Charge Donated by the Framework, Reactivity Expressed at the Metal: Tetrathiafulvalene-Programmed Nitrate Reduction to Ammonia
Year: 2026
Type: preprint
Abstract: The decisive challenge in nitrate-to-ammonia electrosynthesis is not simply supplying electrons, but ensuring that successive nitrogen intermediates remain chemically convertible. Here, we establish a molecular strategy that differentiates framework-derived electronic character from metal-directed reaction selectivity through TU-420, a crystalline covalent organic framework integrating electron-donating tetrathiafulvalene and electron-accepting, metal-coordinating bipyridine units. Electronic-structure analysis identifies complementary donor-associated and acceptor-like states, while Xray absorption spectroscopy reveals distinct approximately six-coordinate Fe–O/N and four-coordinate Cu–O/N environments within the conserved architecture. Remarkably, TU-420-Fe achieves 98.1% ammonia Faradaic efficiency at −0.60 V versus the reversible hydrogen electrode and an ammonia production rate of 4.33 mg h-1 cm-2 at −0.80 V, whereas TU-420-Cu exhibits substantially lower selectivity despite its stronger cathodic response. Isotope-labeling experiments establish nitrate as the nitrogen source, while in situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy, Raman spectroscopy, and differential electrochemical mass spectrometry reveal signatures consistent with evolving nitrogen–oxygen and hydrogenated nitrogen species. Density functional theory identifies the mechanistic distinction: Fe supports a favorable *NHO-mediated reduction sequence with a maximum uphill free-energy increment of 0.30 eV, while substantially alleviating the energetic penalty associated with the competing *NOH-mediated route relative to Cu. These findings identify the energetic fate of partially reduced nitrogen, rather than electron consumption alone, as a determinant of ammonia selectivity and establish electronically differentiated covalent architectures as platforms for programming metal-dependent multielectron catalysis.
Source: ChemRxiv
Language: English
Subfield: Catalysis
Field: Chemical Engineering
Domain: Physical Sciences
Open Access status: green
Awards: Elucidation of electrocatalytic activity of atomically precise metal clusters for the creation of highly active energy and environmental catalysts, G1875653562, Construction of Functional Chemistry SystemUsing Precision Metal Nanoclusters as a Compositional Unit, G4620625083, G714438845, G725513421, G8445925457
OpenAlex ID: W7221753335