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Mechanism Insights, Recent Developments, and Prospects for Electrochemical Ammonia Synthesis from Nitrate Reduction AITranslate

Ruchun Li1,2; Runyan Wu1; Kezhen Qi3; Heng Yang4;
1.Faculty of Chemistry and Chemical Engineering，Yunnan Normal University，Kunming 650500，China
2.National Energy Key Laboratory for New Hydrogen-Ammonia Energy Technologies，Foshan Xianhu Laboratory，Foshan 528200，China
3.College of Pharmacy，Dali University，Dali 671000，China
4.College of Chemistry and Environmental Engineering，Wuhan Polytechnic University，Wuhan 430023，China
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Water pollution has become a crucial issue with the development of urbanization and industrialization in modern society. Nitrate （NO3−） pollutant is a common contaminant in surface and groundwater mainly from agricultural fertilisers，domestic sewage pollution，and industrial wastewater. Excessive nitrate in water will threaten human health and lead to environmental risks. Various techniques have been extensively studied to remove nitrate from water，such as biological denitrification，chemical reduction，reverse osmosis，ion exchange，electrocatalysis，and photocatalysis. Among them，electrocatalytic nitrate reduction is considered to be one of the most promising methods for removing pollutants from water due to its simple operating conditions and environmentally friendliness. In addition，ammonia （NH3） is an important component in industrial chemicals and a potential hydrogen energy carrier. Compared with hydrogen energy，the storage and transportation of ammonia are more convenient and safer，and its volume hydrogen capacity in liquid ammonia is even much larger than liquid hydrogen. Thus，ammonia production has attracted increasing attention since the proposal of carbon peaking and carbon neutrality goals. The electrocatalytic nitrate reduction to NH3 not only removes nitrate from water，but also obtains the high-value chemical ammonia. However，this process involves an 8-electron-multi proton reaction accompanied by many by-products （e.g.，NO3−，NO，N2，NH2OH，etc.），which results in low NH3 selectivity. Thus，the development of suitable and efficient electrocatalysts remains a great challenge to the large-scale production of NH3. This paper summarized the recent progress and challenges of electrocatalytic nitrate to NH3 synthesis in terms of catalytic mechanism and material design. Firstly，the possible catalytic mechanisms of electrocatalytic nitrate to ammonia synthesis technology were discussed. The mechanism of nitrate electroreduction mainly included indirect autocatalytic reduction pathway and direct electrocatalytic reduction pathway. When nitrate did not participate in the electron-transfer process，reduction process could be defined as indirect autocatalytic reduction. The direct nitrate electroreduction was composed of the regulation of active adsorbed hydrogen atoms （Hads） and the electron reduction process. As for nitrate electroreduction to NH3，four catalytic reaction pathways of electrocatalytic nitrate to ammonia synthesis have been proposed through theoretical calculation. These pathways could be classified into O-end，O-side，N-end，and N-side pathways. Secondly，recent advance in electrocatalytic materials design，including noble metal catalysts，non-precious metal catalysts，and non-metallic catalysts，was summarized. Among them，noble metal Pt，Pd，Ru，Rh，Ir，Ag，and Au showed good nitrate reduction activity. By optimizing synthetic strategies，Pd，Ru，Ag，and Au could realize high selectivity toward NH3；moreover，non-precious metal electrocatalysts （Cu，Ni，Fe，Co and Ti） have attracted more and more attention in electrocatalytic nitrate reduction due to low cost and excellent activity. Especially，Cu-based electrocatalysts possessed the highest catalytic activity and were widely used in the electrocatalytic reduction of nitrate. The crystal plane of Cu played an important role on the electrochemical performance. In an alkaline solution，the onset potential of Cu（100） for electrocatalytic reduction of nitrate was lower than that of Cu（111）. Interestingly，in acidic media，the onset potential of both is similar. The ratio of Cu（200）/Cu（111） could regulate the selectivity of nitrate reduction. By reducing the intensity ratio of Cu（200）/Cu（111），higher N2 selectivity could be achieved. Other Cu-based compounds，including CuxO，CuxP，and Cu-MOF materials，also showed good nitrate reduction properties. However，surface self-reconstruction usually occurs at a higher reduction potential，resulting in changes in the structure or the local coordination environment and its catalytic activity or stability of the materials. For instance，in-situ Raman spectra combined with the experimental results confirmed that CuO could be electrochemically converted into Cu/Cu2O during the catalytic process. The obtained Cu/Cu2O as the real catalyst could promote the formation of *NOH intermediates and inhibit the hydrogen evolution reaction. Thus，to reveal the surface self-reconstruction of the materials under reaction conditions was crucial for high NH3 selectivity. Recently，various carbon materials，including graphene and porous carbon，also had outstanding properties in nitrate reduction. The current challenges in nitrate electroreduction to ammonia synthesis were also discussed in depth：1） the catalytic mechanism remained unclear. It was urgent to combine the in-situ characterization method with theoretical calculation to monitor and verify the catalytic mechanism of the electrocatalysts under reaction conditions；2） The catalytic performance，stability and selectivity of the electrocatalysts should be also improved；3） The separation and purification of the products should be further studied；at present，there were few reports on the separation and purification of NH3 product；due to the complex composition in sewage，the separation and purification of ammonia remained an enormous challenge. In future studies，the separation and purification of products should pay more attention. This review was expected to provide reference value for the design of electrocatalysts in efficient nitrate electroreduction to ammonia synthesis and point out the research direction for the future development of electrochemical ammonia synthesis from nitrate reduction.

KeyWords AITranslate

water pollution electrocatalysis nitrate reduction ammonia production selectivity

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Basic Information:

DOI：10.13373/j.cnki.cjrm.XY23120001

Chinese Library Classification Number:TF803.21

Citation Information:

Water pollution has become a crucial issue with the development of urbanization and industrialization in modern society. Nitrate （NO3−） pollutant is a common contaminant in surface and groundwater mainly from agricultural fertilisers，domestic sewage pollution，and industrial wastewater. Excessive nitrate in water will threaten human health and lead to environmental risks. Various techniques have been extensively studied to remove nitrate from water，such as biological denitrification，chemical reduction，reverse osmosis，ion exchange，electrocatalysis，and photocatalysis. Among them，electrocatalytic nitrate reduction is considered to be one of the most promising methods for removing pollutants from water due to its simple operating conditions and environmentally friendliness. In addition，ammonia （NH3） is an important component in industrial chemicals and a potential hydrogen energy carrier. Compared with hydrogen energy，the storage and transportation of ammonia are more convenient and safer，and its volume hydrogen capacity in liquid ammonia is even much larger than liquid hydrogen. Thus，ammonia production has attracted increasing attention since the proposal of carbon peaking and carbon neutrality goals. The electrocatalytic nitrate reduction to NH3 not only removes nitrate from water，but also obtains the high-value chemical ammonia. However，this process involves an 8-electron-multi proton reaction accompanied by many by-products （e.g.，NO3−，NO，N2，NH2OH，etc.），which results in low NH3 selectivity. Thus，the development of suitable and efficient electrocatalysts remains a great challenge to the large-scale production of NH3. This paper summarized the recent progress and challenges of electrocatalytic nitrate to NH3 synthesis in terms of catalytic mechanism and material design. Firstly，the possible catalytic mechanisms of electrocatalytic nitrate to ammonia synthesis technology were discussed. The mechanism of nitrate electroreduction mainly included indirect autocatalytic reduction pathway and direct electrocatalytic reduction pathway. When nitrate did not participate in the electron-transfer process，reduction process could be defined as indirect autocatalytic reduction. The direct nitrate electroreduction was composed of the regulation of active adsorbed hydrogen atoms （Hads） and the electron reduction process. As for nitrate electroreduction to NH3，four catalytic reaction pathways of electrocatalytic nitrate to ammonia synthesis have been proposed through theoretical calculation. These pathways could be classified into O-end，O-side，N-end，and N-side pathways. Secondly，recent advance in electrocatalytic materials design，including noble metal catalysts，non-precious metal catalysts，and non-metallic catalysts，was summarized. Among them，noble metal Pt，Pd，Ru，Rh，Ir，Ag，and Au showed good nitrate reduction activity. By optimizing synthetic strategies，Pd，Ru，Ag，and Au could realize high selectivity toward NH3；moreover，non-precious metal electrocatalysts （Cu，Ni，Fe，Co and Ti） have attracted more and more attention in electrocatalytic nitrate reduction due to low cost and excellent activity. Especially，Cu-based electrocatalysts possessed the highest catalytic activity and were widely used in the electrocatalytic reduction of nitrate. The crystal plane of Cu played an important role on the electrochemical performance. In an alkaline solution，the onset potential of Cu（100） for electrocatalytic reduction of nitrate was lower than that of Cu（111）. Interestingly，in acidic media，the onset potential of both is similar. The ratio of Cu（200）/Cu（111） could regulate the selectivity of nitrate reduction. By reducing the intensity ratio of Cu（200）/Cu（111），higher N2 selectivity could be achieved. Other Cu-based compounds，including CuxO，CuxP，and Cu-MOF materials，also showed good nitrate reduction properties. However，surface self-reconstruction usually occurs at a higher reduction potential，resulting in changes in the structure or the local coordination environment and its catalytic activity or stability of the materials. For instance，in-situ Raman spectra combined with the experimental results confirmed that CuO could be electrochemically converted into Cu/Cu2O during the catalytic process. The obtained Cu/Cu2O as the real catalyst could promote the formation of *NOH intermediates and inhibit the hydrogen evolution reaction. Thus，to reveal the surface self-reconstruction of the materials under reaction conditions was crucial for high NH3 selectivity. Recently，various carbon materials，including graphene and porous carbon，also had outstanding properties in nitrate reduction. The current challenges in nitrate electroreduction to ammonia synthesis were also discussed in depth：1） the catalytic mechanism remained unclear. It was urgent to combine the in-situ characterization method with theoretical calculation to monitor and verify the catalytic mechanism of the electrocatalysts under reaction conditions；2） The catalytic performance，stability and selectivity of the electrocatalysts should be also improved；3） The separation and purification of the products should be further studied；at present，there were few reports on the separation and purification of NH3 product；due to the complex composition in sewage，the separation and purification of ammonia remained an enormous challenge. In future studies，the separation and purification of products should pay more attention. This review was expected to provide reference value for the design of electrocatalysts in efficient nitrate electroreduction to ammonia synthesis and point out the research direction for the future development of electrochemical ammonia synthesis from nitrate reduction.

quote

GB/T 7714-2015 [1] Ruchun Li, Runyan Wu, Kezhen Qi, et al. Mechanism Insights, Recent Developments, and Prospects for Electrochemical Ammonia Synthesis from Nitrate Reduction[J]. Chinese Journal of Rare Metals, 2025, 49(7): 1059-1075. DOI:10.13373/j.cnki.cjrm.XY23120001.
MLA [1] Ruchun Li, et al., "Mechanism Insights, Recent Developments, and Prospects for Electrochemical Ammonia Synthesis from Nitrate Reduction." Chinese Journal of Rare Metals, vol. 49, no. 7, 2025, pp. 1059-1075, https://doi.org/10.13373/j.cnki.cjrm.XY23120001.
APA [1] Ruchun Li, Runyan Wu, Kezhen Qi, & Heng Yang. (2025). Mechanism Insights, Recent Developments, and Prospects for Electrochemical Ammonia Synthesis from Nitrate Reduction. Chinese Journal of Rare Metals, 49(7), 1059-1075. https://doi.org/10.13373/j.cnki.cjrm.XY23120001
IEEE [1] Ruchun Li, Runyan Wu, Kezhen Qi, and Heng Yang, "Mechanism Insights, Recent Developments, and Prospects for Electrochemical Ammonia Synthesis from Nitrate Reduction," Chinese Journal of Rare Metals, vol. 49, no. 7, pp. 1059-1075, 2025, doi: 10.13373/j.cnki.cjrm.XY23120001. keywords: {water pollution;electrocatalysis;nitrate reduction;ammonia production;selectivity}