Scalable Wood Hydrogel Membrane with Nanoscale Channels.

Many efforts have been dedicated to exploring nanofluidic systems for various applications including water purification and energy generation. However, creating robust nanofluidic materials with tunable channel orientations and numerous nanochannels or nanopores on a large scale remains challenging. Here, we demonstrate a scalable and cost-effective method to fabricate a robust and highly conductive nanofluidic wood hydrogel membrane in which ions can transport across the membrane. The ionically conductive balsa wood hydrogel membrane is fabricated by infiltrating poly(vinyl alcohol) (PVA)/acrylic acid (AA) hydrogel into the inherent bimodal porous wood structure. The balsa wood hydrogel membrane demonstrates a 3 times higher strength (52.7 MPa) and 2 orders of magnitude higher ionic conductivity compared to those of natural balsa both in the radial direction (coded as R direction) and along the longitudinal direction (coded as L direction). The ionic conductivity of the balsa wood hydrogel membrane is 1.29 mS cm along the L direction and nearly 1 mS cm along the R direction at low salt concentrations (up to 10 mM). In addition, the surface-charge-governed ion transport also renders the balsa wood hydrogel membrane able to harvest electrical energy from salinity gradients. A current density of up to 17.65 μA m and an output power density of 0.56 mW m are obtained under a 1000-fold salt concentration gradient, which can be further improved to 2.7 mW m by increasing the AA content from 25 wt % to 50 wt %. These findings make contributions to develop energy-harvesting systems and other nanofluidic devices from sustainable wood materials.