The MG811 is an electrochemical sensor that measures $\ce{CO2}$. I think is something like a redox reaction but i don't understant how it produces $\ce{e-}$ so i can read them and get the $\ce{CO2}$ concentration.

I copy you the reaction that makes the sensor measures

When the sensor exposed to $\ce{CO2}$,the following electrodes reaction occurs:

Cathodic reaction: $\ce{2Li+ + CO2 + 1/2O2 + 2e- -> Li2CO3}$

Anodic reaction:$\ce{2Na+ + 1/2O2 + 2e- -> Na2O}$

Overall chemical reaction:$\ce{Li2CO3 + 2Na+ -> Na2O + 2Li+ + CO2}$

The datasheet says that it workings adopting the electrolyte cell Principle and that it's composed by the following cells:

Air,$\ce{Au}$|NASICON|| carbonate|$\ce{Au}$, air,$\ce{CO2}$

I need you to explain me how actually the sensor is working and with which material are made the electrodes.

  • 2
    $\begingroup$ This seems like a homework question. We ‎have a policy which states that you should show your thoughts and/or efforts into solving the ‎problem. It'll make us certain that we aren't doing your homework for you. Otherwise, this ‎question may get closed.‎ $\endgroup$
    – M.A.R.
    Jun 9, 2015 at 11:34

1 Answer 1


The link you gave in the question, actually shows the equation of how this sensor works. You don't need to produce any electrons, you just need to measure the voltage.

Try to write the Nernst equation for the above overall reaction and that will show you what is going on.

  • $\begingroup$ I meant how does the voltage measured is produced in the reaction. $\endgroup$
    – victor
    Jun 9, 2015 at 12:27
  • 1
    $\begingroup$ The potential in any electrochemical reaction is produced because the electron is more stable in some molecules than others. This creates an energy difference that we explain by using the concept of electrochemical potential. The Nernst equation describes the details of this potential. $\endgroup$ Jun 9, 2015 at 12:29
  • $\begingroup$ @Burak_Ulgut I got that last. So between Li2CO2 and Na2O there's a electrical potencial, righy? One more thing why in the cell structure says NASICON and AU but in the reaction Li2CO3 and 2Na? $\endgroup$
    – victor
    Jun 9, 2015 at 12:34

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