Excellent electrocatalytic activity of benzil for direct reduction of CO_2 as well as indirect reduction of pyridine:A kinetic view of the electrocarboxylation process

Benzil, 1,2-diphenylethane-1,2-dione, was used as an excellent electrocatalyst for reduction of carbon dioxide, CO₂. The reduction overpotential of CO₂ was reduced about 900 mV in the presence of a benzil mediator. The chemical reaction of the product of the electrocatalytic reduction of CO₂, (activated CO₂, CO₂^•−) with pyridine at a glassy carbon electrode, GCE, surface and in an acetonitrile-But₄NClO₄ solution was investigated by cyclic voltammetry, chronoamperometry and controlled potential coulometry. By chronoamperometry, the catalytic rate constant, k, for the electron transfer between benzil and CO₂ was obtained as 8.1 ± 0.4 M⁻¹ s⁻¹. The results indicate that pyridine has a strong interaction with the activated CO₂. The coulometry method was used to obtain the product of the pyridine chemical reaction with CO₂^•−. The spectral characterizations of FTIR, ¹H and ¹³C NMR of the coulometry experiment product proved that the pyridine anion radical, Py^•−, was carboxylated by CO₂^•−, and isonicotinic acid is the final major product.