Effect of current pulsing of current efficiencies of the Brown-Walker and Kolbe electrosyntheses
Abstract
The anodic reactions in the electrolysis of aqueous potassium ethyl malonate solutions and acetate solutions using galvanostatic square pulses have been investigated. When unidirectional pulses alone are employed the current efficiencies of the dimerization reactions leading to diethyl succinate and ethane respectively are nearly the same as in continuous d.c. electrolysis, independent of the frequency of pulsing. If, however, a small reverse current is passed between anodic pulses, there now appears a sharply defined minimum in the current efficiency against frequency curve at a characteristic frequency. This appears to arise from the passage in the cathodic direction of a critical quantity of electricity which serves to destroy the electrode conditions necessary for dimer production and to permit oxygen evolution to become an effective competitive reaction. Electrode potential changes during pulsing have been studied oscillographically, and these observations, combined with the current efficiency measurements, clarify the processes occurring initially at the anode surface which lead to dimer production.