Nature of the Catalytic Centers of Porphyrin-Based Electrocatalysts for the ORR: A Correlation of Kinetic Current Density with the Site Density of Fe−N4 Centers

In this work, it has been shown that structural changes of an as-prepared catalyst enable the assignment of the catalytic centers responsible for the direct and indirect oxygen reduction reaction, respectively, of porphyrin-based electrocatalysts. An iron porphyrin (FeTMPPCl)-based catalyst as well as a catalyst based on H2TMPP were prepared using the so-called foaming agent technique (FAT). The obtained iron catalyst was used as a generic material for the post-treatments. Structural changes were analyzed by 57Fe Mossbauer spectroscopy. The catalytic activity toward the oxygen reduction reaction (ORR) was determined using rotating (ring) disc electrode (R(R)DE) experiments. The catalysts exhibit a variation in the iron content between 2.9 and 4.5 wt % caused by the post-treatments. It has been found that the Mossbauer spectra of all catalysts can be fitted assuming two different ferrous Fe−N4 centers, a CFeN2 center (Fe2+, S = 2) and an Fe3C center (Fe0). After the intensities found in the Mossbauer spect...

[1]  P. Gütlich.  Physikalische Methoden in der Chemie: Mößbauer‐Spektroskopie II , 1970 .

[2]  Alfred B. Anderson,et al.  O2 reduction on graphite and nitrogen-doped graphite: experiment and theory. , 2006, The journal of physical chemistry. B.

[3]  H. Tributsch,et al.  Experimental and theoretical modeling of Fe-, Co-, Cu-, Mn-based electrocatalysts for oxygen reduction , 2008 .

[4]  J. V. Veen,et al.  Effect of heat treatment on the performance of carbon-supported transition-metal chelates in the electrochemical reduction of oxygen , 1981 .

[5]  P. Bogdanoff,et al.  Electrocatalysts for oxygen reduction prepared by plasma treatment of carbon-supported cobalt tetramethoxyphenylporphyrin , 2005 .

[6]  R. Larsson,et al.  Pyrolysis behaviour of metalloporphyrins. Part 2.—A mössbauer study of pyrolysed FeIIItetraphenylporphyrin chloride , 1992 .

[7]  P. Bogdanoff,et al.  Catalysts for oxygen reduction from heat-treated carbon-supported iron phenantroline complexes , 2002 .

[8]  R. Taube,et al.  Mössbauer-Spektren von Eisenphthalocyanin-Komplexen , 1969 .

[9]  P. Bogdanoff,et al.  Influence of the Molecular and Mesoscopic Structure on the Electrocatalytic Activity of Pyrolysed CoTMPP in the Oxygen Reduction , 2006 .

[10]  E. Yeager,et al.  In-situ Mössbauer spectroscopy and electrochemical studies of the thermal stability of iron phthalocyanine dispersed in high surface area carbon , 1985 .

[11]  C. Debiemme-Chouvy,et al.  Oxygen electroreduction catalysis: effect of sulfur addition on cobalt tetraazaannulene precursors , 1999 .

[12]  Frédéric Jaouen,et al.  Fe-Based Catalysts for Oxygen Reduction in PEMFCs Importance of the Disordered Phase of the Carbon Support , 2006 .

[13]  J.A.R. van Veen,et al.  On the effect of a heat treatment on the structure of carbon-supported metalloporphyrins and phthalocyanines , 1988 .

[14]  H. Gasteiger,et al.  Activity benchmarks and requirements for Pt, Pt-alloy, and non-Pt oxygen reduction catalysts for PEMFCs , 2005 .

[15]  Patrick Bertrand,et al.  Oxygen reduction catalysts for polymer electrolyte fuel cells from the pyrolysis of FeII acetate adsorbed on 3,4,9,10-perylenetetracarboxylic dianhydride , 1999 .

[16]  E. Yeager,et al.  Transition metal macrocycles supported on high area carbon: pyrolysis-mass spectrometry studies , 1986 .

[17]  G. Amthauer,et al.  Crystal chemistry of iron in natural and in synthetic braunites Mn2 +(Mn3+,Fe3+ )6O8/SiO4 , 1988 .

[18]  S. C. Tang,et al.  On Active-Site Heterogeneity in Pyrolyzed Carbon-Supported Iron Porphyrin Catalysts for the Electrochemical Reduction of Oxygen: An In Situ Mössbauer Study , 2002 .

[19]  P. Bertrand,et al.  Activation and characterization of Fe-based catalysts for the reduction of oxygen in polymer electrolyte fuel cells , 1998 .

[20]  K. Wiesener,et al.  N4-chelates as electrocatalyst for cathodic oxygen reduction , 1986 .

[21]  Reyimjan A. Sidik,et al.  Oxygen Electroreduction on FeII and FeIII Coordinated to N4 Chelates. Reversible Potentials for the Intermediate Steps from Quantum Theory , 2004 .

[22]  Göran Lindbergh,et al.  Oxygen reduction by Fe-based catalysts in PEM fuel cell conditions: Activity and selectivity of the catalysts obtained with two Fe precursors and various carbon supports , 2006 .

[23]  P. Bertrand,et al.  Is nitrogen important in the formulation of Fe-based catalysts for oxygen reduction in solid polymer fuel cells? , 1997 .

[24]  M. R. Tarasevich,et al.  Pyropolymers of N4-complexes: Structure and elegtrocatalytic properties , 1989 .

[25]  Frédéric Jaouen,et al.  Average turn-over frequency of O2 electro-reduction for Fe/N/C and Co/N/C catalysts in PEFCs , 2007 .

[26]  Patrick Bertrand,et al.  Heat-treated iron and cobalt tetraphenylporphyrins adsorbed on carbon black: Physical characterization and catalytic properties of these materials for the reduction of oxygen in polymer electrolyte fuel cells , 1996 .

[27]  R. Savinell,et al.  Heat-treated iron(III) tetramethoxyphenyl porphyrin chloride supported on high-area carbon as an electrocatalyst for oxygen reduction: Part II. Kinetics of oxygen reduction , 1999 .

[28]  S. Marcotte,et al.  Oxygen Reduction Catalysts for Polymer Electrolyte Fuel Cells from the Pyrolysis of Iron Acetate Adsorbed on Various Carbon Supports , 2003 .

[29]  P. Bertrand,et al.  Catalytic activity and stability of heat-treated iron phthalocyanines for the electroreduction of oxygen in polymer electrolyte fuel cells , 1996 .

[30]  Patrick Bertrand,et al.  O-2 reduction in PEM fuel cells: Activity and active site structural information for catalysts obtained by the pyrolysis at high temperature of Fe precursors , 2000 .

[31]  Ernest Yeager,et al.  Heat-treated polyacrylonitrile-based catalysts for oxygen electroreduction , 1989 .

[32]  Frédéric Jaouen,et al.  Fe/N/C non-precious catalysts for PEM fuel cells: Influence of the structural parameters of pristine commercial carbon blacks on their activity for oxygen reduction , 2008 .

[33]  R. Savinell,et al.  Iron(III) tetramethoxyphenylporphyrin(FeTMPP) as methanol tolerant electrocatalyst for oxygen reduction in direct methanol fuel cells , 1998 .

[34]  V. S. Bagotzky,et al.  Electrocatalysis of the oxygen reduction process on metal chelates in acid electrolyte , 1978 .

[35]  R. Larsson,et al.  Electrochemical and mössbauer investigations of polymeric iron phthalocyanine oxygen electrodes , 1982 .

[36]  H Jahnke,et al.  Organic dyestuffs as catalysts for fuel cells. , 1976, Topics in current chemistry.

[37]  H. Tributsch,et al.  Catalysts for the Oxygen Reduction from Heat-Treated Iron(III) Tetramethoxyphenylporphyrin Chloride: Structure and Stability of Active Sites , 2003 .

[38]  L. Epstein,et al.  Mössbauer studies on oxo-bridged iron 3 prophines. , 1972, Journal of the American Chemical Society.

[39]  V. Kahlenberg,et al.  Dehydration experiments on natural omphacites: qualitative and quantitative characterization by various spectroscopic methods , 2007 .

[40]  P. Holland,et al.  Planar three-coordinate high-spin Fe(II) complexes with large orbital angular momentum: Mössbauer, electron paramagnetic resonance, and electronic structure studies. , 2002, Journal of the American Chemical Society.

[41]  R. Savinell,et al.  Methanol-tolerant electrocatalysts for oxygen reduction in a polymer electrolyte membrane fuel cell , 1998 .

[42]  Patrick Bertrand,et al.  Molecular Oxygen Reduction in PEM Fuel Cells: Evidence for the Simultaneous Presence of Two Active Sites in Fe-Based Catalysts , 2002 .

[43]  Frédéric Jaouen,et al.  Heat-treated Fe/N/C catalysts for O2 electroreduction: are active sites hosted in micropores? , 2006, The journal of physical chemistry. B.