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

将二氧化碳电化学转化为具有附加值的碳氢化合物和含氧化合物，即含有氧原子的化合物，提供了一种很有前途的化学方法，用于储存来自可再生能源的间歇性电力。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碳氢化合物，如乙烯。然而，现有技术的铜催化剂表现出单一目标产物的低选择性和低生产率。二氧化碳在非均相铜催化剂上电化学转化的机理途径对外在因素如局部反应微环境很敏感。该研究项目的重点是定制气体扩散电极内的微环境，以同时提高电流和能量效率以及二氧化碳转化为乙烯的产率。这一研究项目的成果将解决国家在利用二氧化碳等温室气体生产可持续替代燃料和化学品方面的利益。研究工作将通过旨在向不同受众传达可再生能源研究成果的外联活动进行补充，包括本科研究人员，中学生和教师，特别是那些在STEM领域代表性不足的群体。以工业相关的生产率将二氧化碳电化学转化为化学品，系统将需要从传统的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体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，例如气体反应物的分压、水浓度和pH值，可以潜在地将活性和选择性转向乙烯生成。该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建模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，该流动电池的特征在于阴极和离子交换膜之间的流动液体电解质。该项目将优化气体扩散电极结构转化为膜电极组件型电池，在提高电流密度的情况下实现更高的能源效率。该研究项目的成果将推进我们对反应物物种传输和碳-碳耦合反应动力学之间相互作用的理解。该奖项反映了NSF的法定使命，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.