Stable MXene/cellulose nanofiber membranes as osmotic energy generators

Osmotic energy is a clean and renewable alternative resource to non-renewable fossil fuel. Harvesting this "blue" energy typically required ion-selective membranes. Two-dimensional (2D) materials are ideal scaffolds for constructing nanofluidic ion-selective membranes in osmotic energy conversion. However, the 2D membranes were often fragile and instable in solutions because of the weak van der Waals interactions between twodimensional nanosheets. Here, stable MXene nanofluidic membranes were constructed by incorporating cellulose nanofiber (CNF) in MXene. The CNF was used as binder to enhance the mechanical stability in solutions. The resulted MXene/CNF membranes were investigated in terms of structure, ion selectivity and osmotic energy generation. The results showed that the MXene/CNF membranes exhibited excellent cation selectivity due to the negative charged carried by MXene and CNF, benefiting the osmotic energy conversion. The maximum power output density reached up to 1.32 and 0.338 W m(-2) at 1000-fold KCl and 50-fold NaCl concentration gradient, respectively. Moreover, this MXene/CNF energy generator exhibited a long-term output stability. This work demonstrated the great potential of nanofluidic generators based on the two-dimensional material and the biomass material cellulose for osmotic energy conversion processes.