“…Apart from hydrogen-bonding interactions, proton-rich structures of MOFs or the chemical microenvironment around the active sites can also serve as proton sources (or proton donors) in ECR, which has attracted attention lately. ,,− When the functional groups acting as Brønsted acid sites (e.g., hydroxyl and amino groups) are located in the vicinity of the metal sites, the intermediates of CO 2 reduction can receive protons from the adjacent Brønsted acid sites rather than directly from the electrolyte. For instance, we recently compared the performances of three polymer-coated Cu-HITP (a 2D MOF with square-planar CuN 4 nodes and interlayer Cu···Cu distance of 3.4 Å) composites, namely, Cu-HITP@PDA (HITP = 2,3,6,7,10,11-hexaiminotriphenylene; PDA = polydopamine, with rich amino groups and phenolic hydroxyl groups as proton donors), Cu-HITP@PANI (PANI = polyaniline, with only amino groups), and Cu-HITP@Poly(p-vinylphenol) (with only phenolic hydroxyl groups) featuring different chemical microenvironments around the same catalytic sites .…”