Electrochemical CO2 reduction improved by tuning the Cu-Cu distance in halogen-bridged dinuclear cuprous coordination polymers

Boosting Electrochemical CO2 Reduction on Copper-Based Metal-Organic Frameworks via Valence and Coordination Environment Modulation

Cu-based metal-organic frameworks (MOFs) have attracted much attention for electrocatalytic CO2 reduction to high value-added chemicals, but they still suffer from low selectivity and instability. Here, an associative design strategy for the valence and coordination environment of the metal node in Cu-based MOFs is employed to regulate the CO2 electroreduction to ethylene. A novel "reduction-cleavage-recrystallization" method is developed to modulate the Cu(II)-Trimesic acid (BTC) framework to form a Cu(I)-BTC structure enriched with free carboxyl groups in the secondary coordination environment (SCE). In contrast to Cu(II)-BTC, the Cu(I)-BTC shows higher catalytic activity and better ethylene selectivity (≈2.2-fold) for CO2 electroreduction, which is further enhanced by increasing the content of free carboxyl groups, resulting in ethylene Faraday efficiency of up to 57% and the durability of the catalyst could last for 38 h without performance decline. It indicates that the synergistic effect between Cu(I)-O coordinated structure and free carboxyl groups considerably enhances the dimerization of *CO intermediates and hinders the hydrogenation of *CO intermediates in these competitive pathways. This work unravels the strong dependence of CO2 electroreduction on the Cu valence state and coordination environment in MOFs and provides a platform for designing highly selective electrocatalytic CO2 reduction catalysts.

Steering the Selectivity of Carbon Dioxide Electroreduction from Single-Carbon to Multicarbon Products on Metal-Organic Frameworks via Facet Engineering

Although metal-organic frameworks (MOFs) have attracted more attention for the electrocatalytic CO2 reduction reaction (CO2RR), obtaining multicarbon products with a high Faradaic efficiency (FE) remains challenging, especially under neutral conditions. Here, we report the controlled synthesis of stable Cu(I) 5-mercapto-1-methyltetrazole framework (Cu-MMT) nanostructures with different facets by rationally modulating the reaction solvents. Significantly, Cu-MMT nanostructures with (001) facets are acquired using isopropanol as a solvent, which favor multicarbon production with an FE of 73.75% and a multicarbon:single-carbon ratio of 3.93 for CO2RR in a neutral electrolyte. In sharp contrast, Cu-MMT nanostructures with (100) facets are obtained utilizing water, promoting single-carbon generation with an FE of 63.98% and a multicarbon: single-carbon ratio of only 0.18. Furthermore, this method can be extended to other Cu-MMT nanostructures with different facets in tuning the CO2 reduction selectivity. This work opens up new opportunities for the highly selective and efficient CO2 electroreduction to multicarbon products on MOFs via facet engineering.

A Conductive Dinuclear Cuprous Complex Mimicking the Active Edge Site of the Copper(100)/(111) Plane for Selective Electroreduction of CO 2 to C 2 H 4 at Industrial Current Density

Inorganic solids are a kind of important catalysts, and their activities usually come from sparse active sites, which are structurally different from inactive bulk. Therefore, the rational optimization of activity depends on studying these active sites. Copper is a widely used catalyst and is expected to be a promising catalyst for the electroreduction of CO 2 to C 2 H 4 . Here, we report a conductive dinuclear cuprous complex with a short Cu···Cu contact for the electroreduction of CO 2 to C 2 H 4 . By using 1 H -[1,10]phenanthrolin-2-one and Cu(I) ions, a dinuclear cuprous complex [Cu 2 (ophen) 2 ] (Cuophen) with a remarkable conductivity (3.9 × 10 −4 S m −1 ) and a short intramolecular Cu···Cu contact (2.62 Å) was obtained. Such a short Cu···Cu contact is close to the distance of 2.54 Å between 2 adjacent Cu atoms in the edge of the copper(100)/(111) plane. Detailed examination of Cuophen revealed a high activity for the electroreduction of CO 2 to C 2 H 4 with a Faradaic efficiency of 55(1)% and a current density of 580 mA cm −2 , and no obvious degradation was observed over 50 h of continuous operation. Comparing the properties and mechanisms of Cuophen and 2 other copper complexes with different Cu···Cu distances, we found that the shorter Cu···Cu distance is conducive not only for a *CO species to bridge 2 copper ions into a more stable intermediate transition state but also for C–C coupling.

Electrochemical reduction of carbon dioxide to C2 products using a copper-sulfide, nanoparticle electrode synthesized by thermal decomposition of sulfur and copper-amine complex ink

A copper sulfide electrode was synthesized by thermal decomposition of sulfur and copper-amine complex ink.