II International Symposium on Carbon for Catalysis ABSTRACTS

PP-I-17
INFLUENCE OF MOLECULAR CARBON STRUCTURE AND MORPHOLOGY ON
THE ELECTROCATALYTIC ACTIVITY OF PYROLYSED CoTMPP IN OXYGEN
REDUCTION
Herrmann I., Bogdanoff P., Fiechter S. and Tributsch H.
Hahn-Meitner-Institut, Glienicker Str. 100, 14109 Berlin, Germany
e-mail: iris.herrmann@hmi.de
Currently, carbon-supported platinum catalysts are established as state of the art cathode
material in polymer electrolyte membrane fuel cells (PEM-FC). Although they reveal high
activity and stability in the oxygen reduction in acid media, their meaningful disadvantages,
i.e. increasing price due to an increasing demand, easy inhibition, unsuitable material for the
direct methanol fuel cell as well as migration and aggregation of the platinum nano particles
on carbon surface, require the development of noble metal free catalysts. In the last decades,
N 4 macrocycles (porphyrines and phthalocyanines) have drawn attention as alternative as a
cheap and highly active cathode material in the PEM-FC.
The activity and stability are significantly improved when organometallic complexes are heat
treated in an inert atmosphere. Thereby, the molecules are disintegrated forming a conductive
carbon matrix in which the catalytic centres are molecularly embedded. The catalytic centres have
been characterised as MeN x moieties by EXAFS, XANES and Mößbauer spectroscopy [1, 2].
However, the constitution of the in-situ formed carbon matrix has been neglected in the past
research, although its morphology and molecular structure play a key role in the catalytic process.
In the work presented, based on cobalt-tetramethoxyphenylporphyrin (CoTMPP) the pyrolysis
process and the molecular structure of the formed carbon matrix are characterised by
thermogravimetric measurements, Raman spectroscopy and X-Ray diffractometry (XRD) and
correlated to the electrochemical activity (Rotating-Disc-Electrode and cyclovoltametry).
Thus, fundamental characteristics of the carbon matrix have been found which provide a basis
for the development of new preparation strategies. Higher electrochemical activities could be
achieved when the catalyst consists of extended graphen layers with restored CoN X centres.
The high catalytic potential of the chelate-based eletrocatalysts could be elaborated by the
preparation with structure forming agents (metal oxalates) [3, 4]. Thereby, meso-porous
catalysts particles (up to 800 m 2 /g) have been produced, which show kinetic current density
like commercial platinum catalysts (10 % Pt/C). Related to the low metal loading (< 1 wt-%
Co and < 2 wt-% Fe) in the CoTMPP-based electrocatalyst, the activity of the chelate-based
centres is three times higher than the one of the platinum catalyst. The molecular structure of
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