Nacre‐Inspired Mechanically Robust Films for Osmotic Energy Conversion

Abstract MXene, a new class of 2D layered materials, is considered a candidate for the reverse electrodialysis (RED) film because the laminated MXene nanochannels with charged functional groups provide an excellent ionic selectivity and conductivity. However, the MXene‐based ion‐exchange films suffer from weak mechanical properties and instability in water due to the poor binding force between the nanosheets, which limits their RED performance. Here, inspired by natural nacre structure, a class of cation‐MXene/cation holocellulose nanofibers (C‐MXene/C‐HNF) composite film with high performance for harvesting nanofluidic osmotic is developed. C‐HNF acts as interlocking agent to connect the MXene nanosheets by hydrogen bonding, resulting a mechanically robust and water stable film. The introduction of C‐HNF not only increases the interlayer interaction force, but also enhances the ion transport flux. When the content of C‐HNF is 20%, the tensile stress, fracture strain, and toughness of the composite film reach up to 127.75 ± 1.61 MPa, 3.50 ± 0.1%, and 2.95 ± 0.52 MJ m −3 , respectively. Additionally, the composite film can produce an impressive output power density of up to 1.09 W m −2 under a 50‐fold salinity gradient (0.01/0.5 m NaCl), and only decreases by 4.58% after 50 days, demonstrating good stability and durability.