A new type of bipolar membrane (BPM) with a high interfacial area 3D water splitting junction has been fabricated and tested. BPMs were made by single and dual fiber electrospinning, followed by dimethylformamide vapor exposure and hot-pressing, with sulfonated poly(ether ether ketone) as the cation-exchange polymer and quaternized poly(phenylene oxide) as the anion-exchange material. Al(OH)(3) nanoparticles were added to the junction to facilitate water splitting. The resultant trilayer membrane had an inner bipolar junction (interpenetrating anion-exchange and cation-exchange polymer nanofibers) similar to 10 mu m in thickness with dense/neat ionomer outer layers. The extended bipolar reaction zone enabled water splitting at ultra-high current densities (up to 1.1 A cm(-2)) with no evidence of membrane dehydration or blistering, which is common for a planar junction BPM. The novel electrospun membrane morphology offers significant benefits for electrodialysis separations, electrochemical hydrogen generation, and self-humidifying fuel cells, where high operating current densities and membrane stability are required.