CN107991366B

CN107991366B - Anti-interference quick-response breath hydrogen sensor

Info

Publication number: CN107991366B
Application number: CN201711249024.0A
Authority: CN
Inventors: 方馨; 郑李纯; 韩杰
Original assignee: Wuxi Sunvou Medical Electronics Co ltd
Current assignee: Wuxi Sunvou Medical Electronics Co ltd
Priority date: 2017-12-01
Filing date: 2017-12-01
Publication date: 2020-05-08
Anticipated expiration: 2037-12-01
Also published as: CN107991366A

Abstract

The invention provides a high-stability and anti-interference hydrogen electrochemical sensor taking Pt-Ir noble metal alloy nanoparticles and a three-dimensional porous graphene compound as sensing electrode materials. The sensor comprises a shell, a gas detection unit and a gas filtering device. The gas detection unit comprises a working electrode, a counter electrode, a reference electrode and electrolyte. The sensor is mainly used for detecting the concentration of hydrogen in oral expiration, and has the advantages of high sensitivity, interference resistance, short response time and high stability.

Description

Anti-interference quick-response breath hydrogen sensor

Technical Field

The invention relates to the field of gas sensors, in particular to an anti-interference and fast-response breath hydrogen sensor.

Background

Exhaled hydrogen is a gas that is metabolized by intestinal bacteria to produce exhaled gas through the lungs. The expiratory hydrogen concentration is normally in the order of 0-1ppm, but can be obviously increased by more than 20ppm under pathological conditions such as small intestine bacterial overgrowth and the like. Therefore, the breath hydrogen test was proposed and used to detect gastrointestinal disorders as early as 80 s in the last century. Currently, the commercial breath hydrogen measurement technology mainly includes two types, one is a gas chromatography instrument based on gas chromatography column gas separation and solid state sensor detection of U.S. QUINTRON, and the other is a portable or handheld product based on electrochemical hydrogen sensor of multi-family companies in europe and america. The biggest current drawbacks of these techniques include:

(1) the sensor has poor anti-interference capability and stability on CO and other expiratory components and humidity, and an operator must frequently use a gas distribution steel cylinder to check and calibrate and perform daily maintenance on an instrument;

(2) the sensor has long response time, needs longer expiration and analysis time, and has poor fit of the subject.

For the above reasons, commercial products have been marketed for over 30 years, but have not yet gained widespread clinical use, and such a technique is generally called "hydrogen breath test" clinically. In fact, these commercial breath test products employ electrochemical hydrogen sensors primarily from british urban technology, british ALPHASENSE or MEMBRAPOR, switzerland. The response time of these sensors is typically over 40 seconds, the level of CO interference can reach 20% even with CO filters, and there is a zero drift equivalent to a 10-35ppm hydrogen detected concentration.

Through patent and literature search, a sensor which is specially used for and meets the breath hydrogen detection requirement is not found at present. Although recent patents, such as CN106596684, US20150247818, CN 104483365, etc., disclose techniques that can improve the performance of existing hydrogen sensors, these techniques are mainly used for industrial and environmental gas detection, and neither solve or simultaneously solve the two problems presented above for the exhaled hydrogen test.

The invention aims to develop an electrochemical sensor suitable for testing hydrogen in expiration, and solves the problems of poor anti-interference capability, long response time and frequent calibration and maintenance in the prior art.

Disclosure of Invention

The invention aims to provide an anti-interference quick-response and high-stability breath hydrogen electrochemical gas sensor which is mainly used for detecting the concentration of hydrogen in human exhaled breath.

In electrochemical gas sensors, the first thing that determines the sensitivity, stability and selectivity of gas detection is the catalytic activity and stability of the electrode material. At present, most of electrochemical sensor electrodes are made of materials such as carbon black, graphite, activated carbon, carbon fiber and the like, wherein noble metal catalysts are loaded on conductive carbon particles. Because the surface effect of the catalyst requires that the surface area of the catalyst is as large as possible, it is necessary to support the catalyst on the surface of an electrically conductive support material with a large surface area to fully exert the catalytic function of the catalyst. Although the carbon powder can provide a large specific surface, the electrical activity is limited and the property is unstable; although the catalytic activity of the noble metal nano-particles is high, the agglomeration is easy to occur in the preparation process of the electrode. Therefore, the preparation of the electrode material with high and stable activity is the key for preparing the sensor with high stability, high sensitivity and good selectivity. At the same time, the stability, sensitivity and selectivity are very challenging.

Among carbon materials, graphene is attracting attention because of its unique advantages such as large specific surface area, good electronic conductivity and mechanical properties. Precious metal nanoparticles and graphene composite materials are used as sensing electrodes of electrochemical gas sensing and are only reported, and a patent CN 104483365 disclosed previously proposes an electrochemical gas sensor using precious metal and graphene composite materials as sensing electrodes, but two-dimensional sheet graphene is adopted, the structure is unstable, the graphite structure is easy to accumulate, the specific surface is reduced rapidly, and the requirements of an expiratory hydrogen test cannot be met.

Different from two-dimensional graphene, three-dimensional graphene is a graphene material with a space porous structure formed by further assembling traditional two-dimensional graphene sheet materials, and has the advantages of larger specific surface area, higher mechanical strength, more active sites and faster proton transfer. The porous graphene structure mainly comprises a graphene nano mesh structure (GNM) (namely a porous structure of a graphene sheet layer), a folded graphene structure (CG) and a graphene network framework structure (GF) (the graphene sheet layer is used as a framework unit framework), and the prepared three-dimensional graphene nanospheres can be connected with one another to form the porous three-dimensional nano structure.

Three-dimensional graphene can be synthesized by various methods such as a hydrothermal method, a chemical reduction method, a photoelectric plasma scoring technology and a template control chemical vapor deposition method. However, how to precisely control the shape and size of the porous graphene pores to maintain the structural stability and high electron conduction performance significantly affects the performance of the final electrode.

The three-dimensional graphene is prepared by a template-optimized control chemical vapor deposition method, the nickel powder is preferably selected to replace the traditional foam nickel to be used as a catalyst and a template, and the three-dimensional graphene with required pore diameter and required size network is obtained by selecting a proper carbon source, controlling the reaction temperature, time, the concentration of an etching solvent and the like. Through continuous trials, the optimal conditions of the method are that a gaseous carbon source CH4 is selected as a carbon source, the reaction temperature is 900 ℃, the etching solvent is HCl solution, the concentration is 6M, and the graphene prepared under the conditions has a small pore size and high-quality graphene with a more refined three-dimensional network.

Many documents show that the composite noble metal has higher catalytic activity than a single metal, the Pt nano particles are catalysts with higher activity, the Pt and second metal particles (such as iridium, gold, rhodium, ruthenium, palladium, silver and the like) form alloy particles, the Pt content in the Pt-based catalyst can be reduced, the catalytic activity of the Pt-based catalyst can be obviously improved, and in addition, the catalyst availability can be greatly improved by selecting a carrier material with large specific surface area, the uniform dispersion of the catalyst particles is facilitated, the catalytic activity is improved, and the sensitivity is further improved. The Pt-Ir noble metal alloy is preferred as the catalyst in the present invention because of the strongest stability of Ir nanoparticles among these noble metal nanoparticles. In addition, the catalytic carrier of the Pt-Ir alloy nano particles is three-dimensional porous graphene, and the porous graphene has a larger contact area, so that the diffusion and gas transmission of chemical substances in the reaction process are facilitated, the large specific surface area is favorable for the uniform dispersion of the Pt-Ir alloy nano particles, and in addition, the graphene is not easy to be corroded by electrochemistry and dissolved by active elements.

The Pt-Ir alloy nanoparticles uniformly loaded on the surface of the three-dimensional porous graphene are prepared by a simple and rapid one-step wet chemical method. The dispersion degree and size of the alloy nanoparticles on the surface of the three-dimensional graphene can be controlled by selecting a proper reducing agent, and controlling the concentration ratio, temperature, time and pH value of each substance. The morphology is greatly influenced in the synthesis process of the Pt-Ir alloy nano particles and the three-dimensional graphene compound by selecting a proper reducing agent, hydrazine hydrate with mild reducing capability is preferred, and the prepared alloy nano particles have regular structures with uniform sizes. In addition, in order to prepare high-quality uniformly-dispersed and morphologically-regular NaNO alloy particles, a proper amount of structure directing agent NaNO2 and dispersant polyvinylpyrrolidone (PVP) need to be added, and the NaNO particles which are uniformly dispersed and have uniform appearances cannot be generated when the amount is large or small. When 5wt% of NaNO2 and 0.25wt% of PVP are adopted, the Pt-Ir alloy nanoparticle material which is uniformly loaded on the surface of the three-dimensional graphene and has a regular morphology is prepared, the particle size is lower than 20nm, and the Pt-Ir alloy nanoparticle material has high catalytic activity and good stability.

Adding a proper amount of binder, diluent and the like into the Pt-Ir alloy nano particles and the three-dimensional graphene compound, fully mixing, silk-screening slurry formed by ball milling on an electrode film by using a silk-screen printing method, and then sintering. The temperature program for sintering the electrode is very important, and the preferred temperature range of the present invention is 50-200 degrees.

Gas filtration devices may also be used to further increase the interference rejection capability of the sensor. The packing material can selectively adsorb CO, thereby increasing the selectivity of the sensor. The adsorbent, which preferably has a higher adsorption capacity for CO, may be a metal oxide or metal salt, such as copper, silver or tin salts or oxides and mixtures thereof impregnated or exchanged on activated carbon, alumina or zeolites. Because the selected adsorbent has high adsorption efficiency on CO, and the concentration of CO in the human mouth expiration is lower than 7ppm for non-smokers and rarely exceeds 30ppm for heavy smokers. Considering the filtering requirement of 50ppm, selecting proper CO filtering material, filling volume and filling porosity can reduce the interference of CO and make H2 small molecule diffuse to the electrode surface through the main flow of expiration to generate electrode reaction. It is common practice to provide a dense CO filter membrane in the sensor package, which also increases the response time of the hydrogen. Therefore, aiming at the breath hydrogen test, the filter layer formed by the activated alumina desiccant with CO filtering and dehumidifying effects is preferably arranged at the air inlet of the sensor, so that the effects of CO interference resistance and humidity resistance are achieved, the response time of the breath hydrogen diffusing into the sensor is not influenced, and the replacement is convenient.

The gas sensor of the present invention may be packaged and connected to an external sensing circuit using the structure and method of a three-electrode electrochemical sensor. The packaged sensor must be processed according to the aging process used for electrochemical sensors before use. The test proves that the breath hydrogen sensor has the response time of about 10s and has the long-term moisture resistance and CO interference resistance.

Compared with the prior art, the invention has the following advantages:

(1) the sensor has strong anti-interference capability on CO and other expiratory molecules and humidity, has good stability, and does not need to be calibrated frequently;

(2) the sensor has fast response, T90 is only about 10s, the required expiration and analysis time is short, and the application is convenient.

Drawings

Fig. 1 is a schematic structural view of an expiratory hydrogen sensor of the invention.

Fig. 2 is a graph of the response of the present invention expiratory hydrogen sensor to H2.

DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION

The invention will now be further described with reference to the accompanying drawings and specific embodiments.

As shown in fig. 1, the electrochemical sensor for hydrogen in expiration comprises a housing 10, a gas detection unit 20 disposed in the housing 10, the gas detection unit 20 comprising a working electrode 21, a counter electrode 22, a reference electrode 23 and an electrolyte 24, and a gas filtering device 60 located at an air inlet.

An air inlet 50 is formed on the left side of the top end of the sensor housing 10, so that the inside of the housing 10 can be communicated with the external environment, and the aperture of the air inlet can control the sensitivity of the sensor. An air outlet 70 is formed on the right side of the top end of the sensor housing 10, and the air outlet is made of a waterproof and breathable film. A small hole 80 is formed in the bottom of the housing 10 for the passage of electrolyte during the sensor manufacturing process, as well as for the supply of oxygen and to accelerate the sensor to equilibrate with the ambient pressure. However, in the invention, because the sensor is used for measuring the hydrogen in the exhaled breath of a human body, the measuring range is small, O2 is contained in the exhaled breath of the mouth, and finally the small hole can be blocked, the pollution of the external environment is isolated, the cleanliness of the sensor is improved, and the sensor is more stable. The material of the sensor shell can be ABS plastic, PP plastic, PC plastic and the like.

Electrolyte 24 in the interior cavity of housing 10 is H2SO4, preferably H2SO4 at a concentration of 3-7M. The bottom surface of the housing 10 is provided with pins 90, and the pins 90 are respectively connected with the working electrode 21, the counter electrode 22 and the reference electrode 23, and are used for being conducted with an external circuit, outputting and transmitting a sensor signal to the external circuit.

The working electrode 21, the counter electrode 22 and the reference electrode 23 are separated by

liquid absorption films

30 and 40 to prevent the electrodes from contacting with each other, and the electrodes can be soaked by the absorbed electrolyte to realize the proton transfer among the electrodes. The liquid-absorbing film may be glass fiber, carbon fiber, etc.

The working electrode, the counter electrode and the reference electrode are made of the same material and are all gas diffusion electrodes. The three-electrode material adopts a compound of Pt-Ir alloy nano particles and three-dimensional graphene as a catalytic material, a certain diluent such as ethylene glycol and a proper amount of binder such as Nafion solution are added, and the mixture is mixed uniformly and ball-milled into slurry with proper viscosity and then is printed on an electrode film by a screen printing method. The electrode membrane is preferably a porous, gas permeable material, such as a PTFE membrane. And then sintering the electrode by adopting a temperature programming mode, wherein the temperature programming is adopted in the sintering process and is increased from 50 ℃ to 200 ℃. And then shearing the prepared electrode, assembling the electrode into a sensor shell according to the structure shown in the figure 1, adding 6M H2SO4 electrolyte, carrying out final packaging, and finally plugging the bottom small hole and dispensing to block the small hole. The small hole at the bottom is plugged, so that the sensor can be isolated from the external environment, the cleanliness is higher, and the sensor is more stable.

According to the invention, the gas filtering device 60 is arranged at the gas inlet 50 of the sensor, the internal filling material can selectively adsorb CO, preferably metal oxide or metal salt with high adsorption capacity to CO, and in order to simultaneously remove the interference of moisture in the breath, the gas filtering device is preferably formed by a way of impregnating copper salt on the surface of an activated alumina desiccant. The method has remarkable CO interference resistance and humidity resistance, and does not influence the response time of H2.

Specific embodiments are designed to illustrate the present invention in more detail.

Example one

This example demonstrates how the electrochemical H2 sensor shown in fig. 1 can be prepared as described in the summary of the invention.

The three-dimensional porous graphene is prepared by using nickel powder as a catalyst and a template and combining a chemical vapor deposition technology. Weighing a proper amount of nickel powder, paving the nickel powder in a ceramic boat treated by acetone and alcohol, and placing the ceramic boat in a heating zone of a tube furnace. And (3) pumping out the air in the tube, flushing the inner pressure of the tube to normal pressure by using argon, opening a valve, and continuously introducing the argon to maintain the inert atmosphere until the reaction is finished. Under the protection of argon, the temperature of the tube furnace is increased to 900 ℃ at the speed of 30 ℃/min, hydrogen is introduced in the temperature increasing process, after the temperature reaches 900 ℃, the temperature is kept, and the nickel powder is annealed for 25 min. After annealing, the temperature was maintained continuously and the hydrogen was turned off. Carbon source was introduced, where the methane gas valve was opened, as per CH 4: and introducing Ar into the tubular furnace at a flow ratio of 40:200sccm until the reaction is finished, wherein the reaction time is 30 min. And finally, taking out the nickel powder after the chemical vapor deposition growth, etching the nickel powder by using a 6M HCL solution, and repeatedly replacing the hydrochloric acid solution until the three-dimensional porous graphene is suspended to the liquid level. And then, repeatedly carrying out suction filtration and cleaning, taking out the three-dimensional porous graphene, and drying in a drying oven to obtain the three-dimensional powder graphene.

The Pt-Ir alloy nanoparticle and three-dimensional porous graphene composite are prepared as follows: according to the weight ratio of platinum: chloroplatinic acid, chloroiridic acid and an appropriate amount of NaNO2 were added to a continuously stirred solution containing polyvinylpyrrolidone (PVP) (0.25 wt%) and 2mg of the above-prepared three-dimensional graphene at an iridium molar mass ratio of 0.9:1, and the pH was adjusted to 12 with a 1M NaOH solution. Subsequently, the mixture was stirred continuously in an ice bath, and after adding an appropriate amount of hydrazine hydrate (80 wt%), stirring was continued in the ice bath for 30 min. Finally, the precipitate was collected by centrifugation and washed thoroughly with ethanol and water until PVP-free. And finally, drying in a vacuum box to obtain the three-dimensional graphene composite material with the surface loaded with the Pt-Ir composite noble metal nano particles. The above reagents are all purchased from the chemical pure products of the fine chemicals of supemarrhui.

Then, three electrodes are prepared by adopting a screen printing mode. Weighing a certain amount of Pt-Ir alloy nanoparticles and a three-dimensional graphene compound into a ball milling tank, adding a proper amount of ethylene glycol, ultrapure water (18.2M omega) and Nafion (20%) (Sigma), uniformly stirring, placing into a ball mill (QM-3 SP2 planetary ball mill, Nanjing university Instrument factory), setting a proper rotating speed and time, heating the obtained uniform slurry to a viscosity suitable for printing by using steam after the ball milling is finished, then silk-screening into electrodes on a screen printing machine, preparing porous electrodes serving as a working electrode, a counter electrode and a reference electrode respectively after temperature programming sintering at 50-200 ℃, and finally assembling into the electrochemical H2 sensor shown in figure 1 according to the implementation mode described above. Furthermore, a gas filtration device filled with an activated alumina desiccant surface-impregnated with tin salt was prepared, placed at the gas inlet of the sensor.

Example two

This example describes the preparation of 5H 2 sensors with and without gas filtration means, each for use in the standard H2 test, according to the method described in example one.

10H 2 sensors were aged with 0mV of working electrode relative to reference electrode for 14 days, after which the following performance tests were performed on 0mV biased aged plates:

a) the performance results of the test using the 5 sensors with the gas filtration device described above with air as carrier gas with 40ppm of standard H2 gas are shown in table 1. As can be seen from Table 1, the sensors all had T90 less than 15s and a resolution R less than 0.5 ppm. A typical response curve for a sensor is shown in the graph of fig. 2. The results show that the prepared H2 sensor with gas filtering device has high sensitivity, short response time and high precision.

TABLE 1 sensitivity, resolution and T90 of H2 sensor

b) 50ppm of CO standard gas is added into 10ppm of standard H2 gas distribution, the mixed gas and 10ppm of standard H2 are respectively introduced into 5 sensors (1 # -5 #) with gas filtering devices and 5 sensors (6 # -10 #) without gas filtering devices, and the test results are shown in Table 2. As can be seen from Table 2, 5H 2 sensors with gas filtering devices have strong anti-interference capability to CO, and the signal interference generated by 50ppm of standard CO gas is less than 2 ppm. While the 5H 2 sensors without the gas filtering device had a relatively clear response signal to CO, 50ppm CO produced an interference signal of 15-20 ppm. The gas filtering device arranged at the gas inlet of the sensor is filled with tin salt which selectively adsorbs CO, so that the CO gas entering the sensor is obviously reduced, and the selectivity is obviously improved.

TABLE 2 CO interference data for two H2 sensors

c) Standard H2 gas with a relative humidity of 40ppm and 90% was prepared by using air as carrier gas, and passed into 5 sensors (1 # -5 #) with gas filtering device and 5 sensors (6 # -10 #) without gas filtering device, respectively, and the test results are shown in Table 3. As can be seen from Table 3, the 5H 2 sensors with gas filtering devices have strong moisture resistance, and the humidity of 90RH% has no influence on the sensor response; while the 5H 2 sensors without the gas filtration unit were more affected by humidity, the baseline of the sensors was also affected, resulting in an increase in the test values. The air filtering device arranged at the air inlet of the sensor is provided with an active alumina desiccant, so that the interference of water molecules can be effectively removed, and the dehumidifying capacity is stronger. The sensor with the filtering device can effectively solve the influence caused by humidity.

Table 3 humidity effect data on H2 sensor

Claims

1. An anti-interference and fast-response breath hydrogen sensor comprises a sensor shell, a working electrode, a counter electrode, a reference electrode and a gas filtering device, wherein the working electrode, the counter electrode and the reference electrode are in ion conduction through electrolyte, and the sensor is characterized in that a catalytic material of the working electrode consists of noble metal alloy nano particles and a three-dimensional porous graphene composite material; the electrode materials of the reference electrode and the counter electrode are the same as those of the working electrode; the three-dimensional porous graphene composite material is prepared by adopting nickel powder as a catalyst and a template and combining a chemical vapor deposition method, and the specific process comprises the following steps:

1) weighing a proper amount of nickel powder into a ceramic boat treated by acetone and alcohol, paving the ceramic boat, placing the ceramic boat in a heating zone of a tube furnace, pumping out air in the tube, flushing the inner pressure of the tube to normal pressure by using argon, opening a valve, and continuously introducing the argon to maintain inert atmosphere until the reaction is finished;

2) under the protection of argon, heating the tube furnace to 900 ℃ at the speed of 30 ℃/min, introducing hydrogen in the heating process, keeping the temperature after the temperature reaches 900 ℃, and carrying out annealing treatment on the nickel powder for 25 min;

3) after annealing, continuously maintaining the temperature, and closing hydrogen;

4) carbon source was introduced, where the methane gas valve was opened, as per CH 4: introducing Ar into the tubular furnace at a flow ratio of 40:200sccm until the reaction is finished, wherein the reaction time is 30 min;

5) taking out the nickel powder after the chemical vapor deposition growth, etching the nickel powder by using a 6M HCL solution, and repeatedly replacing the hydrochloric acid solution until the three-dimensional porous graphene is suspended to the liquid level;

6) and repeatedly carrying out suction filtration and cleaning, taking out the three-dimensional porous graphene, and drying in a drying oven to obtain the three-dimensional powder graphene.

2. The anti-tamper fast-response exhaled hydrogen sensor of claim 1, wherein: the noble metal alloy nanoparticles and the noble metal alloy nanoparticles in the three-dimensional porous graphene composite catalytic material are Pt-Ir alloy nanoparticles; the Pt-Ir alloy nanoparticles and the three-dimensional porous graphene compound are uniformly dispersed on the surface of the three-dimensional porous graphene in a Pt-Ir alloy nanoparticle form with regular and uniform appearance by a one-step wet chemical method, and the particle size of the alloy nanoparticles is not more than 20 nm.

3. The anti-tamper fast-response exhaled hydrogen sensor of claim 2, wherein: the specific process for preparing the Pt-Ir alloy nano particles and the three-dimensional porous graphene compound by the one-step wet chemical method comprises the following steps:

1) according to the weight ratio of platinum: adding chloroplatinic acid, chloroiridic acid and an appropriate amount of NaNO2 to a continuously stirred solution containing 0.25wt% of polyvinylpyrrolidone and 2mg of the above-prepared three-dimensional graphene, adjusting the pH to 12 with a 1M NaOH solution, with iridium being in a molar mass ratio of 0.9: 1;

2) continuously stirring the mixed solution in an ice bath, adding a proper amount of 80 wt% hydrazine hydrate solution, and continuously stirring in the ice bath for 30 min;

3) centrifuging to collect precipitate, and fully washing with ethanol and water until no polyvinylpyrrolidone exists;

4) and drying in a vacuum box to obtain the three-dimensional graphene composite material with the surface loaded with the Pt-Ir composite noble metal nano particles.

4. The anti-tamper fast-response exhaled hydrogen sensor of claim 2, wherein: according to the Pt-Ir alloy nano-particle, Ir in the Pt-Ir alloy nano-particle is replaced by one of gold, rhodium, ruthenium, palladium and silver.

5. The anti-tamper fast-response exhaled hydrogen sensor of claim 1, wherein: the gas filtration device is used to dehumidify and remove CO with an efficiency that ensures that its residual content is insufficient to cause a signal detectable by the sensor.

6. The anti-tamper fast-response exhaled hydrogen sensor of claim 1, wherein: the gas filtering device is composed of an active alumina desiccant and a metal salt which is impregnated on the surface of the active alumina desiccant and selectively adsorbs CO, wherein the metal salt is one of copper, silver and tin salt.

7. The anti-tamper fast-response exhaled hydrogen sensor of claim 1, wherein: the gas filtering device is installed at a gas inlet of the sensor.