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edl的理论自19世纪50年代以来就已经为人所知，但它们的结构和动力学在纳米多孔介质的受限几何结构中却鲜为人知。与平面几何相比，大的界面曲率和相反界面的重叠edl会导致显著的性质变化。此外，EDL的形成会导致单孔尺度下力学界面应力的变化，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水电解质的EDL的结构和动力学有关。为此，实验和分子模拟将从纳米尺度的单孔尺度结合到多孔介质的宏观尺度。我们将合成具有高比表面积、定义孔径（1- 10nm）和孔几何形状的导电纳米多孔碳。这将允许与孔隙体积的其余部分相比，界面区域的效果进行微调。通过在碳结构中加入杂原子并控制缺陷浓度，引入了不同的表面化学性质（疏水与亲水性）。根据电解质和固体之间的外加电压，表面化学和孔径，我们将研究材料中EDL的形成和机械驱动。我们将重点关注简单盐的水溶液，并研究盐浓度在其他参数中的作用。我们将使用基于同步加速器的x射线散射来研究EDL的运行过程，特别关注电荷/放电以及离子传输动力学。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表面的结构特性。这将使我们能够推导出几何受限电解质的结构、热力学和输运性质，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。除了对几何约束下的水电解质的这些基本见解之外，这些研究还为绿色水基电解质的超级电容器提供了基础。他们还将有助于基于新型驱动原理的机电致动器材料的开发，避免通常含有主要对环境有害材料（如铅）的压电陶瓷系统。

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.