Regenerative gas sensor

1. A gas sensor comprising:

a housing;

a membrane electrode assembly disposed in the housing, the membrane electrode assembly comprising a sensing electrode comprising a catalyst on a conductive support, a counter electrode comprising a catalyst on a conductive support, and a polymer membrane disposed between the sensing electrode and the counter electrode, wherein said polymer membrane includes an ionic liquid retained therein;

said housing including a reference gas chamber to which the counter electrode is exposed, and a test gas chamber to which the sensing electrode is disposed;

a pathway for test gas to enter the test gas chamber;

a measurement electrical circuit connecting the sensing electrode and the counter electrode;

an electrical circuit configured to polarize the sensing electrode with positive voltage greater than 1.2 V versus Standard Hydrogen Electrode to remove contaminants from the catalyst when it is partially or completely deactivated by contaminants.

2. The sensor of claim 1 , wherein said contaminants comprise sulfur.

3. The sensor of claim 1 , wherein the catalyst conductive supports comprises a conductive doped or undoped metal oxide.

4. The sensor of claim 1 , wherein the positive voltage applied to the sensing electrode is different than a gas detection voltage.

5. The gas sensor of claim 1 , wherein the catalyst in the sensing electrode and/or the counter electrode is a catalytic metal or alloy comprising iridium, rhenium, palladium, platinum, copper, indium, rubidium, silver, or gold.

6. The gas sensor of claim 1 , the sensor being free of a liquid water reservoir.

7. The sensor of claim 1 , wherein the polymer membrane comprises a proton-conducting ionomer matrix.

8. The sensor of claim 7 , wherein the ionomer has a molecular structure that comprises a hydrophobic portion and a hydrophilic portion, wherein the hydrophobic portion comprises a fluoropolymer repeat unit.

9. The sensor of claim 7 , wherein the ionomer has a molecular structure that comprises a hydrophobic portion and a hydrophilic portion, wherein the hydrophilic portion comprises a sulfonic acid group, a phosphonic acid group, or a sulfonamide acid group.

10. The sensor of claim 1 , wherein the ionic liquid is a proton-conducting ionic liquid.

11. The sensor of claim 1 , wherein the ionic liquid comprises an imidazolium, pyridinium, tetralkylammonium, pyrrolidinium, trialkylsulfonium, pyrazolium, triazolium, thiazolium, oxazolium, pyridazinium, pyrimidinium, or pyrazinium cation.

12. The sensor of claim 1 , wherein the ionic liquid comprises one or more cations according to the formula:

wherein R and R1 are independently H, substituted or unsubstituted alkyl of 1 to 30 carbon atoms, or substituted or unsubstituted aryl of 6 to 30 carbon atoms; and

X is an anion.

13. The sensor of claim 12 , wherein the ionic liquid comprises one or more anions selected from the group consisting of Cl, Br, BF 4 , PF 6 , AlCl 4 , SCN, HSO 4 , HCO 3 , CH 3 SO 3 , CH 3 CH 2 SO 4 , (CH 3 (CH 2 ) 3 O) 2 POO, (CF 3 SO 2 ) 2 N, dicyanamide, CF 3 SO 3 , (CF 3 CF 2 SO 2 ) 2 N, L-(+)-lactate, CH 3 SO 4 , and CH 3 COO.

14. The sensor of claim 1 , wherein either or both of the sensing electrode and the counter electrode has an ionic liquid retained within the electrode.

15. A method of sensing a gas, comprising:

generating a difference in electrochemical potential between a sensing electrode comprising a catalyst on a conductive support and a counter electrode comprising a catalyst on a conductive support, the sensing electrode and the counter electrode separated by a polymer membrane that includes an ionic liquid retained therein, wherein said difference in electrochemical potential is responsive to the presence and/or concentration of a component in a gas being tested;

measuring voltage or current in an electrical circuit connecting the sensing electrode and the reference electrode, converting the measured voltage or current to a reading indicative of the presence and/or concentration of the component in the gas being tested; and

periodically applying an electrical potential difference across the sensing electrode and the counter electrode to polarize the sensing electrode with positive voltage greater than 1.2 V and remove contaminants from the catalyst when it is partially or completely deactivated by contaminants.

16. The method of claim 15 , wherein said component is hydrogen sulfide and said contaminants comprise sulfur.

17. The method of claim 15 , wherein either or both of the sensing electrode and the counter electrode further comprises a proton-conducting ionomer in which anionic liquid is retained.

18. The method of claim 15 , wherein the conductive support comprises conductive metal oxides and the sensor is free of a liquid water reservoir.

19. The sensor of claim 1 , wherein either or both of the sensing electrode and the counter electrode further comprises a proton-conducting ionomer.

20. The sensor of claim 14 , wherein either or both of the sensing electrode and the counter electrode further comprises a proton-conducting ionomer in which the ionic liquid is retained.

21. The sensor of claim 20 , wherein either or both of the sensing electrode and the counter electrode comprises an agglomerate comprising metal or metal oxide particles, catalyst particles, and the proton-conducting ionomer as a binder.

22. The sensor of claim 1 , wherein the electrical circuit is configured to apply positive potential electrical pulses to the sensing electrode at a pre-set frequency in between gas sensing measurements, with relaxation periods allowed to the sensor to restore baseline response and/or by applying an electrical pulse following detection of H 2 S by the sensor.