SusChEM: CO2 Photo-Electrochemistry on Metal Oxides Surfaces Studied by Vibrational Sum Frequency Generation Spectroscopy and Density Functional Theory

催化剂是一种化学物质，它提供较低能量的反应途径来加快化学反应的速度。在化学反应过程中，催化剂可以多次循环使用。一些催化剂，称为光电催化剂，能够利用光作为能源来产生感兴趣的反应。在这个由化学系化学催化计划资助的项目中，L.Robert Baker教授和Aravind Asthagiri教授结合了一种称为和频率产生(SFG)的振动光谱的实验技术和称为密度泛函理论(DFT)的计算模型来研究一系列含铜和铜/铁的光电催化剂对二氧化碳(CO2)的还原。SFG振动光谱能够显示在二氧化碳还原中起重要作用的分子如何在反应过程中与催化剂表面相互作用。DFT计算被用来帮助解释在反应过程中产生的SFG数据。这两种技术的结合导致了对表面反应机理的完整了解，从而可以更好地设计催化剂和光电催化过程。利用太阳光光电化学减少二氧化碳的能力有可能使我们能够回收碳，并稳定汽车和其他来源排放的二氧化碳对环境的影响。这项研究有助于解决以环境友好和经济可行的方式制造燃料的挑战。这些研究活动与改善科学、技术、工程和数学(STEM)领域招生和留住学生的外联计划相结合。通过俄亥俄州立大学的TEK8项目，本科生和K-12教师可以在研究人员的研究小组中获得实践经验。然后，学生们通过适合年龄的学习模块将这些经验转化为中学生，这些模块旨在激励K-12学生继续未来的STEM教育。理解光电催化剂上的二氧化碳表面化学的挑战需要结合金属氧化物表面化学和半导体光物理的知识，半导体光物理确定负责驱动还原化学的光激发电子的局域原子位置。在这项由化学系化学催化计划资助的项目中，L.Robert Baker教授和Aravind Asthagiri教授正在使用和频率产生(SFG)光谱和互补密度泛函理论(DFT)计算模型来研究CO2在一系列CuO/CuFeO2表面上的活化和随后的还原作为相对相组成的函数。不同CuO和CuFeO2含量的CuO/CuFeO2催化剂在乙酸酯和甲酸酯的合成中表现出可调的选择性。探测与这些反应途径相关的分子中间体的能力，再加上调节这些相对速度的能力，为深入研究表面性质提供了一个有价值的案例研究，这些表面性质调节了反应动力学，从而为二氧化碳还原提供了可调的选择性。利用飞秒软X射线光谱进行的互补测量表明，电子的热化动力学和特定位置的电荷定域化具有元素专一性。通过软X射线光谱和DFT导出的能带结构的信息，该团队获得了氧化物表面中位置光激发电子的还原电势，并将这些电势与计算出的这些原子上的基元台阶形成自由能的变化进行了比较。这种方法的结合将半导体光物理领域与表面化学和催化相结合，以便为理解金属氧化物表面的二氧化碳光电化学的选择性提供一个基本的框架。这项研究有助于解决环境友好和经济稳定的燃料生产挑战，并使用富含稀土的金属氧化物催化剂从二氧化碳中进行化学合成。这些研究活动与改善STEM领域招生和留住学生的外联计划相结合。通过俄亥俄州立大学的TEK8项目，本科生和K-12教师可以在研究人员的研究小组中获得实践经验。然后，他们通过适合年龄的学习模块将这些经验转化为中学生，这些模块旨在激励K-12学生继续未来的STEM教育。

Catalysts are chemical substances that provide lower-energy reaction pathways to increase the speed of a chemical reaction. Catalysts can be recycled many times during a chemical reaction. Some catalysts, called photo-electrocatalysts, are able to use light as an energy source to produce the reaction of interest. In this project, funded by the Chemical Catalysis Program of the Chemistry Division, Professors L. Robert Baker and Aravind Asthagiri are using a combination of an experimental technique called sum frequency generation (SFG) vibrational spectroscopy and computational modeling called density functional theory (DFT) to investigate carbon dioxide (CO2) reduction by a series of copper and copper/iron containing photo-electrocatalysts. SFG vibrational spectroscopy is able to show how molecules important in CO2 reduction interact with the catalyst surfaces during the reaction. DFT calculations are used to help explain the SFG data generated during the reaction. The combination of the two techniques leads to a complete picture of the surface reaction mechanism, allowing for better design of the catalyst and the photo-electrocatalysis process. The ability to photo-electrochemically reduce CO2 using sunlight has the potential to enable us to recycle carbon and stabilize the environmental impacts of CO2 emissions from automobiles and other sources. This research helps to address the challenge of making fuels in an environmentally friendly and economically viable way. These research activities are integrated with an outreach plan to improve student recruitment and retention in science, technology, engineering and mathematics (STEM) fields. Through the TEK8 program at the Ohio State University, undergraduate students and K-12 teachers gain hands-on experience in the investigators' research groups. The students then translate this experience to middle school students through age-appropriate learning modules designed to inspire K-12 students to pursue future STEM education.The challenge of understanding CO2 surface chemistry on a photo-electrocatalyst requires a combined knowledge of metal oxide surface chemistry as well as the semiconductor photo-physics that determine the localized atomic sites of photo-excited electrons responsible for driving the reductive chemistry. In this project funded by the Chemical Catalysis Program of the Chemistry Division, Professors L. Robert Baker and Aravind Asthagiri are using sum frequency generation (SFG) spectroscopy and complementary density functional theory (DFT) computational modeling to investigate CO2 activation and subsequent reduction on a series of CuO/CuFeO2 surfaces as a function of relative phase composition. CuO/CuFeO2 catalysts with varying amounts of CuO and CuFeO2 show tunable selectivity between acetate and formate production. The ability to probe the molecular intermediates associated with these reaction pathways, coupled with the ability to tune these relative rates, is providing a valuable case study for a thorough mechanistic investigation of the surface properties that mediate reaction kinetics leading to tunable selectivity for CO2 reduction. Complementary measurements using femtosecond soft x-ray spectroscopy show electron thermalization kinetics and site-specific charge localization with element specificity. Through information from the soft x-ray spectroscopy and DFT-derived band structure, the team obtains the reduction potential of site-localized photo-excited electrons in the oxide surface and compares these potentials to the calculated change in free energy of formation of elementary steps on these respective atomic sites. This combination of approaches bridges the fields of semiconductor photo-physics with surface chemistry and catalysis in order to provide a fundamental framework for understanding the selectivity of CO2 photo-electrochemistry on metal oxides surfaces. This research helps to address the challenge of environmentally friendly and economically stable fuel production and chemical synthesis from CO2 using earth-abundant metal oxide catalysts. These research activities are integrated with an outreach plan to improve student recruitment and retention in STEM fields. Through the TEK8 program at the Ohio State University, undergraduate students and K-12 teachers gain hands-on experience in the investigators' research groups. They then translate this experience to middle school students through age-appropriate learning modules designed to inspire K-12 students to pursue future STEM education.