Catalytic Selectivity Control in Electrochemical Systems using Self-Assembled Monolayers

合成燃料和化学品的许多化学过程的一个主要限制是形成不想要的副产品。催化剂经常被用来引导化学反应生成所需的产品。将电化学与催化(即电催化)相结合，不仅为提高工艺选择性打开了大门，而且通过风能、太阳能和生物质等能源的可持续和/或可再生能源，还可以提高能源效率和减少对环境的影响。这项研究调查了被称为有机自组装单分子层(SAMS)的表面涂层对电催化剂组成的修饰。SAMS可以与电催化剂一起使用，将生物质等可再生材料转化为更高价值的燃料和化学品。该项目将包括对博士后研究人员、研究生以及社区大学教师和学生的培训。该项目的教师和学生将准备在线电化学教学材料，并将广泛传播。该项目将开发新的选择性控制工具，使用外加电压来操纵催化剂的结构，从而控制其催化性能。虽然以前曾使用“被动”自组装膜来改善催化剂性能，但这里的重点将放在“主动”自组装膜的使用上，这种自组装膜会根据表面电荷的变化而改变其结构。催化剂将被配体修饰，这些配体发生可逆的偶联反应，或者由于电位的变化而与表面形成键。然后，将使用外加电压作为提高性能的新控制，对选择性是主要挑战的反应进行评估。该项目将推进关于如何设计有机近表面环境来控制电催化剂的选择性的知识，并确定设计可切换表面的方法，这些表面可以假想地使用电信号来打开或关闭特定的催化剂功能。为了开发具有电响应涂层的催化剂，该项目将专注于在钯、铂和金等后过渡金属表面沉积有机硫酸盐自组装膜，以及已被证明经历了氧化态、形状和/或化学键的电位依赖变化的自组装膜结构。该项目的目标是(I)对已在热催化中进行彻底研究的反应体系在电化学条件下使用SAM修饰的催化剂进行初步调查，以确定电化学环境如何影响SAM；(Ii)开发控制SAM中的交联性和表面密度的新方法，这将提供有关电位响应系统设计规则的基本信息；以及(Iii)使用电活性SAM修饰催化剂，使其能够实现电位驱动的催化剂性能切换。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

A major limitation of many chemical processes for synthesis of fuels and chemicals is the formation of unwanted byproducts. Catalysts are often used to direct chemical reactions towards desirable products. Combining electrochemistry with catalysis (i.e., electrocatalysis) opens the door not only to improved process selectivity, but also to improved energy efficiency and reduced environmental impact via sustainable and/or renewable energy from power sources such as wind and solar energy, and biomass. The study investigates modifications to electrocatalyst composition by surface coatings known as organic self-assembled monolayers (SAMS). The SAMS can be used in conjunction with electrocatalysts to convert renewable materials such as biomass to higher-value fuels and chemicals. The project will include training of postdoctoral researchers, graduate students, and community college instructors and students. Faculty and students on the project will prepare online instructional materials on electrochemistry that will be broadly disseminated.This project will develop new tools for selectivity control that employ an applied voltage to manipulate the structure of the catalyst, and thus its catalytic properties. Although “passive” SAMs have been used previously to improve catalyst performance, here the focus will be on the use of “active” SAMs that change their structure in response to the electric charge on the surface. Catalysts will be modified with ligands that undergo reversible coupling reactions or form bonds to the surface as a result of changes in electric potential. Such SAM-modified catalysts will then be evaluated for reactions where selectivity is a major challenge, using applied voltage as a new control for enhancing performance. The project will advance knowledge of how the organic near-surface environment can be designed to control selectivity on electrocatalysts and identify methods to design switchable surfaces that can hypothetically turn particular catalyst functions “on” or “off” using an electrical signal. To develop catalysts with electrically responsive coatings, the project will focus on the deposition of organothiolate SAMs on late transition metal surfaces such as Pd, Pt, and Au, and on SAM structures that have been shown to undergo potential-dependent changes in oxidation state, shape, and/or chemical bonding. The objectives of the project are to (i) conduct initial investigations of the use of SAM-modified catalysts under electrochemical conditions for a reaction system that has been thoroughly investigated in thermal catalysis to identify how the electrochemical environment affects the SAM; (ii) develop new methods to control cross-linking and surface density in SAMs that will provide fundamental information on design rules for potential-responsive systems; and (iii) modify catalysts with electroactive SAMs that enable potential-driven switching of catalyst performance.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.