Nonlinear Optical Studies of High Temperature Surface Chemistry in Energy Conversion Systems

在蒙大拿州立大学化学系化学测量和成像项目的支持下，沃克教授正在开发新的光谱方法，能够检测燃料电池系统表面发生的化学过程，这与能量存储和转换技术有关。煤气化、蒸汽重整和太阳能热能生产等过程需要高达1000摄氏度的温度。在这样的高温下，化学降解会加速发生，导致效率下降，最终导致过程失败。了解可持续运行的机制以及影响性能的机制对于设计新型、耐用的电化学发电化学系统至关重要。沃克教授和他的学生正在努力扩大使用最先进的光谱学技术，以确定和量化负责能量转换过程的化学反应。除了为参与该项目的研究生和本科生提供跨学科研究经验外，沃克教授还通过蒙大拿学徒计划（MAP）和校园内的美国印第安人研究机会（AIRO）办公室积极接触来自代表性不足的少数群体的学生，并与学生志愿者一起帮助组织和评判整个波兹曼公立学区的小学科学博览会。在这个项目中，Walker教授使用二阶非线性光谱学来研究通常用于热太阳能和固体氧化物燃料电池的复杂混合价金属氧化物的相变和表面化学。具体来说，共振增强二次谐波产生（SHG）用于检测温度高于600℃和强氧化或还原性气氛下的铈、钇、氧化镍等材料的表面性能。SHG非常适合在化学腐蚀性环境中对材料进行非侵入性研究。SHG信号可能来自缺乏反演对称性的块状材料，但表面贡献仍然可以通过分析信号的相位和波长相关的共振行为来提取。共振增强确保了化学（或材料）的选择性，这是回答氧化态、相形成和传质等特定问题所必需的。这些研究可以显著地扩大化学系统的窗口，能够研究表面特异性，二阶非线性光谱学。这项工作的目标有两个方面：1)开发和应用二阶NLO技术来研究高温表面化学，2)测试描述材料偏析和新相形成的机制，特别强调电化学活性陶瓷电极的可逆和不可逆变化。沃克教授的研究项目积极支持来自科学界代表性不足群体的有抱负的科学家。他通过蒙大拿学徒计划（MAP）和校园内的美国印第安人研究机会办公室（AIRO），在他的研究项目中招募了来自代表性不足的少数群体的学生。他的外展活动旨在为他的学生提供一个平台，培养他们强大的沟通技巧和指导能力。

With support from the Chemical Measurement and Imaging Program in the Division of Chemistry, Professor Walker at Montana State University is developing new spectroscopic methods capable of examining chemical processes that occur on surfaces of fuel cell systems, which are relevant to energy storage and conversion technologies. Processes such as coal gasification, steam reforming and solar-thermal energy production require temperatures as high as 1000 C. At these high temperatures, chemical degradation can happen at an accelerated rate, leading to decreased efficiencies and, ultimately, process failure. Understanding the mechanisms responsible for sustainable operation as well as those that compromise performance is critical for designing new, durable chemical systems capable of electrochemical power generation. Professor Walker and his students are working to expand the use of state of the art spectroscopy techniques to identify and quantify the chemical reactions responsible for energy conversion processes. In addition to providing interdisciplinary research experiences to both graduate and undergraduate students involved in the project, Professor Walker actively reaches out to students from underrepresented minority groups through the Montana Apprenticeship Program (MAP) and American Indian Research Opportunities (AIRO) Office on campus and works with student volunteers to help organize and judge elementary school science fairs throughout the Bozeman Public School District.In this project, Professor Walker employs second-order nonlinear optical spectroscopy to study phase changes and surface chemistry for complex, mixed valent metal oxides commonly used in thermal solar and solid oxide fuel cell applications. Specifically, resonance enhanced second harmonic generation (SHG) is used to examine the surface properties of ceria, yttria, nickel oxide and other materials at temperatures above 600 C and under strongly oxidizing or reducing atmospheres. SHG is a well suited for stand-off, noninvasive studies of materials in chemically aggressive environments. SHG signal can arise from bulk materials that lack inversion symmetry but the surface contribution can still be extracted through analysis of the signal's phase and wavelength dependent resonance behavior. Resonance enhancement ensures the chemical (or material) selectivity necessary for answering specific questions about oxidation states, phase formation, and mass transfer. These studies could significantly expand the window of chemical systems capable of being studied with surface specific, second-order nonlinear optical spectroscopy. The goals of this work are two-fold: 1) developing and applying second-order NLO techniques to study high temperature surface chemistry, and 2) testing proposed mechanisms that describe material segregation and new phase formation with a particular emphasis on reversible and irreversible changes in electrochemically active ceramic electrodes. Professor Walker's research program actively supports aspiring scientists from underrepresented groups in science. He engages students from underrepresented minority groups in his research projects through the Montana Apprenticeship Program (MAP) and American Indian Research Opportunities (AIRO) Office on campus. His outreach activities are structured to provide a platform for his students to develop strong communication skills and mentoring abilities.