Interlayer confinement toward short hydrogen bond network construction for fast hydroxide transport

Driven by boosting demands for sustainable energy, highly conductive hydroxide exchange membranes (HEMs) are urgently required in electrochemical conversion devices. The hydrogen bonds shorter than 2.5 angstrom are expected to accelerate the ion transport. However, short hydrogen bonds (SHBs) can hardly form naturally because of the electron-withdrawing capability of O atom, which impedes its applications in water-mediated ion transport. This work develops an interlayer confinement strategy to construct SHB networks in a two-dimensional (2D) nanocapillary assembled by bismuth oxyiodide (BiOI) nanosheets and boost the ionic conductivity of HEMs. With confined nanochannels and adjustable hydrophilic groups in BiOI-based HEMs, the number of SHBs increases by 12 times, creating a shortcut for the Grotthuss-type anion transport, which in turn affords a high ionic conductivity of 168 millisiemens per centimeter at 90°C, higher than polymeric HEM and 2D-based HEM. This work demonstrates the facile approach to generating SHB networks in 2D capillaries and opens a promising avenue to developing advanced HEMs.