I am trying to compute the Nernst Potential of a 80C (353K) PEM fuel cell operating at 1 bar (100 kPs). I am going to be operating the cell with pure H2 and ambient air (not pure O2). The standard pressure Nernst potential at 80C is 1.18 V.

Since I am operating with pure H2, then I assumed the mole fraction of that is 1 and the mole fraction of the oxygen is 0.21 since air is 21% oxygen.

When I went to go calculate the nernst Potential, I am getting something above the standard nernst potential which shouldnt be happening. The calculation I am using is

E = E0 + (R*T/2F)*ln(PH2*sqrt(PO2)/PH2O)

With the mole fractions, the partial pressures of H2, O2, and H2O are 100 kPa, 21 kPa, and 100 kPa, respectively. I keep getting a Nernst potential of 1.20 V which is higher than the standard Nernst Potential