Biomimetic cellulose membrane enables high-performance salinity gradient energy conversion: Coupling surface charge and nanopore structure

Surface charge and nanoscale porous structure of ion-selective membranes have been considered prominent in affecting conversion capability of salinity gradient energy-to-power, while the synergistic contribution of them is conventionally overlooked, thus limiting their further development toward high-performance harvesting of salinity gradient energy. Herein, bioinspired by organisms achieving effective intracellular ion transport through their surface-charged nanochannels, we designed porous-charged cellulose membrane (PCC) by simultaneously engineering surface charge and pore structure, followed by desirably chemical and structural distinctions, such as high zeta potential and sulfonic acid group content of -44 mV and 1.22 mmol/g, large porosity of 84 % and pore volume of 0.01 cm3/g (d <= 10 nm), while just -23 mV, 42 %, 0.0036 cm3/g and 0 mmol/g for pristine cellulose. Such distinctions endow PCC with excellent ion transport rate and capability (high t+ of 0.97 and eta of 44.18 % in 0.001/0.01 M), correspondingly superhigh power density of 21.6 W/m2 (0.01/5 M), which surpasses that of most membrane materials, including biomass materials, synthesized polymers, and even some composite materials. By a tandem 30 PCC units, the output voltage of the designed PCC device reaches 2.24 V, which successfully powers calculator and light-emitting diode. In addition, our PCC demonstrates excellent stability in various pH system (from 3 to 11) during 30-day testing. The PCC with environmentally friendly, low cost, and large-scale advantages demonstrates strong competitiveness in advanced membrane materials toward high-performance manipulating ion transport.