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

技术：去合金化是一种腐蚀过程，其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，剩余的更贵的合金组分沿着不断增长的合金/电解质界面扩散，以形成具有从约2 nm到许多微米可调的孔径的开放纳米多孔金属。表现出这种行为的原型材料是通过从Ag/Au合金中脱合金化银而制成的纳米多孔金（NPG）。虽然现在已经确定了一些微观过程，导致脱合金过程中的孔隙度演变，扩散和溶解的动力学，以及它们之间的相互关系的许多基本问题，是在最好的理解。PI将采用纳米多孔金作为焦点材料，研究纳米尺度下原子扩散和溶解的热力学和动力学。最近的新模型的孔隙度演变的纳米多孔金涉及扩散的原子沿着合金/电解质界面，以及这种扩散如何竞争与溶解在一个复杂的舞蹈，导致形成一个复杂的微观结构。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是普遍存在的，本程序将有助于所有这些领域。以下基本问题将是主要的兴趣：（1）什么是纳米多孔金的微观结构？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度。(2)纳米多孔金属粗化过程中界面扩散有多快？界面扩散速率将通过仔细的表面扩散测量，通过电化学电位控制下的纳米多孔金粗化，特别是在零电荷的电位附近进行探测。(3)金属/电解质界面快速界面扩散的微观起源是什么？快速界面扩散的起源的线索将通过耦合的温度/电位测量粗化进行评估。(4)脱合金过程中纳米孔隙演化的扩散/溶解耦合模型有多普遍？为了测试我们的孔隙度演变模型的通用性，PI将检查模型非水电解质中的脱合金。非技术性：理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、形态控制金属方面的应用开发。同样的理解也将影响腐蚀科学，无论是在开发现有材料的防腐策略，以及新的耐腐蚀材料。这些背景为本科生研究和高中研究项目提供了很好的关注点。本科生将通过在各种新应用中使用纳米多孔金来参与研究工作，包括陶瓷纳米颗粒催化剂和染料敏化太阳能电池中的高表面积电极的支持。作为实验研究的补充，PI将继续开发一种称为MESOSIM的动力学蒙特卡罗模拟和结构可视化工具。虽然PI主要科学地使用该程序来研究去合金化，但该程序在其应用中更为通用，并且可用于研究薄膜生长，纳米颗粒形态稳定性等，以及晶体结构可视化。PI将继续开发MESOSIM作为材料科学教育的工具（该计划的模拟输出已被纳入流行的材料科学入门文本），特别是通过开发课程模块，将广泛分布的程序。

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.