Chinese Journal of Catalysis ›› 2026, Vol. 88: 129-182.DOI: 10.1016/S1872-2067(26)65143-1
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Haoye Wanga, Bingjie Qiua, Richard, Jr L. Smithb, Xinhua Qia,*(
)
Received:2025-09-28
Accepted:2026-02-11
Online:2026-09-18
Published:2026-09-05
About author:Xinhua Qi (College of Environmental Science and Engineering, Nankai University) received his B.S. in environmental chemistry and Ph.D. in environmental science from Nankai University in 1998 and 2003, respectively. He worked as a JSPS Postdoctoral Fellow at Tohoku University with Professor Richard Lee Smith, Jr (Sendai, Japan) from Oct. 2006 to Nov 2010. Currently, he is a distinguished professor of Nankai University. His research interest mainly focuses on green processes for biomass conversion into value-added materials and chemicals. He has published more than 180 peer-reviewed scientific papers, and these papers have been cited over 8200 times with H index 51. He also has co-authored over 20 patents, 5 books on environmental engineering and biomass resource utilization. Prof. Qi has been selected as leading talent in the National Ten Thousand Talents Plan and Elsevier’s “Highly Cited Chinese Researchers” (2024‒2025).
Supported by:Haoye Wang, Bingjie Qiu, Richard, Jr L. Smith, Xinhua Qi. Electrocatalytic nitrate reduction systems for chemical production: Mechanisms, process engineering and challenges[J]. Chinese Journal of Catalysis, 2026, 88: 129-182.
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URL: https://www.cjcatal.com/EN/10.1016/S1872-2067(26)65143-1
| Review topic | Focus | Emphasis | Identified challenges | Ref. | |||
|---|---|---|---|---|---|---|---|
| Ammonia synthesis | |||||||
| Low-concentration nitrate remediation toward field deployment | feasibility, mechanisms and engineering strategies for < 0.1 mol L-1 NO3- | 1. enrichment and mass-transfer enhancement 2. NH3 vs. N2 pathway selection and safety 3. electrolyzer, electrolyte and by-product control | [49] | ||||
| Active-hydrogen-centric NO3RR pathway design | comprehensive hydrogen lifecycle management from water activation to utilization | 1. active hydrogen generation, transport and coupling suppression 2. *H vs. PCET mechanisms 3. catalyst design and characterization toolbox | 1. maintaining dynamic *H balance to avoid HER or H2 by-product 2. bridging lab-scale principles to real wastewater | [41] | |||
| Tandem catalytic sites for NO3RR | applications and mechanisms of tandem catalytic sites in electrocatalytic NO3RR | 1. classification of tandem catalytic sites (alloys, heterostructures, single-atom catalysts) 2. mechanistic actions in NO3- adsorption, activation, and hydrogenation | 1. incomplete removal of total nitrogen 2. poisoning in complex wastewater systems 3. low treatment efficiency for low-concentration wastewater 4. separation of ammonia products 5. insufficient power density of catalytic flow batteries | [42] | |||
| Electrocatalytic NO3RR to ammonia | mechanisms, influencing factors, catalyst types and industrialization of electrocatalytic NO3RR. | 1. catalyst design (metals, oxides, non-metals composite materials) 2. reaction pathways 3. in-situ characterization techniques 4. reactor design optimization | 1. complex multi-intermediate pathways 2. evolution of dynamic active sites 3. catalyst stability 4. energy consumption 5. economic feasibility and industrialization | [43] | |||
| Electrocatalytic NO3RR to ammonia | fundamental mechanisms, catalyst design, and performance optimization | 1. summary of mechanisms 2. catalyst types 3. performance descriptors | 1. reaction complexity 2. HER competition 3. catalyst selectivity and stability | [44] | |||
| Electrocatalytic nitrate reduction for wastewater treatment | bridging lab-scale catalyst innovation to field-scale implementation | 1. emphasis on scalability 2. economics 3. real-world applicability | 1. ionic interferences 2. energy cost 3. reactor design 4. by-product control | [50] | |||
| Electrocatalytic NO3RR to ammonia | catalyst design strategies for enhancing NO3RR performance | 1. structural engineering (alloying, doping, single-atom, size, nanoconfinement, tandem catalysis) | 1. reaction kinetics optimization 2. catalyst selectivity and stability 3. HER competition 4. low-concentration wastewater treatment | [10] | |||
| C-N coupling reaction | |||||||
| Catalyst design strategies for NOx species in electrochemical C-N coupling reactions | electrocatalytic C-N coupling reactions involving NOx (NO3-, NO2-, NO) for synthesis of high-value-added nitrogen-containing chemicals | 1. control of reaction selectivity, efficiency 2. defect engineering, coordination environment, dual-site synergy 3. interface engineering, emerging structures | 1. unstable intermediates 2. low selectivity 3. competitive side reactions 4. substrate adsorption mismatch 5. Insufficient dynamic structural response | [45] | |||
| Electrocatalytic reduction of nitrate to nitrogen-containing products (ammonia, urea, amino acids) | three key pathways from nitrate: (i) selective reduction to ammonia (ii) C-N coupling to synthesize urea (iii) amino acids via NO2-/NH2OH intermediates | 1. nitrogen cycle closed-loop 2. control of reactive nitrogen intermediates 3. catalyst design and microenvironment 4. reactor engineering and economics | 1. poor amino acid selectivity 2. short intermediate lifetime 3. competition from HER 4. lack of modular systems 5. incomplete life cycle assessment | [46] | |||
| Electrocatalytic C-N coupling using N2, NO2-, NO3- as N sources | mechanisms and catalyst design for C-N bond formation | 1. transition metal catalysts (Cu, Ni, Fe, etc.) for NO3RR to *NH2/*NH2OH 2. coupling with CO2/*CO | 1. low Faradaic efficiency 2. poor selectivity 3. catalyst stability 4. complex reaction pathways | [47] | |||
| Electrocatalytic urea synthesis via C-N coupling of CO2 and NO3-/NO2- | catalyst and electrode design for selective urea formation | 1. NO3- reduction to *NH2/*NH2OH, coupling with *CO 2. GDE design for mass transfer | 1. competing HER and NH3 formation 2. GDE flooding 3. low urea selectivity 4. catalyst stability | [48] | |||
| Electrocatalytic nitrate reduction systems for chemical production | 1. reaction pathways and mechanisms of electrocatalytic nitrate reduction to ammonia, urea, amino acid and nitrogen-containing organic compounds 2. selection of anode reactions to replace OER 3. practical application strategies | 1. mechanism and performance comparison of catalysts in NO3RR and C-N coupling reactions 2. system energy consumption, Product value, coordinated pollutant treatment 3. technical readiness level (TRL) of nitrate reduction systems | 1. long-term catalyst activity and selectivity 2. matching anode reaction with cathode NO3RR 3. energy consumption of product separation 4. dual functionality of catalyst 5. continuous processes and economic models | This work | |||
Table 1 Selected reviews on electrocatalytic nitrate reduction systems.
| Review topic | Focus | Emphasis | Identified challenges | Ref. | |||
|---|---|---|---|---|---|---|---|
| Ammonia synthesis | |||||||
| Low-concentration nitrate remediation toward field deployment | feasibility, mechanisms and engineering strategies for < 0.1 mol L-1 NO3- | 1. enrichment and mass-transfer enhancement 2. NH3 vs. N2 pathway selection and safety 3. electrolyzer, electrolyte and by-product control | [49] | ||||
| Active-hydrogen-centric NO3RR pathway design | comprehensive hydrogen lifecycle management from water activation to utilization | 1. active hydrogen generation, transport and coupling suppression 2. *H vs. PCET mechanisms 3. catalyst design and characterization toolbox | 1. maintaining dynamic *H balance to avoid HER or H2 by-product 2. bridging lab-scale principles to real wastewater | [41] | |||
| Tandem catalytic sites for NO3RR | applications and mechanisms of tandem catalytic sites in electrocatalytic NO3RR | 1. classification of tandem catalytic sites (alloys, heterostructures, single-atom catalysts) 2. mechanistic actions in NO3- adsorption, activation, and hydrogenation | 1. incomplete removal of total nitrogen 2. poisoning in complex wastewater systems 3. low treatment efficiency for low-concentration wastewater 4. separation of ammonia products 5. insufficient power density of catalytic flow batteries | [42] | |||
| Electrocatalytic NO3RR to ammonia | mechanisms, influencing factors, catalyst types and industrialization of electrocatalytic NO3RR. | 1. catalyst design (metals, oxides, non-metals composite materials) 2. reaction pathways 3. in-situ characterization techniques 4. reactor design optimization | 1. complex multi-intermediate pathways 2. evolution of dynamic active sites 3. catalyst stability 4. energy consumption 5. economic feasibility and industrialization | [43] | |||
| Electrocatalytic NO3RR to ammonia | fundamental mechanisms, catalyst design, and performance optimization | 1. summary of mechanisms 2. catalyst types 3. performance descriptors | 1. reaction complexity 2. HER competition 3. catalyst selectivity and stability | [44] | |||
| Electrocatalytic nitrate reduction for wastewater treatment | bridging lab-scale catalyst innovation to field-scale implementation | 1. emphasis on scalability 2. economics 3. real-world applicability | 1. ionic interferences 2. energy cost 3. reactor design 4. by-product control | [50] | |||
| Electrocatalytic NO3RR to ammonia | catalyst design strategies for enhancing NO3RR performance | 1. structural engineering (alloying, doping, single-atom, size, nanoconfinement, tandem catalysis) | 1. reaction kinetics optimization 2. catalyst selectivity and stability 3. HER competition 4. low-concentration wastewater treatment | [10] | |||
| C-N coupling reaction | |||||||
| Catalyst design strategies for NOx species in electrochemical C-N coupling reactions | electrocatalytic C-N coupling reactions involving NOx (NO3-, NO2-, NO) for synthesis of high-value-added nitrogen-containing chemicals | 1. control of reaction selectivity, efficiency 2. defect engineering, coordination environment, dual-site synergy 3. interface engineering, emerging structures | 1. unstable intermediates 2. low selectivity 3. competitive side reactions 4. substrate adsorption mismatch 5. Insufficient dynamic structural response | [45] | |||
| Electrocatalytic reduction of nitrate to nitrogen-containing products (ammonia, urea, amino acids) | three key pathways from nitrate: (i) selective reduction to ammonia (ii) C-N coupling to synthesize urea (iii) amino acids via NO2-/NH2OH intermediates | 1. nitrogen cycle closed-loop 2. control of reactive nitrogen intermediates 3. catalyst design and microenvironment 4. reactor engineering and economics | 1. poor amino acid selectivity 2. short intermediate lifetime 3. competition from HER 4. lack of modular systems 5. incomplete life cycle assessment | [46] | |||
| Electrocatalytic C-N coupling using N2, NO2-, NO3- as N sources | mechanisms and catalyst design for C-N bond formation | 1. transition metal catalysts (Cu, Ni, Fe, etc.) for NO3RR to *NH2/*NH2OH 2. coupling with CO2/*CO | 1. low Faradaic efficiency 2. poor selectivity 3. catalyst stability 4. complex reaction pathways | [47] | |||
| Electrocatalytic urea synthesis via C-N coupling of CO2 and NO3-/NO2- | catalyst and electrode design for selective urea formation | 1. NO3- reduction to *NH2/*NH2OH, coupling with *CO 2. GDE design for mass transfer | 1. competing HER and NH3 formation 2. GDE flooding 3. low urea selectivity 4. catalyst stability | [48] | |||
| Electrocatalytic nitrate reduction systems for chemical production | 1. reaction pathways and mechanisms of electrocatalytic nitrate reduction to ammonia, urea, amino acid and nitrogen-containing organic compounds 2. selection of anode reactions to replace OER 3. practical application strategies | 1. mechanism and performance comparison of catalysts in NO3RR and C-N coupling reactions 2. system energy consumption, Product value, coordinated pollutant treatment 3. technical readiness level (TRL) of nitrate reduction systems | 1. long-term catalyst activity and selectivity 2. matching anode reaction with cathode NO3RR 3. energy consumption of product separation 4. dual functionality of catalyst 5. continuous processes and economic models | This work | |||
Scheme 1. Electrocatalytic nitrate reduction system for production of value-added chemicals.
Fig. 1. (A) Frost-Ebsworth diagram of nitrogen species at (red) pH 0.0 and (blue) pH 14.0. (B) Pourbaix diagram of nitrogen species. Reproduced from Ref. [62] with permission, copyright 2018, Elsevier B. V. (C) Overview of mechanisms for electrochemical reduction of nitrate in aqueous media. Reproduced from Ref. [9] with permission, copyright 2024, Elsevier B.V.
| Entry No. | Electrocatalyst a | Electrolyte | pH | Applied potential (V vs. RHE) | FE (%) | NH3 productivity | Stability | Reaction mechanism | Key intermediate b | RDS b | TRL | Ref. | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Background | NO3- | ||||||||||||
| Ru | |||||||||||||
| 1 | Ru-ST-12 | 1 mol L-1 KOH | (1 mol L-1)/(1.01*105 ppm) KNO3 | 14 | -0.8 | > 96 | 19.89 mg cm-2 h-1 | 100 h | EE | *H2NO | *HNO → *H2NO | 3 | [77] |
| 2 | 2D-Ru/NC | 0.5 mol L-1 K2SO4 | (1 mol L-1)/(1.01*105 ppm) KNO3 | 7 | -1.1 | > 99 | 55.4 mg cm-2 h-1 | 6 h | EE | *NOH | *NO → *NOH | 3 | [79] |
| 3 | Ru20Ni80 alloy | 0.5 mol L-1 K2SO4 | (0.1 mol L-1)/(1.0*104 ppm) KNO3 | 7 | -0.35 | 98.02 | 55.4 mg cm-2 h-1 @-0.65 V | 12 h | EE | *NHO | *NO → *NHO | 4 | [1] |
| 4 | Ru/MSN- WO3-x | 0.25 mol L-1 K2SO4 + 0.5 mol L-1 phosphate | (0.1 mol L-1)/(1.0*104 ppm) KNO3 | 7 | 0 | 95.1 | 12.38 mg cm-2 h-1 @-0.6 V | 20 cycles | ECE | *NOH | *NO → *NOH | 3 | [80] |
| 5 | Ru-MCA | 0.5 mol L-1 Na2SO4 | (0.05 mol L-1)/(4250 ppm) NaNO3 | 2.5 | -1.13 | 79.8 | 4.18 mg cm-2 h-1 | 200 min | ECE | — | — | 4 | [81] |
| Pd | |||||||||||||
| 6 | Pd (111) | 0.1 mol L-1 Na2SO4 | (0.1 mol L-1)/(8500 ppm) NaNO3 | 7 | -0.7 | 79.91 | 0.5485 mmol h-1 cm-2 | 20 h | EE | *NOH | *NH3 → NH3 | 3 | [82] |
| 7 | Pd (111) + (100) | 0.1 mol L-1 NaOH | (0.02 mol L-1)/(1700 ppm) NaNO3 | 14 | -0.2 | 35 | 306.8 μg h-1 mgPd-1 | — | — | — | — | 3 | [83] |
| 8 | PdCu | 0.5 mol L-1 K2SO4 | (0.1 mol L-1)/(1.0*104 ppm) KNO3 | 7 | -0.8 | 90.9 | 295 mg h-1 mgcat-1 | 10 cycles | ECE | *NOH | *NO → *NOH | 3 | [86] |
| 9 | CuPd (100) | 1.0 mol L-1 KOH | (0.02 mol L-1)/(2000 ppm) KNO3 | 14 | -0.6 | 84.1 | 6.97 mol h-1 g-1 | 10 cycles | EE | *NH2OH | — | 3 | [87] |
| 10 | Bi1Pd | 1.0 mol L-1 KOH | (0.1 mol L-1)/(1.0*104 ppm) KNO3 | 14 | -0.6 | 99.6 | 33.8 mg h-1 cm-2 | 20 h | ECE | *NOH | *NO → *NOH | 4 | [88] |
| 11 | PdCuSnCoNi | 0.5 mol L-1 K2SO4 | (4.95 mmol L-1)/(500 ppm) KNO3 | 7 | -0.8 | 99.5 | 4.1 mg h-1 mgcat-1 | 50 h | EE | *NO2 | *NO3 → *NO2 | 4 | [89] |
| 12 | Pd/Zr-MOF | 0.1 mol L-1 Na2SO4 | (5.88 mmol L-1)/(500 ppm) NaNO3 | 7 | -1.3 | 58.1 | 287.31 mmol h-1 gcat-1 | 10 cycles | — | — | — | 3 | [90] |
| 13 | Pd/TiO2 | 1 mol L-1 LiCl | (0.25 mol L-1)/(17250 ppm) LiNO3 | 7 | -0.7 | 92.1 | 1.12 mg cm-2 h-1 | 12 h | ECE | *NO2 | *NH2 → *NH3 | 4 | [91] |
| Others | |||||||||||||
| 14 | Pt93Pd7 (100) | 0.1 mol L-1 HClO4 | (0.1 mol L-1)/(8500 ppm) NaNO3 | 1 | — | — | — | — | — | *NOH | *NO → *NOH | 3 | [92] |
| 15 | Rh NFs | 0.1 mol L-1 Na2SO4 | (0.1 mol L-1)/(8500 ppm) NaNO3 | 11.5 | 0.2 | 95 | — | 10 h | ECE | *NOH | *NO → *NOH | 3 | [93] |
| 16 | RhNi@Rh BMLs | 0.1 mol L-1 HClO4 | (0.05 mol L-1)/(5050 ppm) KNO3 | 1 | 0.05 | 98.4 | 13.4 mg h-1 mgcat-1 | >400 h | EE | *NOH | *NO → *NOH | 4 | [95] |
Table 2 Summary of catalytic performance of noble metal-based electrocatalysts.
| Entry No. | Electrocatalyst a | Electrolyte | pH | Applied potential (V vs. RHE) | FE (%) | NH3 productivity | Stability | Reaction mechanism | Key intermediate b | RDS b | TRL | Ref. | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Background | NO3- | ||||||||||||
| Ru | |||||||||||||
| 1 | Ru-ST-12 | 1 mol L-1 KOH | (1 mol L-1)/(1.01*105 ppm) KNO3 | 14 | -0.8 | > 96 | 19.89 mg cm-2 h-1 | 100 h | EE | *H2NO | *HNO → *H2NO | 3 | [77] |
| 2 | 2D-Ru/NC | 0.5 mol L-1 K2SO4 | (1 mol L-1)/(1.01*105 ppm) KNO3 | 7 | -1.1 | > 99 | 55.4 mg cm-2 h-1 | 6 h | EE | *NOH | *NO → *NOH | 3 | [79] |
| 3 | Ru20Ni80 alloy | 0.5 mol L-1 K2SO4 | (0.1 mol L-1)/(1.0*104 ppm) KNO3 | 7 | -0.35 | 98.02 | 55.4 mg cm-2 h-1 @-0.65 V | 12 h | EE | *NHO | *NO → *NHO | 4 | [1] |
| 4 | Ru/MSN- WO3-x | 0.25 mol L-1 K2SO4 + 0.5 mol L-1 phosphate | (0.1 mol L-1)/(1.0*104 ppm) KNO3 | 7 | 0 | 95.1 | 12.38 mg cm-2 h-1 @-0.6 V | 20 cycles | ECE | *NOH | *NO → *NOH | 3 | [80] |
| 5 | Ru-MCA | 0.5 mol L-1 Na2SO4 | (0.05 mol L-1)/(4250 ppm) NaNO3 | 2.5 | -1.13 | 79.8 | 4.18 mg cm-2 h-1 | 200 min | ECE | — | — | 4 | [81] |
| Pd | |||||||||||||
| 6 | Pd (111) | 0.1 mol L-1 Na2SO4 | (0.1 mol L-1)/(8500 ppm) NaNO3 | 7 | -0.7 | 79.91 | 0.5485 mmol h-1 cm-2 | 20 h | EE | *NOH | *NH3 → NH3 | 3 | [82] |
| 7 | Pd (111) + (100) | 0.1 mol L-1 NaOH | (0.02 mol L-1)/(1700 ppm) NaNO3 | 14 | -0.2 | 35 | 306.8 μg h-1 mgPd-1 | — | — | — | — | 3 | [83] |
| 8 | PdCu | 0.5 mol L-1 K2SO4 | (0.1 mol L-1)/(1.0*104 ppm) KNO3 | 7 | -0.8 | 90.9 | 295 mg h-1 mgcat-1 | 10 cycles | ECE | *NOH | *NO → *NOH | 3 | [86] |
| 9 | CuPd (100) | 1.0 mol L-1 KOH | (0.02 mol L-1)/(2000 ppm) KNO3 | 14 | -0.6 | 84.1 | 6.97 mol h-1 g-1 | 10 cycles | EE | *NH2OH | — | 3 | [87] |
| 10 | Bi1Pd | 1.0 mol L-1 KOH | (0.1 mol L-1)/(1.0*104 ppm) KNO3 | 14 | -0.6 | 99.6 | 33.8 mg h-1 cm-2 | 20 h | ECE | *NOH | *NO → *NOH | 4 | [88] |
| 11 | PdCuSnCoNi | 0.5 mol L-1 K2SO4 | (4.95 mmol L-1)/(500 ppm) KNO3 | 7 | -0.8 | 99.5 | 4.1 mg h-1 mgcat-1 | 50 h | EE | *NO2 | *NO3 → *NO2 | 4 | [89] |
| 12 | Pd/Zr-MOF | 0.1 mol L-1 Na2SO4 | (5.88 mmol L-1)/(500 ppm) NaNO3 | 7 | -1.3 | 58.1 | 287.31 mmol h-1 gcat-1 | 10 cycles | — | — | — | 3 | [90] |
| 13 | Pd/TiO2 | 1 mol L-1 LiCl | (0.25 mol L-1)/(17250 ppm) LiNO3 | 7 | -0.7 | 92.1 | 1.12 mg cm-2 h-1 | 12 h | ECE | *NO2 | *NH2 → *NH3 | 4 | [91] |
| Others | |||||||||||||
| 14 | Pt93Pd7 (100) | 0.1 mol L-1 HClO4 | (0.1 mol L-1)/(8500 ppm) NaNO3 | 1 | — | — | — | — | — | *NOH | *NO → *NOH | 3 | [92] |
| 15 | Rh NFs | 0.1 mol L-1 Na2SO4 | (0.1 mol L-1)/(8500 ppm) NaNO3 | 11.5 | 0.2 | 95 | — | 10 h | ECE | *NOH | *NO → *NOH | 3 | [93] |
| 16 | RhNi@Rh BMLs | 0.1 mol L-1 HClO4 | (0.05 mol L-1)/(5050 ppm) KNO3 | 1 | 0.05 | 98.4 | 13.4 mg h-1 mgcat-1 | >400 h | EE | *NOH | *NO → *NOH | 4 | [95] |
Fig. 2. (A) Aberration-corrected HAADF-STEM image and EELS elemental map of Ru-ST-12. (B) FENH3 and JNH3 of Ru-ST-12 under applied potential of -0.2 V vs. RHE during 100 periods of 1 h electrocatalytic NO3RR. (C) Gibbs energy diagram of intermediates generated during electrocatalytic NO3RR over pure Ru surface and strained Ru surface. Reproduced with permission from Ref. [77]. Copyright 2020, American Chemical Society. (D,E) CV curves for storing protons of MSN-WO3, MSN-WO3-x, and Ru/MSN-WO3-x. (F) Reaction energies for intermediates on HyWO3-x and Ru/HyWO3-x surfaces. Reproduced with permission from Ref. [80]. Copyright 2025, Royal Society of Chemistry. (G) NH3 productivity and FE of Pd (111), Pd (110) and Pd (100) at -0.7 V vs. RHE. Reproduced with permission from Ref. [82]. Copyright 2021, Elsevier B.V. (H,I) Volcano-shaped correlation of ΔEad (*NO3) and ΔEad (*NO2) with NO3RR activity on Pd metallene with various transition metal dopants. Reproduced with permission from Ref. [86]. Copyright 2024, Wiley VCH.
| Entry No. | Electrocatalysta | Electrolyte | pH | Applied potential (V vs. RHE) | FE (%) | NH3 productivity | Stability | Reaction mechanism | Key intermediateb | RDSb | TRL | Ref. | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Background | NO3- | ||||||||||||
| Cu | |||||||||||||
| 1 | a/c-Cu | 1 mol L-1 KOH | (0.2 mol L-1) (2.02 × 104 ppm) KNO3 | 14 | — | 92 @1.5 A cm-2 | 15.5 mmol h-1 cm-2 @2.6 V | 300 h | ECE | *NO2 | *NO3H → *NO2 | 4 | [103] |
| 2 | CuNi | 1 mol L-1 KOH | (0.1 mol L-1) (1.01 × 104 ppm) KNO3 | 14 | -0.2 | 95.33 | 8.65 mmol h-1 cm-2 @-0.4 V vs. RHE | 120 h | — | — | — | 5 | [107] |
| 3 | c-Co3O4/a-CuO | 0.2 mol L-1 K2SO4 | (0.1 mol L-1) (1.01 × 104 ppm) KNO3 | 7 | -0.8 | 90 | 412.5 µmol h-1 mg-1 | 20 h | EE | *NO2 | — | 4 | [108] |
| 4 | CuCoFe LDH-VO | 0.2 mol L-1 K2SO4 | (5 mmol L-1) (500 ppm) KNO3 | 7 | -0.6 | 95.6 | 1615 μg h-1 cm-2 | 8 cycles | EE | *NOH | *NO → *NOH | 4 | [109] |
| 5 | (Cu7/Ag3)7- Ru3/C | 1 mol L-1 KOH | (0.1 mol L-1) (1.01 × 104 ppm) KNO3 | 14 | -0.9 | 93.48 | 3.45 mmol h-1 cm-2 | 60 h | ECE | *NO2, *NOH | — | 4 | [110] |
| 6 | Cu2O/NiO | 0.5 mol L-1 Na2SO4 | (2.35 mmol L-1) (200 ppm) NaNO3 | 7 | -0.2 | 95.6 | 2.1 mol h-1 cm-2 | 10 cycles | ECE | *N | *NO → *N | 3 | [111] |
| Fe | |||||||||||||
| 7 | Fe SAC | 0.1 mol L-1 K2SO4 | (0.5 mol L-1) (5.05 × 104 ppm) KNO3 | 7 | -0.66 | 75 | 0.46 mmol h-1 cm-2 | 20 cycles | ECE | *NHO | *NO → *NHO | 3 | [118] |
| 8 | Fe2O3/Fe-N-C | 1 mol L-1 KOH | (0.16 mol L-1) (1.62 × 104 ppm) KNO3 | 14 | -0.6 | >95 | 9 mmol h-1 cm-2 @1.95 A cm-2 | 24 h | — | — | — | 3 | [119] |
| 9 | Fe3C-CuOx@NC | 1 mol L-1 KOH | (0.1 mol L-1) (1.01 × 104 ppm) KNO3 | 14 | -0.3 | 98.3 | 257.3 μmol h-1 cm-2 | 10 cycles | ECE | *NOH | *NO → *NOH | 3 | [120] |
| 10 | CoFe-cMOF | 1 mol L-1 Na2SO4 | (0.5 mol L-1) (5.05 × 104 ppm) KNO3 | 7 | -0.7 | 94.3 | 14.1 mg h-1 cm-2 | 20 h | EE | *NH2OH | — | 4 | [121] |
| 11 | Co0.2Ni0.2Zn0.2 Mg0.2Cu0.2)Fe2O4 | 1 mol L-1 KOH | (0.1 mol L-1) (1.01 × 104 ppm) KNO3 | 14 | -0.5 | 98.1 | 2.1 mmol h-1 cm-2 | 50 cycles | ECE | *NO2 | — | 3 | [122] |
| Co | |||||||||||||
| 12 | Co(OH)2 | 1 mol L-1 KOH | (0.1 mol L-1) (1.01 × 104 ppm) KNO3 | 14 | -0.6 | 99.1 | 35.2 mg h-1 cm-2 | — | ECE | *NH2 | *NH → *NH2 | 3 | [126] |
| 13 | Co(OH)2/ CoO@NF | 1 mol L-1 KOH | (0.1 mol L-1) (1.01 × 104 ppm) KNO3 | 14 | -0.2 | 95.6 | 73.9 mg h-1 cm-2 | 96 h | EE | *NOH | *NO → *NOH | 4 | [127] |
| 14 | CoSA-CoNP@ N-CNA/CC | 2 mol L-1 H2SO4 | (0.5 mol L-1) (5.05 × 104 ppm) KNO3 | 1 | -0.6 | 95.6 | 0.275 mmol h-1 cm-2 | 20 cycles | EE | *NHO | *NO → *NHO | 3 | [128] |
| 15 | Cr-Co(OH)2 | 1 mol L-1 KOH | (0.1 mol L-1) (1.01 × 104 ppm) KNO3 | 14 | -0.4 | 97.36 | 58.92 mg h-1 cm-2 | 52 h | EE | *NH | *NHOH → *NH | 3 | [129] |
| 16 | Co6Ni4 | 1 mol L-1 KOH | (0.1 mol L-1) (1.01 × 104 ppm) KNO3 | 14 | -0.476 | 99.21 | 93.55 mg h-1 cm-2 | 120 h | EE | *NOH | *NO → *NOH | 4 | [130] |
| Others | |||||||||||||
| 17 | Ni5P4 | 1 mol L-1 KOH | (0.05 mol L-1) (5050 ppm) KNO3 | 14 | -0.4 | 97.6 | 0.61 mmol h-1 cm-2 | 10 cycles | ECE | *NOH | *NO → *NOH | 5 | [131] |
| 18 | TiCF | 0.1 mol L-1 NaOH + 0.45 mol L-1 Na2SO4 | (0.1 mol L-1) (8500 ppm) NaNO3 | 14 | -0.7 | 56 | — | — | ECE | *NH3 | *NH2 → *NH3 | 3 | [132] |
| 19 | Bi-CoS2 | 1 mol L-1 KOH | (0.1 mol L-1) (1.01 × 104 ppm) KNO3 | 14 | -0.2 | 87.18 | 944.64 μg h-1 cm-2 | 12 h | ECE | *NH2 | *NH → *NH2 | 4 | [133] |
Table 3 Summary of catalytic performance of non-noble metal-based electrocatalysts.
| Entry No. | Electrocatalysta | Electrolyte | pH | Applied potential (V vs. RHE) | FE (%) | NH3 productivity | Stability | Reaction mechanism | Key intermediateb | RDSb | TRL | Ref. | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Background | NO3- | ||||||||||||
| Cu | |||||||||||||
| 1 | a/c-Cu | 1 mol L-1 KOH | (0.2 mol L-1) (2.02 × 104 ppm) KNO3 | 14 | — | 92 @1.5 A cm-2 | 15.5 mmol h-1 cm-2 @2.6 V | 300 h | ECE | *NO2 | *NO3H → *NO2 | 4 | [103] |
| 2 | CuNi | 1 mol L-1 KOH | (0.1 mol L-1) (1.01 × 104 ppm) KNO3 | 14 | -0.2 | 95.33 | 8.65 mmol h-1 cm-2 @-0.4 V vs. RHE | 120 h | — | — | — | 5 | [107] |
| 3 | c-Co3O4/a-CuO | 0.2 mol L-1 K2SO4 | (0.1 mol L-1) (1.01 × 104 ppm) KNO3 | 7 | -0.8 | 90 | 412.5 µmol h-1 mg-1 | 20 h | EE | *NO2 | — | 4 | [108] |
| 4 | CuCoFe LDH-VO | 0.2 mol L-1 K2SO4 | (5 mmol L-1) (500 ppm) KNO3 | 7 | -0.6 | 95.6 | 1615 μg h-1 cm-2 | 8 cycles | EE | *NOH | *NO → *NOH | 4 | [109] |
| 5 | (Cu7/Ag3)7- Ru3/C | 1 mol L-1 KOH | (0.1 mol L-1) (1.01 × 104 ppm) KNO3 | 14 | -0.9 | 93.48 | 3.45 mmol h-1 cm-2 | 60 h | ECE | *NO2, *NOH | — | 4 | [110] |
| 6 | Cu2O/NiO | 0.5 mol L-1 Na2SO4 | (2.35 mmol L-1) (200 ppm) NaNO3 | 7 | -0.2 | 95.6 | 2.1 mol h-1 cm-2 | 10 cycles | ECE | *N | *NO → *N | 3 | [111] |
| Fe | |||||||||||||
| 7 | Fe SAC | 0.1 mol L-1 K2SO4 | (0.5 mol L-1) (5.05 × 104 ppm) KNO3 | 7 | -0.66 | 75 | 0.46 mmol h-1 cm-2 | 20 cycles | ECE | *NHO | *NO → *NHO | 3 | [118] |
| 8 | Fe2O3/Fe-N-C | 1 mol L-1 KOH | (0.16 mol L-1) (1.62 × 104 ppm) KNO3 | 14 | -0.6 | >95 | 9 mmol h-1 cm-2 @1.95 A cm-2 | 24 h | — | — | — | 3 | [119] |
| 9 | Fe3C-CuOx@NC | 1 mol L-1 KOH | (0.1 mol L-1) (1.01 × 104 ppm) KNO3 | 14 | -0.3 | 98.3 | 257.3 μmol h-1 cm-2 | 10 cycles | ECE | *NOH | *NO → *NOH | 3 | [120] |
| 10 | CoFe-cMOF | 1 mol L-1 Na2SO4 | (0.5 mol L-1) (5.05 × 104 ppm) KNO3 | 7 | -0.7 | 94.3 | 14.1 mg h-1 cm-2 | 20 h | EE | *NH2OH | — | 4 | [121] |
| 11 | Co0.2Ni0.2Zn0.2 Mg0.2Cu0.2)Fe2O4 | 1 mol L-1 KOH | (0.1 mol L-1) (1.01 × 104 ppm) KNO3 | 14 | -0.5 | 98.1 | 2.1 mmol h-1 cm-2 | 50 cycles | ECE | *NO2 | — | 3 | [122] |
| Co | |||||||||||||
| 12 | Co(OH)2 | 1 mol L-1 KOH | (0.1 mol L-1) (1.01 × 104 ppm) KNO3 | 14 | -0.6 | 99.1 | 35.2 mg h-1 cm-2 | — | ECE | *NH2 | *NH → *NH2 | 3 | [126] |
| 13 | Co(OH)2/ CoO@NF | 1 mol L-1 KOH | (0.1 mol L-1) (1.01 × 104 ppm) KNO3 | 14 | -0.2 | 95.6 | 73.9 mg h-1 cm-2 | 96 h | EE | *NOH | *NO → *NOH | 4 | [127] |
| 14 | CoSA-CoNP@ N-CNA/CC | 2 mol L-1 H2SO4 | (0.5 mol L-1) (5.05 × 104 ppm) KNO3 | 1 | -0.6 | 95.6 | 0.275 mmol h-1 cm-2 | 20 cycles | EE | *NHO | *NO → *NHO | 3 | [128] |
| 15 | Cr-Co(OH)2 | 1 mol L-1 KOH | (0.1 mol L-1) (1.01 × 104 ppm) KNO3 | 14 | -0.4 | 97.36 | 58.92 mg h-1 cm-2 | 52 h | EE | *NH | *NHOH → *NH | 3 | [129] |
| 16 | Co6Ni4 | 1 mol L-1 KOH | (0.1 mol L-1) (1.01 × 104 ppm) KNO3 | 14 | -0.476 | 99.21 | 93.55 mg h-1 cm-2 | 120 h | EE | *NOH | *NO → *NOH | 4 | [130] |
| Others | |||||||||||||
| 17 | Ni5P4 | 1 mol L-1 KOH | (0.05 mol L-1) (5050 ppm) KNO3 | 14 | -0.4 | 97.6 | 0.61 mmol h-1 cm-2 | 10 cycles | ECE | *NOH | *NO → *NOH | 5 | [131] |
| 18 | TiCF | 0.1 mol L-1 NaOH + 0.45 mol L-1 Na2SO4 | (0.1 mol L-1) (8500 ppm) NaNO3 | 14 | -0.7 | 56 | — | — | ECE | *NH3 | *NH2 → *NH3 | 3 | [132] |
| 19 | Bi-CoS2 | 1 mol L-1 KOH | (0.1 mol L-1) (1.01 × 104 ppm) KNO3 | 14 | -0.2 | 87.18 | 944.64 μg h-1 cm-2 | 12 h | ECE | *NH2 | *NH → *NH2 | 4 | [133] |
Fig. 3. (A) Stability test at 1.5 A cm-2 over a/c-Cu. (B) HRTEM images of a/c-Cu catalyst and corresponding FFT patterns acquired from several regions. (C) Reaction pathways of NO3RR on Cu(100) and a/c-Cu. Reproduced with permission from Ref. [103]. Copyright 2025, Springer Nature. (D) Schematic illustration of CuO/NiO phase transformation. (E) Free-energy diagrams for NO3RR on the interface of Cu2O/NiO (red line), Cu2O region in Cu2O/NiO (blue line), and NiO region in Cu2O/NiO (yellow line) at U = 0 V. Reproduced with permission from Ref. [111]. Copyright 2023, Wiley VCH.
Fig. 4. Gibbs energy diagram of hydrogen proton coupling (A) and nitrate reduction to NH3 (B) on Fe3C, Cu2O and Cu. Reproduced with permission from Ref. [120]. Copyright 2025, Elsevier B.V. (C) Gibbs energy profiles for NO3RR catalysis on CoFe-cMOFs models and simplified structures of reaction intermediates for a NO3RR pathway. (D) NH3 yield rate of Co-cMOFs and CoFe-cMOFs with different Fe atomic ratios in voltage range of -0.5 to -0.8 V vs. RHE. Reproduced with permission from Ref. [121]. Copyright 2025, Wiley VCH. (E) Structural evolution of Co3O4 (111) during NO3RR operation. (F) Reaction energy diagrams of intermediates on Co3O4 pristine (111) and (111)-4/3 ML Ov during NO3RR. Reproduced with permission from Ref. [126]. Copyright 2024, American Chemical Society. (G) Schematic of Cr-mediated dynamic reconstruction mechanism. (H) Schematic of NO3RR over Cr-Co(OH)2/Co heterostructure with *H participation from interfacial H2O dissociation. (I) Gibbs energy diagrams of NO3RR on Co, Co(OH)2, and Cr-Co(OH)2. Reproduced with permission from Ref. [129]. Copyright 2025, Royal Society of Chemistry.
| Reaction | E0 |
|---|---|
| Nitrogen reduction reaction | |
| N2 + H+ + e‒ ⇌ N2H(g) | ‒3.2 VRHE |
| N2 + 2H+ + 2e‒ ⇌ N2H2(g) | ‒1.1 VRHE |
| N2 + 4H+ + 4e‒ ⇌ N2H4(g) | ‒0.33 VRHE |
| N2 + 4H2O + 6e‒ ⇌ N2H4 + 4OH‒ | ‒1.16 VRHE (pH = 14) |
| N2 + 5H+ + 4e‒ ⇌ N2H5+(aq) | ‒0.23 VRHE |
| N2 + e‒ ⇌ N2‒(aq) | ‒3.37 VRHE (pH = 14) |
| Nitrate reduction reaction (pH = 14) | |
| 2NO3- + 12H+ + 10e‒ → N2 + 6H2 | 2.00 VRHE |
| NO3‒ + 9H+ + 8e‒ → NH3 + 3H2 | 0.71 VRHE |
| *NO3- + e‒ → *NO32‒ | ‒0.06 VRHE |
| *NO2 + e‒ → *NO2- | 1.87 VRHE |
| *NO+ + e‒ → NO | 2.11 VRHE |
| *NO2‒ + e- → *NO22‒ | 0.36 VRHE |
| *NO‒ + H+ + e- → *NOH | 0.05 VRHE |
| *NO + NO + H++ e‒ → *N2HO2 | 0.83 VRHE |
| *N2HO2 + H+ + e‒ → *N2O + H2O | 2.42 VRHE |
| *NOH + H+ + e‒ → *NH2O | 1.35 VRHE |
| *NOH2 + H+ + e‒ → *NH2OH | 1.73 VRHE |
| H2NOH + 2H+ + 2e‒ → NH3 + H2O | 1.25 VRHE |
Table 4 Equilibrium potential for nitrogen reduction reaction and nitrate reduction reaction.
| Reaction | E0 |
|---|---|
| Nitrogen reduction reaction | |
| N2 + H+ + e‒ ⇌ N2H(g) | ‒3.2 VRHE |
| N2 + 2H+ + 2e‒ ⇌ N2H2(g) | ‒1.1 VRHE |
| N2 + 4H+ + 4e‒ ⇌ N2H4(g) | ‒0.33 VRHE |
| N2 + 4H2O + 6e‒ ⇌ N2H4 + 4OH‒ | ‒1.16 VRHE (pH = 14) |
| N2 + 5H+ + 4e‒ ⇌ N2H5+(aq) | ‒0.23 VRHE |
| N2 + e‒ ⇌ N2‒(aq) | ‒3.37 VRHE (pH = 14) |
| Nitrate reduction reaction (pH = 14) | |
| 2NO3- + 12H+ + 10e‒ → N2 + 6H2 | 2.00 VRHE |
| NO3‒ + 9H+ + 8e‒ → NH3 + 3H2 | 0.71 VRHE |
| *NO3- + e‒ → *NO32‒ | ‒0.06 VRHE |
| *NO2 + e‒ → *NO2- | 1.87 VRHE |
| *NO+ + e‒ → NO | 2.11 VRHE |
| *NO2‒ + e- → *NO22‒ | 0.36 VRHE |
| *NO‒ + H+ + e- → *NOH | 0.05 VRHE |
| *NO + NO + H++ e‒ → *N2HO2 | 0.83 VRHE |
| *N2HO2 + H+ + e‒ → *N2O + H2O | 2.42 VRHE |
| *NOH + H+ + e‒ → *NH2O | 1.35 VRHE |
| *NOH2 + H+ + e‒ → *NH2OH | 1.73 VRHE |
| H2NOH + 2H+ + 2e‒ → NH3 + H2O | 1.25 VRHE |
| Entry No. | Electrocatalysta | C sourceb | Applied potential (V vs. RHE) | Electrolytec | Intermediateb | Product | FE (%) | Production rate/Yield | Byproductsb | TRL | Ref. | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Background | NO3- | |||||||||||
| 1 | Fe1/MoS2 | CO2 | -0.5 | 0.1 mol L-1 KHCO3 | (0.1 mol L-1)(1.01 × 104 ppm) KNO3 | *CO2NH2 | urea | 55 | 18.98 mmol h-1 g-1 | NH3, NO2-, H2, N2, N2H4, CO | 4 | [164] |
| 2 | PCOF- 34-Fe | CO2 | -0.5 | 0.1 mol L-1 KHCO3 | (0.1 mol L-1)(1.01 × 104 ppm) KNO3 | *CO + *NH2 | urea | 90 | 135.6 mmol g-1 h-1 | NH3, NO2-, N2, CO | 4 | [165] |
| 3 | CuPc- Amino | CO2 | -1.6 | 0.1 mol L-1 KHCO3 | (0.05 mol L-1)(5050 ppm) KNO3 | *CO + *NO | urea | 11.9 | 103.1 mmol h-1 g-1 | — | 3 | [166] |
| 4 | Cu4Pt/CF | FA | -0.5 | 0.08 mol L-1 HCOOH | (0.1 mol L-1)(1.01 × 104 ppm) KNO3 | *CO + *NH2 | urea | 58.1 | 40.08 mg h-1 cm-2 | NH3, NO2-, H2, CO | 4 | [167] |
| 5 | CoPc/CNT | α-keto acid | -0.57 | 0.4 mol L-1 H2SO4 + 0.2 mol L-1 α-ketoacid | (1 mol L-1)(1.01 × 105 ppm) KNO3 | NH2OH, oxime | alanine | 61 | 33% | NH3, NH2OH, LA, oxime | 3 | [34] |
| 6 | Pb1Bi0.1 | PA | -1.5 V vs. SHE | 1.5 mol L-1 H2SO4 + 0.25 mol L-1 PA | (0.25 mol L-1)(2.125 × 104 ppm) NaNO3 | NH2OH | alanine | 59.7 | — | LA, oxime | 3 | [170] |
| 7 | PdCu NBWs | PA | -0.3 | 0.05 mol L-1 PA | (1 mol L-1)(1.01 × 105 ppm) KNO3 | NH2OH, pyruvic oxime | alanine | — | 54.8% | LA, oxime | 4 | [171] |
| 8 | adFe-TiOx/ Ti | GXA | -0.7 | 0.5 mol L-1 H2SO4 + 0.1 mol L-1 GXA | (1 mol L-1)(8.5 × 104 ppm) NaNO3 | NH2OH, GXO | glycine | — | 236.1 μmol h-1/80.2% | GO, GA | 3 | [172] |
| 9 | Cu/Bi-C @CF | GXA | — | 0.1 mol L-1 HCl + 0.02 mol L-1 GXA | (0.3 mol L-1)(3.03 × 104 ppm) KNO3 | NH2OH, oxime | glycine | 65.9 | — | NH3, GA, oxime | 3 | [173] |
| 10 | PbSnBi | OA | 1.5 V vs. SCE | 1.5 mol L-1 H2SO4 + 0.25 mol L-1 OA + 0.01 mol L-1 ILs | (0.25 mol L-1)(2.125 × 104 ppm) NaNO3 | NH2OH + GA | glycine | 57.2 | 1.125 mmol h-1 cmcat-2 | GA, GXO | 3 | [175] |
| 11 | CoPc-NH2/CNT | CO2 | -0.92 | 0.1 mol L-1 KHCO3 | (0.5 mol L-1)(5.05 × 104 ppm) KNO3 | NH2OH + HCHO | methylamine | 13 | — | H2, CO, CH3OH, NO2-, NH3, etc. | 3 | [178] |
| 12 | Cu nanoparticle | CO2 | -1 | 1.0 mol L-1 KHCO3 | (0.1 mol L-1)(1.01 × 104 ppm) KNO3 | acetaldehyde oxime | ethylamine | 0.3 | — | H2, CO, CH4, C2H4, HCOOH, etc. | 3 | [180] |
| 13 | Ag/Cu | CO2 | -0.4 | 0.1 mol L-1 KHCO3 | (0.05 mol L-1)(2020 ppm) KNO3 | *CO + *NH2 | N,N-dimethylformamide | 28.6 | 1.24 mmol h-1 gcat-1 | — | 3 | [181] |
Table 5 Summary of performance in electrochemical synthesis of nitrogen-containing organic compounds from nitrate and carbon species.
| Entry No. | Electrocatalysta | C sourceb | Applied potential (V vs. RHE) | Electrolytec | Intermediateb | Product | FE (%) | Production rate/Yield | Byproductsb | TRL | Ref. | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Background | NO3- | |||||||||||
| 1 | Fe1/MoS2 | CO2 | -0.5 | 0.1 mol L-1 KHCO3 | (0.1 mol L-1)(1.01 × 104 ppm) KNO3 | *CO2NH2 | urea | 55 | 18.98 mmol h-1 g-1 | NH3, NO2-, H2, N2, N2H4, CO | 4 | [164] |
| 2 | PCOF- 34-Fe | CO2 | -0.5 | 0.1 mol L-1 KHCO3 | (0.1 mol L-1)(1.01 × 104 ppm) KNO3 | *CO + *NH2 | urea | 90 | 135.6 mmol g-1 h-1 | NH3, NO2-, N2, CO | 4 | [165] |
| 3 | CuPc- Amino | CO2 | -1.6 | 0.1 mol L-1 KHCO3 | (0.05 mol L-1)(5050 ppm) KNO3 | *CO + *NO | urea | 11.9 | 103.1 mmol h-1 g-1 | — | 3 | [166] |
| 4 | Cu4Pt/CF | FA | -0.5 | 0.08 mol L-1 HCOOH | (0.1 mol L-1)(1.01 × 104 ppm) KNO3 | *CO + *NH2 | urea | 58.1 | 40.08 mg h-1 cm-2 | NH3, NO2-, H2, CO | 4 | [167] |
| 5 | CoPc/CNT | α-keto acid | -0.57 | 0.4 mol L-1 H2SO4 + 0.2 mol L-1 α-ketoacid | (1 mol L-1)(1.01 × 105 ppm) KNO3 | NH2OH, oxime | alanine | 61 | 33% | NH3, NH2OH, LA, oxime | 3 | [34] |
| 6 | Pb1Bi0.1 | PA | -1.5 V vs. SHE | 1.5 mol L-1 H2SO4 + 0.25 mol L-1 PA | (0.25 mol L-1)(2.125 × 104 ppm) NaNO3 | NH2OH | alanine | 59.7 | — | LA, oxime | 3 | [170] |
| 7 | PdCu NBWs | PA | -0.3 | 0.05 mol L-1 PA | (1 mol L-1)(1.01 × 105 ppm) KNO3 | NH2OH, pyruvic oxime | alanine | — | 54.8% | LA, oxime | 4 | [171] |
| 8 | adFe-TiOx/ Ti | GXA | -0.7 | 0.5 mol L-1 H2SO4 + 0.1 mol L-1 GXA | (1 mol L-1)(8.5 × 104 ppm) NaNO3 | NH2OH, GXO | glycine | — | 236.1 μmol h-1/80.2% | GO, GA | 3 | [172] |
| 9 | Cu/Bi-C @CF | GXA | — | 0.1 mol L-1 HCl + 0.02 mol L-1 GXA | (0.3 mol L-1)(3.03 × 104 ppm) KNO3 | NH2OH, oxime | glycine | 65.9 | — | NH3, GA, oxime | 3 | [173] |
| 10 | PbSnBi | OA | 1.5 V vs. SCE | 1.5 mol L-1 H2SO4 + 0.25 mol L-1 OA + 0.01 mol L-1 ILs | (0.25 mol L-1)(2.125 × 104 ppm) NaNO3 | NH2OH + GA | glycine | 57.2 | 1.125 mmol h-1 cmcat-2 | GA, GXO | 3 | [175] |
| 11 | CoPc-NH2/CNT | CO2 | -0.92 | 0.1 mol L-1 KHCO3 | (0.5 mol L-1)(5.05 × 104 ppm) KNO3 | NH2OH + HCHO | methylamine | 13 | — | H2, CO, CH3OH, NO2-, NH3, etc. | 3 | [178] |
| 12 | Cu nanoparticle | CO2 | -1 | 1.0 mol L-1 KHCO3 | (0.1 mol L-1)(1.01 × 104 ppm) KNO3 | acetaldehyde oxime | ethylamine | 0.3 | — | H2, CO, CH4, C2H4, HCOOH, etc. | 3 | [180] |
| 13 | Ag/Cu | CO2 | -0.4 | 0.1 mol L-1 KHCO3 | (0.05 mol L-1)(2020 ppm) KNO3 | *CO + *NH2 | N,N-dimethylformamide | 28.6 | 1.24 mmol h-1 gcat-1 | — | 3 | [181] |
Fig. 5. Reaction pathways for synthesis of urea by co-reduction of NO3- and CO2.
Fig. 6. (A) Gibbs energy profiles of UENC pathway on MoS2-edge and Fe1-S3 motif of Fe1/MoS2. (B) Charge density difference of Fe1/MoS2. (C) Calculated transition-state (TS) energy barriers for migration of *CO2NH2 from the Fe1-S3 motif to the MoS2-edge. Reproduced with permission from Ref. [164]. Copyright 2024, American Chemical Society. (D) Reaction Gibbs energy diagrams for initial CO2 reduction on PCOF-34-M (M = 2H, Fe, Ni, Cu). (E) Pathway for NO3RR and C-N coupling leading to urea production on PCOF-34-Fe. (F) Schematic representation of twin iron sites in PCOF-34-Fe with a spacing of 8.8 Å. Reproduced with permission from Ref. [165]. Copyright 2025, Springer Nature. (G) Infrared signal over 1200-2400 cm-1 at several applied potentials for CuPc-Amino during co-electrolysis. (H) Infrared signal at -1.6 V vs. RHE for CuPc-Amino during the electrocoupling of 14NO3-/15NO3- and CO2 processes. Reproduced with permission from Ref. [166]. Copyright 2024, Springer Nature. (I) Product FE of coupling reaction at different potentials. (J) Adsorption Gibbs energies of *CO and *NH2 on the Cu4Pt. (K) Energy profile of C-N coupling on Cu4Pt, Pt, and Cu. Reproduced with permission from Ref. [167]. Copyright 2025, Wiley VCH.
Fig. 7. (A) Gibbs energy diagram at an applied potential (U) of 0.0 V vs. RHE for the NO3RR to NH2OH on CoPc and CoPc/CNT. (B) Adsorption energy of *NO3 and *Pyr on MPc/CNT (M = Co, Ni, Cu) and adsorption energy of pyruvic oxime on CoPc/CNT. (C) Proposed reaction pathway for C-N coupling and Ala formation from NO3- and Pyr. Reproduced with permission from Ref. [34]. Copyright 2024, American Chemical Society. (D) In-situ ATR-SEIRAS spectra collected at various times up to 50 min at −0.3 V vs. RHE in a buffer with 1 mol L−1 KNO3 and 50 mmol L−1 PA. (E) Overall tandem electrochemical-chemical-electrochemical reaction of C-N coupling. Reproduced with permission from Ref. [171]. Copyright 2023, Wiley VCH. Gibbs energy changes of NO3- (F) and GO (G) reduction reaction on surfaces of adFe-TiOx and TiOx. Calculated adsorption energy of NO3- (H) and GA (I) on the surface of TiO2, TiOx, and adFe-TiOx. Reproduced with permission from Ref. [172]. Copyright 2024, Wiley VCH.
Fig. 8. (A) Proposed reaction pathway of eight-step cascade electrosynthesis of methylamine from CO2 and NO3- catalyzed by CoPc-NH2/CNT. Reproduced with permission from Ref. [178]. Copyright 2021, Springer Nature. (B) Proposed reaction pathway to form acetaldoxime and ethylamine from electrochemical co-reduction of CO2 and NO3-. Reproduced with permission from Ref. [180]. Copyright 2022, Elsevier B. V. (C) Schematic of DMF formation from reductive (above dashed line) and oxidative (below dashed line) coupling on Ag/Cu catalyst, involving multiple slow C-hydrogenation steps and fast coupling steps. Reproduced with permission from Ref. [181]. Copyright 2025, Wiley VCH.
Scheme 2. Several classes of alternative anodic oxidation reactions.
| Designation | Anodic oxidation reaction | Reactants/feedstocks a (priceb ($ kg-1)) | Redox potential (V vs. RHE) | Products a | Product price b ($/kg) |
|---|---|---|---|---|---|
| oxygen evolution reaction (OER) | H2O | 1.23 | O2 | 0.024-0.04 | |
| Class I | urea oxidation reaction (UOR) | urea | 0.37 | N2, CO2 | — |
| hydrazine oxidation reaction (HzOR) | N2H4 | -0.33 | N2, H2O | — | |
| hydrogen oxidation reaction (HOR) | H2 | 0 | H2O | — | |
| Class II | chlorine evolution reaction (CER) | Cl- | 1.36 | Cl2 | 5.5-7.5 |
| Class III | methanol oxidation reaction (MOR) | CH3OH (0.35-0.5) | 0.10 | FA | 0.97-1.08 |
| formaldehyde oxidation reaction (FOR) | HCHO (0.22) | -0.22 | FA | 0.97-1.08 | |
| ethylene glycol oxidation reaction (EGOR) | EG (0.6-0.65) | 0.57 | FA | 0.97-1.08 | |
| GA | 1.84 | ||||
| glycerol oxidation reaction (GlyOR) | glycerol (0.4-0.7) | 0.69 | FA | 0.97-1.08 | |
| LA | 0.96-1.2 | ||||
| glucose oxidation reaction (GluOR) | glucose (0.5-0.8) | 0.05 | FA | 0.97-1.08 | |
| GRA | 50 | ||||
| 5-hydroxymethylfurfural oxidation reaction (HMFOR) | HMF (20-30) | 0.3 | FDCA | 35-41 | |
| benzyl alcohol oxidation reaction (BAOR) | BA (0.3-0.5) | 0.48 | BAD | 1.18-2.11 | |
| sulfide oxidation reaction (SOR) | sulfide (0.68) | -0.48 | S | 6-10 | |
| benzylamine oxidation reaction (BOR) | benzylamine (4-5) | 0.76 | BN | — |
Table 6 Replacement anodic oxidation reactions for oxygen evolution reaction in nitrate reduction systems.
| Designation | Anodic oxidation reaction | Reactants/feedstocks a (priceb ($ kg-1)) | Redox potential (V vs. RHE) | Products a | Product price b ($/kg) |
|---|---|---|---|---|---|
| oxygen evolution reaction (OER) | H2O | 1.23 | O2 | 0.024-0.04 | |
| Class I | urea oxidation reaction (UOR) | urea | 0.37 | N2, CO2 | — |
| hydrazine oxidation reaction (HzOR) | N2H4 | -0.33 | N2, H2O | — | |
| hydrogen oxidation reaction (HOR) | H2 | 0 | H2O | — | |
| Class II | chlorine evolution reaction (CER) | Cl- | 1.36 | Cl2 | 5.5-7.5 |
| Class III | methanol oxidation reaction (MOR) | CH3OH (0.35-0.5) | 0.10 | FA | 0.97-1.08 |
| formaldehyde oxidation reaction (FOR) | HCHO (0.22) | -0.22 | FA | 0.97-1.08 | |
| ethylene glycol oxidation reaction (EGOR) | EG (0.6-0.65) | 0.57 | FA | 0.97-1.08 | |
| GA | 1.84 | ||||
| glycerol oxidation reaction (GlyOR) | glycerol (0.4-0.7) | 0.69 | FA | 0.97-1.08 | |
| LA | 0.96-1.2 | ||||
| glucose oxidation reaction (GluOR) | glucose (0.5-0.8) | 0.05 | FA | 0.97-1.08 | |
| GRA | 50 | ||||
| 5-hydroxymethylfurfural oxidation reaction (HMFOR) | HMF (20-30) | 0.3 | FDCA | 35-41 | |
| benzyl alcohol oxidation reaction (BAOR) | BA (0.3-0.5) | 0.48 | BAD | 1.18-2.11 | |
| sulfide oxidation reaction (SOR) | sulfide (0.68) | -0.48 | S | 6-10 | |
| benzylamine oxidation reaction (BOR) | benzylamine (4-5) | 0.76 | BN | — |
Fig. 9. (A) Calculated adsorption energy of nitrate at the WO3 and WP surface. (B) LSV curves for WP/NF//WP/NF in two-electrode configuration with NO3RR//OER, NO3RR//UOR, and NO3RR//HzOR. (C) Chronoamperometry curve of unbiased perovskite photovoltaic cells system combining WP/NF(NO3RR)//WP/NF(HzOR) with perovskite solar cell. Reproduced with permission from Ref. [214]. Copyright 2023, Wiley VCH. (D) LSV curves of TiO2 nanosheet for NO3RR at different pH values. (E) Discharge curve of alkaline-acidic hybrid Zn-NO3- battery and corresponding power density. (F) Discharge curve of N2H4-nitrate fuel cell and corresponding power density. (G) Gibbs energy diagram for NO3- reduction on the TiO2 and FePc/TiO2. Reproduced with permission from Ref. [215]. Copyright 2023, Springer Nature. (H) Chronopotentiometry curve of HNFB under 100 mA cm-2. Inset of (H) illustrates the membrane electrode assembly flow reactors. Reproduced with permission from Ref. [216]. Copyright 2023, Wiley VCH.
| Entry No. | Anodic reaction | Cathode//anode a | Electrolytecath | Electrolyteanode b | FENH3 (%) | Production rateNH3 | Productanode b | FEanode (%) | ΔE (mV) @J (mA cm-2) c | TRL | Ref. | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | MOR | CuCo2O4/CFs// CuCo2O4/CFs | 1.0 mol L-1 KOH + 0.1 mol L-1 KNO3 | 1.0 mol L-1 KOH + 1.0 mol L-1 CH3OH | 81.9 | 394.5 mmol h-1 g-1 | FA | — | 360 @10 | 3 | [240] | ||||||||
| 2 | CuCo/CN// CuCo/CN | 1.0 mol L-1 KOH + 1.98 mmol L-1 KNO3 | 1.0 mol L-1 KOH + 1.0 mol L-1 CH3OH | 93.6 | 0.23 mmol h-1 cm-2 | FA | 95 | 190 @50 | 3 | [2] | |||||||||
| 3 | Ni2FeP@NC// Ni2FeP@NC | 1.0 mol L-1 KOH + 0.2 mol L-1 KNO3 | 1.0 mol L-1 KOH + 2.0 mol L-1 CH3OH | 93 | 0.47 mmol h-1 cm-2 | FA | 95 | 100 @10 | 3 | [239] | |||||||||
| 4 | FOR | Cu2O//Cu2O | 1.0 mol L-1 KOH + 3.96 mmol L-1 KNO3 | 1.0 mol L-1 KOH + 1.0 mol L-1 HCHO | 97.6 | — | FA | — | 1900 @20 | 3 | [245] | ||||||||
| 5 | Ag1@Cu2O// Ag1@Cu2O | 1.0 mol L-1 KOH + 2.47 mmol L-1 KNO3 | 1.0 mol L-1 KOH + 0.2 mol L-1 HCHO | >90 | 184.4 mg h-1 cm-2 | FA | 98.5 | 1690 @100 | 5 | [246] | |||||||||
| 6 | EGOR | Vo-NiCo2O4// Vo-NiCo2O4 | 1.0 mol L-1 KOH + 0.1 mol L-1 KNO3 | 1.0 mol L-1 KOH + 1.0 mol L-1 EG | 96.3 | 1.38 mmol h-1 cm-2 | FA | 94.2 | 280 @100 | 4 | [253] | ||||||||
| 7 | Co-N-C// PdNi alloy | 1.0 mol L-1 KOH + 0.05 mol L-1KNO3 | 1.0 mol L-1 KOH + 1.0 mol L-1 EG | 95.5 | 20.5 mg h-1 mgcat.-1 | GA | 96.6 | 540 @10 | 4 | [254] | |||||||||
| 8 | GlyOR | V-Cu NAE//NF | 0.5 mol L-1 K2SO4 + 1.98 mmol L-1 KNO3 | — | >90 | 7853 µg h-1 cm-2 | FA | — | 260 @50 | 5 | [259] | ||||||||
| 9 | NiCu-OH// NiCu-OH | 1.0 mol L-1 KOH + 0.1 mol L-1KNO3 | 1.0 mol L-1 KOH + 0.1 mol L-1Glycerol | — | 23.8 mg h-1 cm-2 | FA | — | 285 @100 | 4 | [261] | |||||||||
| 10 | Cu-NiCo/NF// Cu-NiCo/NF | 1.0 mol L-1 KOH + 0.1 mol L-1KNO3 | 1.0 mol L-1 KOH + 0.1 mol L-1 Glycerol | 97.9 | 733.9 μmol cm-2 h-1 | FA | 93.8 | 290 @10 | 4 | [260] | |||||||||
| 11 | CNs@CoP// CNs@CoP | 1.0 mol L-1 NaOH + 0.1 mol L-1 NaNO3 | 1.0 mol L-1 NaOH + 0.1 mol L-1 Glycerol | 95.1 | 43.9 mg h-1 cm-2 | FA | 93.5 | 200 @300 | 4 | [38] | |||||||||
| 12 | Co-Fe-P//Co-Fe-P | 0.1 mol L-1 K2SO4 + 0.1 mol L-1KNO3 | 0.1 mol L-1 K2SO4 + 0.1 mol L-1 Glycerol | 98.9 | 21.11 mg h-1 mgcat-1 | LA | — | 90 @10 | 3 | [262] | |||||||||
| 13 | GluOR | D-FeCoNiCu-LDH/NF //D-FeCoNiCu-LDH/NF | 1.0 mol L-1 KOH + 0.1 mol L-1 KNO3 | 1.0 mol L-1 KOH + 0.1 mol L-1 glucose | — | — | GRA | — | 200 @100 | 4 | [264] | ||||||||
| 14 | D-CuCo/CoP/NF //D-CuCo/CoP/NF | 1.0 mol L-1 KOH + 0.1 mol L-1KNO3 | 1.0 mol L-1 KOH + 0.1 mol L-1 glucose | 96.9 | 802.9 μmol cm-2 h-1 | FA | 90.3 | 200 @100 | 4 | [267] | |||||||||
| 15 | Ru-Tta-Dfp //Ru-Tta-Dfp | 1.0 mol L-1 KOH + 0.1 mol L-1 KNO3 | 1.0 mol L-1 KOH + 0.1 mol L-1 glucose | 93.93 | 1.16 mg h-1 cm-2 | GRA | — | 600 @50 | 4 | [40] | |||||||||
| 16 | HMFOR | meso-CoCu// meso-CoCu | 0.5 mol L-1 K2SO4 + 0.01 mol L-1 KNO3 | 1.0 mol L-1 KOH + 0.01 mol L-1 HMF | 98.8 | 3.39 mol h-1 g-1 | FDCA | — | 400 @10 | 3 | [271] | ||||||||
| 17 | SC-MHEO// SC-MHEO | 1.0 mol L-1 KOH + 0.1 mol L-1 KNO3 | 1.0 mol L-1 KOH + 0.01 mol L-1 HMF | 91.5 | 15.73 mg h-1 cm-2 | FDCA | 97.7 | — | 3 | [272] | |||||||||
| 18 | ZnCoO-NW// ZnCoO-NW | 0.5 mol L-1 Na2SO4 + 0.1 mol L-1 NaNO3 | 1.0 mol L-1 KOH + 0.005 mol L-1 HMF | 92 | 4.65 mg h-1 cm-2 | FDCA | 91 | — | 3 | [270] | |||||||||
| 19 | BAOR | RuCu@NF// RuTiIr | 0.05 mol L-1 Na2SO4 + 0.588 mmol L-1 NaNO3 | 0.05 mol L-1 Na2SO4 + 10 mol L-1 BA | 96.8 | — | BAD | — | — | 3 | [278] | ||||||||
| 20 | OD-Cu// Pt-Ni(OH)2 | 0.4 mol L-1 KOH + 1.0 mol L-1 K2CO3 + 1.0 mol L-1 KNO3 + 0.1 mol L-1 BA + 0.6 mol L-1 ethanol | 60 | 278 μmol h-1 | CAL | — | — | 3 | [279] | ||||||||||
| 21 | Plastic upcycling (PET) | R-Co/CF// R-NiCo/NF | 1.0 mg L-1 KOH + 0.1 mg L-1 KNO3 | PET hydrolysate | 96.2 | 0.87 mmol h-1 cm-2 | FA | 98.2 | 202 @50 | 5 | [186] | ||||||||
| 22 | Ru-Co(OH)2// Ru-CoOOH | 1.0 mg L-1 KOH + 1.98 mmg L-1 KNO3 | PET hydrolysate | 98.9 | 0.244 mmol h-1 cm-2 | FA | 96.5 | 260 @150 | 5 | [285] | |||||||||
| 23 | CuPd alloy// CuPd alloy | 1.0 mg L-1 KOH + 0.1 mg L-1 KNO3 | 1.0 mol L-1 KOH + 0.1 mol L-1 EG | 92 | — | GA | 93 | 980 @10 | 5 | [287] | |||||||||
| 24 | mPd3Au/NF //mPd3Au/NF | 1.0 mg L-1 KOH + 0.1 mg L-1 KNO3 | PET hydrolysate | 97.3 | 0.71 mmol h-1 cm-2 | GA | 95.3 | 1038 @100 | 4 | [8] | |||||||||
| 25 | r-PdCuene/NF //PdCuene/NF | 1.0 mg L-1 KOH + 1.98 mmg L-1 KNO3 | 1.0 mol L-1 KOH + 1.0 mol L-1 EG | 91.6 | 0.237 mmol h-1 cm-2 | GA | 92.1 | 1060 @50 | 4 | [11] | |||||||||
| 26 | LC-CoOOH/CF //Pd NTs/NF | 1.0 mg L-1 KOH + 1.98 mmg L-1 KNO3 | PET hydrolysate | 97.4 | 0.246 mmol h-1 cm-2 | GA | 87.8 | — | 5 | [286] | |||||||||
| 27 | SOR | MFe2O4// MFe2O4 | 0.1 mg L-1 K2SO4 + 0.1 mg L-1 KNO3 | 1.0 mol L-1 KOH + 1.0 mol L-1 Na2S | 95.2 | 608.9 μmol h-1 cm-2 | sulfur | — | 1480 @10 | 3 | [294] | ||||||||
| 28 | ER-Cu// S-(Ni,Fe)OxHy | 1.0 mg L-1 KOH + 0.1 mg L-1 KNO3 | 1.0 mol L-1 KOH + 1.0 mol L-1 S2- | 96 | 0.391 mmol h-1 cm-2 | sulfur | — | 1100 @50 | 3 | [295] | |||||||||
| 29 | Co-MOF/NF //Co-MOF/NF | 1.0 mg L-1 KOH + 1.98 mmg L-1 KNO3 | 1.0 mol L-1 KOH + 4.0 mol L-1 Na2S | 94.2 | 0.238 mmol h-1 cm-2 | sulfur | — | 1597 @50 | 4 | [291] | |||||||||
| 30 | Fe3C@N-CNTs/IF //Fe3C@N-CNTs/IF | 0.5 mg L-1 Na2SO4 + 2.35 mmg L-1 NaNO3 | 1.0 mol L-1 KOH + 1.0 mol L-1 Na2S | 97.9 | 0.922 mg h-1 cm-2 | sulfur | — | 1100 @10 | 4 | [292] | |||||||||
| 31 | BOR | Ni3Se4//Ni3Se4 | 0.1 mg L-1 KOH + 0.01 mg L-1 KNO3 | 0.1 mol L-1 KOH + 0.01 mol L-1 benzylamine | 87 | 1.091 mmol h-1 cm-2 | BN | 93 | 260 @50 | 4 | [298] | ||||||||
Table 7 Overall cell performance of Class III reactions coupled with NO3RR systems.
| Entry No. | Anodic reaction | Cathode//anode a | Electrolytecath | Electrolyteanode b | FENH3 (%) | Production rateNH3 | Productanode b | FEanode (%) | ΔE (mV) @J (mA cm-2) c | TRL | Ref. | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | MOR | CuCo2O4/CFs// CuCo2O4/CFs | 1.0 mol L-1 KOH + 0.1 mol L-1 KNO3 | 1.0 mol L-1 KOH + 1.0 mol L-1 CH3OH | 81.9 | 394.5 mmol h-1 g-1 | FA | — | 360 @10 | 3 | [240] | ||||||||
| 2 | CuCo/CN// CuCo/CN | 1.0 mol L-1 KOH + 1.98 mmol L-1 KNO3 | 1.0 mol L-1 KOH + 1.0 mol L-1 CH3OH | 93.6 | 0.23 mmol h-1 cm-2 | FA | 95 | 190 @50 | 3 | [2] | |||||||||
| 3 | Ni2FeP@NC// Ni2FeP@NC | 1.0 mol L-1 KOH + 0.2 mol L-1 KNO3 | 1.0 mol L-1 KOH + 2.0 mol L-1 CH3OH | 93 | 0.47 mmol h-1 cm-2 | FA | 95 | 100 @10 | 3 | [239] | |||||||||
| 4 | FOR | Cu2O//Cu2O | 1.0 mol L-1 KOH + 3.96 mmol L-1 KNO3 | 1.0 mol L-1 KOH + 1.0 mol L-1 HCHO | 97.6 | — | FA | — | 1900 @20 | 3 | [245] | ||||||||
| 5 | Ag1@Cu2O// Ag1@Cu2O | 1.0 mol L-1 KOH + 2.47 mmol L-1 KNO3 | 1.0 mol L-1 KOH + 0.2 mol L-1 HCHO | >90 | 184.4 mg h-1 cm-2 | FA | 98.5 | 1690 @100 | 5 | [246] | |||||||||
| 6 | EGOR | Vo-NiCo2O4// Vo-NiCo2O4 | 1.0 mol L-1 KOH + 0.1 mol L-1 KNO3 | 1.0 mol L-1 KOH + 1.0 mol L-1 EG | 96.3 | 1.38 mmol h-1 cm-2 | FA | 94.2 | 280 @100 | 4 | [253] | ||||||||
| 7 | Co-N-C// PdNi alloy | 1.0 mol L-1 KOH + 0.05 mol L-1KNO3 | 1.0 mol L-1 KOH + 1.0 mol L-1 EG | 95.5 | 20.5 mg h-1 mgcat.-1 | GA | 96.6 | 540 @10 | 4 | [254] | |||||||||
| 8 | GlyOR | V-Cu NAE//NF | 0.5 mol L-1 K2SO4 + 1.98 mmol L-1 KNO3 | — | >90 | 7853 µg h-1 cm-2 | FA | — | 260 @50 | 5 | [259] | ||||||||
| 9 | NiCu-OH// NiCu-OH | 1.0 mol L-1 KOH + 0.1 mol L-1KNO3 | 1.0 mol L-1 KOH + 0.1 mol L-1Glycerol | — | 23.8 mg h-1 cm-2 | FA | — | 285 @100 | 4 | [261] | |||||||||
| 10 | Cu-NiCo/NF// Cu-NiCo/NF | 1.0 mol L-1 KOH + 0.1 mol L-1KNO3 | 1.0 mol L-1 KOH + 0.1 mol L-1 Glycerol | 97.9 | 733.9 μmol cm-2 h-1 | FA | 93.8 | 290 @10 | 4 | [260] | |||||||||
| 11 | CNs@CoP// CNs@CoP | 1.0 mol L-1 NaOH + 0.1 mol L-1 NaNO3 | 1.0 mol L-1 NaOH + 0.1 mol L-1 Glycerol | 95.1 | 43.9 mg h-1 cm-2 | FA | 93.5 | 200 @300 | 4 | [38] | |||||||||
| 12 | Co-Fe-P//Co-Fe-P | 0.1 mol L-1 K2SO4 + 0.1 mol L-1KNO3 | 0.1 mol L-1 K2SO4 + 0.1 mol L-1 Glycerol | 98.9 | 21.11 mg h-1 mgcat-1 | LA | — | 90 @10 | 3 | [262] | |||||||||
| 13 | GluOR | D-FeCoNiCu-LDH/NF //D-FeCoNiCu-LDH/NF | 1.0 mol L-1 KOH + 0.1 mol L-1 KNO3 | 1.0 mol L-1 KOH + 0.1 mol L-1 glucose | — | — | GRA | — | 200 @100 | 4 | [264] | ||||||||
| 14 | D-CuCo/CoP/NF //D-CuCo/CoP/NF | 1.0 mol L-1 KOH + 0.1 mol L-1KNO3 | 1.0 mol L-1 KOH + 0.1 mol L-1 glucose | 96.9 | 802.9 μmol cm-2 h-1 | FA | 90.3 | 200 @100 | 4 | [267] | |||||||||
| 15 | Ru-Tta-Dfp //Ru-Tta-Dfp | 1.0 mol L-1 KOH + 0.1 mol L-1 KNO3 | 1.0 mol L-1 KOH + 0.1 mol L-1 glucose | 93.93 | 1.16 mg h-1 cm-2 | GRA | — | 600 @50 | 4 | [40] | |||||||||
| 16 | HMFOR | meso-CoCu// meso-CoCu | 0.5 mol L-1 K2SO4 + 0.01 mol L-1 KNO3 | 1.0 mol L-1 KOH + 0.01 mol L-1 HMF | 98.8 | 3.39 mol h-1 g-1 | FDCA | — | 400 @10 | 3 | [271] | ||||||||
| 17 | SC-MHEO// SC-MHEO | 1.0 mol L-1 KOH + 0.1 mol L-1 KNO3 | 1.0 mol L-1 KOH + 0.01 mol L-1 HMF | 91.5 | 15.73 mg h-1 cm-2 | FDCA | 97.7 | — | 3 | [272] | |||||||||
| 18 | ZnCoO-NW// ZnCoO-NW | 0.5 mol L-1 Na2SO4 + 0.1 mol L-1 NaNO3 | 1.0 mol L-1 KOH + 0.005 mol L-1 HMF | 92 | 4.65 mg h-1 cm-2 | FDCA | 91 | — | 3 | [270] | |||||||||
| 19 | BAOR | RuCu@NF// RuTiIr | 0.05 mol L-1 Na2SO4 + 0.588 mmol L-1 NaNO3 | 0.05 mol L-1 Na2SO4 + 10 mol L-1 BA | 96.8 | — | BAD | — | — | 3 | [278] | ||||||||
| 20 | OD-Cu// Pt-Ni(OH)2 | 0.4 mol L-1 KOH + 1.0 mol L-1 K2CO3 + 1.0 mol L-1 KNO3 + 0.1 mol L-1 BA + 0.6 mol L-1 ethanol | 60 | 278 μmol h-1 | CAL | — | — | 3 | [279] | ||||||||||
| 21 | Plastic upcycling (PET) | R-Co/CF// R-NiCo/NF | 1.0 mg L-1 KOH + 0.1 mg L-1 KNO3 | PET hydrolysate | 96.2 | 0.87 mmol h-1 cm-2 | FA | 98.2 | 202 @50 | 5 | [186] | ||||||||
| 22 | Ru-Co(OH)2// Ru-CoOOH | 1.0 mg L-1 KOH + 1.98 mmg L-1 KNO3 | PET hydrolysate | 98.9 | 0.244 mmol h-1 cm-2 | FA | 96.5 | 260 @150 | 5 | [285] | |||||||||
| 23 | CuPd alloy// CuPd alloy | 1.0 mg L-1 KOH + 0.1 mg L-1 KNO3 | 1.0 mol L-1 KOH + 0.1 mol L-1 EG | 92 | — | GA | 93 | 980 @10 | 5 | [287] | |||||||||
| 24 | mPd3Au/NF //mPd3Au/NF | 1.0 mg L-1 KOH + 0.1 mg L-1 KNO3 | PET hydrolysate | 97.3 | 0.71 mmol h-1 cm-2 | GA | 95.3 | 1038 @100 | 4 | [8] | |||||||||
| 25 | r-PdCuene/NF //PdCuene/NF | 1.0 mg L-1 KOH + 1.98 mmg L-1 KNO3 | 1.0 mol L-1 KOH + 1.0 mol L-1 EG | 91.6 | 0.237 mmol h-1 cm-2 | GA | 92.1 | 1060 @50 | 4 | [11] | |||||||||
| 26 | LC-CoOOH/CF //Pd NTs/NF | 1.0 mg L-1 KOH + 1.98 mmg L-1 KNO3 | PET hydrolysate | 97.4 | 0.246 mmol h-1 cm-2 | GA | 87.8 | — | 5 | [286] | |||||||||
| 27 | SOR | MFe2O4// MFe2O4 | 0.1 mg L-1 K2SO4 + 0.1 mg L-1 KNO3 | 1.0 mol L-1 KOH + 1.0 mol L-1 Na2S | 95.2 | 608.9 μmol h-1 cm-2 | sulfur | — | 1480 @10 | 3 | [294] | ||||||||
| 28 | ER-Cu// S-(Ni,Fe)OxHy | 1.0 mg L-1 KOH + 0.1 mg L-1 KNO3 | 1.0 mol L-1 KOH + 1.0 mol L-1 S2- | 96 | 0.391 mmol h-1 cm-2 | sulfur | — | 1100 @50 | 3 | [295] | |||||||||
| 29 | Co-MOF/NF //Co-MOF/NF | 1.0 mg L-1 KOH + 1.98 mmg L-1 KNO3 | 1.0 mol L-1 KOH + 4.0 mol L-1 Na2S | 94.2 | 0.238 mmol h-1 cm-2 | sulfur | — | 1597 @50 | 4 | [291] | |||||||||
| 30 | Fe3C@N-CNTs/IF //Fe3C@N-CNTs/IF | 0.5 mg L-1 Na2SO4 + 2.35 mmg L-1 NaNO3 | 1.0 mol L-1 KOH + 1.0 mol L-1 Na2S | 97.9 | 0.922 mg h-1 cm-2 | sulfur | — | 1100 @10 | 4 | [292] | |||||||||
| 31 | BOR | Ni3Se4//Ni3Se4 | 0.1 mg L-1 KOH + 0.01 mg L-1 KNO3 | 0.1 mol L-1 KOH + 0.01 mol L-1 benzylamine | 87 | 1.091 mmol h-1 cm-2 | BN | 93 | 260 @50 | 4 | [298] | ||||||||
Fig. 10. (A) HCHO oxidation over Cu2O and OER over Pt. (B) Mechanistic scheme of anodic HCHO oxidation via tandem reaction. (C) LSV curves for the system combining anodic OER/Pt with cathodic NO3RR/Cu, NO3RR/Cu2O and NO3RR/CuO. (D) Schematic illustration of dual-electrode Cu2O//Cu2O for NO3RR//FOR. (E) LSV curves for several reaction conditions in dual-electrode Cu2O//Cu2O electrolyzer. (F) Nitrate conversion and FE for NO3RR//FOR over Cu2O//Cu2O at several potentials for 2 h electrolysis time. (G) Cycling tests of NO3RR//FOR over Cu2O//Cu2O at 1 V for 2 h. Reproduced with permission from Ref. [245]. Copyright 2023, Royal Society of Chemistry. FEs (H) and yield rates (I) of NH3 on Ag1@Cu2O NWs in 1 mol L?1 KOH for varying nitrate concentration. (J) Gibbs energy diagrams of NO3RR on Ag1@Cu2O and Cu2O. (K) LSVs of Ag1@Cu2O NWs, Cu2O NWs, and Cu foam in 1 mol L?1 KOH with 0.2 mol L?1 HCHO. (L) FEs and yield rates of FA on Ag1@Cu2O NWs at several potentials. Reproduced with permission from Ref. [246]. Copyright 2025, Royal Society of Chemistry.
Fig. 11. (A) Diagram of MEA configuration by coupling NO3RR with EGOR over VO-NiCo2O4. (B) LSV curves of HER//OER, NO3RR//OER, HER//EGOR, and NO3RR//EGOR electrolyzers. (C) FENH3 and yield of NH3 on VO-NiCo2O4/NF under different potentials. (D) FEFA and yield of FA for the VO-NiCo2O4/NF at different potentials. (E) Raman characteristic peaks of VO-NiCo2O4/NF for EGOR. Characteristic peaks of VO-NiCo2O4/NF (F) and VO-Co3O4/NF (G) for NO3RR. Reproduced with permission from Ref. [253]. Copyright 2024, Elsevier B. V. (H) NO3- adsorption on Co-N4. (I) Gibbs energy diagrams of NO3RR on Co-N-C. (J) Gibbs energy diagrams for EG to GA oxidation on PdNi/CBC. (K) LSV curves of NO3RR//EGOR and NO3RR//OER over Co-N-C//PdNi/CBC. (L) FENH3 at each given potential. (M) Production rate of NH3 and GA at each given potential. Reproduced with permission from Ref. [254]. Copyright 2024, Wiley VCH.
Fig. 12. (A) Schematic illustration for cathodic reduction reconstruction of a nanocomposite of NiCu-OH to form a reconstructed sample R-NiCu-OH nanocomposite. (B) Schematic illustration for anodic oxidation reconstruction of NiCu-OH-derived NiCuO to form R-NiCuO. (C) Schematic illustration of a paired electrochemical refinery (NO3RR//GlyOR) over R-NiCu-OH//R-NiCuO. (D) LSV curves using paired electrochemical refinery with and without glycerol at anode. Reproduced with permission from Ref. [261]. Copyright 2022, Royal Society of Chemistry. (E) In-situ Raman spectra of NO3RR with the Co-Fe-P in 0.1 mol L-1 K2SO4 and 0.1 mol L-1 KNO3. (F) Contact angles of water and glycerol droplet on Co-Fe-P. (G) PDOS diagram of d-bands for Co-Fe-P (200) and corresponding d-band centers. (H) Calculated reaction Gibbs energies of NO3RR process over Co-Fe-P, CoP and FeP. ΔG from NO3- to *NO3- (I) and RDS energy barriers (J) of Co-Fe-P, CoP and FeP. (K) LSV curves using electrolyzer with and without glycerol at anode. Reproduced with permission from Ref. [262]. Copyright 2024, Elsevier B. V.
Fig. 13. (A) LSV curves of GluOR and OER using D-CuCo/CoP/NF as a working electrode. (B) Yield and FE of FA at different potentials. (C) FE and yield rate of NH3 for D-CuCo/CoP/NF under different potentials. (D) In-situ Raman spectra of D-CuCo/CoP/NF in 1.0 mol L?1 KOH with 0.1 mol L?1 glucose. (E) OCP of CuCoAl/CoP/NF and D-CuCo/CoP/NF in 1.0 mol L?1 KOH with and without glucose. (F) LSV curves for the GluOR//NO3RR, OER//NO3RR, GluOR//HER, and OER//HER hybrid electrolytic cells. Reproduced with permission from Ref. [267]. Copyright 2025, Wiley VCH. (G) High-magnification TEM and HAADF-STEM images and corresponding equalized rainbow color image. (H) Detailed electrochemical mechanism of meso-CoCu for selective NO3- to NH3 electrocatalysis. (I) Reaction energy barriers for selective NO3- to NH3 electrocatalysis. Reproduced with permission from Ref. [271]. Copyright 2024, Wiley VCH. (J) High-resolution TEM image, and corresponding FT pattern and structural model images of SC-MHEO. (K) Capacitive currents of SC-MHEO, SC-M-Co3O4, and P-HEO. (L) Gibbs energies of HMFOR electrocatalysis via pathway I and pathway II by SC-MHEO and SC-M-Co3O4. (M) LSV curves of SC-MHEO collected in 1.0 mol L?1 KOH with and without 0.10 mol L?1 KNO3. Reproduced with permission from Ref. [272]. Copyright 2024, Springer Nature.
Fig. 14. Gibbs energy profiles for NO3- to NO2- (A) and for HER (B) on Cu and Co(OH)2. (C) CV curves of R-NiCo/NF, R-Ni/NF and R-Co/NF in 1.0 mol L?1 KOH. (D) Schematic illustration of electrocatalytic system for NO3RR and EGOR. (E) LSV curves of NO3RR//PET hydrolysate oxidation and NO3RR//OER over R-Co/CF//R-NiCo/NF. (F) TEA of NO3RR//OER, NO3RR//EGOR, and NO3RR//PET hydrolysate oxidation on the basis of 1 tonne of NH3 with values in US dollars (year 2024 of economic data). Reproduced with permission from Ref. [186]. Copyright 2025, Wiley VCH. (G) PDOS of CuPd/NF and Pd/NF. EG adsorption energy (H) and GA desorption energy (I) on CuPd/NF and Pd/NF. (J) Gibbs energy diagram of NO3RR on CuPd/NF, Pd/NF, and Cu/NF. (K) Schematic diagram of direct EG fuel cell and its electrical output mode. (L) Polarization curves and power density curves of direct EG fuel cells. Reproduced with permission from Ref. [287]. Copyright 2025, American Chemical Society.
Scheme 3. Workflow for applying machine learning techniques in the development of catalytic materials.
Fig. 15. (A) Schematic representation of MEA-BPM configuration. (B) Schematic representation of MEA-AEM configuration. Reproduced with permission from Ref. [312]. Copyright 2024, American Chemical Society. (C) A schematic of PSE reactor design and how this design can utilize the proposed cation shielding effect to suppress the unwanted HER side reaction and improve NO3RR performance. (IHP, inner Helmholtz plane and OHP, outer Helmholtz plane). Reproduced with permission from Ref. [313]. Copyright 2024, Springer Nature. (D) Schematic diagram of the pilot-scale electrochemical reactor. Reproduced with permission from Ref. [314]. Copyright 2021, American Chemical Society.
Fig. 16. (A) Schematic illustration of the sequential NO3RR and NH3 collection system. Reproduced with permission from Ref. [316]. Copyright 2023, American Chemical Society. (B) Schematic illustration of formate and NH4Cl production from PET bottle and nitrate wastewater. Reproduced with permission from Ref. [317]. Copyright 2025, Royal Society of Chemistry. (C) Schematic of the glycolate product synthesis from post-reaction anolyte. Reproduced with permission from Ref. [318]. Copyright 2025, Elsevier B. V. XRD patterns of synthesized formate (D) and glycolate (E). (F) Workflow overview of the tandem electrochemical-chemical upgrading of nitrate and formaldehyde into HCOONH4 solid at a 10 g scale. Reproduced with permission from Ref. [246]. Copyright 2025, Royal Society of Chemistry.
Fig. 17. (A) TEA comparison of constant potential and 3-step pulse NO3RR applying a protocol reactor of 20 cm2 at 2.0 A. Reproduced with permission from Ref. [326]. Copyright 2025, Wiley VCH. (B) Estimated costs for NO3RR in an MEA system. (C) Contour map illustrating NH3 synthesis costs as a function of current densities and electricity prices. Reproduced with permission from Ref. [327]. Copyright 2025, Royal Society of Chemistry. (D) TEA of NO3RR//GlyOR and NO3RR//OER coupling systems. Reproduced with permission from Ref. [328]. Copyright 2025, Wiley VCH. (E) TEA of NO3RR//PET hydrolysate oxidation coupled system. (F) TEA results of NO3RR//PET hydrolysate oxidation coupled system at 500 mA cm-2. Reproduced with permission from Ref. [329]. Copyright 2025, American Chemical Society. (G) Schematic assembly of C-N coupling reaction//PET hydrolysate oxidation coupling system. (H) LSV curves of urea electrosynthesis coupled to OER and PET hydrolysate oxidation. (I) Faradaic efficiency of urea and glycolic acid at several potentials in coupled systems. Reproduced with permission from Ref. [330]. Copyright 2025, Wiley VCH.
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