate, acetic acid, pyridinium triflate, 1,2-dimethylimidaozlium triflate, n,n-diethyl-n-methylammonium triflate, 2,2,2-trifluoroethanol, and 2-butyl-1,1,3,3-tetramethylguanidinium triflate.
2. The method of claim 1 , wherein the electrochemically reducing the oxygen occurs with improved oxygen reduction thermodynamics, kinetics, or both, relative to electrochemical oxygen reduction in the ionically conductive medium without the protic ionic liquid.
3. The method of claim 1 , wherein the oxygen is electrochemically reduced using a catalyst.
4. The method of claim 1 , wherein the electrochemically reducing the oxygen occurs in an electrochemical cell.
5. The method of claim 1 , wherein the aprotic ionic liquid comprises at least one cation that has at least one strongly bound proton.
6. The method of claim 1 , wherein the protic ionic liquid comprises at least one cation comprising at least one reversible proton with a pKa smaller than or equal to 16.
7. The method of claim 1 , wherein the presence of the proton enhances reversibility of an air cathode of the metal-air ionic liquid battery.
8. The method of claim 1 , wherein at least one of the protic ionic liquid and aprotic ionic liquid is a low temperature ionic liquid.
9. The method of claim 1 , wherein at least one of the protic ionic liquid and aprotic ionic liquid is a room temperature ionic liquid (RTIL).
10. The method of claim 1 , wherein the electrochemically reducing the oxygen occurs in a metal-air ionic liquid battery comprising a metal electrode and an air electrode.
11. The method of claim 1 , further comprising flowing the low temperature ionic liquid in a gap between a metal electrode and an air electrode.
12. The method of claim 1 , further comprising forming metal-oxide by-products at a metal fuel electrode.
13. The method of claim 1 , further comprising storing the metal-oxide by-products at a metal electrode.
14. The method of claim 1 , further comprising forming metal-oxide by-products at an air electrode.
15. The method of claim 1 , wherein the ratio of the concentration of the protic ionic liquid to the aprotic ionic liquid is at least about 1:100.
16. The method of claim 1 , wherein the presence of the proton produces a shift of greater than or equal to 200 mV in the turn-on potential for oxygen reduction versus the ionically conductive medium without the at least one protic ionic liquid.
17. The method of claim 1 , wherein the presence of the proton produces an increase in the current density at the half-wave potential versus the ionically conductive medium without the at least one protic ionic liquid.
18. The method of claim 1 , wherein the presence of the proton produces a shift of greater than or equal to about 1 Yin the half-wave potential for oxygen reduction versus the ionic liquid without the added an oxygen reduction enhancing compound.