Selective Ethylene Production from Carbon Dioxide Electroreduction via Gas Diffusion Electrode Engineering

电化学将二氧化碳转化为增值的碳氢化合物和含氧化合物（含氧原子的化合物），为储存来自可再生能源的间歇性电力提供了一种很有前途的化学手段。这种能力将减少对化石燃料的依赖，并减轻人为二氧化碳排放的负面影响。铜是一种很有前途的金属电催化剂，能够将二氧化碳转化为乙烯等碳氢化合物。然而，最先进的铜催化剂表现出低选择性和单一目标产物的低收率。二氧化碳在非均相铜催化剂上的电化学转化机理受局部反应微环境等外在因素的影响较大。该研究项目的重点是定制气体扩散电极内的微环境，同时提高电流和能源效率，以及二氧化碳到乙烯转化的产量。这项研究项目的成果将解决国家对从二氧化碳等温室气体中生产可持续替代燃料和化学品的兴趣。研究工作将辅以外联活动，旨在将可再生能源研究成果传达给不同的受众，包括本科生研究人员、中学生和教师，特别是那些在STEM领域代表性不足的群体。为了以工业相关的生产速率将二氧化碳转化为化学品，系统需要从传统的h型玻璃电池过渡到包含气体扩散电极的模块化和可扩展的固态电解槽。气体扩散电极是决定气供式电解槽性能的关键部件。控制气体扩散电极内铜催化剂周围的局部反应微环境，如气体反应物的分压、水浓度和pH值，可能会潜在地引导乙烯生成的活性和选择性。本研究项目旨在通过微调气体扩散电极的宏观和微观结构来操纵局部反应微环境。研究人员将通过一系列实验测量和表征以及多尺度数值模拟来表征气体扩散电极的宏观和微观结构与二氧化碳还原性能之间的关系。首先，气体扩散电极的宏观和微观结构将在一个定制的流动电池中进行研究，该电池在阴极和离子交换膜之间具有流动的液体电解质。该项目将把优化的气体扩散电极结构转化为膜电极组装型电池，在更高的电流密度下实现更高的能量效率。本研究项目的结果将促进我们对反应物物种运输和碳-碳耦合反应动力学之间相互作用的理解。这些知识可以应用于提高二氧化碳到乙烯的转化，同时提高生产效率和速率。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。

Electrochemical conversion of carbon dioxide into value-added hydrocarbons and oxygenates, compounds that contain oxygen atoms, offers a promising chemical means of storing intermittent electricity from renewable energy sources. This capability would reduce dependence on fossil fuels and mitigate the negative impact of anthropogenic carbon dioxide emissions. Copper is a promising metal electrocatalyst capable of converting carbon dioxide into hydrocarbons such as ethylene. However, state-of-the-art copper catalysts exhibit low selectivity and low production rates of a single target product. Mechanistic pathways for the electrochemical conversion of carbon dioxide on heterogeneous copper catalysts are sensitive to extrinsic factors such as the local reaction microenvironment. This research project focuses on customizing the microenvironment within a gas diffusion electrode to simultaneously increase current and energy efficiencies as well as the yield for the carbon dioxide-to-ethylene conversion. The outcomes of this research project will address the national interest in producing sustainable alternative fuels and chemicals from greenhouse gases such as carbon dioxide. The research efforts will be complemented by outreach activities designed to communicate the outcomes of renewable energy research to diverse audiences, including undergraduate researchers, middle school students, and teachers, especially those groups that are underrepresented in STEM fields.To deliver the electrochemical conversion of carbon dioxide into chemicals at industrially relevant production rates, systems will need to transition from conventional H-type glass cells to modular and scalable solid-state electrolyzers incorporating gas diffusion electrodes. The gas diffusion electrode is the critical component that determines the performance of gas-fed electrolyzers. Control over the local reaction microenvironment, such as the partial pressure of gas reactants, water concentration, and pH value, around the copper catalyst within the gas diffusion electrode could potentially steer the activity and selectivity towards ethylene generation. This research project aims to manipulate the local reaction microenvironment by finely tuning the macro- and micro-structures of the gas diffusion electrode. The investigators will characterize relationships between macro- and micro-structures of the gas diffusion electrode and carbon dioxide reduction performance through a series of experimental measurements and characterizations as well as multiscale numerical modeling. At first, the macro- and micro-structures of the gas diffusion electrode will be studied in a custom flow cell that features a flow liquid electrolyte between the cathode and ion exchange membrane. The project will translate optimized gas diffusion electrode structures into a membrane electrode assembly-type cell that achieves higher energy efficiency at elevated current densities. The outcomes of this research project will advance our understanding of the interplay between reactant species transport and carbon-carbon coupling reaction kinetics. Such knowledge can be applied to improving carbon dioxide-to-ethylene conversion with simultaneously high production efficiencies and rates.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.