Abstract: The present invention relates to an improved apparatus of the type containing membranes which are selectively permeable to ion transport and a related method. The apparatus comprises at least one guard membrane located adjacent to a first membrane. A conductive bridge is formed between the guard and first membrane, either by adding an adhesive layer between the membranes or by treating the surface of the guard membrane. The adhesive layer between the guard and first membranes is preferably highly water swollen. The apparatus comprises at least one unit cell comprising at least one first membrane and one guard membrane which are held together by a static ionically conductive layer or interface. The guard membranes of the present invention are particularly useful in weak acid systems and prevent the formation of a non-conducting layer which greatly increases potential across the cell.