High performance nanofluidic thermoelectricity using smooth polarized surfaces

排放到大气中的废热能是清洁、无燃料和廉价能源的最大来源之一。最常用的将废热转化为电能的技术是固态热电发电机和基于液体的热电化学电池。尽管它们的品质因数不断提高，但由于材料限制、成本和效率低下，它们仍然不足以转化低品位废热。另一种将热能转化为电能的方法是基于电解质填充的纳米通道：当沿着通道施加温度梯度时，就会产生一个电场，驱动电流。这种纳米流体装置的效率可以达到最好的固态热电材料的效率，当通过低摩擦表面上产生的液-固滑动来提高时。然而，高性能也需要高表面电荷，这对滑动是有害的。在这种情况下，我们最近已经表明，极化的石墨烯表面显示出非常有利的电荷滑移耦合;因此，这些表面可以提供优异的热电转换。因此，该项目的第一个目标是通过研究石墨烯纳米通道中的热电能转换来确定具有高转换效率的特别有前途的配置。我们初步研究的另一个结果是，特别是当液体性质随温度的变化非常明显时，实现了有效的能量转换。这是接近流体临界点（跨临界条件）的情况，因此该项目的第二个目标是探索在这种跨临界条件下的热电能转换潜力。为了全面了解纳米流体通道中的热电性，我们将使用多尺度方法，结合原子模拟来捕获界面纳米附近的分子效应，并使用连续力学模拟来描述更大尺度的整个系统。具体来说，原子模拟将提供边界条件或表面方程的连续模型。这种方法的结果最终将在极端限制的情况下进行分子模拟测试。我们的目标是确定具有高热电能量转换效率的配置，特别是具有极化石墨烯壁的通道和接近临界点的操作制度，为未来热电能量转换器的发展提供理论指导。

Waste heat energy discharged into the atmosphere is one of the largest sources of clean, fuel-free and inexpensive energies available. The most commonly used technologies to convert waste heat to electric energy are solid-state thermoelectric generators and liquid-based thermoelectrochemical cells. Despite the continuous improvement in their figures-of-merit, they are still inadequate for the conversion of low-grade waste heat due to material limitations, cost and poor efficiencies. A promising alternative method to convert thermal into electric energy is based on electrolyte-filled nanochannels: when a temperature gradient is applied along the channel, an electric field is created that drives an electric current. The efficiency of such nanofluidic devices could reach that of the best solid-state thermoelectric materials, when boosted by liquid-solid slip arising on low-friction surfaces. However, high performance also requires high surface charge, which is detrimental to slip. In that context, we have recently shown that polarized graphene surfaces display a very favorable charge-slip coupling; consequently, these surfaces could provide excellent thermoelectric conversion. Therefore, the first objective of the project is to identify especially promising configurations with high conversion efficiency by studying thermoelectric energy conversion in graphene nanochannels. Another result of our preliminary studies is that efficient energy conversion is achieved especially when the variation of liquid properties with temperature is very pronounced. This is the case close to the critical point of the fluid (transcritical conditions), and the second objective of the project is therefore to explore the potential of thermoelectric energy conversion under such transcritical conditions. To develop a comprehensive picture of thermoelectricity in nanofluidic channels, we will use a multiscale approach, combining atomistic simulations, to capture molecular effects in the nanometric vicinity of the interface, and continuum-mechanical simulations, to describe the entire system at a larger scale. Specifically, atomistic simulations will provide boundary conditions or surface equations for the continuum models. The results of this approach will finally be tested against molecular simulations in situations of extreme confinement. Our goal is to identify configurations with high thermoelectric energy conversion efficiency, especially channels with polarized graphene walls and operation regimes close to the critical point, providing theoretical guidelines for the development of future thermoelectric energy converters.