Cobalt(II)–tetraphenylporphyrin–pyridine complex fixed on a glassy carbon electrode and its prominent catalytic activity for reduction of carbon dioxide

Abstract

Cobalt(ii)-tetraphenylporphyrin (CoVpp)-fixed glassy carbon (GC) electrodes were prepared using 4-aminopyridine (pyNH2) in the form of Colltpp-pyNH-CO/GC, which were active for electroreduction of C 0 2 to CO at potentials 100 mV more positive than water-soluble Coil porphyrins, and the overall turnover number of Coiltpp for CO production exceeded 105.Metalloporphyrins have been reported to be active as catalysts in the electroreduction of C 0 2 in aqueous' and nonaqueous2 media. In aqueous media, water-soluble CoIItetraphenylporphyrin sulphonate and CoTTrneso-tetracarboxyphenylporphyrin have been reported to be catalytically active for the electroreduction of C 0 2 . Pyridine (py) is reported to coordinate at the axial position of planar CoII(sa1en) (H2salen = bissalicylideneethylenediamine) and stabilizes C 0 2 in the opposite coordination site.3 In the present work, we attempted to obtain a CoIItpp-py (tpp = tetraphenylporphyrin) complex-fixed electrode by applying the water-insoluble CoIItpp on glassy carbon (GC) substrate plates modified initially with 4-aminopyridine (pyNH2). 4-Aminopyridine is expected not only to immobilize CoIItpp on the G C electrode, but also to provide the CoIItpp-fixed GC electrode with new properties.CoIItpp-pyNH-CO/GC (I) was prepared as follows Glassy carbon (GC) plates (Tokai GC-30, 27 mm x 5 mm, 1 mm thick) were subjected to anodic oxidation in 0.5 mol dm-3 H2S04, and refluxed in SOC12 for 24 h, for chlorination as COCl/GC. The electrodes were then immersed in 4-aminopyridine-saturated benzene solution for 24 h at room temperature to produce pyNH-CO/GC (11). Finally, the electrodes were refluxed in a 0.6 mmol dm-3 CoIItpp solution in benzene for 24 h to produce I.The fixation of 4-aminopyridine was confirmed by the diffuse reflectance FT IR spectrum of 11, which showed a peak at 1665 cm-1 due to C=O stretching of the -CO-NH-amide group together with pyridine ring C=C and C=N stretching peaks at 1610 and 1537 cm-1, respectively. These results showed that 4-aminopyridine was fixed in the form of pyNH-CO/GC. Fig. l(a) shows the diffuse reflectance UV-VIS spectrum of I, together with spectra of ( b ) CoIItpp and (c) CoIItpp-py in CH2C12 for comparison. Spectra ( a ) and (c) show the Soret band at 440 nm, whereas that of ( b ) is at 420 nm. These spectra indicated that Co**tpp was fixed as the pyridine complex, CoIItpp-py, and the electron density of the central ColI ions of I was increased by the pyridine 1igand.s Fig. 2 shows cyclic voltammograms (CV) of I in standard phosphate buffer solution at pH 6.86 saturated with He or C02. No CoIItpp/CoItpp redox peak was observed, but this is probably due to the small amount of CoIItpp distributed on the electrode which has a high roughness factor (3 x 103). The surface concentration of CoIItpp of (10-12 mol cm-2; apparent surface area) was evaluated by ESCA. A pronounced increase of the cathodic current was observed at potentials more negative than -0.95 V [vs. saturated calomel electrode (SCE)] in C02-saturated solution, this increase st...

Water Facilitated Electrochemical Reduction of CO2 on Cobalt-Porphyrin Catalysts

“…2,[4][5][6][7][8][9][10][11][12][13][14] Among such catalysts, cobalt porphyrin complexes are considered to be one of the promising candidates since it selectively reduces CO 2 to CO with relatively small overpotential in aqueous solutions. 15,16 Recently, drastic improvements in terms of stability in aqueous medium, high selectivity in CO 2 reduction, and low overpotential, have been achieved by the immobilization to the graphite electrode 9,[17][18][19][20] or by using as the building blocks of COF (covalent organic frame-works) 8 and MOF (metal organic frameworks). 11 To achieve further improvement, understanding of catalytic effects of cobalt porphyrin complexes is quite important and, therefore, analyses using electronic structure calculations have been carried out.…”

Covalently Grafting Cobalt Porphyrin onto Carbon Nanotubes for Efficient CO2 Electroreduction

“…[17][18][19][20][21] To improve the catalyst'sd ispersion, strengthening the interaction between the molecular catalysts and supports as ameans to overcome self-stacking is necessary. [19,22,23] Another approach is to directly graft molecular catalysts onto the conductive substrates via covalent bonding.Y ao et al covalently linked ac obalt porphyrin complex with peripheral acetylene groups to ad iamond surface decorated with alkyl azides by azidealkyne cycloaddition. [19,22,23] Another approach is to directly graft molecular catalysts onto the conductive substrates via covalent bonding.Y ao et al covalently linked ac obalt porphyrin complex with peripheral acetylene groups to ad iamond surface decorated with alkyl azides by azidealkyne cycloaddition.…”

“…[16] This can be realized by coordination of the metal centers and pyridine groups to the support. [19,22,23] Another approach is to directly graft molecular catalysts onto the conductive substrates via covalent bonding.Y ao et al covalently linked ac obalt porphyrin complex with peripheral acetylene groups to ad iamond surface decorated with alkyl azides by azidealkyne cycloaddition. [24] Maurin et al successfully modified carbon nanotubes by attaching Fe-porphyrin through acovalent bond between the peripheral carboxylic acid group and the surface amine group,obtaining ahigh CO selectivity and aturnover at 500 mV overpotential.…”

Molecular Catalysis for Utilizing CO2 in Fuel Electro-Generation and in Chemical Feedstock

“…Fujita et al later reported that iron(IV) and cobalt(III) corrole complexes similarly catalyze the reduction of CO2 to CO at −1.7 V vs. SCE under homogeneous conditions (Scheme 5) [60,61]. Cobalt porphyrin (CoTPP) and phtalocyanine (CoPc) complexes were also found to be catalytically active in water on carbon electrodes film-coated with the complexes [24,[62][63][64][65]. By using the Co(TPP) (Scheme 6) deposited on a carbon black gas-diffusion electrode, CO is produced at −0.76 V vs. SHE (overpotential = 230 mV) at 97% FE in a 0.5 M KHCO3 solution under a high CO2 pressure Cobalt porphyrin (CoTPP) and phtalocyanine (CoPc) complexes were also found to be catalytically active in water on carbon electrodes film-coated with the complexes [24,[62][63][64][65].…”

“…Cobalt porphyrin (CoTPP) and phtalocyanine (CoPc) complexes were also found to be catalytically active in water on carbon electrodes film-coated with the complexes [24,[62][63][64][65]. By using the Co(TPP) (Scheme 6) deposited on a carbon black gas-diffusion electrode, CO is produced at −0.76 V vs. SHE (overpotential = 230 mV) at 97% FE in a 0.5 M KHCO3 solution under a high CO2 pressure Cobalt porphyrin (CoTPP) and phtalocyanine (CoPc) complexes were also found to be catalytically active in water on carbon electrodes film-coated with the complexes [24,[62][63][64][65]. By using the Co(TPP) (Scheme 6) deposited on a carbon black gas-diffusion electrode, CO is produced at −0.76 V vs. SHE (overpotential = 230 mV) at 97% FE in a 0.5 M KHCO 3 solution under a high CO 2 pressure of 20 atm.…”