Electrochemical method to determine the sensitivity of a gas sensor by pulse sequences

Abstract

An electrochemical method for determining the sensitivity of at least one gas sensor. The method includes applying at least two electrical pulses to at least two parts of at least two electrodes of the gas sensor, recording the change of the current pattern induced in the at least two electrodes by the at least two pulses over time, calculating at least one value for the sensor sensitivity by applying an algorithm to the current pattern induced by the at least two pulses, and comparing the calculated sensitivity value to known gas sensitivity calibration data.

Claims

1. An electrochemical method for determining the sensitivity of at least one gas sensor comprising: applying at least two electrical pulses to at least two parts of at least two electrodes of at least one gas sensor, wherein the at least two electrical pulses comprise a first pulse and a second pulse; recording a change of a plurality of parameters over time in a current pattern induced in the at least two electrodes by the at least two pulses over time, wherein the current pattern induced by the at least two pulses is described by the plurality of parameters, and wherein the plurality of parameters comprises: an area under curve of the current pattern based on the first pulse (AUC1), and an area under curve of the current pattern based on the second pulse (AUC2); calculating at least one sensitivity value for the at least one gas sensor by applying an algorithm to the change of the plurality of parameters over time in the current pattern induced by the at least two pulses; and comparing the at least one calculated sensitivity value to known gas sensitivity calibration data.

2. The method according to claim 1, wherein the at least two pulses are voltage pulses.

3. The method according to claim 1, wherein the at least two pulses are varied from each other by at least one of pulse height (mV), pulse length (sec), or type of pulse.

4. The method according to claim 3, wherein the plurality of parameters, for which the change is recorded, are the same or different based on each of the at least two pulses.

5. The method according to claim 1, wherein the at least two electrical pulses are applied in opposite directions to the at least one gas sensor.

6. The method according to claim 1, wherein a sequence of more than two electrical pulses is applied to the at least one gas sensor.

7. The method according to claim 1, wherein a sequence of four or more electrical pulses is applied to the at least one gas sensor.

8. The method according to claim 1, wherein the current pattern induced by the at least two pulses is described by at least 2 parameters.

9. The method according to claim 8, wherein the algorithm for calculating the at least one sensitivity value for the at least one gas sensor is generated based on the at least 2 parameters of the current pattern induced by the at least two pulses.

10. The method according to claim 1, wherein the current pattern induced by the at least two pulses is described by at least 8 parameters.

11. The method according to claim 1, wherein the plurality of parameters further comprises one of the following parameters: a maximal or minimal peak of the current pattern corresponding to pulse height of the first pulse; a resting peak of the current pattern based on a first pulse (RestPeak 1); a maximal or minimal peak of the current pattern corresponding to pulse height of the second pulse; or a resting peak of the current pattern based on the second pulse (RestPeak 2).

12. The method according to claim 1, wherein the gas sensitivity calibration data are previously obtained from the same gas sensor type.

13. The method according to claim 1, wherein the at least one gas sensor comprises an electrolyte selected from a group comprising: at least one ionic liquid with at least one additive portion; an aqueous salt solution; a mineral acid; a base; and an organic salt solution.

14. The method according to claim 13, wherein: the aqueous salt solution is an aqueous LiCl solution; the mineral acid is H.sub.2SO.sub.4 or H.sub.3PO.sub.4; the base is KOH; or the organic salt solution comprises LiPF.sub.6 in dimethylcarbonate glycol and/or ethylenecarbonate glycol.

15. The method according to claim 13, wherein the at least one additive portion comprises at least one organic additive, at least one organometallic additive, or at least one inorganic additive.

16. The method according to claim 13, wherein the at least one gas sensor comprises the at least two electrodes being in electrical contact with the at least one ionic liquid, the at least two electrodes being separated from one another by a separator or by space.

17. The method according to claim 1, wherein the electrodes comprise independently, the same or different: a metal selected from the group of Cu, Ni, Ti, Pt, Ir, Au, Pd, Ag, Ru, Rh; an oxide Cu, Ni, Ti, Pt, Ir, Au, Pd, Ag, Ru, or Rh and mixtures thereof or carbon.

18. The method according to claim 17, wherein the carbon comprises graphite.

19. The method according to claim 1, wherein the gas sensor is adapted for the detection of gases selected from the group of acid gases, basic gases, neutral gases, oxidizing gases, reducing gases, halogen gases, halogen vapors, and hydride gases.

20. The method according to claim 1, wherein the gas sensor is adapted for the detection of gases selected from the group of F.sub.2, Cl.sub.2, Br.sub.2, I.sub.2, O.sub.2, O.sub.3, ClO.sub.2, NH.sub.3, SO.sub.2, H.sub.2S, CO, CO.sub.2, NO, NO.sub.2, H.sub.2, HCl, HBr, HF, HCN, PH.sub.3, AsH.sub.3, B.sub.2H.sub.6, GeH.sub.4, and SiH.sub.4.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is explained in more details by means of examples with reference to the figures. It shows:

(2) FIG. 1 is a first diagram illustrating the current pattern in response of the gas sensor to two electrical pulses;

(3) FIG. 2 is a second diagram illustrating the current pattern in response of the gas sensor to two electrical pulses with designated parameters;

(4) FIG. 3 is a third diagram illustrating the course of the sensitivity calculated according to the present method applying a complex model (calc sens 2nd) and of the measured sensitivity (sens) for two gas sensors;

(5) FIG. 4 is a fourth diagram illustrating the course of the sensitivity calculated according to the present method applying a complex model (calc sens 2nd) and a simplified model (calc sens PM) and of the measured sensitivity (sens);

(6) FIG. 5 is a fifth diagram illustrating the current pattern in response of the gas sensor to two or three electrical pulses when stored at 80° C.; and

(7) FIG. 6 is a sixth diagram illustrating the current pattern in response of the gas sensor to two or three electrical pulses when overgassed including the recovery behavior after overgassing.

DESCRIPTION OF THE INVENTION

(8) For the purposes of the following detailed description, it is to be understood that the invention may assume various alternative variations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific compositions, coated substrates, multilayer coatings and methods described in the following specification are simply exemplary embodiments of the invention. Moreover, other than in any operating examples, or where otherwise indicated, all numbers expressing, for example, quantities of ingredients used in the specification and claims are to be understood as being modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the Doctrine of Equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

(9) Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

(10) Also, it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of “1 to 10” is intended to include all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10.

(11) It is to be understood that the invention may assume various alternative variations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification, are simply exemplary embodiments of the invention. Hence, specific dimensions and other physical characteristics related to the embodiments disclosed herein are not to be considered as limiting. Certain preferred and non-limiting embodiments or aspects of the present invention will be described with reference to the accompanying figures where like reference numbers correspond to like or functionally equivalent elements.

(12) In this application, the use of the singular includes the plural and plural encompasses singular, unless specifically stated otherwise. In addition, in this application, the use of “or” means “and/or” unless specifically stated otherwise, even though “and/or” may be explicitly used in certain instances. Further, in this application, the use of “a” or “an” means “at least one” unless specifically stated otherwise.

(13) The diagram of FIG. 1 illustrates the current pattern in response of the gas sensor to two electrical pulses. The two pulses are in each case characterized by their pulse height, pulse length, pulse direction, and pulse type. In the case of FIG. 1, a first pulse is applied to a predetermined pulse height, for example, between 5-15 mV for 1-10 sec and a second opposite pulse with a pulse height, for example, between 20-40 mV is applied for 1-10 sec. This is followed by the sensor reaction getting back to its original potential.

(14) In the diagram of FIG. 2, specific parameters are designated to the current curve or current pattern induced by the two voltage peaks in the gas sensor. The parameters are: minimal peak (corresponding to pulse height) of a first pulse P1, a resting peak of the first pulse P1 (RestPeak 1), the area under curve of the first pulse (AUC1), a maximal peak (corresponding to pulse height) of a second pulse P2, a resting peak of second pulse P2 (RestPeak 2), the area under curve of the second pulse (AUC2), minimal peak corresponding to sensor recovery height (MinPeak3 initial), and the area under the recovery curve (AUC3). These parameters are used in a specific algorithm for determining the calculated sensitivity of the sensor.

(15) The diagram of FIG. 3 illustrates the course of the sensitivity calculated according to the present method applying a complex model (calc sens 2nd) and of the measured sensitivity (sens) for two gas sensors;

(16) The diagram of FIG. 4 illustrates the course of the sensitivity calculated according to the present method applying a complex model (calc sens 2nd) and a simplified model (calc sens PM) and of the measured sensitivity (sens);

(17) The diagram of FIG. 5 illustrates the current pattern in response of the gas sensor to two electrical pulses when stored at 80° C. for 4 weeks, 10 weeks and 3 months, respectively. The long term storage causes a sensitivity loss. The current flow decreases gradually within the storage period of 3 months until no current is generated any longer.

(18) The diagram of FIG. 6 illustrates the current pattern in response of the gas sensor to two electrical pulses when overgassed. Specifically the gas sensor is gassed with a high concentration of Cl.sub.2 gas. This causes a slower signal (current) decrease probably due to a reversible adhesion of the gas molecules to the surface of the graphite electrode.

Example

(19) The calculation is based on the current response to the sensor to an applied voltage pulse (see also FIG. 1). The current response can be divided in 8 parameters that are recorded independently from each other during the experiment. The 8 parameters are depicted in the diagram of FIG. 2.

(20) a) Calibration

(21) A first calibration of the sensor comprises the recording of a first voltage pulse and gassing with the target gas (in this case 10 ppm Cl.sub.2) in order to determine the actual gas sensitivity of the sensor. In the specific example, the calibration measurement provided the following parameters shown in Table 1 (all parameters except the initial sensitivity are provided without any unit since values digitally converted by the sensor electronic are used).

(22) TABLE-US-00001 TABLE 1 Value for Value for sensor 1 sensor 2 Parameter (t0) Abbreviation at day 0 at day 0 Initial Sensitivity Sens initial −932 nA/ppm −965 nA/ppm MinPeak 1 initial MP1 initial −7689.7 −7739.6 MaxPeak2 initial MP2 initial 21032.3 21162.4 MinPeak3 initial MP3 initial −10781.7 −11277.6 RestPeak1 initial RP1 initial −1718.7 −1454.6 RestPeak2 initial RP2 initial 4457.3 3761.4 AreaUnderCurve 1 initial AUC1 initial −54723.0 −51718.0 AreaUnderCurve 2 initial AUC2 initial 144726.0 136475.0 AreaUnderCurve 3 initial AUC3 initial −90415.0 −81775.0

(23) b) Recording of Data for Modelling

(24) The previous test is repeated in regular intervals (applying the pulse and measuring the sensitivity by target gas calibration) and values for gas sensor sensitivity and the 8 parameters of the current response to the pulse are determined. This provides for every experiment a data set of the following parameters shown in Table 2.

(25) TABLE-US-00002 TABLE 2 Value for Value for sensor 1 sensor 2 Parameter (t1) Abbreviation at day 13 at day 13 Sensitivity Sens −978 nA/ppm −1017 nA/ppm MinPeak 1 MP1 −7688.9 −7715.0 MaxPeak2 MP2 21061.1 21099.0 MinPeak3 MP3 −10788.9 −11268.0 RestPeak1 RP1 −1693.9 −1456.0 RestPeak2 RP2 4463.1 3746.0 AreaUnderCurve 1 AUC1 −54533.0 −51716.0 AreaUnderCurve 2 AUC2 145215.0 136440.0 AreaUnderCurve 3 AUC3 −89705.0 −83666.0

(26) A difference of the values of Table 2 and the initial values of Table 1 is calculated in order to follow the change of the value over time.

(27) Following general equation is applied: Δ parameter=parameter(t1)−parameter(t0).

(28) Said differences are used for the actual sensitivity calculation and are shown in Table 3.

(29) TABLE-US-00003 TABLE 3 Value for Value for sensor 1 sensor 2 Parameter Abbreviation at day 13 at day 13 Change of Sensitivity ΔSens −46 nA/ppm −52 nA/ppm Change MinPeak 1 ΔMP1 0.8 24.6 Change MaxPeak2 ΔMP2 28.8 −63.4 Change MinPeak3 ΔMP3 −7.2 9.6 Change RestPeak1 ΔRP1 24.8 −1.4 Change RestPeak2 ΔRP2 5.8 −15.4 Change AreaUnderCurve 1 ΔAUC1 190.0 2.0 Change AreaUnderCurve 2 ΔAUC2 489.0 −35.0 Change AreaUnderCurve 3 ΔAUC3 710.0 −1891.0

(30) In this way, multiple pair of values were recorded over 260 days while the gas sensors were stored at different environmental conditions in order to cause sensitivity fluctuations. Some sensors were stored at 10% humidity, 85% humidity, or at normal humidity. Besides, some sensors were exposed to high chlorine concentrations in order to cause a reduction of sensitivity (the overloading with high chlorine concentrations is a known error modus of the sensors).

(31) c) Modelling

(32) The above set of data was subjected to a multi-linear regression in order to determine a correlation between the change of sensitivity and the change of parameters. Thereby, the focus can be directed to the best possible regression (I) or to a simplified model (II).

(33) I. Best Regression

(34) The time course of the Δ-values were used as input and the change of sensitivity was used as output and different models were tested. The calculated sensitivity (“calc sens”) is correlated to the actual sensitivity. The data processing and modelling were done using Minitab Version 16/17.

(35) If a good adaptation of the values is desired, the following model is provided from the regression using 7 parameters (“2nd order complex model”):

(36) Calculated Sensitivity ‘calc sens’=Sens initial+ΔSens.

(37) $Δ Sens = c + a_{1} * Δ MP 1 + a_{2} * Δ MP 3 + a_{3} * Δ RP 2 + a_{4} * Δ AUC 1 + a_{5} * Δ AUC 2 + a_{6} * {(Δ MP 2)}^{2} + a_{7} * {(Δ MP 3)}^{2} + a_{8} * {(Δ RP 2)}^{2} + a_{9} * Δ MP 1 * Δ MP 2 + a_{10} * Δ MP 2 * Δ MP 3 + a_{11} * Δ MP 2 * Δ RP 2 + a_{12} * Δ MP 3 * Δ RP 2 + a_{13} * Δ RP 1 * Δ AUC 1 + a_{13} * Δ RP 1 * Δ AUC 2$

(38) Following constants and factors were used for the model that provide the highest accuracy of prediction:

(39) TABLE-US-00004 Value for ‘2nd Factor order complex model’ C −12.36 a.sub.1 1.578 a.sub.2 2.224 a.sub.3 −1.612 a.sub.4 −0.1013 a.sub.5 −0.04842 a.sub.6 −0.005888 a.sub.7 −0.01461 a.sub.8 −0.005588 a.sub.9 −0.000852 a.sub.10 −0.01814 a.sub.11 0.01127 a.sub.12 0.01859 a.sub.13 −0.000112 a.sub.14 −0.000075

(40) This model provides a high correlation (R2 corrected=72.8%) of the sensitivities exclusively calculated based on pulse data and calibration values and the measured sensitivity.

(41) For the example, the sensors course of measured and exclusively calculated sensitivities are shown in the diagram of FIG. 3. Here, each point in the diagram corresponds to a measured value recording, i.e., applying the pulse and measuring sensitivity at a certain day. As can be seen in the diagram of FIG. 3, both sensors show good correlations between measured sensitivity (“sens”) and sensitivity calculated with the “2nd order complex model” (“calc sens 2nd”).

(42) II. Simplified Model

(43) Since the values of the curve areas require a calculation, the model can be simplified by using only punctual values of the current response curve for modelling and regression (PM=point-model).

(44) This provides a simplified model using 5 parameters:

(45) $Sens (P M) = Sens initial + Δ Sens (P M)$ $Δ Sens (P M) = c + a_{1} * Δ MP 1 + a_{2} * Δ MP 2 + a_{3} * Δ MP 3 + a_{4} * Δ RP 1 + a_{5} * Δ RP 2 + a_{6} * {(Δ MP 1)}^{2} + a_{7} * {(Δ MP 3)}^{2} + a_{8} * Δ MP 1 * Δ MP 3 + a_{9} * Δ MP 1 * Δ RP 2 + a_{10} * Δ MP 2 * Δ RP 1 + a_{11} * Δ MP 2 * Δ RP 2 + a_{12} * Δ MP 3 * Δ RP 1 + a_{13} * Δ MP 3 * Δ RP 2 + a_{14} * Δ RP 1 * Δ RP 2$

(46) The following constants and factors are used for the “point-model”:

(47) TABLE-US-00005 Values for ‘2nd Factor order point model’ C −6.93 a.sub.1 −0.821 a.sub.2 1.578 a.sub.3 2.675 a.sub.4 −1.139 a.sub.5 2.5 a.sub.6 −0.02731 a.sub.7 −0.008428 a.sub.8 0.03046 a.sub.9 −0.02787 a.sub.10 −0.01059 a.sub.11 −0.006318 a.sub.12 −0.01663 a.sub.13 0.005691 a.sub.14 0.01199

(48) Even though this simplification does not reduce the number of factors, however, the calculations of the curve areas are not required. Furthermore, the minimal required pulse length can be reduced since only singular point values and not time depending areas are used in the model.

(49) The correlation of the calculated sensitivity using the simplified point model and the measured sensitivity for the example sensors is shown in the diagram of FIG. 4. Here, the measured sensitivity (“sens”), the calculated sensitivity using the 2nd order complex model (“calc sens 2nd”), and the calculated sensitivity using the 2nd order point model (“calc sens PM”) are illustrated and compared.

(50) By reducing the parameters from 7 to 5, a deterioration of the model quality can be seen in the overall correlation. The accuracy of the regression (determined based on the R2 corrected value) is reduced from 72.8% to 68.6%. However, the course of sensitivity still shows a very good correlation.

(51) As can be seen, disclosed is an electrochemical method for determining the sensitivity of at least one gas sensor comprising: applying at least two electrical pulses to at least two parts of at least two electrodes of the gas sensor, recording a change of a current pattern induced in the at least two electrodes by the at least two pulses over time, calculating at least one value for the sensor sensitivity by applying an algorithm to the current pattern induced by the at least two pulses, and comparing the calculated sensitivity value to known gas sensitivity calibration data.

(52) The at least two pulses can be voltage pulses.

(53) The at least two pulses can be varied by one of the following pulse parameters: pulse height (mV), pulse length (sec), and type of pulse.

(54) The parameters can be the same or different for each of the at least two pulses.

(55) The at least two electrical pulses can be applied in opposite directions to the gas sensor.

(56) A sequence of more than two electrical pulses can be applied to the at least one gas sensor.

(57) A sequence of four or more electrical pulses can be applied to the at least one gas sensor.

(58) The current pattern induced by the at least two pulses can be described by at least 2, or 5, or 7, or 8 parameters.

(59) The current pattern induced by the at least two pulses can be described by one of the following parameters: a maximal or minimal peak (corresponding to pulse height) of a first pulse P1, a resting peak of a first pulse P1 (RestPeak 1), an area under curve of the first pulse (AUC1), a maximal or minimal peak (corresponding to pulse height) of a second pulse P2, a resting peak of the second pulse P2 (RestPeak 2), and an area under curve of the second pulse (AUC2).

(60) The algorithm for calculating the at least one value for the sensor sensitivity can be generated based on the at least 2 parameters of the current pattern induced by the at least two pulses.

(61) The gas sensitivity calibration data can be previously obtained from the same gas sensor type.

(62) The at least one gas sensor can comprise an electrolyte selected from a group comprising: at least one ionic liquid with at least one additive portion; an aqueous salt solution; a mineral acid; a base; and an organic salt solution.

(63) The aqueous salt solution can be an aqueous LiCl solution. The mineral acid can be H.sub.2SO.sub.4 or H.sub.3PO.sub.4. The base can be KOH. The organic salt can be LiPF.sub.6 in dimethylcarbonate glycol and/or ethylenecarbonate glycol.

(64) The at least one additive portion can comprise at least one organic additive, at least one organometallic additive, or at least one inorganic additive.

(65) The sensor can comprise at least two electrodes in electrical contact with the ionic liquid. The electrodes can be separated from one another by a separator or by space.

(66) The electrodes can comprise independently, the same or different: a metal selected from the group of Cu, Ni, Ti, Pt, Ir, Au, Pd, Ag, Ru, Rh, an oxide of Cu, Ni, Ti, Pt, Ir, Au, Pd, Ag, Ru, or Rh, and mixtures thereof, or carbon such as graphite.

(67) The gas sensor can be adapted for the detection of gases selected from the group of acid gases, basic gases, neutral gases, oxidizing gases, reducing gases, halogen gases, halogen vapors, and hydride gases.

(68) Finally, the gas sensor can be adapted for the detection of gases selected from the group of F.sub.2, Cl.sub.2, Br.sub.2, I.sub.2, O.sub.2, O.sub.3, ClO.sub.2, NH.sub.3, SO.sub.2, H.sub.2S, CO, CO.sub.2, NO, NO.sub.2, H.sub.2, HCl, HBr, HF, HCN, PH.sub.3, AsH.sub.3, B.sub.2H.sub.6, GeH.sub.4, and SiH.sub.4.

(69) Although the invention has been described in detail for the purpose of illustration based on what is currently considered to be the most practical and preferred embodiments, it is to be understood that such detail is solely for that purpose and that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover modifications and equivalent arrangements that are within the spirit and scope of the appended claims. For example, it is to be understood that the present invention contemplates that, to the extent possible, one or more features of any embodiment can be combined with one or more features of any other embodiment.

Electrochemical method to determine the sensitivity of a gas sensor by pulse sequences

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G01N27/4045

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G01N33/0006

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G01N33/007

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Abstract

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