Selective electrochemical reduction of CO 2 to CO was studied using a new electrocatalyst and a gas-electrolysis cell utilized a polymer-electrolyte-membrane (PEM) reactor. A selective and active electrocatalyst was prepared by partial pyrolysis of electrocatalyst precursor of Co-4,4'-dimethyl-2,2'-bipyridine (4,4'-dmbpy) supported on Ketjenblack (KB). A heat-treatment temperature of the Co-4,4'-dmbpy/KB significantly influenced on its electrocatalytic activity and 573~673 K treatments were suitable for a selective CO 2 reduction. A high performance of CO formation (331 mmol h À1 cm À2 , 217 TOF(Co) h À1 ) at 20 mA cm À2 with 72 % faradic efficiency was performed by using the optimized Co-4,4'-dmbpy/KB electrocatalyst at -0.75 V (SHE) and 273 K. Electrochemical silent Co species in CV studies promoted electrochemical reduction of CO 2 to CO.The CO 2 conversion processes into useful chemicals (e. g., CO, CH 4 , HCOOH and CH 3 OH) would be promising not only for solution of the global warming but also for the break from the dependency on petroleum resources, if we can obtain enough renewable energy such as solar and wind power. Various CO 2 conversion methods have been proposed [1][2][3][4] and electrochemical reduction of CO 2 is one of desirable conversion methods. Electroreduction of CO 2 to CO using a PEM (polymer-electrolyte-membrane) reactor with Co-compound cathodes was studied in this work. CO is a useful industrial material and carbonylation reagent to produce a variety of chemicals such as CH 3 OH, HCHO, and hydrocarbons (Fischer-Trö psch process). An equilibrium potential between CO 2 and CO is not so negative (eq. 1); however, it is usually recognized that the rate determining step is one electron reduction of CO 2 to CO 2 C À having a negative reduction potential (eq. 2) and second one electron reduction is fast (eq. 3).In the CO 2 reduction, hydrogen evolution reaction can easily take place (eq. 4) to compare with the rate-determining step (eq. 2). How to suppress the formation of H 2 is essential for the selective reduction of CO 2 to CO; therefore, the majority of previous works have been done using higher pH and carbonate solutions saturated CO 2 or under pressure conditions to suppress reduction to H + to H 2 (E8/V = 0.00 -0.059 pH). In 1994, various metal electrodes were screened for the electroreduction of CO 2 and it was revealed that the Cu electrode was active for the reduction forming CO and hydrocarbons. [4] After this attractive study, a lot of studies have been done and the Au, Ag and Zn electrodes were reported for the selective reduction of CO 2 to CO. [5] In case of none metal electrodes, selective electroreduction of CO 2 to CO using carbon supported Fe-, Mn-, Co-porphyrin and phthalocyanine electrodes were reported. [6] Recently, unique electrocatalysis of metal-free Ndoped CNF materials was reported for the selective reduction of CO 2 to CO and formate. [7] Fe and/or Mn-containing N-doped carbon materials synthesized from poly-aniline, FeCl 3 and/or MnCl 2 showed particular elect...

To contribute a solution for the global warming problem, the selective electrochemical reduction of CO 2 to CO was studied in the gas phase using a [CO 2 (g), Co–N–C cathode | Nafion-H | Pt/C anode, H 2 /water] system without using carbonate solutions. The Co–N–C electrocatalysts were synthesized by partial pyrolysis of precursors in inert gas, which were prepared from various N-bidentate ligands, Co(NO 3 ) 2 , and Ketjenblack (KB). The most active electrocatalyst was Co–(4,4′-dimethyl-2,2′-bipyridine)/KB pyrolyzed at 673 K, denoted Co–4,4′-dmbpy/KB(673K). A high performance of CO formation (331 μmol h –1 cm –2 , 217 TOF h –1 ) at 0.020 A cm –2 with 78% current efficiency was obtained at −0.75 V (SHE) and 273 K under strong acidic conditions of Nafion-H. Characterization studies using extended X-ray absorption fine structure (EXAFS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy–energy-dispersive X-ray (TEM-EDX), X-ray diffraction (XRD), and temperature-programmed desorption with mass spectrometry (TPD-MS) indicated the active site as Co coordinated with four N atoms bonding the surface of KB, abbreviated Co–N 4 –C x structure. A model of the reduction mechanism of CO 2 on the active site was proposed.

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A new compound prepared from poly(4-vinylpyridine), Co(NO 3 ) 2 , and Ketjenblack (KB, Lion Special Chemical) by partial pyrolysis in Ar at 673 K, Co(PV4Py)/KB(673 K), effectively catalyzed electroreduction of CO 2 to CO in the solid polymer electrolyte (SPE) electrolysis gas cell without using carbonate solutions. Characterization studies using extended X-ray absorption fine structure (EXAFS), X-ray photoelectron spectroscopy (XPS), etc. indicated the active site as Co-coordinated four N atoms bonding the surface of KB, abbreviated CoN 4 C x . An onset potential of −0.25 V [versus standard hydrogen electrode (SHE)] for the reduction of CO 2 to CO was close to the standard redox potential at −0.109 V.