Abstract
The rapid development of science, technology, and engineering in the 21st century has offered a remarkable rise in our living standards. However, at the same time, serious environmental issues have emerged, such as acid rain and the greenhouse effect, which are associated with the ever-increasing need for energy consumption, 85% of which comes from fossil fuels combustion. From this combustion process, except for energy, the main greenhouse gases-carbon dioxide and steam-are produced. Moreover, during industrial processes, many hazardous gases are emitted. For this reason, gas-detecting devices, such as electrochemical gas sensors able to analyze the composition of a target atmosphere in real time, are important for further improving our living quality. Such devices can help address environmental issues and inform us about the presence of dangerous gases. Furthermore, as non-renewable energy sources run out, there is a need for energy saving. By analyzing the composition of combustion emissions of automobiles or industries, combustion processes can be optimized. This review deals with electrochemical gas sensors based on solid oxide electrolytes, which are employed for the detection of hazardous gasses at high temperatures and aggressive environments. The fundamentals, the principle of operation, and the configuration of potentiometric, amperometric, combined (amperometric-potentiometric), and mixed-potential gas sensors are presented. Moreover, the results of previous studies on carbon oxides (COx), nitrogen oxides (NOx), hydrogen (H2), oxygen (O2), ammonia (NH3), and humidity (steam) electrochemical sensors are reported and discussed. Emphasis is given to sensors based on oxygen ion and proton-conducting electrolytes.
Highlights
In many industrial fields, such as metallurgy, nuclear or thermal power plants, and the petrochemical industry, high temperatures are required
We provide the principle of operation and the configuration of the types of solid oxide gas sensors, followed by a discussion on the results of previous studies dealing with the detection of several gasses (H2, O2, carbon oxides (COx), nitrogen oxides (NOx), NH3, and steam) at high temperatures and harsh operating environments
All the discussed gas sensors were designed for operation at intermediate or high temperatures, and they are based on oxide ion-conducting electrolytes and proton-conducting electrolytes
Summary
In many industrial fields, such as metallurgy, nuclear or thermal power plants, and the petrochemical industry, high temperatures are required. EGSs, among other gas sensing technologies, seem to be the most promising technology, offering simple design and operation, high sensitivity, real-time response, and the possibility of miniaturization even in really difficult environments The output of these sensors is an electrical signal that directly provides information about the measured chemical compounds. Regardless of the type, in EGS, system functionality is based mainly on the solid oxide electrolyte separating the two electrodes and offering the required ionic conductivity, combined with thermal, mechanical, and thermodynamic stability in harsh operating environments. We provide the principle of operation and the configuration of the types (potentiometric, amperometric, combined, and mixed potential) of solid oxide gas sensors, followed by a discussion on the results of previous studies dealing with the detection of several gasses (H2 , O2 , COx , NOx , NH3 , and steam) at high temperatures and harsh operating environments. Our presentation focuses on sensors based on proton-conducting and oxygen ion electrolytes
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