Kh. B. Kushkhov, M. N. Ligidova, J. Z. Ali, A. A. Khotov, M. R. Tlenkopachev, R. Kh. Karatsukova.
ABSTRACT
The regularities of the electrochemical behavior of melts of a mixture of alkali metal carbonates K2CO3–Na2CO3 and K2CO3–Na2CO3–Li2CO3 on platinum and gold electrodes in an atmosphere of air and carbon dioxide under an overpressure of up to 10∙105 Pa were established. The peculiarities of the current-voltage dependences of alkali metal carbonate melts are explained taking into account acid-base equilibria with the participation of the carbonate ion CO32- CO2 + O2-. It was shown that in the eutectic melt K2CO3–Na2CO3, the carbonate ion is stable, i.e. Na+ and K+ cations possess weakly pronounced oxoacidic properties and do not exhibit electrochemical activity up to the discharge potentials of alkali metal cations. Under these conditions, the electroreduction of CO32– occurs together with Na+ and K+ cations, or a secondary reduction of the carbonate ion by the liberated alkali metal takes place. The addition of lithium carbonate containing a cation with a higher polarizing force (greater oxoacidity) to the K2CO3–Na2CO3 melt shifts the acid – base equilibrium toward the formation of CO2 and affects the electrochemical behavior of carbonate melts, leading to the appearance of a cathodic wave of CO2 reduction to elemental carbon. The creation of excess pressure of carbon dioxide over the melt of the K2CO3–Na2CO3 and K2CO3–Na2CO3–Li2CO3 mixture to 10 ∙ 105 Pa leads to saturation of the melts with carbon dioxide, and the polarization of the platinum and gold electrodes in these systems leads to the reduction of CO2 to elemental carbon. It was shown that the product of galvanostatic electrolysis in a wide range of current densities of 0.25–2.0 A/cm2 of the equimolar mixture Na2CO3–Li2CO3 and the eutectic mixture K2CO3–Na2CO3–Li2CO3 at a temperature of 873 K consists of graphite phases, C60 and C70 fullerenes, and carbon nanotubes.
KEYWORDS:
alkali metal carbonates melts, electroreduction, electrolysis, acid-base equilibria, CO2 overpressure, electrodeposition of carbon nanostructures.
DOI: 10.31857/S0235010620040040