Electrochemistry of dissolved gases: II. Reduction of oxygen at platinum, palladium, nickel and other metal electrodes

Abstract

The reduction of dissolved oxygen has been studied at Pt, Pd, Ni, Ag, Au, Ta, W, Cu and Pb electrodes. Voltammetric and chronopotentiometric studies have established the effect of supporting electrolyte. solution-pH and electrode preconditioning upon the electrode reactions. Oxygen reduction at pre-oxidized metal electrodes is pH-dependcnt ; for the Pt, Pd and Ni electrodes the electrode reaction for oxygen reduction is M(OH) 2+ 2 e − → M + 2 OH-. The oxygen in solution re-oxidizes the electrode which is then re-reduced. The reduction of oxygen at all pre-oxidizcd metal electrodes except Ag and Au appears to occur by the same mechanism. The half-wave potential for oxygen reduction at pre-reduccd metal electrodes is −0.18 to −0.24 V vs. S.C.E, and is independent of pH ; hydrogen peroxide is the primary reduction product. A sequence of reactions is proposed to account for the formation of H 2O 2 in acidic solutions by a pH-independent mechanism. Potassium iodide causes the reduction of oxygen to become pH-indcpendent at Pt, Pd and Ni electrodes; the potential for reduction becomes dependent, however, upon iodide concentration. The formal reduction potentials for the Pt(OH) 2. Pd(OH) 2and Ni(OH) 2 electrodes in 0.1 F K 2SO 4 have been evaluated; the average values are −0.14, −0.19 and −0.74 V vs. N.H.E., respectively.