Mechanistic aspects of cathodic oxygen reduction

Abstract

An investigation of cathodic oxygen reduction in pure and contaminated solutions using the ring-disc technique showed:o(1)On Pt and Ag under clean conditions the four-electron reduction of O2 is operative, only small amounts of H2O2 are produced. In contaminated solution, a decrease of the catalytically active surface of Pt is observed, but on Ag the H2O2 formation significantly increases.(2)The two-electron reduction of O2 to H2O2 takes place only on Au and C. On Pt and Ag under clean conditions the four-electron reduction of O2 is operative, only small amounts of H2O2 are produced. In contaminated solution, a decrease of the catalytically active surface of Pt is observed, but on Ag the H2O2 formation significantly increases. The two-electron reduction of O2 to H2O2 takes place only on Au and C. The results are interpreted considering different models of the O2 adsorption. The different behaviour of Au and Ag, both having almost identical electronic and crystallographic structures, is explained on the basis of simple MO calculations. An influence of the metal ionization potential on the type of the reaction is postulated which might be generalized for sp-materials.