Converting greenhouse gas carbon dioxide (CO₂) to value-added chemicals is an appealing approach to tackle CO₂ emission challenges. The chemical transformation of CO₂ requires suitable catalysts that can lower the activation energy barrier to minimize the energy penalty associated with the CO₂ reduction reaction. Cu is the only monometallic catalyst that can produce an appreciable amount of C2+ products from CO2, while the C2+ selectivity of Cu must be further improved in order to be considered for commercialization. Here, we will present our work in developing an integrated two-stage electrolyzer stack system for the conversion of CO₂ to alcohols. The first stage utilizes a silver catalyst in a flow cell capable of reducing CO₂ to CO with faradaic efficiencies of >95% and partial current densities of >200 mA/cm². For the second stage, a CO reduction flow cell using alkaline electrolyte can reduce CO to C2+ products with high selectivity and high current density. We recently constructed a high-performance CO flow electrolyzer with a well-controlled electrode-electrolyte interface that can reach total current densities up to 1 A/cm² together with improved C₂₊ selectivities. Computational transport modelling and isotopic C¹⁸O reduction experiments suggest that the enhanced activity is due to a higher surface pH under CO reduction conditions, which facilitated the production of acetate. At optimal operating conditions, we achieved a C₂₊ Faradaic efficiency of ~91% with a C₂₊ partial current density over 630 mA/cm². Further investigations show that maintaining an efficient triple-phase boundary at the electrode-electrolyte interface is the most critical challenge to achieving a stable CO/CO₂ electrolysis process at high rates.

Additionally, we will present a new study demonstrating electrochemical production of acetamide with nearly 40% Faradaic efficiency at a current density of 300 mA/cm², where the carbon-nitrogen (C-N) bond is formed through CO electroreduction in the presence of ammonia. Full solvent quantum mechanical calculations showed earlier that the under neutral or basic conditions the reaction mechanism involves CO dimerization and sequential transfer of H from two surface water to form the (HO)C*-C*OH intermediate that subsequently leads through two separate pathways to form C₂H₄ (90%) and ethanol (10%). We show now that (HO)C*-C*OH is also hydrolyzed to *C=C=O, which in turn reacts with NH₃ to form intermediates leading to acetamide while suppressing formation of other C₂ products. We also successfully extended the range of C-N containing products to N-methylacetamide, N-ethylacetamide, N,N-dimethylacetamide, acetic monoethanolamide, and aceturic acid. Our results provide useful mechanistic insights into Cu-catalyzed CO₂/CO electroreduction and demonstrate the construction of carbon-heteroatom bonds in CO₂/CO electrolysis. This largely expands the scope of electrocatalytic CO₂ utilization pathways for sustainable chemical production.

References:

1. Jouny, M.#, Hutchings, G. S.#,* & Jiao, F.* Carbon monoxide electroreduction as an emerging platform for carbon utilization. Nature Catalysis 2, 1062-1070 (2019). doi: 10.1038/s41929-019-0388-2
2. Jouny, M.#, Lv, J. J.#, Cheng, T.#, Ko, B. H., Zhu, J. J., Goddard, W. A.* & Jiao, F.* Formation of carbon-nitrogen bonds in carbon monoxide electrolysis. Nature Chemistry 11, 846-851 (2019). doi: 10.1038/s41557-019-0312-z
3. Jouny, M., Luc, W., & Jiao, F.* High-rate electroreduction of carbon monoxide to multi-carbon products. Nature Catalysis 1, 748-755 (2018). doi:10.1038/s41929-018-0133-2

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