Electrolysis: processes – compositions used therein – and methods – Electrolytic analysis or testing – For oxygen or oxygen containing compound
Patent
1994-09-12
1996-07-23
Bell, Bruce F.
Electrolysis: processes, compositions used therein, and methods
Electrolytic analysis or testing
For oxygen or oxygen containing compound
2057825, 205783, 2057855, 205786, 2057835, 204415, 204431, 204432, 204421, 204414, 204430, 204412, 422 88, 422 98, G01N 2726
Patent
active
055386202
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The present invention concerns an electrochemical sensor with which to determine the concentration of hydrogen, carbon monoxide and silane, fluorine, bromine, iodine, oxygen, sulfur dioxide, methane, ethane, ethylene, acetylene and other gases. This sensor may be used for instance in the manufacture of portable, self-powered and easily operated apparatus to measure and monitor the gas concentration.
Gas concentration analyzers to continuously monitor the surrounding medium are widely used in many fields, for instance in automatic process control, in explosion protection, ecological checking etc. Such analyzers may be electrochemical sensors. A variety of sensor types for measurement and monitoring are known.
A known kind of sensor (N.I. Globa, Razrabotka i issledvoanie elektrochimicheskich datchikov konzentratsii kisloroda i vodoroda", author's dissertation paper Leningrad Institute of Technology, 1985, pp 11-14), contains a measuring electrode and an associated electrode both located in a liquid electrolyte. The measuring electrode consists in part or in whole of a catalytically active, ie a catalytic material. The associated electrode is made of a an electrochemically active material. If this material evinces low electrical conductivity, the associated electrode will be manufactured from a mixture of this material and carbon, the carbon increasing the electrical conductivity. Illustratively the associated electrode is made of a mixture of manganese dioxide and carbon in a hydrogen sensor and is made of lead in an oxygen sensor.
When a gas of which the concentration must be measured is fed to the sensor, electrochemical oxidation or reduction (for lead or manganese dioxide) of the electrochemically active associate-electrode material takes place. This 2-electrode system generates an electric current in an external electric circuit, the current magnitude being proportional to the gas concentration. This current magnitude can be taken as a measure of the gas concentration.
The active material of the associated electrode (lead or manganese dioxide) is consumed during the chemical reactions and consequently the sensor life is limited.
Spurious measurement signals may ensue by the surface of the associated electrode being passivated by products of chemical reactions taking place on this electrode and by reaction products diffusing toward the measuring electrode, whereby sensor reliability will be degraded. To prevent such effects, sensors operating on the above stated principle must be comparatively large and must contain high quantities of material.
Another known sensor for measuring gas concentrations (Japanese patent document A 59 28358) contains a measuring electrode made from a catalytic material, further an electrolyte and an associated electrode consisting of a mixture of carbon and of an electrochemically active organic substance such as chloroquinone or monomeric and polymeric iron- and cobalt-phthalocyanine. The electrochemically active substance acts as a catalyst in the electrochemical reduction of oxygen.
The gas concentration to be measured and fed to the sensor is oxidized at the measuring electrode. Accordingly atmospheric-oxygen reduction takes place at the associated electrode or electrode reduction of especially supplied oxygen, made possible by the active components (catalysts). The catalysts are alternatingly oxidized and reduced during sensor operation. However these two reactions are not wholly reversible and consequently the catalysts are consumed and sensor life is limited. Moreover sensor reliability is poor because the surface of the associated electrode may be passivated by the oxygen-reduction products and by their diffusion toward the measuring electrode. The sensor incurs a further drawback in that the liquid electrolyte may dry out. However using a solid electrolyte in such a sensor also entails difficulties because of the need to generate a four-phase boundary "carbon-catalyst-electrolyte-oxygen".
Another restriction on using sensors of the above kind is that they
REFERENCES:
patent: 4029563 (1977-06-01), Binder et al.
patent: 4662996 (1987-05-01), Venkatasetty
patent: 5215643 (1993-06-01), Kusanagi et al.
Bell Bruce F.
MST Micro-Sensor Technologie GmbH
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