Hi!
I would like to know how does MQ135 gas sensor work, I mean, what is the electrolyte inside and the reference electrode. I was checking its datasheet, it says that MQ135 has a SnO2 layer for sensing, maybe as working electrode, Au as counter electrode and Pt as reference electrode, but I not sure. In my proyect, I´m working with NH3, ethanol, CO2 and Benzene.
Whatever you found, the sensing component of the MQ135 is the SnO2 layer. Interacting with reducing and oxidizing gases, the oxygen content increases resp. decreases - thus altering conductivity. (Don't think of it as SnO2 - think about SnO2+-x!)
Au may be used for bond pads, Pt to build the heater trace. None of these 2 has to do with the sensing properties.
Thanks for your help!
But, I have a doubt, the datasheet says that a Ni-Cr alloy serves as heater, and this sensor maybe works according to potentiometric principle, so, Pt could function as reference electrode.
Hello,
Pt is not used as a reference electrode - just as the electrode to make the contact with the SnO2. (At the same time acting as a diffusion barrier.)
My assumption was that they use it as well for the heater, because I know similar sensors that do that. But they are clearly free to choose NiCr for that. (Though this requires some more process steps etc.).
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