CAS: Bridging Surface Chemistry and Photophysics to Understand Photo-Electrochemical CO2 Reduction on Solar Photocathodes

在化学催化（CAT）和化学结构、动力学和机理-a （CSDM-A）项目的支持下，俄亥俄州立大学（OSU）的L. Robert Baker和Aravind Asthagiri正在研究利用地球上丰富的金属氧化物作为光催化剂将二氧化碳转化为有用产品。减少二氧化碳的能力有可能关闭碳循环并稳定二氧化碳排放对环境的影响。因此，这个项目将有助于解决与环境友好型能源生产和化学合成有关的科学和技术的紧迫挑战之一。虽然已经做了很多工作来了解金属表面的电催化作用，但半导体光催化剂更为复杂。在这个项目中，我们将建立一个实验和理论相结合的框架来探索金属表面电催化和半导体表面光电催化之间的知识差距。该提案的研究活动还将与旨在改善STEM（科学、技术、工程和数学）教育的学生招聘和保留的外展计划相结合。为了实现这一目标，这些pi将参加俄勒冈州立大学的TEK8本科生奖学金项目。通过这个项目，本科生研究人员获得了实践研究经验，然后他们通过互动的、适合年龄的学习模块将这些经验传授给中学生，这些模块旨在让学生接触到现实世界的研究挑战，并激励他们接受STEM教育。这个研究项目是由俄亥俄州立大学的L. Robert Baker和Aravind Asthagiri合作进行的，他们致力于加深对利用地球上丰富的金属氧化物作为催化剂，将二氧化碳光催化转化为有用产品的机理细节的理解。该研究是建立在理论学家Asthagiri（密度泛函理论- DFT）和实验学家Baker（振动和频率生成（VSFG）和元素特异性极紫外（XUV）光谱）之间的协同合作基础上的。这些研究将集中在光电催化实验上，使用CuFeO2作为模型p型半导体，具有高的co2还原选择性。在Aim 1中，DFT计算将研究CuFeO2上co2还原过程中基本步骤的自由能，并生成稳定表面中间体的预测。利用operando SFG光谱对表面物质的直接观察将检验这些预测，从而完善表面反应机理的理论模型。目的2将这些研究扩展到超快时间分辨SFG，以检测瞬态表面中间体并揭示第一次质子/电子转移到CO2过程中的分支途径。光谱结果将与DFT势垒高度计算相比较，显示各种质子/电子转移途径的动力学。这个目标的目标将是解决协调质子耦合电子转移（PCET）和顺序电子/质子转移（ET/PT）之间的问题，并说明这个分支点最终如何指导CO2R选择性。目标3将建立在目标1和目标2的基础上，通过研究具有公式AFeO2 （a = Cu， Ag和Au）的一系列p型delafote阴极中阳离子取代的电子动力学函数。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。

With the support of the Chemical Catalysis (CAT) and Chemical Structure, Dynamics, and Mechanisms-A (CSDM-A) programs in the Division of Chemistry, L. Robert Baker and Aravind Asthagiri of Ohio State University (OSU) are studying the conversion of CO2 to useful products using earth-abundant metal oxides as photocatalysts. The ability to reduce CO2 has the potential to close the carbon cycle and to stabilize the environmental impacts of CO2 emissions. Consequently, this project will help to address one of the pressing challenges for science and technology related to environmentally friendly energy production and chemical synthesis. Although much work has been performed to understand electrocatalysis on metal surfaces, semiconductor photocatalysts are more complex. In this project we will establish a combined experimental and theoretical framework to explore the knowledge gap between electrocatalysis on metal surfaces and photo-electrocatalysis on semiconductor surfaces. The research activities of this proposal will also be integrated with an outreach plan designed to improve student recruitment and retention in STEM (science, technology, engineering and mathematics) education. To accomplish this, the PIs will participate in the TEK8 undergraduate fellowship program at OSU. Through this program, undergraduate researchers gain hands-on research experience, which they then translate to middle school students through interactive, age-appropriate learning modules designed to expose students to real-world research challenges and inspire them to pursue STEM education. This research project, partnering L. Robert Baker and Aravind Asthagiri of Ohio State University, endeavors to increase understanding of the mechanistic details of the photocatalytic conversion of CO2 to useful products using earth-abundant metal oxides as catalysts. The study is built around a synergistic collaboration between theorist Asthagiri (density functional theory - DFT) and experimentalist Baker [vibrational sum frequency generation (VSFG) and element-specific, extreme ultraviolet (XUV) spectroscopy]. These studies will focus on photo-electrocatalysis experiments using CuFeO2 as a model p-type semiconductor showing high selectivity for CO2-reduction. In Aim 1, DFT calculations will investigate the free energy of elementary steps during CO2-reduction on CuFeO2 and generate predictions of stable surface intermediates. Direct observation of surface species by operando SFG spectroscopy will test these predictions in order to refine theoretical models of the surface reaction mechanism. Aim 2 will extend these studies to ultrafast time-resolved SFG in order to detect transient surface intermediates and reveal the branching pathways during the first proton/electron transfer to CO2. Spectroscopic results will be compared to DFT barrier height calculations showing the kinetics of various proton/electron transfer pathways. The goal of this aim will be to resolve between concerted proton coupled electron transfer (PCET) and sequential electron/proton transfer (ET/PT) and to illustrate how this branching point ultimately guides CO2R selectivity. Aim 3 will build on Aims 1 and 2 by investigating electron dynamics as a function of cation substitution in a series of p-type delafossite cathodes having the formula AFeO2 (A = Cu, Ag, and Au).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.