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Electrocatalytic reactions involving aqueous nitrate and nitrite

Nature Protocols (2026) Cite this article

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Abstract

Electrocatalytic upgrading of aqueous nitrate (\({\rm{NO}}_{3}^{-}\)) and nitrite (\({\rm{NO}}_{2}^{-}\)) represents a sustainable and increasingly important approach for producing valuable nitrogenous chemicals from abundant and hazardous feedstocks. Recent advances have demonstrated the ability to selectively convert \({\rm{NO}}_{3}^{-}\)/\({\rm{NO}}_{2}^{-}\) into products such as inorganic nitrogenous species including ammonia (NH3), hydroxylamine (NH2OH), hydrazine (N2H4) and organonitrogen compounds (e.g., urea, oximes and amines). However, the absence of standardized protocols has hindered reproducibility and cross-laboratory comparisons. Herein, we present a comprehensive protocol for aqueous \({\rm{NO}}_{3}^{-}/{\rm{NO}}_{2}^{-}\)-involved electrocatalytic reactions. Our protocol includes electrode preparation, electrolyzer assembly, electrolysis, product quantification and purification, in situ characterization and technoeconomic analysis. The protocol includes essential safety guidelines for toxic intermediate handling. Moreover, it remains adaptable to different levels of experimental capability. This protocol is suitable for initial screenings and mechanistic investigations spanning small-scale reactors (<30 ml) to liter-level systems and takes ~2 weeks to complete. This work is designed for researchers in green and sustainable chemistry, electrocatalysis, nanotechnology and environmental science and aims to establish reproducible workflows that accelerate the development of electrochemical \({\rm{NO}}_{3}^{-}/{\rm{NO}}_{2}^{-}\) upgrading strategies. More importantly, we hope that the protocol can motivate researchers to design catalytic strategies to upgrade renewable chemical sources beyond \({\rm{NO}}_{3}^{-}/{\rm{NO}}_{2}^{-}\).

Key points

  • Waste nitrates/nitrites are an environmental problem but are also sources of fixed nitrogen. This protocol provides experimental strategies for choosing catalysts and optimizing reaction conditions for aqueous \({\rm{NO}}_{3}^{-}/{\rm{NO}}_{2}^{-}\) electrocatalytic reactions.

  • This approach includes options for in situ and operando characterization as well as technoeconomic analysis. It is exemplified by the preparation of ammonia as well as NH2OH, N2H4 and organonitrogen compounds but could be extended to other feedstocks and products.

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Fig. 1: Comprehensive workflow for electrocatalytic reactions involving aqueous \({\bf{NO}}_{\bf{3}}^{\bf{-}}/{\bf{NO}}_{\bf{2}}^{\bf{-}}\).
The alternative text for this image may have been generated using AI.
Fig. 2: Fabrication of powder catalyst electrodes.
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Fig. 3: Preparation and assembly of a self-standing electrode.
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Fig. 4: Assembly of single cell and H-type cell three-electrode measurements.
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Fig. 5: Assembly of the flow cell.
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Fig. 6: Quantitative determination of NH3.
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Fig. 7: Quantitative determination of NH2OH.
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Fig. 8: Colorimetric quantification of \({\bf{NO}}_{\bf{2}}^{\bf{-}}\) and \({\bf{NO}}_{\bf{3}}^{\bf{-}}\).
The alternative text for this image may have been generated using AI.
Fig. 9: Colorimetric quantification of N2H4.
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Fig. 10: Quantification of nitrogenous products by 1H NMR.
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Fig. 11: GC quantification of cyclohexanone oxime.
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Fig. 12: Electrochemical pathway and mechanistic characterization of cyclopentanone-mediated NH2OH synthesis from \({\rm{NO}}_{3}^{-}\).
The alternative text for this image may have been generated using AI.

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Data availability

The data in this protocol are available from the corresponding author upon request. Source data are provided with this paper.

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Acknowledgements

The work was supported by Strategic Priority Research Program (A) of the Chinese Academy of Sciences (XDA0390402), the National Natural Science Foundation of China (22293015 and 22121002), the Shanxi Research Institute of Huairou Laboratory (2024SY3004) and the Photon Science Center for Carbon Neutrality. The X-ray absorption spectroscopy measurements were performed at the BL14W1 and BL17B1 beamline of the Shanghai Synchrotron Radiation Facility. The authors thank the staff at the Centre for Physiochemical Analysis & Measurement of ICCAS for catalyst characterizations.

Author information

Authors and Affiliations

  1. Beijing National Laboratory for Molecular Sciences, CAS Laboratory of Colloid and Interface and Thermodynamics, CAS Research/Education Center for Excellence in Molecular Sciences, Center for Carbon Neutral Chemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing, China

    Shunhan Jia  (贾顺涵), Ruhan Wang  (王茹涵), Hanle Liu  (刘涵乐), Limin Wu  (吴丽敏), Libing Zhang  (张礼兵), Qian Li  (李骞), Xiaoyu Zhang  (章小余), Junfeng Xiang  (向俊锋), Zhijuan Zhao  (赵志娟), Xiaofu Sun  (孙晓甫) & Buxing Han  (韩布兴)

  2. School of Chemical Sciences, University of Chinese Academy of Sciences, Beijing, China

    Shunhan Jia  (贾顺涵), Ruhan Wang  (王茹涵), Hanle Liu  (刘涵乐), Xiaofu Sun  (孙晓甫) & Buxing Han  (韩布兴)

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  1. Shunhan Jia  (贾顺涵)
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Contributions

S.J., X.S. and B.H. conceived and supervised the project. S.J. drafted the manuscript, with revisions provided by X.S. and B.H. Q.L. and J.X. carried out the NMR analyses. X.Z. and Z.Z. performed the XPS characterizations. R.W., H.L., L.W. and L.Z. participated in discussions and provided helpful suggestions. All authors contributed to data analysis and manuscript revision.

Corresponding authors

Correspondence to Xiaofu Sun  (孙晓甫) or Buxing Han  (韩布兴).

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Key references

Wang, R. et al. Angew. Chem. Int. Ed. Engl. 64, e202425262 (2025): https://doi.org/10.1002/anie.202425262

Song, X. et al. Angew. Chem. Int. Ed. Engl. 64, e202501830 (2025): https://doi.org/10.1002/anie.202501830

Wu, L. et al. Chem. 11, 102591 (2025): https://doi.org/10.1016/j.chempr.2025.102591

Jia, S. et al. Nat. Commun. 15, 8567 (2024): https://doi.org/10.1038/s41467-024-52825-1

Jia, S. et al. J. Am. Chem. Soc. 146, 10934–10942 (2024): https://doi.org/10.1021/jacs.4c01961

Extended data

Extended Data Fig. 1 Pre-treatment of a Nafion 117 membrane.

a, Immersion of a cut Nafion 117 membrane in H2O2 aqueous solution. b, Acid treatment of the membrane. c, Final rinsing and storage in water.

Extended Data Fig. 2 In situ Raman spectroscopy.

a, Disassembled view of the in situ Raman electrochemical flow cell. b, A fully assembled flow cell configured with a three-electrode system: a catalyst-coated working electrode, a carbon rod counterelectrode and a reference electrode. c, Operational setup of the flow cell mounted under a Raman microscope with a 532-nm excitation laser for real-time spectral acquisition under electrochemical control.

Extended Data Fig. 3 In situ ATR-FTIR characterization.

a, Disassembled view of the ATR electrochemical cell. b, Assembled ATR cell configured with a three-electrode system. c, Operational configuration of the ATR-FTIR setup integrated with a spectrometer.

Extended Data Fig. 4 Quasi-operando sample holder for XPS analysis.

a, Schematic illustration of the custom-designed quasi-operando sample holder. b, Workflow of sample preparation and transfer. c, Photo of the sample holder being introduced into the XPS vacuum chamber for quasi-operando measurement.

Extended Data Fig. 5 In situ XAS cell.

a, Disassembled view of the in situ XAS cell. b, Operational setup of the in situ XAS cell at a synchrotron beamline.

Extended Data Fig. 6 Separation of cyclohexanone oxime from the post-electrolysis solution.

a, Liquid-liquid extraction using a separatory funnel after salting out the aqueous phase. b, Solvent removal from the combined organic extracts using a rotary evaporator. c, Concentrated crude cyclohexanone oxime. d, Final dried solid oxime product.

Source data

Source Data Fig. 6 (download XLSX )

UV–visible absorption spectra and calibration curve

Source Data Fig. 7 (download XLSX )

UV–visible absorption spectra and calibration curve

Source Data Fig. 8 (download XLSX )

UV–visible absorption spectra and calibration curve

Source Data Fig. 9 (download XLSX )

UV–visible absorption spectra and calibration curve

Source Data Fig. 10 (download XLSX )

Calibration curve

Source Data Fig. 11 (download XLSX )

GC chromatogram and calibration curve

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Jia, S., Wang, R., Liu, H. et al. Electrocatalytic reactions involving aqueous nitrate and nitrite. Nat Protoc (2026). https://doi.org/10.1038/s41596-026-01350-0

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