The Role of Catalyst Microstructure in Gas Diffusion Electrosynthesis of C2+ Products

斯坦福大学的Matthew Kanan教授受化学系化学催化（CAT）项目的支持，研究了铜催化剂的结构与其对一氧化碳（CO）电化学转化的催化性能之间的关系。该项目涉及使用采用气体扩散电极（GDEs）的电化学电池，这可以最大限度地提高气体进出催化剂材料的运输，从而实现高产品合成率。最终目标是将二氧化碳转化为燃料和有用的化学物质。将二氧化碳转化为一氧化碳的技术已经有了，但随后通过电解将一氧化碳转化为更有用的化学品和燃料的技术还没有很好地建立起来。该项目侧重于提高阴极上铜催化剂材料性能的方法，阴极是CO与电子和质子结合形成碳氢化合物、醇或羧酸等产品的电极。使用铜催化剂大规模生产所需产品的可行性取决于调整其结构的能力，以最大限度地提高活性、选择性和耐久性。可再生电力的快速增长和成本下降，增加了利用电力为二氧化碳和水合成燃料和化学品提供动力的吸引力。研究微观结构如何影响电化学CO转化的性能，可以揭示在能量转化和工业化学合成中重要的其他催化过程中利用微观结构的策略。为了补充研究活动，该小组通过电化学转化演示和实验室模块向当地高中生进行科学推广，以说明核心化学概念，并激励学生追求科学事业。基于低电流密度下的固相研究，已经提出了许多铜催化二氧化碳和一氧化碳还原的结构-活性模型。然而，实际的电合成将需要使用GDE在更高的电流密度下操作。目前尚不清楚在液相电解中阐明的结构-活性关系是否适用于在高电流密度的gde中工作的Cu材料。此外，可能影响Cu材料本征催化性能的微观结构特征与gde催化剂层复杂的非均相结构有关，gde催化剂层通常由催化剂颗粒、碳颗粒、氟化聚合物和离聚体组成。该项目的研究旨在建立一种方法来阐明在GDE中运行的Cu催化剂的微观结构影响，并将这些影响从依赖于GDE催化剂层结构的形态和质量传输现象中分离出来。针对具有晶界密度和几何形状可控、定义良好的铜纳米颗粒，开发了新的合成方法。利用透射菊池衍射和其他电子衍射和x射线衍射技术绘制了晶粒结构。接下来，使用定制的电化学电池，综合评估微观结构不同样品在gde中的催化活性。这些研究试图确定晶界与特定C2+产物的活性或选择性之间的相关性，并评估这些相关性如何依赖于电流密度/过电位、电解质和其他参数。同时，开发了喷涂程序来改变GDE催化剂层的厚度、孔隙率和润湿性。这些程序用于优化GDE的结构，以在最小过电压下实现高电流密度，并评估结构与催化剂微观结构在该状态下的相对重要性。该奖项反映了美国国家科学基金会的法定使命，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。

Professor Matthew Kanan of Stanford University is supported by the Chemical Catalysis (CAT) Program of the Division of Chemistry to investigate the relationship between the structure of copper catalysts and their catalytic properties for the electrochemical conversion of carbon monoxide (CO). The project involves the use of electrochemical cells employing gas diffusion electrodes (GDEs), which maximize the transport of gases to and from the catalyst material and hence enable high product synthesis rates. The ultimate goal is to convert carbon dioxide (CO2) to fuels and useful chemicals. The technology to convert CO2 to CO is already available, but the subsequent conversion of CO into more useful chemicals and fuels via electrolysis is not well established. The project focuses on means to enhance the performance of the copper catalyst material on the cathode, the electrode where CO is combined with electrons and protons to form products such as hydrocarbons, alcohols, or carboxylic acids. The viability of using copper catalysts for scalable production of the desired product hinges on the ability to tailor its structure to maximize activity, selectivity, and durability. The rapid growth and falling costs of renewable electricity have increased the attraction of using electricity to power the synthesis of fuels and chemicals from carbon dioxide and water. The study of how microstructure affects performance in electrochemical CO conversion may unveil strategies for exploiting microstructure in other catalytic processes that are important to energy conversion and industrial chemical synthesis. To complement the research activities, the group engages in scientific outreach to local high school students by using electrochemical conversion demonstrations and lab modules to illustrate core chemical concepts and inspire students to pursue scientific careers.Numerous structure - activity models have been proposed for Cu-catalyzed carbon dioxide and carbon monoxide reduction based on solution-phase studies at low current density. However, practical electrosynthesis will require operating at much higher current density using a GDE. It is unclear if the structure - activity relationships that have been elucidated in solution-phase electrolyses are applicable to Cu materials operating in GDEs at high current densities. Moreover, microstructural features that may influence the intrinsic catalytic properties of Cu materials are convoluted with the complex, heterogeneous architecture of the catalyst layer of GDEs, which typically is composed of catalyst particles, carbon particles, fluorinated polymers, and ionomers. The research in this project seeks to establish a methodology for elucidating microstructural effects on Cu catalysts operating in GDEs and disentangle these effects from morphological and mass transport phenomena that depend on the architecture of the GDE catalyst layer. New synthetic methods are developed to target well-defined Cu nanoparticles with controllable grain boundary density and geometry. The grain structures are mapped using transmission Kikuchi diffraction and other electron diffraction and x-ray diffraction techniques. Next, the catalytic activity of microstructurally variant samples is comprehensively evaluated in GDEs using custom electrochemical cells. These studies seek to identify correlations between grain boundaries and the activity or selectivity for specific C2+ products and assess how these correlations depend on current density/overpotential, electrolyte, and other parameters. In parallel, spray-coating procedures are developed to vary the thickness, porosity, and wettability of the catalyst layer of a GDE. These procedures are used to optimize the architecture of the GDE for high current density at minimal overvoltage and assess the relative importance of architecture vs catalyst microstructure in this regime.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.