Salinity Gradient-Induced Power Generation in Nanochannels: The Role of pH-Sensitive Polyelectrolyte Layers

By varying the pH values (pH_R) and types of salt solution, we investigate the salinity gradient-induced electrical and mechanical flow energies inside a reservoir-connected charged nanochannel with a grafted pH-sensitive polyelectrolyte layer (PEL) on the inner surfaces. The aqueous solutions of KCl, LiCl, BaCl₂, BeCl₂, AlCl₃, and Co(en)₃Cl₃ salts are used as the working fluid in the current investigation. We examine the associated ionic transport and flow field, aiming to understand the underlying physics behind the generation of electrical and hydraulic energy through alterations in pH_R and types of salt solution. Our results reveal that the PEL space charge density decreases with increasing pH_R at lower values, while it remains almost insensitive to higher pH_R values. The electrical conductance and maximum pore power of the Co(en)₃Cl₃ solution are significantly higher compared to salts with monovalent and divalent cations. Furthermore, the magnitude of these two parameters decreases with lower pH_R and becomes insensitive to higher pH_R values. The results illustrate that the maximum electrical energy conversion efficiency enhances with pH_R, reaching its highest level for the Co(en)₃Cl₃ solution. We expect that the findings of the current work will have a significant bearing on the design and development of a state-of-the-art salinity gradient-based energy convertor as a potential candidate for renewable energy sources.