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Freestanding bipolar membranes (BPMs) with an extended-area water splitting junction were fabricated utilizing electrospinning. The junction layer was composed of a mixed fiber mat that was made by concurrently electrospinning sulfonated poly(ether ether ketone) (SPEEK) and quaternized poly(phenylene oxide) (QPPO), with water splitting catalyst nanoparticles intermittently deposited between the fibers. The mat was sandwiched between solution cast SPEEK and QPPO films and hot-pressed to form a dense trilayer BPM with an extended-area junction of finite thickness, composed of QPPO nanofibers embedded in a SPEEK matrix with the catalyst nanoparticles interspaced between the two polymers. The composition, ion-exchange capacity, and catalyst type/loading in the junction were varied, and the water splitting characteristics of the membranes were assessed. The best BPMs fabricated in this work employed a graphene oxide catalyst and exhibited a low trans-membrane voltage drop of about 0.82 V at 1000 mA/cm 2 in water splitting experiments with 0.5 M Na 2 SO 4 and stable water splitting operation for 60 h at 800 mA/cm 2 .

The electrical relaxation and polarization phenomena of electrospun PVDF (P)/Nafion (N) blended fiber mats ([P/N 0.9 ] M and β-[P] M ) and membranes ([P/N 0.9 ] MM ) are compared with those of the solvent-cast membrane of identical composition ([N] C and [P/N 0.9 ] C ). The nature of the interactions between the two blended polymer components, that plays a pivotal role in the electrical nature of the resulting materials, is found to be governed by the fabrication method, with those materials obtained via electrospinning undergoing a "reciprocal templating" phenomenon that renders their electrical behavior (especially when in the dry state) significantly different from that of the blended membrane obtained via solvent casting. Broadband Electrical Spectroscopy (BES) demonstrates that the electric response of the blended materials is modulated by polarization phenomena and by α, β, and γ dielectric relaxation events of Nafion domains supported on β-PVDF. The coupling between the relaxations of β-PVDF with those of Nafion matrix is directly correlated to the "reciprocal templating" effect, which modulates the interactions between Nafion and PVDF in electrospun membranes. Two types of conductivity mechanisms characterize the H + migration within the polymer blends: (1) interdomain H + migration events by "charge-exchange" phenomena along percolation pathways and (2) H + exchange between delocalization bodies (DBs) at binding sites at the interface between domains with different ε, size, and morphology. The electrical response of the electrospun membranes also suggests that they do not comprise water clusters with a large size such as those typically observed in pristine Nafion. Rather, the adsorbed H 2 O molecules, under wet conditions, form thin solvation shells wrapping the polar side chains of the Nafion component. At T = 80 °C, the conductivity of the studied materials decreases in the order [N] C (0.043 S·cm -1 ) ≈ [P/N 0.9 ] C (0.042 S·cm -1 ) > [P/N 0.9 ] M (0.031 S·cm -1 ) > [P/N 0.9 ] MM (0.011 S·cm -1 ).