CAREER: Probing and Controlling Acidic Electrocatalytic Oxidation Mechanisms and Catalyst Degradation Processes

随着全球能源格局的演变，风能、太阳能和水力发电等可再生电力的比例越来越大，电化学过程将成为燃料和化学品的主要来源。氢是许多燃料和化学品的关键组成部分，因此，美国的氢需求预计将在未来30年增长2-5倍。质子交换膜（PEM）电解槽是一项很有前途的技术，可以大规模、可持续地从水中生产氢，但在酸性条件下开发高效、稳定的水氧化催化剂一直是广泛实施的一个长期障碍。该项目将1)研究一类精确调谐的催化剂材料，该材料旨在承受PEM电解槽的恶劣氧化和酸性条件，同时最少使用昂贵的战略性贵金属；2)表征催化剂结构和反应机制之间的关键关系，如反应速率和电能的有效利用。这项工作的科学成果将提高利用可再生电力生产燃料和化学品的可持续过程的技术可行性。此外，通过与芝加哥公立高中教师的合作，该研究将与合作开发和实施新课程和课堂活动的可持续计划相结合，强调学生的参与，以提高来自不同背景的学生的保留率，并实现下一代科学标准。本项目重点研究酸性条件下的水氧化反应，这是一个关键但相对简单的电化学氧化反应，对钙钛矿氧化物催化剂的反应机理、表面结构演变和失活过程进行基础研究，作为其电子和几何结构性质的函数。与IrO2和Ir/C基准催化剂相比，钙钛矿氧化物结构为系统地调节催化剂的表面和整体性能提供了一个可调平台，同时利用了更低的铱负载。原位光谱和动力学同位素研究将探索反应机制的趋势，并评估催化剂表面重组程度与材料性质（氧化态、金属-氧键共价、金属-氧-金属键角等）和反应条件的关系。显微镜、电化学石英晶体微天平和阻抗谱将监测形貌、质量变化和电荷输运效应，作为长期测试的结果，为各种失活过程提供见解。这项工作还将建立催化剂材料的固有稳定性指标，以补充更普遍的性能稳定性指标，以指导高性能电催化系统的开发。从这项工作中产生的基本机制见解和结构理解将填补设计和系统控制驱动广泛选择性电化学氧化反应的金属氧化物催化剂的主要知识空白。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。

As our global energy landscape evolves to incorporate a greater fraction of renewable electricity from sources such as wind, solar, and hydroelectric technologies, electrochemical processes will become a major source of fuels and chemicals. Hydrogen is a critical component of many fuels and chemicals, such that hydrogen demand in the US is projected to increase 2-5 times over the next 30 years. Proton exchange membrane (PEM) electrolyzers are a promising technology for large-scale, sustainable production of hydrogen from water, but development of efficient and stable catalysts for water oxidation in acidic conditions has been a longstanding roadblock for widespread implementation. The project will 1) investigate a class of precisely tuned catalyst materials that are designed to withstand the harsh oxidative and acidic conditions of PEM electrolyzers with minimal use of expensive and strategic precious metals, and 2) characterize critical relationships between catalyst structures and reaction mechanisms, as related to reaction rates and efficient utilization of electrical energy. The scientific outcomes of this work will lead to improved technological feasibility of sustainable processes for production of fuels and chemicals from renewable electricity sources. Furthermore, the research will be integrated with a sustainable plan for collaborative development and implementation of new curriculum and classroom activities that emphasize student engagement to improve retention of students from diverse backgrounds and fulfill Next Generation Science Standards, via work with Chicago Public High School teachers.This project focuses on water oxidation in acidic conditions as a critical, yet comparatively simple, electrochemical oxidation reaction for fundamental study of reaction mechanisms, surface structure evolution, and deactivation processes for perovskite oxide catalysts as a function of their electronic and geometric structure properties. Perovskite oxide structures provide a tunable platform for systematically modulating properties of catalysts both at the surface and in the bulk, while utilizing lower loadings of iridium compared to IrO2 and Ir/C benchmark catalysts. In situ spectroscopy and kinetic isotope studies will probe trends in reaction mechanisms and assess extent of catalyst surface reorganization with relation to material properties (oxidation states, metal-oxygen bond covalency, metal-oxygen-metal bond angle, etc.) and reaction conditions. Microscopy, electrochemical quartz crystal microbalance, and impedance spectroscopy will monitor morphology, mass changes, and charge transport effects as a result of long-term testing to provide insights to various deactivation processes. This work will also establish intrinsic catalyst material stability metrics to complement more ubiquitous performance stability metrics to guide development of high performance electrocatalytic systems. Fundamental mechanistic insights and structural understanding arising from this work will fill major knowledge gaps for design and systematic control of metal oxide catalysts that drive a wide range of selective electrochemical oxidation reactions.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.