The cathodic reduction of CO₂ at copper electrodes in aqueous solutions of bicarbonates was investigated with special attention directed towards the changes in the current efficiency of the principal products (CH₄, C₂H₄, C₂H₅OH) as a function of the electrolysis duration. A severe deactivation of the copper cathode, starting usually 20–30 min after the beginning of the electrolysis run, is shown to be little affected by the pre-electrolysis of the solution as well as by the nature of the electrode pretreatment. A periodic anodic activation procedure is described which, when applied to the copper cathode, allows high hydrocarbon yields to be maintained over prolonged electrolysis runs.