Abstract:
The use of electrospun bipolar membranes (BPMs) with an interfacial
three-dimensional (3D) junction of entangled nano-/microfibers has been recently
proposed as a promising fabrication strategy to develop high-performance BPMs. In
these BPMs, the morphology and physical properties of the 3D junction are of
utmost importance to maximize the membrane performance. However, a full
understanding of the impact of the junction thickness on the membrane performance
is still lacking. In this study, we have developed bipolar membranes with the same
composition, only varying the 3D junction thicknesses, by regulating the
electrospinning time used to deposit the nano-/microfibers at the junction. In
total, four BPMs with 3D junction thicknesses of ∼4, 8, 17, and 35 μm were
produced to examine the influence of the junction thickness on the membrane
performance. Current−voltage curves for water dissociation of BPMs exhibited lower
voltages for BPMs with thicker 3D junctions, as a result of a three-dimensional
increase in the interfacial contact area between cation- and anion-exchange fibers and thus a larger water dissociation reaction area.
Indeed, increasing the BPM thickness from 4 to 35 μm lowered the BPM water dissociation overpotential by 32%, with a current
efficiency toward HCl/NaOH generation higher than 90%. Finally, comparing BPM performance during the water association
operation revealed a substantial reduction in the voltage from levels of its supplied open circuit voltage (OCV), owing to excessive
hydroxide ion (OH−) and proton (H+
) leakage through the relevant layers. Overall, this work provides insights into the role of the
junction thickness on electrospun BPM performance as a crucial step toward the development of membranes with optimal entangled
junctions.
