서강대학교

초록/요약

Carbon dioxide conversion is important not only in removing a greenhouse gas but also in utilizing this most abundant carbon compound toward useful organic compounds. CO2 activation is fundamentally an energy-required process and the development of efficient catalysts is a key issue. In nature, microbes including acetogens and methanogens exhibit C1 chemistry capable of activating CO2 to single or multi-carbon units. Here the microbes are demonstrated to be fascinating electrocatalysts for the conversion of carbon dioxide to useful organic compounds. Among eight microorganisms tested, acetogenic bacteria, Moorella thermoacetica (Mt, formerly Clostridium thermoaceticum, ATCC 35608) and Clostridium formicoaceticum (Cf, DSM 92) converted CO2 efficiently to formate. The current efficiency was reached to 80% for Mt and 100% for Cf when those were electrolyzed in 1 atm CO2 saturated 0.1 M phosphate buffer solution (pH 7.0) at -0.58 V vs. NHE which is near the equilibrium potential of CO2/formate. The CO2 reduction capability in aqueous solution of metal complexes syntheisized from cheap and abundant metals such as Ni, Cu, Co, and Fe were screened and characterized. Incorporation of viologen as a ligand was effective in shifting the redox potential positively to almost equilibrium potential and in selective conversion of CO2 to CO. The incorporation of the metal complexes to the polymeric system based on polyallyamine backbone was also useful in stabilizing the metal complexes and shifting the redox potential positively. Ni-cyclam-PAlA showed the most excellent performance of electrochemical conversion of CO2 to CO with 96 % current efficiency at -0.85 V(vs. Ag/AgCl) which is near thermodynamic potential. More than a dozen of binuclear complexes containing Ni and Cu were tested for their activity of CO2 reduction as electrocatalysts. In most cases CO was a main product upon electrocatalytic CO2 reduction and side product was hydrogen. In case of Ni-binuclear complex 2A, formate was detected as a liquid product with current efficiency of 2 %.