Cu-based catalysts have attracted widespread attention for its capability in electrocatalytically reducing CO₂ to a variety of products. Surface modification of Cu has become an interesting method for tuning the catalytic performance. Here, we use Zr-based metal-organic layers (MOLs) as the additive of the Cu surface, which enhanced the Faradaic efficiency of CH₄ by two times as compared to the untreated polycrystalline Cu foil. Unexpectedly, the MOLs were found to induce in situ nano-structuring of the Cu foil surface within seconds in the electrolysis, as revealed by a combination of scanning electron microscopy (SEM), grazing incidence X-ray diffractometry (GIXRD), and linear sweep voltammetry (LSV) measurements. These surface changes are responsible for the shift of product selectivity. Control experiments suggest that negatively charged µ₃-O⁻ on the Zr-cluster in the MOL might interact with CO-covered Cu surface and induce roughing and nano-structuring. This work reveals a potential role of additive on Cu to induce surface nano-structuring that tunes catalytic activity and selectivity.

Two-dimensional metal-organic layers (MOLs) from alternatively connected benzene-tribenzoate ligands and Zr₆(µ₃-O)₄(µ₃-OH)₄ or Hf₆(µ₃-O)₄(µ₃-OH)₄ secondary building units can be prepared in gram scale via solvothermal synthesis. However, the reason why the monolayers did not pack to form thick crystals is unknown. Here we investigated the surface structure of the MOLs by a combination of sum-frequency generation spectroscopy, nanoscale infrared microscopy, atomic force microscopy, aberration- corrected transmission electron microscopy, and compositional analysis. We found a partial coverage of the monolayer surface by dangling tricarboxylate ligands, which prevent packing of the monolayers. This finding illustrates low-density surface modification as a strategy to prepare new two-dimensional materials with a high percentage of exposed surface.

Reusable solid fluorination reagents and heterogeneous catalysts are ideally suited for late-stage fluorination with fast and clean conversion and simplified work-up. Here we report Pd-functionalized two-dimensional metal-organic layers (MOLs) as solid reagents and heterogeneous catalysts to efficiently fluorinate a broad scope of aromatic compounds. Site isolation in the MOLs provides a unique opportunity to stabilize highly active F-containing species for the chemical conversion. A terpyridine (TPY)-based ligand on the MOL, together with a 2-chloro-1,10-phenanthroline (phenCl) as a co-ligand, chelates Pd^II to form a reactive center. After treatment with Selectfluor/H₂O, an (N-fluoroxy)-(2-chloro)-phenanthrolinium [N-(FO)-phenCl⁺] moiety is produced from the co-ligand on the Pd center. This active species serves as a stochiometric solid fluorination reagent, which shows different regioselectivities and reactivities as compared to homogeneous catalysts that involves Pd^III/^IV-F intermediates in catalytic cycles. The MOLs can also be used as heterogeneous catalysts for fluorination using Selectfluor. This work highlights opportunities in using MOLs to stabilize unique active sites for late-stage fluorination.