Electrochemical reduction of bicarbonate on carbon nanotube-supported silver oxide: An electrochemical impedance spectroscopy study

Abstract

Bicarbonate reduction on a silver-oxide (Ag2O)-based electrode was studied via cyclic voltammetry and electrochemical impedance spectroscopy techniques. The effects of electrode composition, electrolyte concentration and the scan rate (10 -250 mV/s) were investigated at a temperature of 27 °C . An optimum mass ratio of 70/30 (Ag2O/CNT) led to a maximum current density of 83 mAcm -2 at -0.43 V (VS Ag/AgCl). At scan rates between 10 to 250 mV/s, a negative shift with a displacement of around 1.032 V was observedindicating the presence of irreversible reduction reactions. The observed irreversibility suggested that the reaction mechanism can be described by both diffusion and adsorption phenomena. The standard heterogeneous rate constant (ko) and the formal redox potential (Eo) were found to be 1.51×10 -4 cm/s and 1.218 V, respectively. The EIS results confirmed the formation of the inductive loops at reduction potentials -a consequence of the adsorption of the generated species. A reduction in charge transfer resistance and a continual drop in the potential from -0.1 down to -1.4 V was also observed. This was accompanied by H2 evolution 2 and bicarbonate production. The calculated pKa value of 10.20 upon the completion of the bicarbonate reduction reactions, confirmed the conversion of bicarbonate to carbonate ions.

Electrochemical bicarbonate reduction in the presence of Diisopropylamine on sliver oxide in alkaline sodium bicarbonate medium

“…The calculated line's slope above (i.e. 0.129) is not close to the theoretically-expected value of 0.5 for fully diffusion-controlled processes according to the Randles-Sevcik equation [19].…”

Direct Electrochemical Reduction of Bicarbonate to Formate Using Tin Catalyst

“…Many different direct CO 2 electroreduction techniques use bicarbonate solutions previously saturated with pure CO 2 gas to obtain hydrocarbons or alcohols showing significant selectivity. The main inconvenience of these techniques are its practical applications because CO 2 is present in the atmosphere at very low concentrations, and it is almost impossible to saturate a bicarbonate solution with CO 2 using atmospheric air, with just a few studies performing it on non-CO 2 saturated bicarbonate solutions [5][6][7][8][9][10][11]. Theoretically, direct CO 2 electroreduction is performed by CO 2 activation on a catalyst surface and its following reaction with two protons (2H + ).…”

Utilization of Low-Concentration CO2 with Molecular Catalysts Assisted by CO2-Capturing Ability of Catalysts, Additives, or Reaction Media

“…Conducting CO 2 -Red in CO 2 -capturing media is another effective strategy. Amines, − hydroxides, − and alkoxides − are well known as effective additives to capture CO 2 molecules in solutions. Ionic liquids (ILs) have been recently reported as effective solvents for CO 2 -Red.…”