CO2 Electroreduction Over Extremely Small Nanoparticles: Opening New Reaction Pathways

电化学CO2还原反应（CO2RR）是一种很有前途的解决方案，可以将二氧化碳转化为增值化学品，遏制全球变暖。在过去的十年中，人们已经投入了大量的精力来研究几种催化剂（主要是金属基材料）上的反应机理，以推进从CO2RR生产不同化学原料的前景。所获得的理解使一氧化碳和甲酸盐等产物的反应速率和选择性高。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，仍然需要在电催化剂设计上取得突破，才能实现大规模和经济可行的生产。为了设计出高性能的电催化剂，对反应机理的深入了解是至关重要的，特别是对于具有多个复杂反应步骤的碳氢化合物。反应机理的理论描述是基于密度泛函理论（DFT）计算的，主要是基于结晶金属。纳米颗粒通常为25纳米或更大，由于其高表面积也被用于实验。然而，目前还没有系统的研究证明0.5 ~ 2nm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，当粒径从200 nm减小到0.5 nm时，反应途径发生了显著变化。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。初步结果表明，在Cu 0.5 nm上，该材料具有1.6 a /cm2的高电流密度和85%以上的甲烷选择性。本项目由DFT计算、纳米粒子合成、高级表征和电子显微镜等方面的专家组成，旨在系统地合成尺寸控制在0.5 ~ 2 nm的纳米粒子，并将DFT与原位光谱相结合，了解Cu、Ag和Sn及其二元和三元体系的反应机理。本项目获得的新认识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.