Solid-state CO gas sensor

Qi Xin, vibration-zhangwei, Xu, liuxinyu

(China electronics technology group Corporation, Harbin Institute of forty 150001)

1 Introduction

Carbon monoxide (CO) is a colorless, odorless gas that it on animals and humans are highly toxic.

CO reaches 400 × 10-6 volume fractions after 1 ~ 2 h a headache, nausea; reaches 1600 × 10-6 volume fraction, 20 min after feel headache, dizziness, after 1 h would result in death.

CO gas detection means a lot, use of potentials, the electric current, electric conductivity, light refraction, absorption of light wavelength, physical properties testing of physical sensors; the use of chemical, electrochemical reaction, chemical adsorption, chemiluminescence, etc. for testing chemical sensor.

Electrochemical gas sensors with a variety of gas, the concentration of the wide, small size, low price, high precision, can be used at the scene detection, etc., in environmental monitoring and safety, and other areas has been widely applied. At present, in the international market have Japan Riken keiki co., of New Cosmos Electvic company, Germany Drager, Gastech co., United Kingdom United States City Corporation production CO sensor. Domestic in gas sensors, relatively late, even though you have done some work, and international peers still have a long way to go.

Because traditional electrochemical gas sensors use a liquid electrolyte, and electrolyte evaporation or pollution causes the sensor signal decline, short life, in General, life is only about a year.

In order to avoid an aqueous solution of these problems caused by the electrolyte, people naturally will turn our attention to the solid electrolyte. The introduction of solid electrolyte, makes traditional electrochemical gas sensors has entered a new era. Currently, using the same form with polymers manufacture electrolyte (SPE) has become the electrochemical sensor electrochemical gas sensors on the international hot spots. This article uses Nafion membranes developed solid CO gas sensor (sensor), the catalyst and process issues a series of research and improvement.

2 works

With the proliferation of air flows through the CO sensor into electrolyzers, in constant potential working electrode on oxidation, at the same time in the electrode on the reduction, oxidation and reduction reactions to produce the appropriate limit diffusion current, its size and the CO concentration is proportional to the

Type: I-solid state diffusion current; z is the number of electronic transfer; F to Faraday constant; s is the reaction area; D to diffusion constants; δ diffusion layer thickness; C to be logging CO of volume fraction.

In working conditions, Z, F, D, δ 5, are constant, therefore, measured diffusion current I, to get the volume fraction CO.

3 electrodes activation technology research

The sensor's sensitivity and response time depends on the working electrode and work on the electrodes, electrodes and electrode performance is determined by the activity of noble metal catalysts, enhance the activity of noble metal catalyst is the technology critical, therefore, for the activation process of a series of improvements.

Currently, the most common is the aqueous acid direct reduction of gold is gold nanoparticles.

This article on this approach have been improved choice of thiol compounds as ligand-stabilized gold nano-particles, and join the citrate and amphiphilic surfactants, by changing the stabilizer and gold compounds have granular controllable gold nanoparticles. This highly active catalyst preparation out of the high catalytic activity of electrodes, the AFM scanner as shown in Figure 1.

4 liquid electrolyte curing technology research

Sensor life decisions by electrolyte liquid electrolyte dry faster, easier leak, hard seal, therefore, to extend the life of the sensor, the key to curing electrolyte is technology.

Currently, the solid electrolyte consists of inorganic solid electrolyte and polymer electrolyte. Some liquid polymer electrolyte membrane exists (e.g. wettability of Nafion membranes) conductivity is relatively high, but it also increases the use of additional conditions: you must control the external environment of humidity and temperature. Use impregnation Nafion membranes electrolyte, through control of response time and temperature to form different moisture content of Nafion membranes electrolyte. Because water is Nafion membranes and branched-chain acid hydrogen bonding formation of foundations (Figure 2), tightly locked in Nafion membranes internal structure, solid electrolyte is Nafion membranes. At the same time, against the Nation film processing moisturizing process problem carried out a series of explorations, solved the curing of this technology the key electrolytes.

　　

　　

5-jamming the sensor, rugged technology

Sensor life affected by the use of environmental impact.

In order to resist cross interference, high gas, low temperature, humidity, shock, vibration, etc, in terms of structure, circuit design. Sensor electrode structure and increase of a subsidy (Figure 3), atmospheric O2 and Nafion membranes electrolyte of H + synthesis of H2O, grant electrode atmospheric disruptors H2 into H +, the formation of Nafion membranes electrolytes from the water, then, has been plagued by Nafion membranes electrolyte — due to long working hours and lack of water, also solved.

　　

　　

Because the sensor electrode materials using precious metals, in high concentration of gas catalyst poisoning occurs, to avoid reference electrode poisoning, the sensor incorporates a duanfeng dead cylindrical structure, so the reference electrode is not wetted and keep potential constant.

According to the requirements of the working principle, working electrode to maintain a constant to a potential value of (relative to the reference electrode potentials) before normal

Work. How to maintain a constant working electrode potentials is vital in this design, this can be achieved through the operational amplifier. Adjust the potentiometer to select a given potential. Operational amplifier in differential mode, when the in-phase input and RP is the same as the input voltage, output is zero potential, thus ensuring the electrode potential constant at around 300 mV.

6 conclusion

This sensor in 0 ~ 500 × 10-6 volume fraction, sensitivity than 0 μ A/10-6 volume fraction, signal loss rate of 1 per cent.

Use Nafion membranes developed all-solid-state-controlled potential electrolysis of co gas sensor, its performance is all liquid CO gas sensor is raising its service life and signal stability greatly improved for electrochemical sensors to miniaturized, long life in the direction of the had useful exploration.