Efficient carboxysome inspired enzymatic carbon dioxide reduction from low concentration sources through understanding of the local environment Sam Cobb 1 , Azim Dharani 1 , Ana Rita Oliveira 2 , In s A. C. Pereira 2 , Erwin Reisner 1 1 University of Cambridge, UK, 2 Universidade NOVA de Lisboa, Portugal The electrolysis of dilute CO 2 streams suffers from low concentrations of dissolved substrate and its rapid depletion at the electrolyte-electrocatalyst interface. These limitations require first energy-intensive CO 2 capture and concentration, before electrolyzers can achieve acceptable performances. 1 CO 2 reducing enzymes such as formate dehydrogenase are uniquely suited to using low CO 2 concentrations due to their selectivity and high affinity for CO 2 , 2 and can be interfaced with metal oxide electrodes to allow enzymatic CO2 reduction on an electrode. 3 Local environments within porous electrodes are an inherent, but often neglected component of catalysis as the local conversion of reactants to products means catalysis occurs in a very different environment to bulk solution. By understanding and modifying these local environments using a combination of experimental and computational techniques, we have shown how to improve the performance of electrocatalytic reactions to address the climate crisis by efficiently converting renewable energy and concentrated CO 2 to chemical fuels using enzymes as model catalysts. 4,5 For direct electrocatalytic CO 2 reduction from low-concentration sources, we introduce a strategy that mimics the carboxysome in cyanobacteria by utilizing microcompartments with nanoconfined and concentrated enzymes in a porous electrode. 6 A carbonic anhydrase accelerates CO 2 hydration kinetics and minimizes substrate depletion by making all dissolved carbon available for utilization, while a highly efficient formate dehydrogenase reduces CO 2 cleanly to formate; down to even atmospheric concentrations of CO 2. Using finite element modelling the local pH and carbon concentrations have been optimised through solution and system design to drastically (3.7× and 6.4× in 10 and 1% partial CO 2 pressures, respectively) increase the activity of the system. This bio-inspired concept demonstrates that the carboxysome provides a viable blueprint and strategy to achieve the reduction of low- concentration CO 2 streams to chemicals.
Figure: Carboxysome inspired electrocatalysis using enzymes for the reduction of CO 2 at low concentrations References 1. D. W. Keith, G. Holmes, D. St. Angelo and K. Heidel, A Process for Capturing CO 2 from the Atmosphere, Joule , 2018, 2 , 1573–1594.DOI:10.1016/j.joule.2018.05.006 2. A. R. Oliveira et al., Toward the Mechanistic Understanding of Enzymatic CO 2 Reduction, ACS Catal. , 2020, 10 , 3844–3856. DOI:10.1021/acscatal.0c00086 3. M. Miller et al., Interfacing Formate Dehydrogenase with Metal Oxides for the Reversible Electrocatalysis and Solar-Driven Reduction of Carbon Dioxide, Angew. Chemie - Int. Ed. , 2019, 58 , 4601–4605.DOI:10.1002/anie.201814419 4. E. Edwardes Moore, S. J. Cobb, A. M. Coito, A. R. Oliveira, I. A. C. Pereira and E. Reisner, Understanding the local chemical environment of bioelectrocatalysis, Proc. Natl. Acad. Sci. U. S. A. , 2022, 119 , e2114097119.DOI:10.1073/pnas.2114097119 5. S. J. Cobb et al., Fast CO 2 hydration kinetics impair heterogeneous, but improve enzymatic CO 2 reduction catalysis, Nat. Chem. , 2022, 4 , 417–424.DOI:10.1038/s41557-021-00880-2 6. S. J. Cobb, A. M. Dharani, A. R. Oliveira and A. C. Pereira, Carboxysome-inspired electrocatalysis using enzymes for the reduction of CO 2 at low concentrations, ChemRxiv , 2022, preprint , 1–25.DOI:10.26434/chemrxiv-2022-l9vp2
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