Enhanced salinity gradient energy harvesting with oppositely charged bacterial cellulose-based composite membranes

Restricted by the inherent properties of the materials, the membranes used for harvesting the salinity gradient energy generally suffer from low ion selectivity, weak permeability or high internal resistance, which heavily limit the output power density. In this work, the integration of one-dimensional bacterial nanofibers and two-dimensional nanosheets is projected to be an effective novel strategy for composite membranes with strongly enhanced output power density by balancing ion selectivity and permeability. Composite membranes as negatively charged bacterial cellulose/graphene oxide and positively charged bacterial cellulose/layered double hydroxide were used as osmotic power generators. For a pair of energy harvesting systems, superposed electrochemical potential difference and ionic flux were created by complementing the diffusion of oppositely charged ions, which achieved an output power density of up to 0.70 W m−2 using artificial sea water and river water. The maximum output power density of single negatively charged membrane reached 4.86 W m−2. This work demonstrates the practical feasibility and viability of ion-pair laminar membranes as essential platforms for high-performance osmotic power generators by combining nanoconfined coupling surface charge and size effect.