Hydropower Plant on a Chip: Frictionless Nanochannel Systems for Hydroelectric Power Generation

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Water flow through nanoscale channels can create electric power called streaming current. However, such nanoscale hydrodynamic flows have not yet been intensively investigated for practical energy manufacturing systems, particularly due to their low energy conversion efficiency resulting from significant frictional energy loss at the channel walls. This award supports fundamental research on such nanoscale hydrodynamic flows to lay the technical foundation for the development of nanofluidic energy manufacturing systems with high hydroelectric energy conversion efficiency and output power that are meaningful for real applications. Working as a "hydropower plant on a chip" with virtually little energy loss, the frictionless nanofluidic energy manufacturing systems can power small autonomous sensors, their networks, and mobile/wearable devices without batteries. Scaled-up systems (e.g., arrays of such chips) can further serve as reliable power stations for large systems with amplified power output. Scavenging energy from water, a sustainable/renewable resource, will enable such systems to be functional with little influence by ambient conditions. The integrated educational/outreach activities with research will help to prepare the next generation of technology leaders, a necessity for the U.S. to maintain its leadership role in energy manufacturing in a global economy. The objective of this research is to verify the theoretical prediction that a superhydrophobic surface reducing viscous wall friction with significant slip can increase ionic streaming current in nanoscale channel flow and consequently the electrokinetic energy conversion efficiency, potentially close to 100%, and also the output power up to a level two orders of magnitude higher than the current state of the art. To achieve this objective, a parametric study will be performed numerically for the electrostatically and hydrodynamically heterogeneous boundary conditions configurable on various types of superhydrophobic surfaces. The resulting streaming current and flow properties will be computed by coupling the Poisson-Boltzmann and the Navier-Stokes equations and employing the fluidic circuitry based on Onsager reciprocal relations. The theoretical results will then be verified with nanofluidic experiments by testing superhydrophobic nanochannels of regulated sizes for varying electrolytes and flow conditions. The combined theoretical and experimental approaches will reveal the new knowledge of the correlations between the electro-hydrodynamic and -kinetic variables critical for the electrokinetic power generation in nanochannel systems with heterogeneous boundary conditions.