Nature-Inspired Tandem Catalysts for CO₂ Reduction

Because single catalysts cannot selectively convert CO₂ into a specific reduced product more complex than CO either electrochemically or photoelectrochemically, a promising approach is to employ multiple catalysts organized into a tandem cascade, which offers a means of generating complex chemicals with improved specificity by providing a transport channel for the reduction of CO and similar intermediates.^[1] In this project, we aspire to adapt energy conversion methods used by natural photosynthetic systems to steer selectivity (CO₂ from the air into sugars using sunlight) to engineer inorganic systems. For example, photosynthetic organisms counteract the nonproductive photorespiration process by adopting a CO₂ concentration mechanism (CCM), whereby the encapsulation of the Rubisco enzyme maximizes turnover and outcompetes oxygenase activity. A prime example is the Chlamydomonas (green alga) which utilizes three compartments (matrix, thylakoid and stroma) to increase the concentration of CO₂ in the matrix and activate the Rubisco.

Recent work performed in the group provide evidence of CO storage sites on oxide-derived Cu (OD-Cu) nanoparticles through monitoring the dynamic response by switching between CO and inert gas inside a gas diffusion electrode cell.^[2] After CO supply ceases, CO reduction (COR) is found to maintain for several seconds. Microkinetic model suggests presence of at least three distinct sites on the OD-Cu catalyst, including active sites and reservoirs. The rise in reservoir coverage also coincides with increased turnover frequencies to ethylene, further exemplifying the important role of the reservoir sites in promoting formation of higher-order carbon products. The Ager lab focuses on designs of tandem catalytic systems, use of isotope-labeling methods to track products, and identification of site-specific conversion.^[2,3,4] This poster will present kinetic studies of model electrocatalysts using real-time mass spectrometry, micro-Raman, and surface enhanced FTIR toward the eventual goal of enabling timing and spatial control of reaction steps in the tandem cascade.

References
1. Houle, F. A.; Yano, J.; Ager, J. W. Hurry Up and Wait: Managing the Inherent Mismatches in Time Scales in Natural and Artificial Photosynthetic Systems. ACS Catal. 2023, 13 (11), 7139–7158.
2. Kim, C.; Govindarajan, N.; Hemenway, S.; Park, J.; Zoraster, A.; Kong, C. J.; Prabhakar, R. R.; Varley, J. B.; Jung, H.-T.; Hahn, C.; Ager, J. W. Importance of Site Diversity and Connectivity in Electrochemical CO Reduction on Cu. ACS Catal. 2024, 14 (5), 3128–3138.
3. Lum, Y. and Ager, J. W. Sequential Catalysis Controls Selectivity in Electrochemical CO₂ Reduction on Cu. Energy Environ. Sci., 2018, 11, 2935–2944.
4. Lum, Y. and Ager, J. W. Evidence for Product-Specific Active Sites on Oxide-Derived Cu Catalysts for Electrochemical CO₂ Reduction. Nat. Catal. 2019, 2, 86–93.