Harvesting blue energy: pH-regulated nanochannels inspired by carbon nanostructures

Reverse electrodialysis (RED) in soft nanochannels has emerged as a promising approach for energy generation. In this study, we investigate energy production characteristics of RED in soft nanochannels and compare the performance of conical and cylindrical geometries. The significance of the concentration ratio and the influence of the charged polyelectrolyte layer (PEL) properties are examined to optimize energy conversion efficiency. The mathematical model includes Nernst-Planck-Poisson equations and creeping flow equation to describe ionic transport and fluid flow within the nanochannel. The conical and cylindrical geometries of the nanochannel are considered, and the soft layer is modeled as pH-dependent, allowing for unique interfacial interactions. Our results demonstrate that both conical and cylindrical nanochannels exhibit increasing osmotic flows and diffusion potentials with the concentration ratio. However, the cation transfer number decreases with the concentration ratio due to reduced selectivity in higher concentrations. Maximum power generation increases with increasing concentration ratio in both geometries. Remarkably, conical nanochannels consistently outperform cylindrical nanochannels in terms of energy production efficiency. The maximum energy conversion efficiency exhibits a decreasing trend with the concentration ratio, highlighting the importance of utilizing small concentration ratios for economical operation. Additionally, denser PELs with distinct properties from the electrolyte yield higher efficiency levels across a wide range of concentration ratios. Our comprehensive study provides valuable insight into the energy production characteristics of RED in soft nanochannels, emphasizing the superior performance of conical geometries. These findings contribute to advance nanoscale-based energy conversion technologies for sustainable energy production.