ERI: Better by Design: Rational Design and Synthesis of Alloy (Electro)Catalysts Atom-by-Atom

长期以来，催化一直是促进从化石资源有效制造燃料和化学品的关键技术，同时也依赖于来自化石燃料燃烧的热过程能量。 最近向“清洁”能源技术的过渡促进了对替代能源的研究以及对用于化学品制造和减少温室气体排放的电催化过程的相关研究和开发。 为此，该项目探索了两个关键氮反应-氨合成和硝酸还原-的镍基合金电催化剂的设计。 特别是，这个工程研究启动（ERI）项目提供了一个机会，为早期的职业研究人员进一步研究一种新的合金催化剂设计方法-选择性步骤装饰-由他的研究小组提出。 这种改进的催化剂将扩大电催化可以取代传统工艺的规模和范围，同时也支持以K-12学生为重点的相关教育和推广活动。选择性台阶装饰涉及一种类型的金属原子选择性地电化学沉积到另一种金属表面上的台阶边缘上。这产生了一个表面，它暴露出金属的表面位置，如在块体金属合金上，但具有已知的结构和组成，并在纯金属衬底的顶部。该ERI项目的目标是将选择性分步装饰技术扩展为能够合成各种多金属表面合金催化剂的新方法，并使用这些具有明确定义和简单结构的催化剂作为模型试验台，以了解合金组成如何决定催化剂的稳定性，活性和选择性。 实现选择性分步修饰的镍基合金电催化剂的前景需要解决两个问题：（1）必须开发能够直接控制催化剂表面的合金组成和结构的合成技术，以及（2）必须创建将合金催化剂的性能与其结构和组成相关联的简单设计规则。 为了克服这些限制，两个主要目标将追求使用密度泛函理论（DFT）的计算建模和实验的单晶电极具有明确的表面结构的组合。 这些目标是：（1）确定作为各种基质上的Ad-原子/基质对的函数的Ad-原子沉积、溶解（腐蚀）和偏析的驱动力，以理解操作中的合金稳定性，和（2）确定作为Ad-原子/基质对的函数的简单描述符（纯组分的性质）和支配合金催化活性和选择性的一般规则。 确定特定ad-原子在特定基底上的有利沉积、溶解或与特定基底分离的条件将识别特定的ad-原子/基底对，其中选择性步骤装饰是可能的。 此外，该研究还将揭示合金的稳定性与其纯成分的稳定性有何不同。通过DFT，沉积、溶解和偏析的驱动力将被量化，从而能够预测任何一对金属在电化学环境中的表面合金稳定性。 通过使用相同的明确定义的、阶梯装饰的表面合金来测量特定一组反应（氮和一氧化氮还原）的活性和选择性，结合DFT建模，每个合金组分的性质（例如，D带中心、功函数和激烈争论的零电荷电势），这些因素决定了合金催化剂的性能。 此外，还将确定限制纯单金属催化剂的管理规则（如吸附物比例关系）是否适用于合金。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Catalysis has long been a key technology for facilitating the efficient manufacture of fuels and chemicals from fossil resources, while also relying on thermal process energy derived from fossil-fuel combustion. The recent transition to “clean” energy technology has stimulated research in alternative energy sources and associated research and development of electrocatalytic processes for both chemical manufacturing and reduction of greenhouse gas emissions. To those ends, the project explores the design of bimetallic alloy electrocatalysts for two critical nitrogen reactions – ammonia synthesis and nitric acid reduction. In particular, this Engineering Research Initiation (ERI) project provides an opportunity for the early-career researcher to further investigate a novel alloy catalyst design approach – selective step decoration – advanced by his research group. Such improved catalysts will expand the scale and scope with which electrocatalysis can replace traditional processes, while also supporting related educational and outreach activities focused on K-12 students. Selective step decoration involves the electrochemical deposition of one type of metal atom selectively onto step-edges on the surface of another metal. This yields a surface which exposes bimetallic surface sites, as on a bulk bimetallic alloy, but with a known structure and composition, and on top of a pure metal substrate. The goal of this ERI project is to expand the selective step decoration technique into a novel method capable of synthesizing a wide variety of multi-metallic surface alloy catalysts, and to use these catalysts, with their well-defined and simpler structure, as a model testbed to understand how alloy composition dictates catalyst stability, activity, and selectivity. Achieving the promise of selective step decorated bimetallic alloy electrocatalysts requires that two needs be addressed: (1) synthesis techniques must be developed that can directly control both alloy composition and structure at the catalyst surface, and (2) simple design rules must be created that relate performance of the alloy catalyst to its structure and composition. To overcome these limitations, two primary objectives will be pursued using a combination of density functional theory (DFT) computational modeling and experiments on single-crystal electrodes having a well-defined surface structure. Those objectives are: (1) identify the driving forces for ad-atom deposition, dissolution (corrosion), and segregation as a function of ad-atom/substrate pair across a variety of substrates to understand alloy stability in operando, and (2) identify simple descriptors (properties of the pure components) and the general rules which govern alloy catalytic activity and selectivity as a function of ad-atom/substrate pairs. Determining the conditions for a particular ad-atom's favorable deposition on, dissolution from, or segregation with a particular substrate will identify specific pairs of ad-atoms/substrates for which selective step decoration is possible. Additionally, the study will reveal insights into how the stability of an alloy differs from that of its pure components. With DFT, the driving forces for deposition, dissolution, and segregation will be quantified, to enable the prediction of surface alloy stability in the electrochemical environment for any pair of metals. By using the same well-defined, step-decorated surface alloys to measure the activity and selectivity of a particular set of reactions (nitrogen and nitric oxide reduction) in combination with DFT modeling, the properties of each alloy component (e.g., d-band center, work function, and the hotly debated potential of zero charge) that dictate alloy catalyst performance will be determined. Whether the governing rules that limit pure single metal catalysts, such as adsorbate scaling relations, hold true for alloys will also be determined.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.