Bleidioxid als Lösungselektrode

Abstract

Eleki rochemie / Oherjlachenrrscheinurigeri i 0 .ridelektro& Die anodische Abscheidung und die kathodische Auflosung von Bleidioxid in schwachsauren Losungen hoher Bleiionenkonzentrationen auf inerten Basiselektroden aus Platin oder Graphit wurde in einer Modellzelle (gegen die Bleinegative), durch Lade/Entladekurven und mit t lilfe der langsamen z) klischen Voltammetrie untersucht. An frischen Basiselektroden werden bei hoheren Stromdichten Uberspannungen von iiber 300 mV in beiden Richtungen festgestellt. Die Elektronenzahl ist I im geschwindigkeitsbestimmenden Schritt. Bei diinnen Schichten und insbesondere bei mit Bleioxiden vorgelegten Basiselektroden sind die Uberspannungen in beiden Richtungen wesentlich geringer (50 -100 mV), und die Elektronenzahl ist 2. Es wird ein ausgepragter AnioneneinfluO festgestellt, wobei ClO;, NO, und HF, optimal sind. Die experimentellen Befunde fiihren zu einem Mechanismus fur die kathodische Auflosung. der in einem elektrocheniischcn Teilschritt, der protonenassistierten Reduktion \ton Pb4 ' -Ionen im Pb0,-Gitter. und einem langsamen chemischen Teilschriil. der protonenassistierten Auflosung des oberfllchlich gebildeten Pb(OH),, besteht. Wenn der zuletztgenannte Schritt zu langsam ist. kann sich eine Gelschicht an der Oberfliche ausbilden.We hiive investigated the anodic deposition and the cathodic dissolution of lead dioxide in weakly acid solutions of high lead ion concentrations onto inert base electrodes of platinium and graphite in a model cell (in connection with a lead negative electrode), by chargcldischarge curves and with the aid of slow cyclic voltammetry. With freshly prepared base electrodes and higher current densities, we have measured overvoltages of more than 300 mV in both directions. The electron number was I in the rate defermining step. With thin I;iyers and especially with base electrodes precoated with lead oxides, the overvoltages in both directions are much more lower (50 -100 mV), and the electron number 1st 2. A pronounced influence of the anions is observed, CIO;. NO; and BF; being optimal. We have proposed a mechanism for the cathodic dissolution of lead dioxide, which is composed of an electrochemical step, the protonpromoted reduction of Pb4+-ions in the Pb0,-lattice. and a slow chemical step, the protonpromoted dissolution of Pb(OH), generated at the surface. In cases where the last step ist too slow. a gel layer is built up at the surface.

Electrocatalysis of Anodic Oxygen‐Transfer Reactions: Chronoamperometric and Voltammetric Studies of the Nucleation and Electrodeposition of β‐Lead Dioxide at a Rotated Gold Disk Electrode in Acidic Media

“…1), with a time period designated t~, corresponds to rapid growth of PbO~ nuclei with a corresponding transition of the electrode current from virtually zero to a steady-state value (i~). Historically, it is the early part of region B (i.e., '0 < i << is~) which has received the greatest attention in electrocrystallization studies (10,14,(18)(19)(20)(21)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39). For two-dimensional growth, which is assumed for the initial monolayer of oxide, the value of i is predicted to be proportional to (t-t0) ~, whereas for three-dimensional growth, i.e., bulk deposition, i is predicted to be proportional to (t-to) ~ - (37)(38)(39).…”

“…Fleischmann et al (14)(15)(16)(17) were the first to consider in depth the complexity of the mechanism for electrodeposi-tion of PbO~ from aqueous solutions of Pb(II). Their mechanism, summarized by [1]- [4] has received wide support (10,29,(31)(32)(33)(34)(35) OH-~ OHads + e- [1] Pb 2+ + (OH)ad s + OH -'-> Pb(OH)2,ads + (slow) [2] Pb 2 § + (OH)ads + OH-----> Pb(OH)2.ads ~+ + e (slow) [3] Pb(OH)2,ads 2+ ~ PbO2(s) + 2H § [4].…”