Understanding electrochemical and MOX sensors for gas measurement
Sensors play a crucial role in the detection and monitoring of various gases in industrial, environmental and consumer applications
Two widely used technologies are electrochemical and metal-oxide-semiconductor (MOX) sensors. They offer specific properties that are suitable for different requirements.
![[Translate to English:] Das Bild zeigt eine schematische Darstellung eines elektrochemischen Gassensors.](/fileadmin/_processed_/4/7/csm_elektrochem_sensoren_8b502fd0fb.png)
Schematic of an electrochemical gas sensor
The following diagram illustrates the most important components and how an electrochemical gas sensor works. Gases such as nitrogen monoxide (NO) pass through the gas membrane and trigger a reaction at the working electrode. The electrolyte (which contains H⁺ and SO₄² ions) facilitates the electrochemical reaction, while the reference and counter electrodes ensure an accurate measurement. The potentiostat measures the resulting current, which is proportional to the gas concentration.
![[Translate to English:] Komponenten und die Funktionsweise eines elektrochemischen Gassensors](/fileadmin/_processed_/3/d/csm_schema_elektrochem_sensoren_d938b1fbc8.png)
What are MOX sensors?
MOX stands for metal oxide semiconductor sensors, which detect gases through changes in resistance in a metal oxide material. The gases react with the oxygen adsorbed on the sensor surface and thus change the electrical resistance of the sensor.
- Frequently detected gases: Methane (CH₄), ammonia (NH₃), volatile organic compounds (VOCs), carbon monoxide (CO).
- Key features:
- Fast response times for real-time monitoring.
- Durable with a typical service life of 5-10 years.
- They are affordable and therefore ideal for consumer electronics.
![[Translate to English:] MOX-Sensor im konventionellen Modus und im Oberflächenionisationsmodus](/fileadmin/_processed_/5/2/csm_mox-sensor_modi_2534baaa8a.png "[Translate to English:] Abb. 3: MOX-Sensor im konventionellen Modus und im Oberflächenionisationsmodus")
Illustration credits
Abb. 1: Video "How do electrochemical-type sensors detect gas?" by Figaro Engineering
Fig. 2: Reproduced from Smith et al., 'Development of a baseline-temperature correction methodology for
electrochemical sensors and its implications for long-term stability', Sensors and Actuators B: Chemical, Volume 237, 2017, Pages 1161-1170, DOI: doi.org/10.1016/j.snb.2016.08.151, licensed under Creative Commons Attribution 4.0 International (CC BY 4.0).
Fig. 3: Reproduced from Gerhard Müller et al. 'Sensitivity-Selectivity Trade-Offs in Surface Ionization Gas Detection', Nanomaterials, 2018, 8(12), 1017, DOI: doi.org/10.3390/nano8121017. Licensed under Creative Commons Attribution (CC BY).
