A general approach of reinforcing hydrogels for salinity-gradient energy harvesting

Abstract

Salinity-gradient energy (osmotic energy) has attracted considerable attention because of its sustainable and pollution-free nature. Although diverse hydrogel membranes have been fabricated to replace two-dimensional material-based membranes, strategies for producing tough hydrogel membranes for efficient capture of salinity-gradient energy are still unexplored and of significant challenge. Herein, we reported a general approach of reinforcing hydrogels using covalent organic frameworks (COFs). Because of the COF-induced nanochannel confinement effect and the formation of multiple hydrogen bonds between COFs and PVA (polyvinyl alcohol) chains, one hydrogel demonstrated excellent mechanical properties including a fracture stress of ∼6.24 MPa, a fracture strain of ∼589.7 %, and the toughness of ∼16.62 MJ/M³, that were superior to those of the pristine PVA hydrogel. When the hydrogels were used for salinity-gradient energy harvesting, one hydrogel showed an output power density of ∼12.5 W/m² at a rather low resistance of ∼4 KΩ, that was superior to those of most of previously reporting systems using hydrogel membranes. This excellent performance was attributed to the sulfonated group-induced charge density enhancement and the PVA chain fluctuation-induced ions/ion clusters hopping. Our research provides an efficient strategy for the design of tough polymeric hydrogels for efficient capture of the salinity-gradient energy.