NSF Award
2301427
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.<br/> <br/>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.<br/><br/>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.
