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Fuel cell open circuit voltage and pressure of reactants

  1. Feb 8, 2015 #1

    I have some questions regarding the nernst equation at open circuit voltage.

    We know E(OCV) = E0+ ln (PH2*PO2^0.5 / PH2O)

    I have some trouble with this:
    If I have dry gas (both for O2 and H2), and my circuit is open at 25°C and 1 atm I have no water in the circuit so what become the nerst equation ? We have to neglect H2O?
    E(OCV) = E0+ ln (PH2*PO2^0.5 )

    I am wondering why at OCV we take into account water since we don't create water because the circuit is open, and the only way that we could have water is from the reactants?

    Thank you for yout help !
  2. jcsd
  3. Feb 8, 2015 #2


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    Staff: Mentor

    First time I hear about applying Nernst equation to a dry gas mixture. Are you sure you don't misread something and you don't deal with a solution, saturated with hydrogen and oxygen, each at 1 atm?
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