Enhancing electrokinetic energy harvesting via rheology and slip-responsive zeta potential

Source abstract

Abstract The role of complex fluid rheology and surface properties in improving electrokinetic energy conversion (EKEC) remains poorly understood. Combining numerical simulations and regular perturbation technique, we resolve the nonlinear dependence of the zeta potential on slip length and simultaneously capture the inelastic, non-Newtonian response of the working fluid. Results reveal that shear-thinning fluids (n<1) enhance the induced streaming potential (Es∗), whereas it is suppressed for shear-thickening fluids (n>1). However, rheology hardly affects Es∗ beyond the optimum value of the dimensionless slip length (Ls∗) owing to the contrasting mechanisms in the ‘slip-dominated zone’ and the ‘electrokinetic retardation zone’. We report giant augmentation in EKEC efficiency owing to the coupling between Ls∗ and zeta potential (ζ∗), with the effect being more pronounced for shear-thinning fluids, low ζ∗ and overlapping electrical double layers (EDLs). The maximum enhancement in efficiency occurs at a particular Ls∗ for a set of n and ζ∗. While the gain in Es∗ with n=0.5 is limited to a maximum of 50%, a maximum increase of 250% is reported for EKEC. These insights uncover new design pathways for high-performance nanofluidic energy harvesters via synergistic tuning of interfacial slip and non-Newtonian properties.