Salinity gradient power (SGP) has
been identified as a promising
renewable energy source. Reverse electrodialysis (RED) and pressure
retarded osmosis (PRO) are two membrane-based technologies for SGP
harvesting. Developing nanopores and nanofluidic membranes with excellent
water and/or ion transport properties for applications in those two
membrane-based technologies is considered viable for improving power
generation performance. Despite recent efforts to advance power generation
by designing a variety of nanopores and nanofluidic membranes to enhance
power density, the valid pathways toward large-scale power generation
remain uncertain. In this review, we introduce the features of ion
and water transport in nanofluidics that are potentially beneficial
to power generation. Subsequently, we survey previous efforts on nanofluidic
membrane synthesis to obtain high power density. We also discuss how
the various membrane properties influence the power density in RED
and PRO before moving on to other important aspects of the technologies, i.e., system energy efficiency and membrane fouling. We
analyze the importance of system energy efficiency and illustrate
how the delicately designed nanofluidic membranes can potentially
enhance energy efficiency. Previous studies are reviewed on fabricating
antifouling and antimicrobial membrane for power generation, and opportunities
are presented that can lead to the design of nanofluidic membranes
with superior antifouling properties using various materials. Finally,
future research directions are presented on advancing membrane performance
and scaling-up the system. We conclude this review by emphasizing
the fact that SGP has the potential to become an important renewable
energy source and that high-performance nanofluidic membranes can
transform SGP harvesting from conceptual to large-scale applications.