ABSTRACT The following work presents the preparation and investigation of pyrolysed Co porphyrine... more ABSTRACT The following work presents the preparation and investigation of pyrolysed Co porphyrine as an electrocatalyst for the oxygen reduction reaction ORR in acid media. A new preparation method which needs no addition of carbon supports, allows the structural investigation of the pyrolysis products by XPS, Raman spectroscopy and X ray diffractometry without any interferences. Rotating Disc Electrode measurements reveal the high ORR activity which is mainly caused by a well developed porosity and a suitable molecular structure of the formed carbon. Thermogravimetric investigation of the pyrolysis process shows that the addition of sulphur influences the carbonization of the porphyrine in a favorable way. It has been found that extended graphene layers present a particularly suitable matrix for highly active catalytic centers
Pyrolysis of chloroiron-tetramethoxyphenyl-porphyrin (FeTMPP-Cl) in the presence of iron oxalate ... more Pyrolysis of chloroiron-tetramethoxyphenyl-porphyrin (FeTMPP-Cl) in the presence of iron oxalate (± sulphur) leads to the formation of higly porous and active catalysts for the oxygen reduction reaction (ORR). In order to clarify the influence of sulphur the pyrolysis process is analyzed by thermogravimetry (TG) and by high-temperature X-ray diffraction (HT-XRD). In the absence of sulphur iron carbide (Fe x C) is formed which catalyses the proceeding graphitisation of the pyrolysis products. As a result catalytic active centres are decomposed by this reaction. This can be avoided by the addition of sulphur because iron monosulphide (FeS; troilite) is formed instead of Fe x C. Furthermore, FeS can easily be removed in a successive etching step so that nearly all inactive by-products can be removed. The results are in accordance with the higher electrochemical performance of the sulphur containing catalysts.
Low temperature plasma (LTP) treatment of cobalt-tetramethoxyphenylporphyrin (CoTMPP) has been ap... more Low temperature plasma (LTP) treatment of cobalt-tetramethoxyphenylporphyrin (CoTMPP) has been applied as a promising alternative method to the conventional heat treatment in order to attain highly active catalysts for the electroreduction of oxygen. In this contribution it is shown that CoTMPP can be completely transformed into a carbon matrix by adjusting adequate LTP parameters. The carbonisation process of CoTMPP is investigated at different operation conditions by Raman and IR spectroscopy and compared with the structural features of the heat-treated samples. As a result it appears that the LTP occurs via a different carbonisation process, which yields in a more homogeneously defined molecular carbon structure.
6. Conclusion Plasma techniques have been extensively utilized in catalysis. Catalyst preparation... more 6. Conclusion Plasma techniques have been extensively utilized in catalysis. Catalyst preparation using plasma treatment allows to improve dispersion, enhancing the catalyst performance and stability. In this paper, the low-pressure radio frequency (RF) discharge ...
The performance of iron(II) phthalocyanine (FePc) and cobalt tetramethoxyphenylporphyrin (CoTMPP)... more The performance of iron(II) phthalocyanine (FePc) and cobalt tetramethoxyphenylporphyrin (CoTMPP) based oxygen reduction catalysts was studied in view of the application as cathode materials in microbial fuel cells. Galvanostatic and potentiostatic experiments were performed in order to compare the proposed materials to platinum and hexacyanoferrate(III) based systems. Additionally, twochamber microbial fuel cell experiments were carried out to demonstrate that the transition metal based materials are well suitable to fully substitute the traditional cathode materials in microbial fuel cells.
Nine non-noble-metal catalysts (NNMCs) from five different laboratories were investigated for the... more Nine non-noble-metal catalysts (NNMCs) from five different laboratories were investigated for the catalysis of O 2 electroreduction in an acidic medium. The catalyst precursors were synthesized by wet impregnation, planetary ball milling, a foamingagent technique, or a templating method. All catalyst precursors were subjected to one or more heat treatments at 700-1050°C in an inert or reactive atmosphere. These catalysts underwent an identical set of electrochemical characterizations, including rotatingdisk-electrode and polymer-electrolyte membrane fuel cell (PEMFC) tests and voltammetry under N 2 . Ex situ characterization was comprised of X-ray photoelectron spectroscopy, neutron activation analysis, scanning electron microscopy, and N 2 adsorption and its analysis with an advanced model for carbonaceous powders. In PEMFC, several NNMCs display mass activities of 10-20 A g -1 at 0.8 V versus a reversible hydrogen electrode, and one shows 80 A g -1 . The latter value corresponds to a volumetric activity of 19 A cm -3 under reference conditions and represents one-seventh of the target defined by the U.S. Department of Energy for 2010 (130 A cm -3 ). The activity of all NNMCs is mainly governed by the microporous surface area, and active sites seem to be hosted in pore sizes of 5-15 Å. The nitrogen and metal (iron or cobalt) seem to be present in sufficient amounts in the NNMCs and do not limit activity. The paper discusses probable directions for synthesizing more active NNMCs. This could be achieved through multiple pyrolysis steps, ball-milling steps, and control of the powder morphology by the addition of foaming agents and/or sulfur.
ABSTRACT A tailor made horseradish peroxidase HRP bulk composite electrode was developed on the b... more ABSTRACT A tailor made horseradish peroxidase HRP bulk composite electrode was developed on the basis of pyrolyzed cobalt tetramethoxyphenylporphyrin CoTMPP by modifying pore size and surface area of the porous carbon material through varying amounts of iron oxalate and sulfur prior to pyrolyzation. The materials were used to immobilize horseradish peroxidase HRP . These electrodes were characterized in terms of their efficiency to reduce hydrogen peroxide. The heterogeneous electron transfer rate constants of different materials were determined with the rotating disk electrode method and a kS 401 61 s 1 exceeding previously reported values for native HRP was found
ABSTRACT The following work presents the preparation and investigation of pyrolysed Co porphyrine... more ABSTRACT The following work presents the preparation and investigation of pyrolysed Co porphyrine as an electrocatalyst for the oxygen reduction reaction ORR in acid media. A new preparation method which needs no addition of carbon supports, allows the structural investigation of the pyrolysis products by XPS, Raman spectroscopy and X ray diffractometry without any interferences. Rotating Disc Electrode measurements reveal the high ORR activity which is mainly caused by a well developed porosity and a suitable molecular structure of the formed carbon. Thermogravimetric investigation of the pyrolysis process shows that the addition of sulphur influences the carbonization of the porphyrine in a favorable way. It has been found that extended graphene layers present a particularly suitable matrix for highly active catalytic centers
Pyrolysis of chloroiron-tetramethoxyphenyl-porphyrin (FeTMPP-Cl) in the presence of iron oxalate ... more Pyrolysis of chloroiron-tetramethoxyphenyl-porphyrin (FeTMPP-Cl) in the presence of iron oxalate (± sulphur) leads to the formation of higly porous and active catalysts for the oxygen reduction reaction (ORR). In order to clarify the influence of sulphur the pyrolysis process is analyzed by thermogravimetry (TG) and by high-temperature X-ray diffraction (HT-XRD). In the absence of sulphur iron carbide (Fe x C) is formed which catalyses the proceeding graphitisation of the pyrolysis products. As a result catalytic active centres are decomposed by this reaction. This can be avoided by the addition of sulphur because iron monosulphide (FeS; troilite) is formed instead of Fe x C. Furthermore, FeS can easily be removed in a successive etching step so that nearly all inactive by-products can be removed. The results are in accordance with the higher electrochemical performance of the sulphur containing catalysts.
Low temperature plasma (LTP) treatment of cobalt-tetramethoxyphenylporphyrin (CoTMPP) has been ap... more Low temperature plasma (LTP) treatment of cobalt-tetramethoxyphenylporphyrin (CoTMPP) has been applied as a promising alternative method to the conventional heat treatment in order to attain highly active catalysts for the electroreduction of oxygen. In this contribution it is shown that CoTMPP can be completely transformed into a carbon matrix by adjusting adequate LTP parameters. The carbonisation process of CoTMPP is investigated at different operation conditions by Raman and IR spectroscopy and compared with the structural features of the heat-treated samples. As a result it appears that the LTP occurs via a different carbonisation process, which yields in a more homogeneously defined molecular carbon structure.
6. Conclusion Plasma techniques have been extensively utilized in catalysis. Catalyst preparation... more 6. Conclusion Plasma techniques have been extensively utilized in catalysis. Catalyst preparation using plasma treatment allows to improve dispersion, enhancing the catalyst performance and stability. In this paper, the low-pressure radio frequency (RF) discharge ...
The performance of iron(II) phthalocyanine (FePc) and cobalt tetramethoxyphenylporphyrin (CoTMPP)... more The performance of iron(II) phthalocyanine (FePc) and cobalt tetramethoxyphenylporphyrin (CoTMPP) based oxygen reduction catalysts was studied in view of the application as cathode materials in microbial fuel cells. Galvanostatic and potentiostatic experiments were performed in order to compare the proposed materials to platinum and hexacyanoferrate(III) based systems. Additionally, twochamber microbial fuel cell experiments were carried out to demonstrate that the transition metal based materials are well suitable to fully substitute the traditional cathode materials in microbial fuel cells.
Nine non-noble-metal catalysts (NNMCs) from five different laboratories were investigated for the... more Nine non-noble-metal catalysts (NNMCs) from five different laboratories were investigated for the catalysis of O 2 electroreduction in an acidic medium. The catalyst precursors were synthesized by wet impregnation, planetary ball milling, a foamingagent technique, or a templating method. All catalyst precursors were subjected to one or more heat treatments at 700-1050°C in an inert or reactive atmosphere. These catalysts underwent an identical set of electrochemical characterizations, including rotatingdisk-electrode and polymer-electrolyte membrane fuel cell (PEMFC) tests and voltammetry under N 2 . Ex situ characterization was comprised of X-ray photoelectron spectroscopy, neutron activation analysis, scanning electron microscopy, and N 2 adsorption and its analysis with an advanced model for carbonaceous powders. In PEMFC, several NNMCs display mass activities of 10-20 A g -1 at 0.8 V versus a reversible hydrogen electrode, and one shows 80 A g -1 . The latter value corresponds to a volumetric activity of 19 A cm -3 under reference conditions and represents one-seventh of the target defined by the U.S. Department of Energy for 2010 (130 A cm -3 ). The activity of all NNMCs is mainly governed by the microporous surface area, and active sites seem to be hosted in pore sizes of 5-15 Å. The nitrogen and metal (iron or cobalt) seem to be present in sufficient amounts in the NNMCs and do not limit activity. The paper discusses probable directions for synthesizing more active NNMCs. This could be achieved through multiple pyrolysis steps, ball-milling steps, and control of the powder morphology by the addition of foaming agents and/or sulfur.
ABSTRACT A tailor made horseradish peroxidase HRP bulk composite electrode was developed on the b... more ABSTRACT A tailor made horseradish peroxidase HRP bulk composite electrode was developed on the basis of pyrolyzed cobalt tetramethoxyphenylporphyrin CoTMPP by modifying pore size and surface area of the porous carbon material through varying amounts of iron oxalate and sulfur prior to pyrolyzation. The materials were used to immobilize horseradish peroxidase HRP . These electrodes were characterized in terms of their efficiency to reduce hydrogen peroxide. The heterogeneous electron transfer rate constants of different materials were determined with the rotating disk electrode method and a kS 401 61 s 1 exceeding previously reported values for native HRP was found
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