High-performance bipolar membrane for electrochemical water electrolysis

A bipolar membrane (BPM) enables the dissociation of water into protons and hydroxide ions, which in-situ maintains a steady-state pH difference in electrochemical water electrolyzers for optimum electro-kinetics of the anode and cathode electrocatalysts. However, instability and high overpotential requirement of the commercial Fumasep BPMs to drive water dissociation (eta WD > 100 mV at 20 mA cm-2) are major challenges to successfully applying them in electrochemical devices. To circumvent these membrane issues, we present the electrostatic self-assembly strategy to construct Fe(OH)3 colloids-based catalytic layer (FCL), which enhances the internal electric field, necessary to boost the polarization process of water molecules. Kelvin Probe Force Microscopy (KPFM) also confirms the improved work function (WF) of the FCL to establish a stronger built-in electric field for a fast polarization process during water dissociation. Consequently, the fabricated Fe(OH)3 colloids-based BPMs (FCBMs) require very little eta WD (29 mV) than commercial Fumasep BPM (eta WD: 44 mV) at 20 mA cm-2, which indicates the energy-efficient operability of the FCBMs in electrochemical water electrolyzers. This work demonstrates an effective route to fabricate stable and energy-efficient BPMs, ready to install in advanced acidalkaline water electrolysis systems for significantly enhanced hydrogen generation efficiency.