Abstract
Direct implementation of metal-organic frameworks as the catalyst for CO2 electroreduction has been challenging due to issues such as poor conductivity, stability, and limited > 2e− products. In this study, Au nanoneedles are impregnated into a cupric porphyrin-based metal-organic framework by exploiting ligand carboxylates as the Au3+ -reducing agent, simultaneously cleaving the ligand-node linkage. Surprisingly, despite the lack of a coherent structure, the Au-inserted framework affords a superb ethylene selectivity up to 52.5% in Faradaic efficiency, ranking among the best for metal-organic frameworks reported in the literature. Through operando X-ray, infrared spectroscopies and density functional theory calculations, the enhanced ethylene selectivity is attributed to Au-activated nitrogen motifs in coordination with the Cu centers for C-C coupling at the metalloporphyrin sites. Furthermore, the Au-inserted catalyst demonstrates both improved structural and catalytic stability, ascribed to the altered charge conduction path that bypasses the incoherent framework. This study underlines the modulation of reticular metalloporphyrin structure by metal impregnation for steering the CO2 reduction reaction pathway.
Highlights
Direct implementation of metal-organic frameworks as the catalyst for CO2 electroreduction has been challenging due to issues such as poor conductivity, stability, and limited > 2e− products
Combining operando synchrotron X-ray spectroscopy, in-situ IR, and DFT modeling, we ascribe the C–C coupling to a tandem mechanism, where CO generated from the impregnated Au nanoneedles are adducted to *CHO at the Au-activated N sites, and the improved structural and catalytic stability to an altered charge conduction path that bypasses the incoherent framework
In this study, Zirconium-based PCN-222 metalorganic frameworks (MOFs) comprising metalloporphyrin Cu centers and impregnated Au nanoneedles were successfully synthesized by exploiting the ligand carboxylates as the reducing agent
Summary
Direct implementation of metal-organic frameworks as the catalyst for CO2 electroreduction has been challenging due to issues such as poor conductivity, stability, and limited > 2e− products. The high energy barrier for CO2 activation and the linear scaling relation for binding of intermediates constitute two intrinsic challenges for achieving high energy efficiency and product selectivity This necessitates the development of high-performance electrocatalysts for CO2 reduction reactions (CO2RR)[4,5,6]. Among the diverse electrocatalysts explored for CO2RR, metalorganic frameworks (MOFs) represent a unique category with well-defined and tunable topologic/chemical structure comprising atomically isolated active sites that facilitate charge transfer and mass transport, and help furnish mechanistic understanding on the catalytic process[19,20]. When adapted to CO2RR, this allows a tandem pathway for producing >2e− products to be established by exploiting different active sites from different structural moieties[34] In this case, the incorporated metals might effectively alter the charge distribution and conduction path within the MOF framework to further improve the CO2RR behavior
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