A sheet having anion exchange functionality and a sheet having cation exchange functionality are juxtaposed and joined by current bonding into a unitary bipolar membrane. This may be done without added reactants or bonding agents by placing the two-layer assembly between opposed electrodes in a fluid cell, preferably at pressure, and applying power across the cell to split water in a junction region of the membrane assembly. Preferably the anion exchange sheet is treated with an iron salt solution so as to incorporate or immobilize the metal in the polymer during the current bonding process, and enhance operating characteristics of the bipolar junction. Membrane peel strength is comparable to or greater than that of an underlying sheet of ion exchange material, but the bonding is fully reversible, e.g., by soaking in a concentrated solution. Preferably both sheets include an aromatic backbone or cross-linker component. One membrane may be a self supporting membrane, such as a conventional electrodialysis exchange membrane of 5-50 mil (0.12-1.2 mm) thickness, while the other may also be a commercial membrane of opposite exchange type and of similar strength or thickness, or may be specially manufactured to tailor its performance in the completed membrane. For example, one or both starting sheets may be manufactured with a pore former or may otherwise have its porosity, cross-linking, strength, ion rejection characteristics or thickness tailored for more effective bipolar operation--for example, to enhance transport or diffusion, resist shear or mechanical forces, improve chemical resistance to splitting products or species in the intended feed, or the like. Preferably, prior to contacting and bonding, the anion exchange membrane is treated with a group VIII metal salt. The current-bonded unitary bilayer construction remains contact bonded over its surface and resists degradation in normal use.