CO2 Capture, Concentration, and Conversion

Closing the anthropogenic carbon cycle requires selective valorization of CO2 and efficient methods for capture and concentration from dilute streams. The first part of the talk will discuss the challenge of product selectivity in electrocatalytic CO2 reduction to renewable fuels. Desirable CO2 reduction products require proton equivalents, but key catalytic intermediates in CO2 reduction can also be competent for direct proton reduction to H2. Understanding how to manage divergent reaction pathways at these shared intermediates is essential to achieving high selectivity. Both proton reduction to hydrogen and CO2 reduction to formate generally proceed through a metal hydride intermediate. We apply thermodynamic relationships that describe the reactivity of metal hydrides with H+ and CO2 to generate a modified Pourbaix diagram which outlines product favorability as a function of proton activity and hydricity (ÔłćGH-), or hydride donor strength.  We validate use of our diagram experimentally; [Pt(dmpe)2](PF6)2 is a highly selective electrocatalyst for CO2 reduction to formate (>90 % Faradaic efficiency) at an overpotential of less than 100 mV with no evidence of catalyst degradation after electrolysis. 

The second part of the talk will focus on developing more efficient methods for CO2 capture and concentration (CCC). Current methods for CCC are energy intensive due to their reliance on thermal cycles, which are intrinsically Carnot limited in efficiency. In contrast, electrochemically driven CCC (eCCC) can operate at much higher theoretical efficiencies. However, most reported systems are sensitive to O2, precluding their practical use. Prior efforts to chemically modify redox carriers to operate at milder potentials resulted in a loss in CO2 binding. To overcome these limitations, we used common alcohols additives to anodically shift the reduction potential of a quinone redox carrier, 2,3,5,6-tetrachloro-p-benzoquinone (TCQ), by up to 350 mV, conferring O2 stability. We demonstrate a full cycle of eCCC in aerobic simulated flue gas using TCQ and ethanol, two commercially available compounds. Based on the system properties, an estimated minimum of 21 kJ/mol is required to concentrate CO2 from 10% to 100%, or twice as efficient as state-of-the-art thermal amine capture systems and other reported redox carrier-based systems. Furthermore, this approach of using hydrogen-bond donor additives is general and can be used to tailor the redox properties of other quinones/alcohol combinations for specific CO2 capture applications.

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Jenny Y. Yang received her B.S. at UC Berkeley (research with Professor Jeffrey R. Long) and completed her doctoral studies at MIT under the guidance of Professor Daniel G. Nocera. After her postdoctoral position with Dr. Daniel L. Dubois at the Pacific Northwest National Laboratory, she was hired as a research scientist. After a subsequent position as a scientist at the Joint Center for Artificial Photosynthesis, she started her current position as a faculty member at the University of California, Irvine in 2013. In 2019, she was promoted to Associate Professor, and in 2021 to Professor and Chancellor’s Fellow. Her research interests include the discovery and study of inorganic electrocatalysts for the generation and utilization of chemical fuels. Current and prior research includes oxygen activation, hydrogen production and oxidation, and carbon dioxide reduction. These studies have primarily focused on the effect of bio-inspired secondary coordination sphere interactions and the effect of thermochemical properties on catalytic activity.

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