Photoseeded Silver on Two-Dimensional Nanosheets of Cu-Porphyrin Metal–Organic Framework as a Tandem Electrocatalyst for Highly Efficient Electrochemical Reduction of CO2 to CH4

Cu-based metal–organic frameworks (MOFs) have emerged as promising modular materials for the design of electrochemically stable, efficient, and selective electrocatalysts for the electroreduction of carbon dioxide (ERCO2). Herein, we report the design and synthesis of a silver nanoparticle-decorated Cu-MOF-based tandem electrocatalyst that, besides its excellent electrochemical stability, exhibits excellent activity and selectivity toward electroreduction of CO2 to CH4. Specifically, the specially synthesized Cu(II) (metal) plus tetrakis(4-carboxyphenyl porphyrin) (TCPP-linker)-based 2D metal–organic frameworks (Cu-TCPP MOFs) were decorated with silver nanoparticles via a photoseeding approach for the fabrication of AgNP/Cu-TCPP MOFs. The coordination active sites of the as-designed AgNP/Cu-TCPP MOF composites were confirmed by XRD, FE-SEM, EDX, and XPS. Our results suggest that the anchoring of Ag NPs to Cu-TCPP MOFs, besides enhancing the electrochemical stability, significantly improves the electronic conductivity, electrocatalytic performance, and selectivity of these MOFs toward ERCO2. Importantly, the Ag-Np functionalization of Cu-TCPP MOF improves the Faradaic efficiency for CH4 from 5% (for the pristine MOF) to 73% while increasing the current density for CH4 production by a factor of 16 from 3 to 50 mA cm–2 and proportionately reducing the current density for CO and H2 production. With an overpotential of just ca. −1.378 V vs RHE, the AgNP/Cu-TCPP MOF exhibits a turnover number of 4 × 1022 cm–1 h–1 and turnover frequency of 1 × 104 h–1 (2.7 s–1) for CH4 production. The enhanced FE and selectivity of the tandem composite are attributed to the synergistic interaction between the atomically defined Cu sites and the Ag clusters in AgNP/Cu-TCPP MOFs.