Understanding the Giant Gap between Single-Pore- and Membrane-Based Nanofluidic Osmotic Power Generators.

Nanofluidic blue energy harvesting attracts great interest due to its high power density and easy-to-implement nature. Proof-of-concept studies on single-pore platforms show that the power density approaches up to 103 to 106 W m-2 . However, to translate the estimated high power density into real high power becomes a challenge in membrane-scale applications. The actual power density from existing membrane materials is merely several watts per square meter. Understanding the origin and thereby bridging the giant gap between the single-pore demonstration and the membrane-scale application is therefore highly demanded. In this work, an intuitive resistance paradigm is adopted to show that this giant gap originates from the different ion transport property in porous membrane, which is dominated by both the constant reservoir resistance and the reservoir/nanopore interfacial resistance. In this case, the generated electric power becomes saturated despite the increasing pore number. The theoretical predictions are further compared with existing experimental results in literature. For both single nanopore and multipore membrane, the simulation results excellently cover the range of the experimental results. Importantly, by suppressing the reservoir and interfacial resistances, kW m-2 to MW m-2 power density can be achieved with multipore membranes, approaching the level of a single-pore system.