Turning Nitrate Pollution into Green Fuel: A 3D COF Enables Highly Efficient Ammonia Electrosynthesis

Concept of electrocatalytic nitrate reduction (\(\text{NO}_3\text{RR}\)) to ammonia (\(NH_3\)) enabled by the 3D COF TU-82 platform. Nitrate (\(NH_3\)–), a major pollutant in agricultural and industrial wastewater, is converted into value-added \(NH_3\) under ambient conditions through metal-bipyridine catalytic sites embedded within the 3D COF TU-82 framework.
Image Credit: ©Yuichi Negishi et al.

Scientific Frontline: "At a Glance" Summary

• Main Discovery: Development of a highly efficient three-dimensional covalent organic framework, designated TU-82-Fe, for the selective electrocatalytic reduction of nitrate pollutants into ammonia.
• Methodology: Researchers synthesized a [8+2]-connected bcu network via Schiff-base condensation, integrating bipyridine coordination pockets that undergo postsynthetic metalation to host atomically dispersed iron (Fe) active sites within a porous scaffold.
• Key Data: The electrocatalyst achieved a peak Faradaic efficiency of 88.1% at -0.6 V vs RHE and an ammonia yield rate of 2.87 mg h⁻¹ cm⁻² at -0.8 V vs RHE, demonstrating high selectivity and operational durability in alkaline electrolytes.
• Significance: This technology enables the transformation of agricultural and industrial nitrate waste into a valuable carbon-free energy carrier under ambient conditions, providing a sustainable alternative to the energy-intensive Haber-Bosch process.
• Future Application: The 3D COF structural blueprint serves as a versatile platform for designing decentralized ammonia synthesis systems and managing sustainable nitrogen-cycle electrocatalysis on an industrial scale.
• Branch of Science: Materials Chemistry, Reticular Chemistry, and Electrocatalysis.
• Additional Detail: Density functional theory calculations reveal that the superior activity of the Fe-based framework is driven by a significantly lowered energy barrier of 0.354 eV for the rate-determining step: \(\text{NO}^* \rightarrow \text{NHO}^*\).

Schematic representation of the non-interpenetrated bcu topology of TU-82 with [8+2] connectivity and postsynthetic metalation at bipyridine coordination pockets to generate TU-82-Fe with isolated Fe active sites.
Image Credit: ©Yuichi Negishi et al.

Ammonia (\(NH_3\)) is essential for fertilizers and emerging carbon-free energy technologies, yet its conventional production via the Haber-Bosch process is energy-intensive and \(\mathrm{CO_2}\)-emitting.

Researchers from Tohoku University and collaborating institutions have established a structural blueprint for deploying 3D COFs in electrocatalysis, opening new routes toward sustainable nitrate management and decentralized ammonia synthesis. The work was published in the Journal of Materials Chemistry A on February 02,2026

The researchers achieved this breakthrough by developing a topologically intricate three-dimensional intricate three-dimensional covalent organic framework (COF), TU-82, that delivers highly selective electrocatalytic nitrate reduction to ammonia (\(\text{NO}_3\text{RR}\)). By precisely metalating bipyridine pockets within a [8+2]-connected bcu network, the team created TU-82-Fe with atomically dispersed Fe active sites, achieving a peak Faradaic efficiency of 88.1% at −0.6 V vs RHE and an ammonia yield rate of 2.87 \(\mathrm{mg \cdot h^{-1} \cdot cm^{-2}}\) at −0.8 V vs RHE.

Ammonia (\(NH_3\)) is attracting renewed attention as a next-generation energy carrier because it can be stored and transported more easily than hydrogen and does not emit carbon dioxide when used. However, the dominant Haber-Bosch process relies on high temperature and pressure, and thereby carries a substantial carbon footprint.

Potential-dependent Faradaic efficiency and ammonia yield rate for TU-82-Fe during electrocatalytic nitrate reduction, highlighting high selectivity and productivity under ambient conditions.
Image Credit: ©Yuichi Negishi et al.

An emerging alternative is electrochemical nitrate reduction to ammonia (\(\text{NO}_3\text{RR}\)), which can operate at ambient conditions and simultaneously mitigates nitrate contamination by transforming \(\text{NO}_3\) - into a valuable chemical. Realizing this vision requires catalysts that combine high activity, selectivity, and stability while suppressing competing hydrogen evolution.

Covalent organic frameworks (COFs) are crystalline, porous polymers whose modular structures can host well-defined catalytic sites. Yet, most COF electrocatalysts reported for \(\text{NO}_3\text{RR}\) are two-dimensional, where interlayer stacking can limit mass transport and site accessibility. Three-dimensional COFs, by contrast, offer isotropic diffusion pathways and higher structural robustness―an opportunity that has remained largely untapped for \(\text{NO}_3\text{RR}\).

"By integrating precise topological design with site-specific metal coordination, we can create a truly three-dimensional, porous scaffold that exposes uniform catalytic centers for nitrate-to-ammonia conversion," explains Dr. Saikat Das (Junior Associate Professor, Institute of Multidisciplinary Research for Advanced Materials, Tohoku University).

The team synthesized TU-82 via Schiff-base condensation to form a highly ordered 3D network containing bipyridine units. These bipyridine pockets enable controlled postsynthetic coordination of metal ions, yielding TU-82-Fe and TU-82-Cu without disrupting the underlying framework crystallinity and porosity.

Electrochemical evaluation in alkaline nitrate electrolyte showed that TU-82-Fe outperforms its Cu analogue, delivering a maximum Faradaic efficiency for \(NH_3\) of 88.1% at −0.6 V vs RHE and reaching 2.87 \(\text{mg h}^{-1} \text{ cm}^{-2} \text{ NH}_3\) yield at −0.8 V vs RHE, alongside excellent operational durability. Density functional theory calculations further reveal that the superior activity of TU-82-Fe arises from a lower energy barrier (0.354 eV) for the rate-determining NO*→NHO* step along the NHO-mediated pathway.

"This study shows how three-dimensional reticular design can be used to program catalytic microenvironments and unlock high-performance nitrate-to-ammonia electrosynthesis," remarks Yuichi Negishi (Institute of Multidisciplinary Research for Advanced Materials). "We anticipate 3D COFs will become a powerful platform for sustainable nitrogen-cycle electrocatalysis."

Published in journal: Journal of Materials Chemistry A

Title: Efficient ammonia synthesis via electrocatalytic nitrate reduction over a [8 + 2]-connected three-dimensional metal-bipyridine covalent organic framework

Authors: Tsukasa Irie, Ayumu Kondo, Kai Sun, Kohki Sasaki, Mika Nozaki, Shiho Tomihari, Kotaro Sato, Tokuhisa Kawawaki, Yu Zhao, Saikat Das, and Yuichi Negishi

Source/Credit: Tohoku University

Reference Number: chm020626_01

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