Electrocatalysis of anodic oxygen evolution at the nickel hydroxide electrode by ferric hydroxo species in alkaline electrolytes

Abstract

On the basis of the proposed anodic oxygen evolution (AOE) reaction model at the nickel hydroxide electrode ( nhe) in the presence of an electrocatalytically active additive in the electrolyte, eg ferric hydroxo complexes (FHC), the role of FHC adsorption in the AOE electrocatalysis has been revealed using the data from stationary polarization measurements. Kinetic parameters of the AOE reaction have also been calculated. nhe surface coverage by ferric hydroxo species adsorbed from the electrolyte was shown to exhibit behaviour similar to the Henry adsorption isotherm type reaching nevertheless, significant values (up to the complete coverage in the limiting case). Its independence from electrode potential (at given concenrations of ferric hydroxo complexes in the elecrolyte) throughout the AOE potential region studied (0.50–0.65 V vs Hg/HgO/8 M KOH) has been noted. In situ Mössbauer spectroscopic investigation in the transmission mode on the nhe containing the ferric hydroxide additive on its surface did not reveal any highly oxidized iron states during anodic polarization in the AOE potential region. This does not exclude the possibility of the existence in minor quantities and/or in a scarcely detectable form a highly oxidized iron stae ( eg in the form of mobile unstable intermediates giving no or negligibly small Mössbauer effect).