Robust Cellulose Nanocrystal‐Based Self‐Assembled Composite Membranes Doped with Polyvinyl Alcohol and Graphene Oxide for Osmotic Energy Harvesting

Osmotic energy from the salinity gradients represents a promising energy resource with stable and sustainable characteristics. Nanofluidic membranes can be considered as powerful alternatives to the traditional low‐performance ion exchange membrane to achieve high‐efficiency osmotic energy harvesting. However, the development of a highly efficient and easily scalable core membrane component from low‐cost raw materials remains challenging. Here, a composite membrane based on the self‐assembly of cellulose nanocrystals (CNCs) with polyvinyl alcohol (PVA) and graphene oxide (GO) nanoflakes as additives is developed to provide a solution. The introduction of soft PVA polymer significantly improves the mechanical strength and water stability of the composite membrane by forming a nacre‐like structure. Benefiting from the abundant negative charges of CNC nanorods and GO nanoflakes and the generated network nanochannels, the composite membrane demonstrates a good cation‐selective transport capacity, thus contributing to an optimal osmotic energy conversion of 6.5 W m−2 under a 100‐fold salinity gradient and an exemplary stability throughout 25 consecutive days of operation. This work provides an option for the development of nanofluidic membranes that can be easily produced on a large scale from well‐resourced and sustainable biomass materials for high‐efficiency osmotic energy conversion. A cellulose nanocrystal‐dominated self‐assembled composite membrane doped with polyvinyl alcohol and Graphene nanoflakes is fabricated. The resulting composite membrane with excellent mechanical strength and chemical stability demonstrates an osmotic energy conversion of 6.5 W m−2 under a 100‐fold salinity gradient and exemplary long‐term stability.