CO2 Electroreduction Over Extremely Small Nanoparticles: Opening New Reaction Pathways

电化学CO2还原反应（CO2 RR）是一种将CO2转化为高附加值化学品和抑制全球变暖的有效方法。在过去的十年中，大量的努力一直致力于研究几种催化剂（主要是金属基材料）的反应机理，以推进从CO2 RR生产不同化学原料的前景。所获得的理解使得能够实现对产物如一氧化碳和甲酸盐的高反应速率和选择性。然而，具有巨大应用和市场规模的碳氢化合物，如甲烷和乙烯，仍然等待电催化剂设计的突破，以实现其大规模和经济可行的生产。为了设计高性能的电催化剂，对反应机理的深入理解是至关重要的，特别是对于具有多个复杂反应步骤的烃。反应机理的理论描述是基于密度泛函理论（DFT）计算，主要是晶体金属。纳米颗粒通常为25 nm或更大，也因其高表面积而用于实验中。然而，没有系统的研究来证明0.5至2 nm尺寸的极小纳米颗粒的结构-活性关系。我们对Cu纳米颗粒的初步研究表明，当颗粒尺寸从200 nm减小到0.5 nm时，反应途径显著改变。在大颗粒上，乙烯是主要产物，而在极小颗粒上，甲烷是主要产物。在Cu 0.5 nm上的初步结果显示了1.6 A/cm 2的高电流密度和大于85%的甲烷选择性的创纪录性能。在这个项目中，DFT计算，纳米颗粒合成，先进表征和电子显微镜的专家团队，旨在系统地合成尺寸为0.5至2 nm的可控纳米颗粒，并将联合收割机DFT与原位光谱学结合起来，以了解Cu，Ag和Sn及其二元和三元体系的反应机理。在这个项目中获得的新的理解将开辟新的反应途径，并将改变催化剂设计的范式。

Electrochemical CO2 reduction reaction (CO2RR) is a promising solution to convert carbon dioxide into value-added chemicals and curb the global warming. During the last decade, much effort has been devoted to investigating the reaction mechanism on several catalysts-mostly metal-based materials-to advance the prospects of producing different chemical feedstocks from CO2RR. The attained understanding has enabled achieving high reaction rate and selectivity for products such as carbon monoxide and formate. However, hydrocarbons with huge applications and market size, such as methane and ethylene, still wait for breakthroughs in electrocatalyst design to realize their large-scale and economically feasible production. To design a high performing electrocatalyst, a deep understanding of the reaction mechanism is crucial, especially for hydrocarbons with several complicated reaction steps. Theoretical descriptions of the reaction mechanism are based on the density functional theory (DFT) computations and mostly on crystalline metals. Nanoparticles, usually 25 nm or larger, are also used in experiments for their high surface area. However, there is no systematic study to demonstrate the structure-activity relationship for extremely small nanoparticles with 0.5 to 2 nm sizes. Our preliminary studies on Cu nanoparticles has shown that when the particle size decreases from 200 nm to 0.5 nm, the reaction pathway significantly changes. On large particles, ethylene is the dominant product, while on extremely small particles methane is the main product. The preliminary results on Cu 0.5 nm showed a record performance of high current density of 1.6 A/cm2 and selectivity greater than 85% for methane. In this project, a team of experts in DFT computations, nanoparticles synthesis, advanced characterization, and electron microscopy, aim to systematically synthesize nanoparticles with controlled sizes of 0.5 to 2 nm, and combine DFT with in-situ spectroscopy to understand the reaction mechanism on Cu, Ag, and Sn, and their binary and ternary systems. The novel understanding obtained in this project will open up new reaction pathways and will change the paradigm for catalyst design.