Potential of a Platinum Electrode at Low Partial Pressures of Hydrogen or Oxygen

The open‐circuit potential on bright platinum in 1 M H 2 SO 4 was measured as a function of oxygen or hydrogen partial pressure from 10 −2 to 10 −7 atm. The very low rates of H 2 or O 2 flow which were required were produced by a special gas generator. Potentials predicted by the Nernst equation for the H + /H 2 couple were not observed below 10 −4 atm H 2 partial pressure. A Nernst relation with a slope of 0.06 v/decade of oxygen partial pressure was found. The oxygen leak into the closed system used was found to be about 10 −7 atm. Based on the assumption that the resultant dissolved O 2 decreases the dissolved H 2 concentration in the solution at the electrode surface, an equation was developed for obtaining the effective H 2 partial pressure.