Electrocatalysis of anodic oxygen-transfer reactions at modified lead dioxide electrodes

Abstract

Hsiao, Yun-Lin, "Electrocatalysis of anodic oxygen-transfer reactions at modified lead dioxide electrodes " (1990 INFORMATION TO USERSThe most advanced technology has been used to photograph and reproduce this manuscript from the microfihn master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type of computer printer.The quality of this gggdmctlom Is dependent upon the quality of the copy submitted. Brolm or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction.In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion.Oversize materials (e.g., maps, drawings, charts) are reproduced by sectioning the original, beginning at the upper left-hand corner and continuing from left to right in equal sections with small overlaps. Each original is also photographed in one exposure and is included in reduced form at the back of the book.Photographs included in the original manuscript have been reproduced xerographically in this copy. Higher quality 6" x 9" black and white photographic prints are available for any photographs or illustrations appearing in this copy for an additional charge. Contact UMI directly to order. Signature was redacted for privacy.Signature was redacted for privacy.Signature was redacted for privacy. Relation between 0-transfer and O2 Evolution 11The prerequisite for successful 0-transfer reaction Is proposed to be the anodic discharge of H2O to produce the adsorbed OH radicals (2). 3This process has been determined to be the rate limiting step for both O2 evolution and 0-transfer reactions (3). In the absence of solution reactants, O2 evolution from the electrode surface is the only reaction.The competition between the 0-transfer and O2 evolution for the adsorbed OH radicals can be described by the mechanism shown as follows. /V\ /V\Mechanism II This mechanism requires the adsorption of two OH radicals on one edge site (5). Edge-site Pb ions are in a low coordination state, so it is possible for two OH to adsorb. The mechanism for oxygen evolution on edge Pb is shown as followed. It has been reported that there is a greater charge donation to the electrode from the 0-atoms adsorbed on the edges and corners than on the faces of a SrFeOg anode (5). Also reported was that the activation energy for two oxygen atoms to combine to give site-on bonded O2 from an edge adsorbed O2 is less than 0.8 eV on a SrFeOg anode (5), but no data were reported for that at face sites. Although it needs to break two Pb-O bonds to form one O2 from the edge Pb rather than only one as from the face adsorbed 0-0, edge cations are still concluded to catalyze O2 7 evolution better than face cations (5). How to Modify Lead Dioxide Ele...