Charge Donated by the Framework, Reactivity Expressed at the Metal: Tetrathiafulvalene-Programmed Nitrate Reduction to Ammonia
- 1Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Japan, 980-8577
- 2Department of Physics
- 3SRM University–AP
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.
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BibTeX
@misc{irie2026charge,
title = {{Charge Donated by the Framework, Reactivity Expressed at the Metal: Tetrathiafulvalene-Programmed Nitrate Reduction to Ammonia}},
author = {Tsukasa Irie and Hayato Orui and Sourav Ghosh and Riki Nakatani and Chaoqi Chen and Saranya Sasikumar and Tokuhisa Kawawaki and Ranjit Thapa and Saikat Das and Yuichi Negishi},
howpublished = {ChemRxiv},
year = {2026},
month = oct,
doi = {10.26434/chemrxiv.15010463/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010463/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Charge Donated by the Framework, Reactivity Expressed at the Metal: Tetrathiafulvalene-Programmed Nitrate Reduction to Ammonia
AU - Tsukasa Irie
AU - Hayato Orui
AU - Sourav Ghosh
AU - Riki Nakatani
AU - Chaoqi Chen
AU - Saranya Sasikumar
AU - Tokuhisa Kawawaki
AU - Ranjit Thapa
AU - Saikat Das
AU - Yuichi Negishi
PY - 2026
DA - 2026/10/14
PB - ChemRxiv
DO - 10.26434/chemrxiv.15010463/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010463/v1
AB - 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.
ER -