Cellulose-based bipolar heterogeneous membranes with two-dimensional lamellar composite three-dimensional network structure for osmotic energy conversion

Reverse electrodialysis (RED) technology is extremely promising in harvesting osmotic energy. The exchange membranes, which are the core components of RED systems, especially in the investigation of composite membrane systems, remain a challenge by balancing the key requirements of better compatibility and sufficient stability, ease of fabrication, etc. In view of the excellent compatibility and stability of forest biomass membrane materials, this work reports a two-dimensional (2D) lamellar regenerated cellulose (RC) composite with a three-dimensional (3D) network of bacterial cellulose membrane doped with alkali lignin (BC-AL) heterogeneous membrane. The 2D lamellar structure provides nano-confined channels with high ionic flux, while the asymmetric structure formed by compositing with the 3D porous spatial network positively reduces the energy barrier and effectively weakens the concentration polarization effect to a certain extent, which also results in the formation of bipolar surfaces. Moreover, the large negative charges on the surface of the composite membrane enhance the cation selectivity and ion diffusion rate. The heterogeneous membrane is more advantageous for osmotic energy harvesting, achieving a power density of nearly 2 W·m⁻² under alkaline conditions. Both experimental and simulation analysis have demonstrated the significant potential of this structured heterogeneous membrane in the field of osmotic energy harvesting.