Electrochemical gas sensor, gas measuring device and method for determining a concentration of phosphine in a measuring gas

Abstract

The present invention relates to an electrochemical gas sensor for determining a phosphine concentration in a measurement gas, a gas measuring device for determining a phosphine concentration in a measurement gas, and a method for determining a phosphine concentration in a measurement gas. The gas sensor comprises a working electrode, a counter electrode, and a reference electrode, wherein the reference electrode is inert with respect to phosphine.

Description

The present invention relates to an electrochemical gas sensor, a gas meter, and a method for determining a concentration of phosphine in a measurement gas.For controlling pests, inter alia in cereals, phosphine is used worldwide in agriculture. In this process, which is also referred to as deweasing, cereals are gassed with phosphine (also referred to as phosphine, monophosphine, hydrogen phosphide, pH 3) for example. This attempts to reduce or prevent damage in cereals caused, for example, by insect feeding or by insect excrement. In this case, it is absolutely necessary for a predetermined minimum concentration of phosphine to be achieved in order to achieve a high number of pests potentially present in the grain. At the same time, it is necessary that the concentration of phosphine does not exceed a predetermined maximum concentration, since otherwise the pests fall into a protective barrier in which metabolism of the pests is shut down, so that only little or no phosphine is absorbed any longer.Another problem with using phosphine is that phosphine is a toxic, odourless gas in the pure state. From the aspect of the work protection as well, it is therefore necessary to know the concentration of the phosphine used.It is thus necessary to be able to measure the concentration of phosphine in the environment in which the phosphine is used, in particular in a cereal store.Electrochemical gas sensors for determining the concentration of phosphine are known from the prior art.U.S. Pat. No. 5,997,706 A, EP 0 436 148 B1 and DE 19 832 395 C1 disclose electrochemical gas sensors for detecting phosphine, wherein the gas sensors comprise a working electrode and a reference electrode in an electrolyte space, and wherein the electrolyte space is filled with an electrolyte and is closed off by a gas-permeable membrane.KR 2020 0 082 563 A discloses a working electrode for use in a phosphine sensor.DE 19 939 011 C1 discloses an electrochemical gas sensor with a gas-permeable membrane, in which the working electrode is made of diamond-like carbon and is applied as a thin layer to the gas-permeable membrane.DE 10 159 616 B4 discloses an electrochemical gas sensor for phosphine with an improved cross sensitivity.The electrochemical gas sensors known from the prior art have the disadvantage that they cannot withstand gassing with high phosphine concentrations, i.e. phosphine concentrations in a range of up to 1000 ppm, for a longer period of at least 72 hours without substantial deterioration of the sensor sensitivity or require a complex structure in order to achieve this requirement.In particular, the above-mentioned gas sensors often have the disadvantage that, at the above-mentioned high concentrations of phosphine, the phosphine is not completely reacted at the working electrode when diffusing into the electrochemical gas sensor, so that it can reach as far as the reference electrode. However, this shifts the working potential of the working electrode, which in turn influences the conversion of phosphine at the working electrode. Consequently, the sensitivity of the gas sensors to phosphine and thus the measurement behavior of the gas sensor deteriorates.It is therefore an object of the present invention to provide a simply constructed electrochemical gas sensor, a gas measuring device and a method for determining a concentration of phosphine in a measurement gas, the measurement behavior of which is less sensitive to high concentrations of phosphine.These and other objects are achieved by the subject matter of the independent claims.Advantageous embodiments are specified in the dependent claims, in the description and in the figures.According to the present invention, an electrochemical gas sensor (hereinafter, also referred to merely as a gas sensor) for determining a concentration of phosphine in a measurement gas is provided. The gas sensor includes a working electrode, a counter electrode, and a reference electrode, the reference electrode being inert with respect to phosphine.In the context of the invention, it has been found that a reference electrode which is inert with respect to phosphine (in other words a reference electrode which does not have an electrochemical and / or catalytic interaction with phosphine) leads, even when phosphine reaches the reference electrode, to an electrode potential between reference electrode and working electrode being largely stable and it is thus possible to provide a gas sensor whose measurement behavior is less sensitive to a high concentration of phosphine of up to 1000 ppm, even over relatively long periods of up to 72 hours.Preferably, the reference electrode comprises ruthenium oxide (RuO 2). as electrode material.In the context of the invention, it has been found that ruthenium oxide is a particularly suitable electrode material which is inert with respect to phosphine.Preferably, the working electrode comprises gold and / or platinum as electrode material.In the context of the invention, it has been found that these materials are particularly suitable electrode materials which are reactive with phosphine.Preferably, the gas sensor does not comprise any further working electrode.In this way, the structure of the gas sensor can be simplified. According to the invention, it is possible to dispense with the provision of a further working electrode, sometimes referred to in the prior art as a "guard electrode", which is usually used to prevent phosphine from reaching the reference electrode.Each of the electrodes of the gas sensor may be provided on a support material or on a membrane. Such a carrier material can be configured, for example, as a hydrophilic or hydrophilized nonwoven.The gas sensor may include a housing surrounding the working electrode, the counter electrode, and the reference electrode. The housing may be configured such that phosphine may diffuse through the housing into the electrochemical gas sensor.In a preferred embodiment, the housing can have an opening or a diffusion membrane for this purpose for gas exchange with the environment.In a preferred embodiment, the housing can have an electrolyte-filled reaction space in which the electrodes (i.e. the working electrode, the counter electrode and the reference electrode) can be arranged. In this configuration, the phosphine can diffuse, for example, through the opening or through the diffusion membrane into the reaction space of the gas sensor and thus reach the working electrode. A corresponding forward reaction can take place at the first working electrode, and a reverse reaction can take place at the counter electrode.In a preferred embodiment of the electrochemical gas sensor, the phosphine can diffuse from the environment through a preferably hydrophobic diffusion membrane into the electrochemical gas sensor and reach a three-phase boundary formed by the working electrode, the electrolyte and the phosphine. The analyte gas can react at the working electrode (forward reaction), wherein the reaction products formed at the counter electrode (reverse reaction) finally re-enter the electrolyte. Water can form on the counter electrode as a result of the back reaction.Without being bound by theory, the inventors assume that the following reactions take place at the working electrode and at the counter electrode:Oxidation of phosphine to phosphate at the working electrode (cathode) according to the following equation: PH 3+ 4 H 2 O → H 3 PO 4+ 8 H +Reduction of oxygen to 2 O 2- at the counterelectrode (anode) according to the following equation: 2 O 2 >4 O 2-From both above reactions, also referred to as half-cell reactions, the following overall reaction takes place within the electrochemical gas sensor according to the invention: PH 3+ 2 O 2+ 4 H 2 O → H 3 PO 4+ 4 H 2 O.When the electrochemical gas sensor according to the invention is supplied with phosphine, phosphine is therefore oxidized to phosphoric acid at the working electrode and oxygen is reduced at the counter electrode according to the above equation, without being tied to theory.In a further preferred embodiment, the housing has both a first diffusion membrane and a second diffusion membrane. This has proven to be particularly advantageous since, for example, the electrolyte can be hygroscopic, which can lead to an increase in the volume of the electrolyte during operation. It can therefore be advantageous to arrange a second diffusion membrane in the housing, by means of which a pressure equalization with the environment is made possible. In principle, the second diffusion membrane can be arranged everywhere within the housing.It is preferable that the electrochemical gas sensor includes a first diffusion membrane and a substantially opposing second diffusion membrane.The counter electrode is preferably arranged within the electrochemical gas sensor in such a way that it can easily come into contact with the environment in which oxygen is usually also contained in addition to the phosphine, preferably via a diffusion membrane. The material for the counter electrode is preferably selected such that oxygen can be reduced at the latter in the electrochemical gas sensor according to the invention according to the above equation. All electrode materials known to the skilled person can be considered for the counter electrode.Preferably, the reference electrode is surrounded on at least two sides by a protective layer, wherein the protective layer is impermeable to phosphine.Thus, contact between phosphine and the reference electrode is made more difficult by lengthening a diffusion distance of the phosphine to the reference electrode, which results in a further improvement in the measurement behavior of the gas sensor.The protective layer can be configured, for example, as a film. Particularly preferably, the reference electrode is surrounded on three sides by the protective layer and on another side not surrounded by the protective layer, so that the reference electrode can still be in contact with electrolyte.Preferably, the protective layer is formed of polyvinylidene fluoride (PVDF).In a preferred embodiment, one or more separators can be arranged between the working electrode and the reference electrode and / or between the working electrode and the counter electrode. The separator or separators prevent a short circuit from occurring between the electrodes. The separator or separators can be, for example, glass fleeces. The separator or separators can be configured to be electrolyte permeable. If the separator or separators are hydrophilic, they can take up an aqueous electrolyte and thus form an electrolyte bridge, so that ions can move between the electrodes.Possible electrolytes for use in a gas sensor according to the invention include any electrolytes, preferably aqueous electrolytes, in particular lithium chloride, ionic liquids, sulfuric acid and / or an ethylene carbonate / propylene carbonate (ECPC) solution with a conducting salt, for example tetrabuthylammonium tosylate or mesylate.Ionic liquids (IL) are understood to mean salts which are liquid at temperatures below 100° C.The gas sensor can have an electrical coupling unit which can be configured to connect the electrodes, i.e. the working electrode, the reference electrode and the counter electrode, electrically and / or signal-wise to a control unit for operating the gas sensor. These may be platinum wires, for example.The object according to the invention is furthermore achieved by a gas measuring device for determining a concentration of phosphine in a measurement gas, the gas measuring device having a previously described electrochemical gas sensor, a control unit for operating the electrochemical gas sensor and preferably for determining the concentration of phosphine in the measurement gas, an energy source for supplying the gas measuring device with energy, and optionally a wireless interface for providing the determined concentration of phosphine.The gas measuring device has advantages and effects comparable to the gas sensor. Advantageous configurations and features which are described in connection with the gas sensor are also considered to be disclosed in connection with the gas measuring device and vice versa.The control unit can be configured to measure an electrical current which flows between the working electrode and the counter electrode when phosphine is applied. Thus, the concentration of the phosphine can be determined on the basis of the measured current between the working electrode and the counter electrode.The object according to the invention is furthermore achieved by a method for determining a concentration of phosphine in a measurement gas.The method comprises the steps of: providing a number of gas measurement devices described above in an environment with measurement gas, continuously determining the concentration of phosphine in the environment of the gas measurement device, providing the concentration of phosphine, preferably via the wireless interface.The method has advantages and effects comparable to the gas sensor and to the gas measuring device. Advantageous configurations and features which are described in connection with the gas sensor and / or the gas measuring device are also considered to be disclosed in connection with the gas sensor and the gas measuring device and vice versa.The number of gas measurement devices can be a single number or a plurality.Preferably, the specific concentration of phosphine is provided in real time.In this way, monitoring of the current phosphine concentration can be improved.The method preferably further comprises the steps of: determining a position of the number of gas measurement devices relative to the environment of the gas measurement device, and providing the position, preferably via the wireless interface.In this way, in addition to determining the concentration of the phosphine, information can be provided about the local distribution of the phosphine in the environment.These and further features and advantages of the invention also result from the following description of the figures. The following shows: FIG. 1 shows a cross section of a schematic electrochemical gas sensor according to the invention, FIG. 2 shows a schematic gas measuring device according to the invention, and FIG. 3 shows a flow chart of a method according to the invention.According to the invention, an electrochemical gas sensor 100 (also referred to merely as gas sensor 100) is provided. Such a gas sensor 100 is schematically illustrated in cross section in FIG. 1.The gas sensor 100 is suitable for determining a concentration of phosphine in a measurement gas and has, for this purpose, a working electrode 20, a counter electrode 40 and a reference electrode 30, the reference electrode 30 being inert with respect to phosphine.The gas sensor 100 can further comprise a sensor housing 10, within which the mentioned electrodes are accommodated.The gas sensor 100 may be outwardly bounded by a first diffusion membrane 51 and / or by a second diffusion membrane 52, which is not required.The gas sensor 100 may include a number of separators 61, 62, for example, a first separator 61 and a second separator 62, to space the electrodes 20, 30, 40 apart from each other.The relative arrangement of the electrodes 20, 30, 40 with respect to one another can be substantially arbitrary. In the illustrated example, the working electrode 20 and the counter electrode 40 are disposed on opposite sides of the gas sensor 100, with the reference electrode 30 being disposed between the working electrode 20 and the counter electrode 40.In the exemplary embodiment shown in FIG. 1, the reference electrode 30 can comprise ruthenium oxide as electrode material. Additionally or alternatively, in the exemplary embodiment shown in FIG. 1, the working electrode 20 can comprise gold and / or platinum as electrode material.It is shown in FIG. 1 that the gas sensor 100 preferably does not comprise any further working electrode.It is shown in FIG. 1 that the reference electrode 30 is preferably surrounded on at least two sides by a protective layer 31, wherein the protective layer 31 is impermeable to phosphine. In the example shown, the reference electrode 30 is further preferably enclosed by the protective layer 31 from three sides, which can thus form a kind of pocket in order to accommodate the reference electrode 30.Not shown is that the gas sensor 100 can accommodate an electrolyte.FIG. 2 shows a gas measuring device 200 according to the invention for determining a concentration of phosphine in a measurement gas in a schematic manner.The gas measurement device 200 comprises: a previously described electrochemical gas sensor 100, a control unit 210 for operating the electrochemical gas sensor 100, a power source 220, such as a battery or an accumulator, for supplying the gas measurement device 100 with power, and optionally a wireless interface 230 for providing the determined concentration of phosphine.The gas meter 200 may further comprise a housing, such as a two-part housing with a first housing part 241 and with a second housing part 242, as shown. The first housing part 241 and the second housing part 242 may be configured to be separable to interchangeably accommodate the gas sensor 100 in the gas meter 200. The gas measuring device 200 can furthermore have a fluidic interface 243, through which the gas sensor 100 can enter into fluidic connection with the environment. The fluidic interface 243 can be configured, for example, as one opening or a plurality of openings in the second housing part 242.The control unit 210, the gas sensor 100 and the energy source 220 can be in electrical and / or signal communication.If, as illustrated, a wireless interface 230 is provided as an element of the gas measurement device 200, this can be configured to transmit the determined concentration of phosphine to a receiver by means of electromagnetic radiation 231, for example by means of Bluetooth or WLAN.FIG. 3 shows a schematic flow chart of a method 300 according to the invention for determining a concentration of phosphine in a measurement gas.The method 300 comprises the steps of:S 1 providing a number of gas measurement devices 200 described above in an environment containing measurement gas,S2 Continuously determining the concentration of phosphine in the environment of the gas meter 200,S3 Providing the determined concentration of phosphine, preferably via wireless interface 230.Preferably, the specific concentration of phosphine is provided in real time.The method 300 can further preferably comprise the steps of:S 4 determining a position of the number of gas measurement devices 200 relative to the environment of the gas measurement device 200, andS5 Providing the layer, preferably via the wireless interface 230.Steps S 1, S 2,... of the method 300 may be performed in the order indicated, and this is not required. Also, sequential execution of the steps is not required. Thus, some or all of the steps may also be performed in parallel. For example, steps S 4 and S 5 may be performed before steps S 2 and S 3 or simultaneously with steps S 2 and S 3.All features described herein can be combined with one another as desired, insofar as this does not relate to alternatives or is conflicting.List of reference characters10 Sensor housing 20 Working electrode 30 Reference electrode 31 Protective layer 40 Counter electrode 51 First diffusion membrane 52 Second diffusion membrane 61 First separator 62 Second separator 100 Electrochemical gas sensor, gas sensor 200 Gas measuring device 210 Control unit 220 Energy source 230 Data-technology interface 231 Electromagnetic radiation 241 First housing part 242 Second housing part 243 Flow-technology interface 300 Method S 1, S 2... Method stepsReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedU.S. Pat. No. 5,997,706 A

[0006] EP 0 436 148 B1

[0006] DE 19 832 395 C1

[0006] KR 2020 0 082 563 A

[0007] DE 19 939 011 C1

[0008] DE 10 159 616 B4

[0009]

Claims

Electrochemical gas sensor (100) for determining a concentration of phosphine in a measurement gas, comprising: - a working electrode (20), - a counter electrode (40), and - a reference electrode (30), wherein the reference electrode (30) is inert with respect to phosphine.The electrochemical gas sensor (100) according to claim 1, wherein the reference electrode (30) comprises ruthenium oxide as an electrode material.Electrochemical gas sensor (100) according to Claim 1 or 2, wherein the working electrode (20) comprises gold and / or platinum as electrode material.Electrochemical gas sensor (100) according to one of the preceding claims, wherein the gas sensor (100) does not comprise any further working electrode.Electrochemical gas sensor (100) according to one of the preceding claims, wherein the reference electrode (30) is surrounded on at least two sides by a protective layer (31), wherein the protective layer (31) is impermeable to phosphine.The electrochemical gas sensor (100) according to claim 5, wherein the protective layer (31) is formed of polyvinylidene fluoride.Gas measuring device (200) for determining a concentration of phosphine in a measurement gas, comprising: - an electrochemical gas sensor (100) according to one of the preceding claims, - a control unit (210) for operating the electrochemical gas sensor (100), - an energy source (220) for supplying the gas measuring device (100) with energy, and - optionally a wireless interface (230) for providing the determined concentration of phosphine.Method (300) for determining a concentration of phosphine in a measurement gas, comprising the steps of: - (S1) providing a number of gas measurement devices (200) according to claim 7 in an environment with measurement gas, - (S2) continuously determining the concentration of phosphine in the environment of the gas measurement device (200), - (S3) providing the concentration of phosphine, preferably via the wireless interface (230).The method (300) of claim 8, wherein the providing of the determined concentration of phosphine is in real time.The method (300) according to claim 8 or 9, wherein the method (300) further comprises the steps of: - (S4) determining a location of the number of gas measurement devices (200) relative to the environment of the gas measurement device (200), and - (S5) providing the location, preferably via the wireless interface (230).

Images