Flow-induced surface charge enhancement in alumina nanochannels boosts osmotic energy conversion

Osmotic energy has garnered widespread attention in recent years as a stable, efficient, and sustainable clean energy source. However, nanochannel-based osmotic energy conversion systems still face challenges in practical applications due to limited interfacial charge regulation. Most current studies are conducted under steady-state conditions, while the coupling mechanisms among flow fields, ion distributions, and interfacial reactions in complex environments with fluid disturbances remain poorly understood. In this study, using alumina nanochannels as a model system, we constructed four different flow patterns to systematically investigate the effects of fluid flow on ion distribution, surface charge regulation, and energy conversion performance. Both experimental and simulation results consistently demonstrated that applying flow solely on the high-concentration side significantly enhances current output and improves osmotic energy conversion performance. In contrast, other flow modes were found to degrade energy conversion performance to varying degrees. Multiphysics simulations further revealed that flow-induced ion redistribution dynamically modulates the surface charge density within the nanochannels. Specifically, flow at the high-concentration side enhances surface charge density, while the resulting convective flow synergistically promotes ion transport and power output. These findings elucidate a coupled mechanism of flow field-ion distribution-interfacial reactions, demonstrating that directional flow regulation can markedly enhance osmotic energy harvesting. This mechanistic insight not only provides a theoretical foundation for the design of osmotic energy conversion devices but also paves the way for developing smart responsive membranes and advanced nanofluidic energy conversion systems.