KINETIC STUDIES OF ELECTROLYTIC REDUCTION OF CARBON DIOXIDE ON MERCURY ELECTRODE

The reduction of CO2 to HCOOH has been studied for the Hg electrode in neutral and acidic aqueous solutions in the potential range between -0.8 and -1.9 V(sce). In the neutral pH range all the current is consumed in the production of formic acid, while in acid solutions both HCOOH and H2 are produced. Steady-state polarization curves, cathodic galvanostatic charging curves. current-efficiency measurements, reaction orders with respect to CO2 partial pressure, and double-layer variation have been used to determine possible reaction pathways. In neutral solutions the mechanism may be described by a direct reduction of CO2 in which two consecutive charge-transfer steps occur. In acidic solutions the above process occurs in parallel with the reduction of H3O+ ions. The H atoms formed react in a branching mechanism either with H3 O+ ions and electrons to yield H2, or with CO2 to yield eventually HCOOH. © 1969.