Probing the Kinetics of the Metal/Electrolyte Interface Using Nanoporous Gold

技术：脱合金化是一种腐蚀过程，在这个过程中，合金的元素成分从最初的大块样品中选择性地溶解。在溶解过程中，剩余的贵重合金组分沿着不断增长的合金/电解液界面扩散，形成开放的纳米多孔金属，其孔径从~2 nm到许多微米可调。表现出这种行为的典型材料是纳米多孔金(NPG)，它是由银/金合金中的银去合金化而成的。虽然现在已经确定了在脱合金过程中导致气孔率演化的一些微观过程，但关于扩散和溶解动力学及其相互关系的许多基本问题充其量也是理解不清的。PI将进行一项耦合的实验和理论计划，使用纳米孔金作为焦点材料，在纳米尺度上研究原子扩散和溶解的热力学和动力学。最近关于纳米多孔金中孔隙率演化的新模型涉及原子沿合金/电解液界面的扩散，以及这种扩散如何在复杂的舞蹈中与溶解竞争，从而形成复杂的微结构。这种相互作用在大多数涉及金属沉积或溶解的电化学过程中普遍存在，该计划将对所有这些领域做出贡献。以下是我们最感兴趣的基本问题：(1)纳米多孔金的微观结构是什么？PI将通过先进的透射电子显微镜断层扫描来阐明纳米多孔金的复杂三维孔隙率。(2)纳米多孔金属粗化过程中界面扩散的速度有多快？界面扩散速率将通过在电化学电位控制下，特别是在零电荷电位附近，通过在纳米多孔金上进行粗化来进行仔细的表面扩散测量来探测。(3)金属/电解液界面快速扩散的微观来源是什么？快速界面扩散起源的线索将通过粗化的耦合温度/电位测量来评估。(4)非合金化过程中纳米孔隙度演化的扩散/溶解耦合模型有多普遍？为了测试我们的孔隙率演化模型的通用性，PI将检查模型非水电解液中的去合金化。非技术性：了解纳米多孔金属中的原子尺度动力学将影响在为催化、传感和其他学科提供超高表面积、形态可控金属方面的应用开发。这种同样的理解也将影响腐蚀科学，无论是在为现有材料制定腐蚀预防策略方面，还是在开发新的耐腐蚀材料方面。这些背景为本科生研究和高中研究项目提供了很好的重点。本科生将通过在各种新的应用中使用纳米多孔金来参与研究工作，包括用于陶瓷纳米粒子催化剂的载体和染料敏化太阳能电池的高表面积电极。作为对实验研究的补充，PI将继续开发名为MESOSIM的动力学蒙特卡罗模拟和结构可视化工具。虽然PI主要是科学地使用该程序来研究脱合金化，但该程序的应用要广泛得多，可以用于研究薄膜生长、纳米颗粒的形态稳定性等，以及晶体结构的可视化。PI将继续开发MESOSIM作为材料科学教育的工具(该程序的模拟结果已被纳入一本受欢迎的材料科学入门教材)，特别是通过开发包含该程序的课程模块，该程序将获得广泛的分布。

TECHNICAL: Dealloying is the corrosion process in which an elemental component of an alloy is selectively dissolved from an initially bulk sample. During dissolution, the remaining more noble alloy component diffuses along the ever-growing alloy/electrolyte interface to form an open nanoporous metal with pore size tunable upwards from ~2 nm to many microns. A prototypical material exhibiting this behavior is nanoporous gold (NPG) made by dealloying silver from Ag/Au alloys. While some microscopic processes that lead to porosity evolution during dealloying have now been identified, many fundamental questions about the kinetics of diffusion and dissolution, and their interrelationship, are ill-understood at best. PI will pursue a coupled experimental and theoretical program using nanoporous gold as a focus material to study thermodynamics and kinetics of atom diffusion and dissolution at the nanoscale. Recent new models for porosity evolution in nanoporous gold involve diffusion of atoms along the alloy/electrolyte interface, and how this diffusion competes with dissolution in a complex dance leading to the formation of a complex microstructure. Such interactions are ubiquitous in most electrochemical processes involving deposition or dissolution of metals, and this program will contribute to all of these area. The following fundamental questions will be of primary interest: (1) What is the microstructure of nanoporous gold? PI will clarify the complex three-dimensional porosity of nanoporous gold via advanced transmission electron microscopy tomography. (2) How fast is interfacial diffusion during coarsening of nanoporous metals? Interface diffusion rates will be probed by making careful surface diffusion measurements via coarsening on nanoporous gold under electrochemical potential control, particularly around the potential of zero charge. (3) What is the microscopic origin of fast interface diffusion at the metal/electrolyte interface? Clues to the origin of fast interface diffusion will be assessed by coupled temperature/potential measurements of coarsening. (4) How universal is the coupled diffusion/dissolution model for nanoporosity evolution in dealloying? To test generality of our models for porosity evolution, PI will examine dealloying in model non-aqueous electrolytes. NON-TECHNICAL: Understanding atom-scale kinetics in nanoporous metals will impact applications development in providing ultra-high surface area, morphologically controlled metals for catalysis, sensing and other disciplines. This same understanding will also impact corrosion science, both in developing corrosion prevention strategies for existing materials, as well as new corrosion-resistant materials. These contexts provide good focus for undergraduate research and high school research projects. Undergraduates will participate in the research effort by using nanoporous gold in a variety of new applications including supports for ceramic nanoparticle catalysts and high surface area electrodes in dye-sensitized solar cells. Complementary to experimental studies, PI will continue to develop a kinetic Monte Carlo simulation and structure visualization tool called MESOSIM. While PI has primarily used this program scientifically to study dealloying, the program is much more general in its application, and can be used to study thin film growth, nanoparticle morphological stability, etc., as well as crystal structure visualization. PI will continue the development of MESOSIM as a tool for education in materials science (simulation output from the program has already been incorporated into a popular introductory materials science text), specifically by developing course modules incorporating the program that will find wide distribution.