Thermally stable conductive polymers for electrochemical gas sensor applications

Abstract

Aromatic polymers exhibiting thermal stability and conductivity upon imbibement into an acid are disclosed for electrochemical gas sensor applications. Membrane electrode assemblies for electrochemical gas sensors are also provided, comprising a sensing electrode, a counter electrode, and a polymer membrane comprising the polymers of the present invention, disposed between the sensing electrode and the counter electrode.

Claims

1. A gas sensor comprising: A. a sensing electrode; B. a counter electrode; C. a conductive polymer disposed between the sensing electrode and the counter electrode; D. the conductive polymer comprising aromatic (heterocycle) moieties containing one or more nitrogen groups, wherein said conductive polymer is an aromatic polyether polymer bearing pyridine groups and imbibed with an inorganic acid.

2. The gas sensor of claim 1 wherein said conductive polymer is thermally stable in temperatures of 180° C. to 280° C.

3. The gas sensor of claim 1 where the range of conductivity of the conductive polymer is 0.001 S/m to 1000 S/m.

4. The gas sensor of claim 1, wherein said conductive polymer is any of linear, branched, comb-like, network, cross-linked, and star-shaped in architecture.

5. The gas sensor of claim 1 where the inorganic acid is selected from a group consisting of phosphoric acid, sulfuric acid, hydrochloric acid and nitric acid.

6. The gas sensor of claim 1 comprising a membrane electrode assembly that includes the sensing electrode, the counter electrode and a polymer membrane comprising the conductive polymer.

7. An electrochemical gas sensor comprising a conductive polymer thermally stable in temperatures greater than 180° C., wherein the conductive polymer comprises aromatic (heterocycle) moieties containing one or more nitrogen groups, and wherein the conductive polymer is an aromatic polyether polymer bearing pyridine groups and imbibed with an inorganic acid.

8. The electrochemical gas sensor of claim 7, wherein the conductive polymer is thermally stable in temperatures up to 280° C.

9. The electrochemical gas sensor of claim 7, where the range of conductivity of the conductive polymer is 0.001 S/m to 1000 S/m.

10. The electrochemical gas sensor of claim 7, wherein the conductive polymer is any of linear, branched, comb-like, network, cross-linked, and star-shaped in architecture.

11. The electrochemical gas sensor of claim 7, where the inorganic acid is selected from a group consisting of phosphoric acid, sulfuric acid, hydrochloric acid and nitric acid.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1A is a thermogravimetric analysis of weight loss of 85% phosphoric acid, from room temperature to 280° C. Top trace is weight loss, bottom trace is temperature.

(2) FIG. 1B is a thermogravimetric analysis of weight loss of structure 2 imbibed with 85% phosphoric acid, from room temperature to 280° C. Top trace is weight loss, bottom trace is temperature.

DETAILED DESCRIPTION OF THE INVENTION

(3) The present invention relates to thermally stable conductive polymers with aromatic backbone comprising aromatic or heterocycle groups containing one or more nitrogen groups for electrochemical gas sensors with range of thermal stability between 180° C. and 280° C. and range of conductivity between 0.001 S/m to 1000 S/m when infused in an inorganic acid. In a preferred embodiment, said aromatic copolymers are aromatic polyethers bearing pyridine groups.

(4) The following non-limiting structures of the materials are illustrative of the invention. All documents mentioned herein are incorporated herein by reference.

(5) ##STR00001## ##STR00002##
and cross-linked variations of structures 1 to 7.

(6) The invention also relates to membrane electrode assemblies for electrochemical gas sensors, comprising a sensing electrode, a counter electrode, and a polymer membrane disposed between the sensing electrode and the counter electrode, said polymer membrane comprising the polymers described herein. Compared to conventional sensors, these assemblies have the advantage of being compact, low energy-consuming, useful in high-temperature applications and very resistant to the high soldering temperatures.

(7) The present disclosure is to be considered as an exemplification of the invention, and is not intended to limit the invention to the specific embodiments illustrated by the figures or described in the examples below.

Example 1

(8) An acid-imbibed 2 cm.sup.2 sample of the thermally stable aromatic backbone polymer of structure 2 is subjected to direct contact with molten solder, such as that commonly available (McMaster-Carr, www.mcmaster.com, part number 766A52). Prior to contact with the molten solder, the membrane sample is weighed. After the molten solder has solidified, it is removed and the membrane is weighted again. Table 1 illustrates three replicates of this process, and the resulting percent change in weight between 1.13% and 3.21% illustrates the thermal stability of this material even upon direct contact with molten solder, considered an extreme condition.

(9) TABLE-US-00001 TABLE 1 Structure 2 membrane weight loss upon contact with molten solder Membrane Structure 2 Condition Imbibed with 85% Phosphoric Acid and surface was pat dry Units used Grams Measurement Change in number Before solder After solder mass % change 1 0.0156 0.0151 0.0005 3.21% 2 0.0151 0.0149 0.0002 1.32% 3 0.0708 0.07 0.0008 1.13%

Example 2

(10) An acid imbibed sample of the polymer of structure 2 is subjected to high temperatures for an extended period of time, whereby the percent weight loss is recorded versus temperature. A thermogravimetric analyser is employed with a platinum cup to hold samples. The temperature ramp rate is set to maximum (>50° C. per minute) up to 200° C. whereby the overshoot in temperature, due to the fast ramp rate, extends to 280° C., the point where typical solder reflow occurs. A sample of pure 85% phosphoric acid is first subjected to this sequence in order to measure the amount of water and phosphoric acid vapor that would be lost. This is illustrated in FIG. 1A, whereby a total of 17.3% liquid weight is lost under this thermal profile. A sample of structure 2 is then imbibed with 85% phosphoric acid is subjected to the same thermal profile. FIG. 1B illustrates the results. In this case, a total of 18.5% weight is lost, a difference of 1.3%. Considering that the thermally stable aromatic polymer is subjected to these high temperatures for a much longer time than during a typical solder fabrication operation, FIG. 1B confirms the stability of this material.

(11) The invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings.