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

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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.