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Bio-inspired cofacial Fe porphyrin dimers for efficient electrocatalytic CO2 to CO conversion: Overpotential tuning by substituents at the porphyrin rings.

Zahran ZN, Mohamed EA, Naruta Y - Sci Rep (2016)

Bottom Line: Efficient reduction of CO2 into useful carbon resources particularly CO is an essential reaction for developing alternate sources of fuels and for reducing the greenhouse effect of CO2.The binuclear Ni, Fe-containing carbon monoxide dehydrogenase (CODHs) efficiently catalyzes the reduction of CO2 to CO.By introducing electron-withdrawing/-donating groups, e.g. electron-withdrawing perfluorophenyl, at all meso positions of the porphyrin rings, the catalysis overpotential, η was minimized by ≈0.3 V compared to that obtained by introducing electron-donating mesityl groups.

View Article: PubMed Central - PubMed

Affiliation: Institute for Science and Technology Research, Centre for Chemical Energy Conversion, Chubu University, Kasugai 487-8501, Japan.

ABSTRACT
Efficient reduction of CO2 into useful carbon resources particularly CO is an essential reaction for developing alternate sources of fuels and for reducing the greenhouse effect of CO2. The binuclear Ni, Fe-containing carbon monoxide dehydrogenase (CODHs) efficiently catalyzes the reduction of CO2 to CO. The location of Ni and Fe at proper positions allows their cooperation for CO2 to CO conversion through a push-pull mechanism. Bio-inspired from CODHs, we used several cofacial porphyrin dimers with different substituents as suitable ligands for holding two Fe ions with suitable Fe-Fe separation distance to efficiently and selectively promote CO2 to CO conversion with high turnover frequencies, TOFs. The substituents on the porphyrin rings greatly affect the catalysis process. By introducing electron-withdrawing/-donating groups, e.g. electron-withdrawing perfluorophenyl, at all meso positions of the porphyrin rings, the catalysis overpotential, η was minimized by ≈0.3 V compared to that obtained by introducing electron-donating mesityl groups. The Fe porphyrin dimers among reported catalysts are the most efficient ones for CO2 to CO conversion. Control experiments indicate that the high performance of the current CO2 to CO conversion catalysts is due to the presence of binuclear Fe centers at suitable Fe-Fe separation distance.

No MeSH data available.


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Cyclic voltammograms of the six Fe-porphyrin dimers (0.5 mM) in DMF/10% H2O at 50 mV/s scan rate under Ar (black lines) and CO2 (red lines).Insets: magnified traces of CVs.
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f2: Cyclic voltammograms of the six Fe-porphyrin dimers (0.5 mM) in DMF/10% H2O at 50 mV/s scan rate under Ar (black lines) and CO2 (red lines).Insets: magnified traces of CVs.

Mentions: Under CO2, the CV behaviors of the Fe porphyrin dimers (0.5 mM) are depicted in Fig. 2 (red lines). The reversible 2FeIII/2FeII redox couple observed under Ar is replaced with a new reduction peak due, as we previously reported49, to the dissociation of the Cl− and the coordination of the CO2 molecule to the electro-generated 2FeII species inside the cofacial porphyrin cavity within the time scale of CV. The dissociation of the Cl− and coordination of CO2 is supported by the UV-vis spectra of the chemically reduced o-Fe2IIDTPP that shows the remarkable change of its Soret and Q-bands upon purging of CO2 gas at −30 °C, indicating the binding of CO2 to the FeII porphyrin species49. Indeed, the ability of CO2 to coordinate transition metal complexes is extensively investigated51. However, the coordination of CO2 to the electro-generated FeII species is not observed in the corresponding Fe porphyrin monomer under similar experimental conditions. Upon further scanning to more negative potential the electro-generated CO2-coordinated 2FeII species showed a reversible 2e− redox couple corresponding to the generation of CO2 coordinated 2FeII/2FeI species. The most interesting finding is the observation of a strong catalytic current in the presence of CO2 indicating electro-catalytic reduction of CO2 promoted by the six Fe porphyrin dimers. The appearance of the catalytic peak over the FeIFeI/FeIFe0 redox couple under Ar indicates the starting of the catalytic process once the FeIFe0 porphyrin species is electrochemically generated49. In general, the Fe porphyrin dimer with electron-withdrawing substituents shows electro-catalytic CO2 reduction behavior at more positive potential, i.e. at low η. In other words, the Fe porphyrin dimers are arranged in the following order with respect to their η (small to large) for the CO2 to CO conversion; Fe2DTPFPP < Fe2TPFPP-TMP < Fe2DTF2PP < Fe2DTCl2PP < Fe2DTPP < Fe2DTMP.


Bio-inspired cofacial Fe porphyrin dimers for efficient electrocatalytic CO2 to CO conversion: Overpotential tuning by substituents at the porphyrin rings.

Zahran ZN, Mohamed EA, Naruta Y - Sci Rep (2016)

Cyclic voltammograms of the six Fe-porphyrin dimers (0.5 mM) in DMF/10% H2O at 50 mV/s scan rate under Ar (black lines) and CO2 (red lines).Insets: magnified traces of CVs.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4834491&req=5

f2: Cyclic voltammograms of the six Fe-porphyrin dimers (0.5 mM) in DMF/10% H2O at 50 mV/s scan rate under Ar (black lines) and CO2 (red lines).Insets: magnified traces of CVs.
Mentions: Under CO2, the CV behaviors of the Fe porphyrin dimers (0.5 mM) are depicted in Fig. 2 (red lines). The reversible 2FeIII/2FeII redox couple observed under Ar is replaced with a new reduction peak due, as we previously reported49, to the dissociation of the Cl− and the coordination of the CO2 molecule to the electro-generated 2FeII species inside the cofacial porphyrin cavity within the time scale of CV. The dissociation of the Cl− and coordination of CO2 is supported by the UV-vis spectra of the chemically reduced o-Fe2IIDTPP that shows the remarkable change of its Soret and Q-bands upon purging of CO2 gas at −30 °C, indicating the binding of CO2 to the FeII porphyrin species49. Indeed, the ability of CO2 to coordinate transition metal complexes is extensively investigated51. However, the coordination of CO2 to the electro-generated FeII species is not observed in the corresponding Fe porphyrin monomer under similar experimental conditions. Upon further scanning to more negative potential the electro-generated CO2-coordinated 2FeII species showed a reversible 2e− redox couple corresponding to the generation of CO2 coordinated 2FeII/2FeI species. The most interesting finding is the observation of a strong catalytic current in the presence of CO2 indicating electro-catalytic reduction of CO2 promoted by the six Fe porphyrin dimers. The appearance of the catalytic peak over the FeIFeI/FeIFe0 redox couple under Ar indicates the starting of the catalytic process once the FeIFe0 porphyrin species is electrochemically generated49. In general, the Fe porphyrin dimer with electron-withdrawing substituents shows electro-catalytic CO2 reduction behavior at more positive potential, i.e. at low η. In other words, the Fe porphyrin dimers are arranged in the following order with respect to their η (small to large) for the CO2 to CO conversion; Fe2DTPFPP < Fe2TPFPP-TMP < Fe2DTF2PP < Fe2DTCl2PP < Fe2DTPP < Fe2DTMP.

Bottom Line: Efficient reduction of CO2 into useful carbon resources particularly CO is an essential reaction for developing alternate sources of fuels and for reducing the greenhouse effect of CO2.The binuclear Ni, Fe-containing carbon monoxide dehydrogenase (CODHs) efficiently catalyzes the reduction of CO2 to CO.By introducing electron-withdrawing/-donating groups, e.g. electron-withdrawing perfluorophenyl, at all meso positions of the porphyrin rings, the catalysis overpotential, η was minimized by ≈0.3 V compared to that obtained by introducing electron-donating mesityl groups.

View Article: PubMed Central - PubMed

Affiliation: Institute for Science and Technology Research, Centre for Chemical Energy Conversion, Chubu University, Kasugai 487-8501, Japan.

ABSTRACT
Efficient reduction of CO2 into useful carbon resources particularly CO is an essential reaction for developing alternate sources of fuels and for reducing the greenhouse effect of CO2. The binuclear Ni, Fe-containing carbon monoxide dehydrogenase (CODHs) efficiently catalyzes the reduction of CO2 to CO. The location of Ni and Fe at proper positions allows their cooperation for CO2 to CO conversion through a push-pull mechanism. Bio-inspired from CODHs, we used several cofacial porphyrin dimers with different substituents as suitable ligands for holding two Fe ions with suitable Fe-Fe separation distance to efficiently and selectively promote CO2 to CO conversion with high turnover frequencies, TOFs. The substituents on the porphyrin rings greatly affect the catalysis process. By introducing electron-withdrawing/-donating groups, e.g. electron-withdrawing perfluorophenyl, at all meso positions of the porphyrin rings, the catalysis overpotential, η was minimized by ≈0.3 V compared to that obtained by introducing electron-donating mesityl groups. The Fe porphyrin dimers among reported catalysts are the most efficient ones for CO2 to CO conversion. Control experiments indicate that the high performance of the current CO2 to CO conversion catalysts is due to the presence of binuclear Fe centers at suitable Fe-Fe separation distance.

No MeSH data available.


Related in: MedlinePlus