Atomically Dispersed Ni-N-C Catalysts for Electrochemical Carbon Dioxide Reduction

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Electrochemical carbon dioxide reduction reaction (CO2RR) has the potential to play a key role in addressing major energy and environmental challenges via clean conversion of the atmospheric CO2 from combusting of fossil fuels into value-added products such as fuels and chemicals. The products generated by CO2RR vary depending on the electrocatalyst used at the CO2 electrolyzer cathode,1 which calls for the development of more active, stable, and selective CO2RR electrocatalysts. Atomically dispersed Ni-N-C catalysts have attracted attention due to their superior selectivity for CO generation.2 Their activity and selectivity towards CO2RR are influenced by the metal center and its local coordination environment in Ni-N-C catalysts.3 Ni-N-C catalysts derived from zeolitic imidazolate frameworks (ZIFs) have multiple advantages including a high specific surface area, customizable pore structures, and controllable morphologies, even after the carbonization treatment at high temperatures.In this presentation, we will focus on ZIF-derived Ni-N-C catalysts using a ligand exchange strategy during ZIF synthesis. These ligand-exchanged ZIFs are synthesized by partially replacing 2-methylimidazole (used in ZIF-8 synthesis) with different imidazole-like ligands for the purpose of obtaining structures with increased porosity. The effects of several parameters, including ligand exchange percentage and pyrolysis temperature for synthesizing Ni-N-C catalysts will be evaluated. We will show how the physicochemical characteristics of the Ni-N-C catalyst, i.e., porosity, hydrophobicity, and density of active sites, can be tuned by varying the synthesis parameters. We will focus in particular on the optimization of porosity and accessibility of CO2 to the catalyst’ active sites to maximize CO2RR rate. Acknowledgement Research presented in this work has been supported by the Laboratory Directed Research and Development (LDRD) program of Los Alamos National Laboratory under project number 20230065DR. References (1) Varela, A. S.; Ju, W.; Bagger, A.; Franco, P.; Rossmeisl, J.; Strasser, P. Electrochemical Reduction of CO2 on Metal-Nitrogen-Doped Carbon Catalysts. ACS Catalysis 2019, 9 (8), 7270-7284.(2) Ju, W.; Bagger, A.; Hao, G.-P.; Varela, A. S.; Sinev, I.; Bon, V.; Roldan Cuenya, B.; Kaskel, S.; Rossmeisl, J.; Strasser, P. Understanding activity and selectivity of metal-nitrogen-doped carbon catalysts for electrochemical reduction of CO2. Nature Communications 2017, 8 (1), 944.(3) Liang, S.; Huang, L.; Gao, Y.; Wang, Q.; Liu, B. Electrochemical Reduction of CO2 to CO over Transition Metal/N-Doped Carbon Catalysts: The Active Sites and Reaction Mechanism. Advanced Science 2021, 8 (24), 2102886.