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 (ERCO 2 ). 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 CO 2 to CH 4 . 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 ERCO 2 . Importantly, the Ag-Np functionalization of Cu-TCPP MOF improves the Faradaic efficiency for CH 4 from 5% (for the pristine MOF) to 73% while increasing the current density for CH 4 production by a factor of 16 from 3 to 50 mA cm –2 and proportionately reducing the current density for CO and H 2 production. With an overpotential of just ca. −1.378 V vs RHE, the AgNP/Cu-TCPP MOF exhibits a turnover number of 4 × 10 22 cm –1 h –1 and turnover frequency of 1 × 10 4 h –1 (2.7 s –1 ) for CH 4 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.