NECtAR

Water desalination and sustainable energy harvesting are among the greatest challenges of our society, and nanofluidics offers promising solutions to address them. Nanofluidic energy conversion systems rely on electrokinetic (EK) effects, which couple different types of transport (hydrodynamic, electric, ionic, thermal…) at interfaces. EK effects are sensitive to the molecular detail of interfaces, and should thus depend on their physical chemistry. Yet the possibility to couple surface reactivity and EK transport to enhance the performance of nanofluidic devices has never been studied to the best of our knowledge. Here we will explore these couplings in order to design innovative nanofluidic systems for sustainable energies, focusing on waste heat harvesting. To that aim, we will gather experimentalists and theoreticians who will work on the same systems, and who will probe simultaneously the physical chemistry of the interfaces as well as their transport properties. This strategy opens the way to find optimal situations where reactive interfaces have a large impact on nanofluidic energy conversion. (tasks 1 and 2). Finally, we will use this approach combining modeling and experiments to design a proof-of-principle nanofluidic device using waste heat to produce electricity or drinking water (task 3). In task 1, we will investigate the coupling between reactivity and fluidic transport at water/ceramics interfaces, ubiquitous in solid-state nanofluidic systems. In particular, we will explore the performance of oxide surfaces such as MgO and ZnO, where water can dissociate to form “super-ionic” water. We will use ab initio molecular dynamics simulations to test the role of interfacial chemistry and quantum effects on transport. In parallel, we will combine in a unique experimental setup macroscopic measures of EK transport with non-linear optics characterization of the nanometric structure and dynamics of interfaces. We also propose to adjust the electric charge of some surfaces by using light as an external switch, and to use these surfaces to control and enhance interfacial transport. In task 2, we will consider hydrophobic surfaces, which can amplify EK effects through hydrodynamic slip. The electric charge of these surfaces is generally mobile and can react to the flow. The aim of this task is to provide a fundamental understanding of these effects, so as to propose efficient systems for large energy conversion. On the numerical side, we will investigate the role of charge mobility at various hydrophobic surfaces, using classical molecular dynamics simulations. On the experimental side, we will adapt the methods developed in task 1 to the specific details of hydrophobic surfaces. The last task will be devoted to the study of waste heat harvesting, using EK effects induced by thermal gradients. Indeed, thermal gradients are expected to induce a thermoosmotic flow of water and a thermophoretic motion of ions, generating electricity. Since these phenomena have deserved little attention previously, we will first characterize their amplitude near ceramic and hydrophobic surfaces considered in the preceding tasks, combining simulations and experiments. We will then explore different membrane-based processes to harvest waste heat, in order to propose a proof-of-concept at the end of the project, whose performance will be quantified.