Reduction of Carbon Dioxide at Metal Electrodes

Udapa et al.16 showed that C02 was reduced to formic acid at a mercury electrode in a 0.05 M phosphate buffer (pH 6.8) solution. A current efficiency of 81.5% was obtained at a current density of 20 mA/cm2 and a cell voltage of 3.5 V. On the other hand, Bewick and Greener17 reported that malate and glycolate were produced at Hg and Pb electrodes, respectively, using aqueous quartenary 

Instead of mercury, Ito et a/.18 examined systematically some sp metals, such as Zn Pb, Sn, In, and Cd (5N purity), as the cathode materials for C02 reduction (Fig. 1). Using an In electrode at 3.9 mA/cm2, the highest current efficiency (92%) for formic acid production was obtained in an aqueous Li2C03 solution the potentials at which C02 was reduced at an In electrode were ca. 400 mV less negative than those at an Hg electrode. 

A little later, Russell et al.19 tried to obtain methanol from carbon dioxide by electrolysis. Reduction of carbon dioxide to formate ion took place in a neutral electrolyte at a mercury electrode. On the other hand, formic acid was reduced to methanol either in a perchloric acid solution at a lead electrode or in a buffered formic acid solution at a tin electrode. The largest faradaic efficiency for methanol formation from formic acid was ca. 12%, with poor reproducibility, after passing 1900 C in the perchloric acid solution at Pb in a very narrow potential region (-0.9 to -1.0 V versus SCE). In the buffered formic acid solution (0.25 M HCOOH + 0.1 M 

More recently, Hori et al.23 reported that reduction of C02 by galvanostatic electrolysis (5 mA/cm2) at Au and Ag electrodes gave 

Electrode Electrode potential (V versus SHE) Faradaic efficiency (lower limit/upper limit) (%)  

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