Proximal Symmetry-Enhanced Single-Atom Ni and In Situ Evolved Co Nanoparticle in MOFs for Synergistically Boosted Electrocatalytic Urea Synthesis.

Abstract

Catalysts with synergetic dual sites offer a promising way to drive efficient coupling reactions. Metal-organic frameworks (MOFs) are powerful for integrating diverse functional units, while the precise fabrication of dual sites in close proximity still remains challenging. Herein, Zr-based PCN-222-NiCo with single-atom (SA) Ni and Co precisely decorated on porphyrin ligands and Zr-oxo clusters separately is fabricated. During electrocatalysis, the SA Co sites are in situ reduced to nanoparticles (NPs) decorated on the pore wall of MOFs, which improves the planar symmetry of the Ni─N4 sites and creates tightly coupled Co NP/SA Ni dual-sites. In the electrocatalytic C─N coupling for urea synthesis, the enhanced symmetry of Ni-N4 lowers the *NO-to-*NOH rate-determining step barrier for NO3 - reduction, and the in situ evolved Co NPs facilitate the *COOH-to-*CO conversion for CO2 activation. This unique dual-site architecture minimizes the diffusion distance of *NH2 and *CO intermediates and simultaneously facilitates the formation of the *CONH2 key intermediate. PCN-222-NiCo exhibits a maximum Faradaic efficiency (FE) of 36.8% at -0.4 V vs RHE with a urea yield of 28.1 mmol h-1 gcat -1, outperforming MOFs with single-site counterparts. This work offers a strategy to build proximal synergistic dual sites for efficient coupling reactions.