Leif C. Moberg

Electrochemical and mössbauer investigations of polymeric iron phthalocyanine oxygen electrodes

Abstract Polymeric iron phthalocyanine precipitated on activated carbon has been heated to temperatures in the range 200–500° C and the catalytic activity for the electrochemical reduction of oxygen has been investigated. The catalysts were tested in porous, hydrophobic electrodes. Mossbauer spectra have been obtained for the catalyst powders exposed to different heating temperatures. Heat treatment was found to give electrodes with a higher rate of deactivation for the electrochemical reduction. This was particularly the case for heat treatments at temperatures higher than 300°C. An increase in the intensity of a doublet in the Mossbauer spectra corresponding to oxidized iron was obtained for the heat treated samples. This increase of oxidized iron was found to be correlated to the increased rate of deactivation for the electrodes.

Mössbauer measurements on iron phthalocyanines

Abstract Monomeric and polymeric iron phthalocyanines (FePc) with and without carbon support and subjected to various heat treatments have been studied by Mossbauer spectroscopy. Dispersing FePc on carbon changes the electronic state of the monomer to low spin (S = 0) while the electronic state of the polymer remains unchanged (S = 1). It is suggested that the bonding between polymeric FePc and carbon takes place through the side groups present on the peripheral parts of the polymer and/or through suitable chemical groups present on the carbon surface. The electron-attracting ability of the side-groups deduced from the Mossbauer spectra is discussed. The results will form a basis for a comparison with data from electrochemical measurements.

ESCA and Mössbauer spectra of some iron(III) betadiketonates and tetraphenylporphyrin iron(III) chloride

Abstract X-ray photoelectron spectra and Mossbauer spectra have been recorded for the complexes Fe(1-phenyl-1,3-butanedionate) 3 , Fe(1,3-diphenyl-1,3-propanedionate) 3 , Fe(3-phenyl-2,4-pentanedionate) 3 and meso-tetraphenylporphyrin iron(III) chloride. As an auxiliary tool in the study the IR absorption intensity of the ν CH vibrations of the phenyl groups present in the complexes was measured. By a combination of the XPS binding energies and the IR intensities with previously established relations between these entities and the effective charge of atoms and groups, a rather complete napping of the charge distribution of the complexes was achieved. By a combination of the XPS data with the Mossbauer data is was possible to describe the electron population in the (3rd, 4s, 4p) orbitals of the central iron atom.

Simultaneous electrochemical and mössbauer measurements on polymeric iron phthalocyanine oxygen electrodes

Abstract Mossbauer spectra have been obtained on porous, hydrophobic electrodes in situ when used as oxygen reduction electrodes in sulphuric acid electrolyte. The electrodes consisted of polymeric iron phthalocyanine precipitated on activated carbon. Mossbauer spectra were also obtained on the same kind of electrodes which had been used for different amounts of time. The polymeric iron phthalocyanine was prepared using iron enriched in 57 Fe to get resolvable spectra. The Mssbauer spectra are characterized by the increase of a signal corresponding to oxidized iron as the catalytic activity decreases. A correlation between the amount of iron dissolved into the electrolyte and the electrode potential is seen during the first 100 h of operation. It is suggested that Fe(II) is oxidized to Fe(III) which is dissolved into the electrolyte.

Ligand influence on the Mössbauer isomer shift and the quadrupole splitting in some related iron complexes

Abstract A series of related iron complexes of the form FeL 3 X 2 (L = phenantroline, 2,2′-bipyridyl, glyoxal-bis-N-methylimine and X = ClO 4 − , I − ) has been studied by Mossbauer spectroscopy and the measured parameters have been compared with theoretical estimates. The results have been interpreted by a model based on the molecular orbital picture of the organometallic cation and a point charge correction, representing the field of the counter-ions.