POTENTIAL OF A PLATINUM ELECTRODE AT LOW PARTIAL PRESSURES OF HYDROGEN AND OXYGEN. PART II. AN IMPROVED GAS-TIGHT SYSTEM WITH A NEGLIGIBLE OXYGEN LEAK.

A tight electrochemical system was constructed in which the O2 pressure PO2 above the cell solution was less than 10 to the 9th power atm. A comparison of the potentials obtained with this system with data from AD-624 024 shows that very small amounts of O2 leaking into a closed system can have marked effects on potential behavior at low H2 pressures PH2. Reduction of the O2 leak to negligible proportions showed that a the Nernst equilibrium relation for the HH2 couple holds only for PH2 in excess of 0.000001 atm b at PH2 less than 0.000001 atm, trace amounts of O2 even in the presence of several orders of magnitude more H2, acted as an electrode poison, causing a positive deviation from the theoretical Nernst behavior c in O2-free solution, at PH2 below 0.000001 atm, the potential remained at 0.18 v positive to the normal hydrogen electrode N.H.E. and was independent of PH2. The potential-determining reaction in this region may be an exchange of H in solution with H atoms dermasorbed in the Pt. The potential vs O2 partial pressure relation was essentially the same as found in previous work at this Laboratory. Residual hydrogen associated with Pt at potentials from 0.18 to 0.20 v did not react with oxygen. Author