An electrically driven oxygen separation assembly and method for applying an electrical potential in which the assembly has one or more tubular membrane elements. The potential is applied at two central spaced locations of a tubular membrane element and at least at opposite end locations thereof. As a result the electric current flow through the tubular membrane element is divided into two parts flowing between the two central spaced locations and the opposite end locations. Additionally, the present invention also provides an end seal to be used in connection with tubular membrane elements.