Reduction of carbon dioxide on ruthenium oxide and modified ruthenium oxide electrodes in 0.5 M NaHCO3

Abstract

Electrochemical reduction of carbon dioxide is still of great interest in the fields of theoretical and applied electrochemistry. Ruthenium is one of the metals with an intermediate hydrogen evolution overpotential which adsorbs a considerable amount of hydrogen at underpotentials. Therefore, one can expect that the reduction of CO2 will take place at this electrode at relatively small overpotentials, at which the hydrogen evolution will not be excessive. This will diminish the loss due to concurrent hydrogen evolution. The stability of the electrode surface under vigorous hydrogen evolution enables investigation of the kinetics of CO2 reduction under long-term potentiostatic conditions. Reduction of CO2 at ruthenium and ruthenium modified by Cd and Cu adatoms was investigated in 0.5 M NaHCO3 solutions. Cyclic voltammetry, potentiostatic measurements and long-term electrolysis were performed using standard electrochemical equipment. The analysis of the bulk of the electrolyte was performed with gas chromatography. On the Ru surface as well as on Ru modified by Cu and Cd adatoms and on RuOx + IrOx modified by Cu adatoms and Cd adatoms, CO2 reduction proceeds to give methanol and acetone during 8 h of holding the potential at -0.8 V. The process of methanol formation on Ru modified by Cu and Cd adatoms is catalyzed by the presence of adatoms and the process of acetone formation is independent of the presence of adatoms at the ruthenium surface. For all the examined surfaces and for further investigations the most promising fact is the relatively low observed overvoltage of the holding potential for CO2 reduction, at which methanol and acetone were found in the bulk of the electrolyte. The faradaic efficiencies obtained for methanol production in the case of modified ruthenium surfaces indicate some possibility of practical application