Abstract: A device comprising an electrolyser, a compressor, and a membrane separating device, and to a method for changing the operating mode between normal and standby operation of said device, in the normal operation of which an electrolysis raw product comprising carbon dioxide is converted in the electrolyser into an electrolysis product containing carbon dioxide and carbon monoxide, at least one portion of which is conducted via the compressor and is fed at an increased pressure to the membrane separating device in order to obtain a retentate which is enriched in carbon monoxide and depleted of carbon dioxide compared with the electrolysis product. According to the invention, in order to change from the normal operation into the standby operation, the electrolyser is completely isolated from the membrane separating device in terms of flow and then shut down, wherein the pressure ratios in the membrane separating device are largely maintained.