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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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(a) Bulk electrolysis conducted for 6 hrs at −1.25 V vs. NHE (η = 0.56 V) and (b) products analysis of Fe2DTPFPP (0.5 mM) and GC blank in DMF/10% H2O under CO2.
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f5: (a) Bulk electrolysis conducted for 6 hrs at −1.25 V vs. NHE (η = 0.56 V) and (b) products analysis of Fe2DTPFPP (0.5 mM) and GC blank in DMF/10% H2O under CO2.

Mentions: To test the activity, stability, and selectivity of the Fe porphyrin dimers for the CO2 reduction, a bulk electrolysis experiment was conducted in a gas-tight H shaped two-compartment electrochemical cell with a glass frit to separate the two compartments. The cell was filled with DMF/10% H2O solution (14 mL) containing 0.5 mM of the Fe porphyrin dimer and 0.1 M nBut4NPF6 as a supporting electrolyte. In one compartment, a glassy carbon working electrode (1 cm2) and a Ag/AgCl (3M NaCl) reference one were immersed close to each other (about 2 mm apart) in the solution. In the other compartment, a Pt foil (about 20 cm2) was immersed in the solution and used as a counter electrode. The solution in the two compartments was saturated with CO2 by bubbling CO2 for 30 min prior to the reaction. The products of the electro-catalytic reduction in the gas phase and in the solution phase were analyzed by gas chromatography and capillary electrophoreses, respectively. Figure 5a shows the current density-time profile of the electrolysis at −1.25 V vs. NHE (η = 0.56 V) in the presence and absence of the Fe2DTPFPP (0.5 mM) as a representative example of the Fe porphyrin dimers. The product analysis (Fig. 5b) of the headspace gas and solution shows the formation of CO gas in 92% Faradaic efficiency and H2 gas in 8% Faradaic efficiency. Only a very small amount of HCO2H detected in the solution, that means the Fe2DTPFPP dimer shows a high selectivity for CO2 reduction to CO. The other Fe porphyrin dimers show similar behavior for the CO2 to CO conversion however under slightly higher η. Based on the bulk electrolysis experiment, the catalysis parameters, kcat, TON, and TOF were calculated using equations (11)~(13);


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)

(a) Bulk electrolysis conducted for 6 hrs at −1.25 V vs. NHE (η = 0.56 V) and (b) products analysis of Fe2DTPFPP (0.5 mM) and GC blank in DMF/10% H2O under CO2.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f5: (a) Bulk electrolysis conducted for 6 hrs at −1.25 V vs. NHE (η = 0.56 V) and (b) products analysis of Fe2DTPFPP (0.5 mM) and GC blank in DMF/10% H2O under CO2.
Mentions: To test the activity, stability, and selectivity of the Fe porphyrin dimers for the CO2 reduction, a bulk electrolysis experiment was conducted in a gas-tight H shaped two-compartment electrochemical cell with a glass frit to separate the two compartments. The cell was filled with DMF/10% H2O solution (14 mL) containing 0.5 mM of the Fe porphyrin dimer and 0.1 M nBut4NPF6 as a supporting electrolyte. In one compartment, a glassy carbon working electrode (1 cm2) and a Ag/AgCl (3M NaCl) reference one were immersed close to each other (about 2 mm apart) in the solution. In the other compartment, a Pt foil (about 20 cm2) was immersed in the solution and used as a counter electrode. The solution in the two compartments was saturated with CO2 by bubbling CO2 for 30 min prior to the reaction. The products of the electro-catalytic reduction in the gas phase and in the solution phase were analyzed by gas chromatography and capillary electrophoreses, respectively. Figure 5a shows the current density-time profile of the electrolysis at −1.25 V vs. NHE (η = 0.56 V) in the presence and absence of the Fe2DTPFPP (0.5 mM) as a representative example of the Fe porphyrin dimers. The product analysis (Fig. 5b) of the headspace gas and solution shows the formation of CO gas in 92% Faradaic efficiency and H2 gas in 8% Faradaic efficiency. Only a very small amount of HCO2H detected in the solution, that means the Fe2DTPFPP dimer shows a high selectivity for CO2 reduction to CO. The other Fe porphyrin dimers show similar behavior for the CO2 to CO conversion however under slightly higher η. Based on the bulk electrolysis experiment, the catalysis parameters, kcat, TON, and TOF were calculated using equations (11)~(13);

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