Maximizing Blue Energy via Densely Grafted Soft Layers in Nanopores

Abstract

We investigate energy generation from salinity gradients inside a nanopore that is connected to reservoirs at both ends. We consider that the inner wall surfaces are grafted with a densely grafted polyelectrolyte layer (PEL). We developed the PEL grafting density-dependent correlation of dielectric permittivity, molecular diffusivity, and dynamic viscosity in this endeavor. Using these correlations, we employ the finite element framework to solve the equations describing the ionic and fluidic transport. We use a partially hydrolyzed polyacrylamide polymer solution, which exhibits a shear-thinning fluid, in combination with the KCl electrolyte for energy-harvesting analysis. To describe the shearrate-dependent apparent viscosity of non-Newtonian liquid, we have employed the Carreau model. For a window of right-side reservoir concentration, we investigate the effects of ion-partitioning in conjugation with the change in PEL grafting density on the ionic field, ionic selectivity, pore current, osmotic power, energy conversion efficiency, and flow field. The findings of this endeavor demonstrate how the ion-partitioning effect lowers the screening effect and raises the electrical double layer (EDL) potential by reducing the counterions in PEL. We show that the unique distribution of the ionic field leads to a higher prediction of generated osmotic power and power density due to the ion-parting effect. Additionally, we establish that the augmentation in PEL space charge density leads to improvement in average flow velocity, osmotic power, and consequently energy conversion efficiency. We establish that the generated osmotic power density and the energy conversion efficiency become very high at the higher grafting density. In summary, inferences of this analysis are deemed pertinent in designing the nanoscale device intended for high and efficient osmotic energy generation.