My problem is:

"In an electrochemical H_{2}-pump using a proton conductive membrane (pH ≈ 0), H_{2} can be compressed from low to high pressure. Assume an exchange current density of the HOR/HER on Pt of i_{0} = 100 mA cm_{-2 Pt} with α_{a} = α_{c} (charge transfer coefficient) = 0.5, a H_{2}-partial pressure of 100 kPa on the low and 1000 kPa on the high pressure side. The system is operated at 80 °C and the roughness factor of the electrodes is 100 cm^{2}_{Pt} cm^{-2}. The HFR (High Frequency Resistance) was determined to be 50 mΩ cm^{2}."

"What is the thermodynamic open circuit potential between the two electrodes?"

I have tried using Butler-Volmer or a Tafel Slope equation in order to find the Overpotential but I'm not really getting anywhere. I'm also guessing that Nernst may be involved. Any suggestions?