β-FeOOH-Loaded Polydopamine-Modified Halloysite Nanotubes as a Catalytic Interlayer for Enhanced Water Dissociation in Bipolar Membranes.

Efficient interfacial water dissociation is essential for reducing the operating voltage of bipolar membranes (BPMs), whereas aggregation and nonuniform distribution of nanoscale catalysts can limit active-site utilization. In this study, polydopamine-modified halloysite nanotubes (PDA@HNTs) were used as a support for β-FeOOH loading to construct a composite catalytic interlayer for BPMs. XRD, FTIR, XPS, SEM, TEM, EDS mapping, contact-angle measurements, electrochemical tests, and bipolar membrane electrodialysis were used to evaluate the interlayer structure and membrane performance. At 50 mA cm-2, the β-FeOOH-PDA@HNTs-BPM exhibited a transmembrane voltage of 0.94 V, compared with 2.15 V for the blank BPM, while the interfacial water-dissociation resistance decreased from 3.873 to 0.980 Ω. After 48 h of continuous operation, the voltage increased only from 0.94 to 0.98 V. In electrodialysis, the membrane achieved a current efficiency of 81.4% and an energy consumption of 3.3 kWh kg-1 after 180 min. PDA-functionalized HNTs promote the dispersion and interfacial association of β-FeOOH, improve interfacial wettability and catalytic-site accessibility, and thereby enhance water dissociation and acid/base production in BPMs.