Applications of synchrotron radiation and optical spectroscopic techniques to the study of electrochemical interfaces.

摘要

Electrochemical interfaces, especially structural changes and spectroscopic properties of adsorbed species on electrode surfaces induced by electrode potential have been examined by means of X-ray absorption fine structure and optical spectroscopic techniques.; Potential modulation reflectance spectroscopy and wavelength modulation reflectance technique have been used to monitor the spectral properties of cobalt tetrasulfonated phthalocyanine (CoTsPc) and methylene (MB) blue irreversibly adsorbed on electrode surfaces. With a combination of cyclic voltammetry, linear relationship has been found between the relative reflectivity and the coverage of oxidized species of CoTsPc on the basal plane of highly oriented pyrolytic graphite (HOPG(bp)). Wavelength modulation study has shown that CoTsPc and MB on electrode surfaces exhibit almost the same spectral properties with those when they are in solution phase.; Spectral changes accompanying the one-electron reduction of {dollar}mu{dollar}-oxo(bis) (iron meso-tetrakis(methoxyphenyl)porphyrin) (FeTMPP){dollar}sb2{dollar}O irreversibly adsorbed on Black Pearl (BP) in aqueous electrolyte have been examined in situ through X-ray absorption fine structure. In the pH range 5-10.8, the average iron-to-porphinato nitrogen distance, d(Fe-N{dollar}sb{lcub}rm p{rcub}){dollar} (2.08 {dollar}pm{dollar} 0.01 A) for the ferric species was found to be very similar to that for crystalline (FeTMPP){dollar}sb2{dollar}O. At extreme pHs, d(Fe-N{dollar}sb{lcub}rm p{rcub}{dollar}) values smaller than those observed in the intermediate pH range, which strongly suggest an axially coordinated dihydroxy (at very high pH) and diaquo (at very low pH) complexes as the predominant species. In contrast, the corresponding ferrous counterpart displayed values for d(Fe-N{dollar}sb{lcub}rm p{rcub}{dollar}) (2.04 {dollar}pm{dollar} 0.01 A) consistent with the iron center placed in the plane of the ring over the whole pH region examined.; The XAFS studies of Ni and 9:1 Ni/Fe and 9:1 Ni/Co composite hydroxide have shown that (i) Ni-O and Ni-Ni distances in Ni(OH){dollar}sb2{dollar} system are larger than those in NiOOH produced by oxidation; (ii) iron and cobalt ions replace nickel ions in hydrous oxide lattice forming single phase; (iii) iron and cobalt do not undergo oxidation state changes upon oxidizing Ni(OH){dollar}sb2{dollar} to NiOOH, but remain as 3+ state.; The XAFS studies of FeS{dollar}sb2{dollar} and its Li ion intercalated species have shown that electrochemical insertion of Li ion brings about a marked decrease in the amplitude of the EXAFS and makes Fe-S distance longer. (Abstract shortened by UMI.)