No abstract

The electrocatalytic N2 reduction reaction (NRR) is one of the most promising methods for the on-site and on-demand production of NH3. Single-metal-atom-doped covalent organic frameworks (COFs) are expected to function as efficient NRR electrocatalysts because a designed coordination environment of metal centers is available as a consequence of the wide range of possible designs of COFs. Herein, we used density functional theory (DFT) to systematically investigate the theoretical NRR activity of various single-3d-metal atoms doped into COFs with different coordination numbers to attain a general design guideline for the development of efficient NRR catalysts. The adsorption strength of NRR intermediates decreased as either the coordination number or the number of d-electrons of the metal centers increased. The potential-determining step switched between N–N bond activation and NH3 desorption depending on the adsorption strength of the NRR intermediates. Therefore, an optimal NRR catalyst exhibits a moderate binding strength with intermediates. Among the investigated metal-doped COFs, an Fe metal center with a coordination number of three exhibited the highest theoretical onset potential (−0.49 eV vs the computational hydrogen electrode). In this catalyst, the charge-density and density-of-state analyses revealed moderate π back-donation and σ donation between Fe 3d orbitals and the π* orbital of N–N bonds, which resulted in the optimal binding strength of intermediates.

No abstract

The electrochemical CO2 reduction reaction (CO2RR) is a promising strategy for closing the carbon cycle. Increasing the current density (  J) for CO2RR products is a critical requirement for the social implementation of this technology. Herein, nanoscale tin–oxide‐modified copper–oxide foam is hybridized with a carbon‐based gas‐diffusion electrode (GDE). Using the resultant electrode, the Jformate is increased to −1152 mA cm−2 at −1.2 V versus RHE in 1 m KOH, which is the highest value for CO2‐to‐formate electrolysis. The formate faradaic efficiency (FEformate) reaches ≈99% at −0.6 V versus RHE. The achievement of ultra‐high‐rate formate production is attributable to the following factors: i) homogeneously‐modified Sn atoms suppressing H2 evolution and ii) the hydrophobic carbon nanoparticles on GDEs penetrating the macroporous structure of the foam causing the increase in the thickness of triple‐phase interface. Additionally, the FEformate remains at ≈70% under a high J of −1.0 A cm−2 for more than 20 h.