The electrochemical carbon dioxide reduction reaction (CO2RR) produces diverse chemical species. Cu clusters with a judiciously controlled surface coordination number (CN) provide active sites that simultaneously optimize selectivity, activity, and efficiency for CO2RR. Here we report a strategy involving metal-organic framework (MOF)-regulated Cu cluster formation that shifts CO2 electroreduction toward multiple-carbon product generation. Specifically, we promoted undercoordinated sites during the formation of Cu clusters by controlling the structure of the Cu dimer, the precursor for Cu clusters. We distorted the symmetric paddle-wheel Cu dimer secondary building block of HKUST-1 to an asymmetric motif by separating adjacent benzene tricarboxylate moieties using thermal treatment. By varying materials processing conditions, we modulated the asymmetric local atomic structure, oxidation state and bonding strain of Cu dimers. Using electron paramagnetic resonance (EPR) and in situ X-ray absorption spectroscopy (XAS) experiments, we observed the formation of Cu clusters with low CN from distorted Cu dimers in HKUST-1 during CO2 electroreduction. These exhibited 45% C2H4 faradaic efficiency (FE), a record for MOF-derived Cu cluster catalysts. A structure-activity relationship was established wherein the tuning of the Cu-Cu CN in Cu clusters determines the CO2RR selectivity.
KAUST Repository Item: Exported on 2020-10-01
Acknowledged KAUST grant number(s): OSR-2017-CPF-3325-03
Acknowledgements: This work was supported financially by the Natural Sciences and Engineering Research Council (NSERC) of Canada (RGPIN-2017-06477), the Ontario Research Fund: Research Excellence Program (ORF-RE-RE08-034). This publication is based upon work supported by the King Abdullah University of Science and Technology (KAUST) Office of Sponsored Research (OSR) under Award No. OSR-2017-CPF-3325-03. This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2017R1A6A3A03004826). The authors thank Dr. T. P. Wu, Dr. Z. Finfrock, and Dr. L. Ma for technical support at the 9BM beamline of the Advanced Photon Source (Lemont, IL). C.M.G. acknowledges NSERC for funding in the form of a postdoctoral fellowship. P.D.L acknowledges NSERC for funding in the form of a Canada Graduate Scholar-Doctoral Scholarship.