Aqueous Electrolytes in Nanoporous Media: Structure, Dynamics and Electrochemo-Mechanical Actuation

靠近带电固体表面的电解质溶液形成双电层（EDL）。虽然自19世纪50年代以来，人们就已经知道了EDLs的理论，但在纳米多孔介质的受限几何形状中，人们对它们的结构和动力学知之甚少。在那里，大的界面曲率和相对界面的重叠EDL可以导致与平面几何形状相比的显著的性质变化。此外，EDL的形成可以导致在单个孔隙尺度下的机械界面应力的变化，从而导致宏观材料变形。在这个项目中，这种电化学机械驱动将与纳米多孔碳中的水性电解质的EDL的结构和动力学有关。为此，我们将结合实验和分子模拟，从纳米级的单孔尺度到多孔介质的宏观尺度，合成具有高比表面积、确定孔径（1 - 10 nm）和孔几何形状的导电纳米多孔碳。这将允许与孔体积的其余部分相比微调界面区域的效果。通过向碳结构中添加杂原子并控制缺陷浓度，引入了不同的表面化学性质（疏水性与亲水性）。根据电解质和固体之间施加的电压、表面化学和孔径，我们将研究材料中的EDL形成和机械致动。我们将专注于简单盐的水溶液，并研究盐浓度在其他参数中的作用。我们将使用同步加速器为基础的X射线散射研究的EDL在operando，特别注意的充电/放电，从而离子传输动力学。我们将使用分子动力学模拟来表示纳米多孔介质和电解质的表面的结构特性。这将使我们能够推导出几何限制电解质的结构，热力学和传输特性，并将它们与实验结果联系起来，无论是在电化学-机械耦合方面，还是在单孔和多孔介质的尺度上的电荷容量。除了这些对几何限制中的水性电解质的基本见解之外，这些研究还为具有绿色，水基电解质。它们还将有助于开发基于新型致动原理的机电致动器材料，避免使用通常的压电陶瓷系统，这些系统主要含有铅等对环境有害的材料。

An electrolyte solution near a charged solid surface forms an electric double layer (EDL). While the theory of EDLs has been known since the 1850s, their structure and dynamics are much less understood in the confined geometry of nanoporous media. There, large interfacial curvatures and overlapping EDLs of opposing interfaces can lead to significant property changes compared to planar geometries. Furthermore, EDL formation can lead to changes in mechanical interfacial stresses at the single pore scale and thus to macroscopic material deformation. In this project, this electrochemo-mechanical actuation will be related to the structure and dynamics of the EDL for aqueous electrolytes in nanoporous carbons. For this purpose, experiments and molecular simulation will be combined from the nanoscopic single-pore scale to the macroscopic scale of the porous medium.We will synthesize electrically conducting nanoporous carbons with high specific surface area, defined pore sizes (1-10 nm) and pore geometries. This will allow fine-tuning of the effect of the interfacial region compared to the rest of the pore volume. By adding heteroatoms to the carbon structure and controlling the defect concentrations, different surface chemistries (hydrophobic vs. hydrophilic) are introduced. Depending on the applied electrical voltage between electrolyte and solid, the surface chemistry and the pore diameter, we will investigate EDL formation and mechanical actuation in the material. We will focus on aqueous solutions of simple salts and investigate the role of salt concentration among other parameters. We will use synchrotron-based X-ray scattering to study the EDL in-operando, with special attention to the charge/discharge and thus ion transport kinetics. We will use molecular dynamics simulations to represent the structural properties of the surface of the nanoporous medium and the electrolyte. This should allow us to derive the structural, thermodynamic and transport properties of the geometrically confined electrolyte and relate them to the experimental results, both in terms of the electrochemo-mechanical couplings and the charge capacities at the scale of the single pore and the porous medium.In addition to these fundamental insights into aqueous electrolytes in geometric confinement, these studies provide the basis for supercapacitors with green, water-based electrolytes. They will also contribute to the development of materials for electromechanical actuators based on novel actuation principles, avoiding the usual piezoceramic systems that contain predominantly environmentally hazardous materials, such as lead.