ELECTROCHEMICAL REDUCTION OF CARBON DIOXIDE TO FORMIC ACID AT TIN CATHODE IN DIVIDED AND UNDIVIDED CELLS: EFFECT OF OPERATING PARAMETERS

The electrochemical reduction of carbon dioxide is considered a relevant topic for both the synthesis of chemicals and the decrease of global warming. Electrochemical processes could utilize excess energy from intermittent renewable sources to convert carbon dioxide in various products such as CO, formate and formic acid, methane and ethylene in water and oxalic acid, formic acid, CO as well as carboxylic acids (by reaction with suitable reagents such as aromatic ketones or benzylic halides) in aprotic solvents [1-3]. It has been shown that the selectivity of the process dramatically depends on the nature of the cathode. Four distinct classes of metal catalysts have been identified on the bases of the main products obtained by the cathodic reduction in water: (i) metals that mainly form formic acid (Pb, Hg, In, Sn, Cd, Ti); (ii) metals that mainly form carbon monoxide (Au, Ag, Zn, Pd, Ga); (iii) metals that mainly form H2 (Pt, Ni, Fe, Ti); (iv) metals that form significant amounts of hydrocarbons such as methane and ethylene (Cu) [2]. In the last years, an increasing attention has been devoted to the conversion of carbon dioxide to formic acid in water. In particular, it has been shown that the utilization of cheap tin cathodes allow the production of formic acid with good Faradic Efficiencies (FE) [4], even higher under suitable operating conditions than that obtained at lead cathode. The engineering and economic feasibility of large-scale electrochemical reduction of carbon dioxide to formate salts and formic acid at tin cathodes was evaluated by Agarwal et al. [10] that concluded that this process could be operationally profitable. Both undivided and divided cells can be used for the electrochemical reduction of carbon dioxide [4]. Divided cells allow an effective separation of anodic and cathodic processes, thus preventing or minimizing the anodic oxidation of electrogenerated formic acid. On the other hand, the utilization of undivided cells would be appealing in order to avoid the potential penalties given by the presence of the separator in divided cells. In the present work the electrochemical reduction of CO2 to formic Acid at tin cathode was studied in both divided and undivided cells in order to evaluate the performances of the process. The effect of some operating conditions was also studied