Au-activated N motifs in non-coherent cupric porphyrin metal organic frameworks for promoting and stabilizing ethylene production

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.

Metal-organic frameworks are promising catalysts for CO₂ electroreduction, yet limited by their poor conductivity and stability. Here, Au nanoneedles are inserted into the metalloporphyrin framework to activate C-C coupling and stabilize the structure for much enhanced ethylene production.