Geometry design and mechanism analysis of artificial nanoroughness for enhanced osmotic energy conversion

Nanofluidic osmotic energy conversion is widely regarded as a promising technology for the conversion of clean salinity-gradient energy into electricity. Surface roughness can increase the surface charge of nanochannels, but its effect on the ion flux and osmotic energy generation has rarely been investigated. In this study, we propose artificial nanoroughness with rectangular units in nanochannels to enhance ion selectivity and osmotic energy conversion of nanochannels without obvious influence on the ion flux. The osmotic energy conversion performance is separated into an ion selectivity-sufficient zone, a driving force-sufficient zone, and a transition region called balanced zone according to the ion concentration ratio. The artificial nanoroughness significantly increases the ion selectivity in the balanced zone and the driving force-sufficient zone by improving the space charge density in the concave region. The artificial nanoroughness distributed in the rear region of the nanochannel can generate higher osmotic power than that in the frontal region. Moreover, either the maximum osmotic power or energy conversion efficiency can be realized by manipulating the height of artificial nanoroughness under a concentration ratio less than 100, whereas both of them can be achieved simultaneously by reducing the width or pitch of the artificial nanoroughness under all concentration ratios. The current work paves a promising path to consolidate ion selectivity and osmotic power generation through the interfacial design of nanochannels.