Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Methods for nitrogen activation by reduction and oxidation

Abstract

The industrial Haber–Bosch process to produce ammonia (NH3) from dinitrogen (N2) is crucial for modern society. However, N2 activation is inherently challenging and the Haber–Bosch process has significant drawbacks, as it is highly energy intensive, is not sustainable owing to substantial CO2 emissions primarily from the generation of H2 and requires large, centralized facilities. New strategies of sustainable N2 activation, such as low-temperature thermochemical catalysis and (photo)electrocatalysis, have been pursued, but progress has been hindered by the lack of rigour and reproducibility in the collection and analysis of results. In this Primer, we provide a holistic step by step protocol, applicable to all nitrogen-transformation reactions, focused on verifying genuine N2 activation by accounting for all contamination sources. We compare state-of-the-art results from different catalytic reactions following the protocol’s framework, and discuss necessary reporting metrics and ways to interpret both experimental and density functional theory results. This Primer covers various common pitfalls in the field, best practices to improve reproducibility and cost-efficient methods to carry out rigorous experimentation. The future of nitrogen catalysis will require an increase in rigorous experimentation and standardization to prevent false positives from appearing in the literature, which can enable advancing towards practical technologies for the activation of N2.

This is a preview of subscription content

Access options

Buy article

Get time limited or full article access on ReadCube.

$32.00

All prices are NET prices.

Fig. 1: Historical development of N2 activation.
Fig. 2: Fundamental challenges of N2 activation.
Fig. 3: General flow chart of experimentation.
Fig. 4: Experimental set-up for electrochemical and thermochemical N2 activation.
Fig. 5: Isotopic and non-isotopic NH3 detection methods.
Fig. 6: State-of-the-art literature overview of electrochemical, photo(electro)chemical and thermochemical N2 activation.
Fig. 7: Example data of lithium-mediated NH3 synthesis in THF with LiClO4 salt and EtOH as the proton source.
Fig. 8: Recommended reports of catalytic performances for thermal NH3 synthesis.
Fig. 9: Density functional theory results.
Fig. 10: Homebuilt glass circulation pump and full gas recirculating set-up with homebuilt activated copper catalyst for gas cleaning.

References

  1. Cottrell, T. L. The Strengths of Chemical Bonds 2nd edn (Butterworth, 1958).

  2. Jia, H.-P. & Quadrelli, E. A. Mechanistic aspects of dinitrogen cleavage and hydrogenation to produce ammonia in catalysis and organometallic chemistry: relevance of metal hydride bonds and dihydrogen. Chem. Soc. Rev. 43, 547–564 (2014).

    Article  Google Scholar 

  3. Noxon, J. F. Atmospheric nitrogen fixation by lightning. Geophys. Res. Lett. 3, 463–465 (1976).

    ADS  Article  Google Scholar 

  4. Rivera Ortiz, J. M. & Burris, R. H. Interactions among substrates and inhibitors of nitrogenase. J. Bacteriol. 123, 537–545 (1975).

    Article  Google Scholar 

  5. Yang, Z. Y. et al. Evidence that the Pi release event is the rate-limiting step in the nitrogenase catalytic cycle. Biochemistry 55, 3625–3635 (2016).

    Article  Google Scholar 

  6. Hoffman, B. M., Lukoyanov, D., Yang, Z., Dean, D. R. & Seefeldt, L. C. Mechanism of nitrogen fixation by nitrogenase: the next stage. Chem. Rev. 114, 4041–4062 (2014).

    Article  Google Scholar 

  7. Smil, V. Enriching the Earth: Fritz Haber, Carl Bosch, and the Transformation of World Food Production (MIT Press, 2001).

  8. Hager, T. The Alchemy of Air: A Jewish Genius, a Doomed Tycoon, and the Discovery that Changed the Course of History (Broadway Books, 2008).

  9. [No authors listed.] Science and food supply. Nature 126, 193–194 (1930).

  10. Ihde, A. J. The Development of Modern Chemistry (Dover Books on Chemistry) (Dover, 1984).

  11. Chen, J. G. et al. Beyond fossil fuel-driven nitrogen transformations. Science 360, eaar6611 (2018). This review covers the thermochemistry of all nitrogen-transformation reactions and the challenges and opportunities associated with these reactions in overcoming reliance on fossil fuels.

    Article  Google Scholar 

  12. Smith, C., Hill, A. K. & Torrente-Murciano, L. Current and future role of Haber–Bosch ammonia in a carbon-free energy landscape. Energy Environ. Sci. 13, 331–344 (2020).

    Article  Google Scholar 

  13. Aika, K. & Tamara, K. in Ammonia (ed. Nielsen, A.) 103–148 (Springer, 1995).

  14. Ertl, G. Reactions at surfaces: from atoms to complexity (Nobel Lecture). Angew. Chem. Int. Ed. 47, 3524–3535 (2008).

    Article  Google Scholar 

  15. Erisman, J. W., Sutton, M. A., Galloway, J., Klimont, Z. & Winiwarter, W. How a century of ammonia synthesis changed the world. Nat. Geosci. 1, 636–639 (2008).

    ADS  Article  Google Scholar 

  16. Smil, V. Nitrogen and food production: proteins for human diets. Ambio 31, 126–131 (2002).

    Article  Google Scholar 

  17. Stewart, W. M., Dibb, D. W., Johnston, A. E. & Smyth, T. J. The contribution of commercial fertilizer nutrients to food production. Agron. J. 97, 1–6 (2005).

    Article  Google Scholar 

  18. USGS National Minerals Information Center. Nitrogen Statistics and Information, Mineral Commodity Summaries (U.S. Geological Survey, 2020).

  19. Apodaca, L. E. Nitrogen (fixed) — Ammonia 116–117 (US Geological Survey, 2021).

  20. Smil, V. Detonator of the population explosion. Nature 400, 415–415 (1999).

    ADS  Article  Google Scholar 

  21. Schlögl, R. Carbons in Handbook of Heterogeneous Catalysis (eds Ertl, G., Knozinger, H., Schüth, F. & Weitkamp, J.) 357–427 (Wiley-VCH, 2008).

  22. IHS Markit. Ammonia — Chemical Economics Handbook (IHS Markit, 2020).

  23. Klerke, A., Christensen, C. H., Nørskov, J. K. & Vegge, T. Ammonia for hydrogen storage: challenges and opportunities. J. Mater. Chem. 18, 2304 (2008).

    Article  Google Scholar 

  24. Zamfirescu, C. & Dincer, I. Using ammonia as a sustainable fuel. J. Power Sources 185, 459–465 (2008).

    ADS  Article  Google Scholar 

  25. Brightling, J. Ammonia and the fertiliser industry: the development of ammonia at Billingham a history of technological innovation from the early 20th century to the present day. Johnson Matthey Technol. Rev. 62, 32 (2018).

    Article  Google Scholar 

  26. Brown, T. Ammonia production causes 1% of total global GHG emissions. Ammonia Industry https://ammoniaindustry.com/ammonia-production-causes-1-percent-of-total-global-ghg-emissions/ (2016).

  27. Soloveichik, G. Electrochemical synthesis of ammonia as a potential alternative to the Haber–Bosch process. Nat. Catal. 2, 377–380 (2019).

    Article  Google Scholar 

  28. MacFarlane, D. R. et al. A roadmap to the ammonia economy. Joule 4, 1186–1205 (2020). This paper covers three different generations of technological advancement needed to produce NH3 sustainably.

    Article  Google Scholar 

  29. Stephens, I. & Nilsson, A. Research needs towards sustainable production of fuels and chemicals. Energy-X https://www.energy-x.eu/research-needs-report/ (2019).

  30. Erisman, J. W., Bleeker, A., Galloway, J. & Sutton, M. S. Reduced nitrogen in ecology and the environment. Environ. Pollut. 150, 140–149 (2007).

    Article  Google Scholar 

  31. Good, A. G. & Beatty, P. H. Fertilizing nature: a tragedy of excess in the commons. PLoS Biol. 9, 1–9 (2011).

    Article  Google Scholar 

  32. Singh, A. R. et al. Electrochemical ammonia synthesis — the selectivity challenge. ACS Catal. 7, 706–709 (2017). This viewpoint elucidates the selectivity challenge by covering a qualitative analysis of electrochemical NH3 synthesis and suggests strategies to circumvent the issue.

    Article  Google Scholar 

  33. Comer, B. M. et al. Prospects and challenges for solar fertilizers. Joule 3, 1578–1605 (2019).

    Article  Google Scholar 

  34. ARPA-E. Renewable Energy to Fuels Through Utilization of EnergyDense Liquids (REFUEL) Program Overview 1–16 https://arpa-e.energy.gov/sites/default/files/documents/files/REFUEL_ProgramOverview.pdf (2016).

  35. Rouwenhorst, K. H. R., Kim, H. H. & Lefferts, L. Vibrationally excited activation of N2 in plasma-enhanced catalytic ammonia synthesis: a kinetic analysis. ACS Sustain. Chem. Eng. 7, 17515–17522 (2019).

    Article  Google Scholar 

  36. Rouwenhorst, K. H. R. et al. Plasma-driven catalysis: green ammonia synthesis with intermittent electricity. Green Chem. 22, 6258–6287 (2020).

    Article  Google Scholar 

  37. Kim, H. H., Teramoto, Y., Ogata, A., Takagi, H. & Nanba, T. Atmospheric-pressure nonthermal plasma synthesis of ammonia over ruthenium catalysts. Plasma Process. Polym. 14, 1600157 (2016).

    Article  Google Scholar 

  38. Mehta, P. et al. Overcoming ammonia synthesis scaling relations with plasma-enabled catalysis. Nat. Catal. 1, 269–275 (2018).

    Article  Google Scholar 

  39. Han, G.-F. et al. Mechanochemistry for ammonia synthesis under mild conditions. Nat. Nanotechnol. 16, 325–330 (2020).

    ADS  Article  Google Scholar 

  40. Tricker, A. W. et al. Mechanocatalytic ammonia synthesis over TiN in transient microenvironments. ACS Energy Lett. 5, 3362–3367 (2020).

    Article  Google Scholar 

  41. IHS Markit. Nitric Acid — Chemical Economics Handbooks (IHS Markit, 2015).

  42. Bard, A. & Faulkner, L. Electrochemical methods: fundamentals and applications. Russ. J. Electrochem. 38, 1364–1365 (2002).

    Article  Google Scholar 

  43. Patil, B. S., Rovira Palau, J., Hessel, V., Lang, J. & Wang, Q. Plasma nitrogen oxides synthesis in a milli-scale gliding arc reactor: investigating the electrical and process parameters. Plasma Chem. Plasma Process. 36, 241–257 (2016).

    Article  Google Scholar 

  44. Birkeland, K. R. On the oxidation of atmospheric nitrogen in electric arcs. Trans. Faraday Soc. 2, 98–116 (1906).

    Article  Google Scholar 

  45. Eyde, S. Oxidation of atmospheric nitrogen and development of resulting industries in norway. Ind. Eng. Chem. 4, 771–774 (1912).

    Article  Google Scholar 

  46. Cherkasov, N., Ibhadon, A. O. & Fitzpatrick, P. A review of the existing and alternative methods for greener nitrogen fixation. Chem. Eng. Process. Process Intensif. 90, 24–33 (2015).

    Article  Google Scholar 

  47. Hessel, V. et al. Industrial applications of plasma, microwave and ultrasound techniques: nitrogen-fixation and hydrogenation reactions. Chem. Eng. Process. Process Intensif. 71, 19–30 (2013).

    Article  Google Scholar 

  48. Rusanov, V. D., Fridman, A. A. & Sholin, G. V. The physics of a chemically active plasma with nonequilibrium vibrational excitationc of molecules. Sov. Phys. Uspekhi 24, 447–474 (1981).

    ADS  Article  Google Scholar 

  49. Li, S., Medrano, J. A., Hessel, V. & Gallucci, F. Recent progress of plasma-assisted nitrogen fixation research: a review. Processes 6, 248 (2018).

    Article  Google Scholar 

  50. Dai, C., Sun, Y., Chen, G., Fisher, A. C. & Xu, Z. J. Electrochemical oxidation of nitrogen towards direct nitrate production on spinel oxides. Angew. Chem. Int. Ed. 59, 9418–9422 (2020).

    Article  Google Scholar 

  51. Fang, W. et al. Boosting efficient ambient nitrogen oxidation by a well-dispersed Pd on MXene electrocatalyst. Chem. Commun. 56, 5779–5782 (2020).

    Article  Google Scholar 

  52. Wang, Y., Yu, Y., Jia, R., Zhang, C. & Zhang, B. Electrochemical synthesis of nitric acid from air and ammonia through waste utilization. Natl Sci. Rev. 6, 730–738 (2019).

    Article  Google Scholar 

  53. Lun Pang, C., Lindsay, R. & Thornton, G. Chemical reactions on rutile TiO2(110). Chem. Soc. Rev. 37, 2328–2353 (2008).

    Article  Google Scholar 

  54. Bickley, R. I. & Vishwanathan, V. Photocatalytically induced fixation of molecular nitrogen by near UV radiation. Nature 280, 306–308 (1979).

    ADS  Article  Google Scholar 

  55. Yuan, S. J. et al. Nitrate formation from atmospheric nitrogen and oxygen photocatalysed by nano-sized titanium dioxide. Nat. Commun. 4, 2249 (2013).

    ADS  Article  Google Scholar 

  56. Kuang, M. et al. Efficient nitrate synthesis via ambient nitrogen oxidation with Ru-doped TiO2/RuO2 electrocatalysts. Adv. Mater. 32, 2002189 (2020).

    Article  Google Scholar 

  57. Wang, S. et al. Universal transition state scaling relations for (de)hydrogenation over transition metals. Phys. Chem. Chem. Phys. 13, 20760–20765 (2011).

    Article  Google Scholar 

  58. Bozso, F., Ertl, G., Grunze, M. & Weiss, M. Interaction of nitrogen with iron surfaces. I. Fe(100) and Fe(111). J. Catal. 49, 18–41 (1977).

    Article  Google Scholar 

  59. Bozso, F., Ertl, G. & Weiss, M. Interaction of nitrogen with iron surfaces. II. Fe(110). J. Catal. 50, 519–529 (1977).

    Article  Google Scholar 

  60. Ertl, G., Lee, S. B. & Weiss, M. Adsorption of nitrogen on potassium promoted Fe(111) and (100) surfaces. Surf. Sci. 114, 527–545 (1982).

    ADS  Article  Google Scholar 

  61. Honkala, K. et al. Ammonia synthesis from first-principles calculations. Science 307, 555–558 (2005).

    ADS  Article  Google Scholar 

  62. Dahl, S. et al. Role of steps in N2 activation on Ru(0001). Phys. Rev. Lett. 83, 1814 (1999).

    ADS  Article  Google Scholar 

  63. Chorkendorff, I. & Niemantsverdriet, J. W. in Concepts of Modern Catalysis and Kinetics. Ch. 3 79–127 (Wiley, 2003).

  64. Medford, A. J. et al. Assessing the reliability of calculated catalytic ammonia synthesis rates. Science 345, 197–200 (2014).

    ADS  Article  Google Scholar 

  65. Wellendorff, J. et al. Density functionals for surface science: exchange-correlation model development with Bayesian error estimation. Phys. Rev. B 85, 235149 (2012).

    ADS  Article  Google Scholar 

  66. Singh, A. R. et al. Strategies toward selective electrochemical ammonia synthesis. ACS Catal. 9, 8316–8324 (2019).

    Article  Google Scholar 

  67. Medford, A. J. et al. From the Sabatier principle to a predictive theory of transition-metal heterogeneous catalysis. J. Catal. 328, 36–42 (2015). This paper discusses scaling relations, activity maps and the d-band model, thereby mapping out the development of trends in transition metal catalysts.

    Article  Google Scholar 

  68. Bare, S. R., Strongin, D. R. & Somorjai, G. A. Ammonia synthesis over iron single-crystal catalysts: the effects of alumina and potassium. J. Phys. Chem. 90, 4726–4729 (1986).

    Article  Google Scholar 

  69. Dahl, S., Taylor, P. A., Törnqvist, E. & Chorkendorff, I. The synthesis of ammonia over a ruthenium single crystal. J. Catal. 178, 679–686 (1998).

    Article  Google Scholar 

  70. Singh, A. R. et al. Computational design of active site structures with improved transition-state scaling for ammonia synthesis. ACS Catal. 8, 4017–4024 (2018).

    Article  Google Scholar 

  71. Montoya, J. H., Tsai, C., Vojvodic, A. & Nørskov, J. K. The challenge of electrochemical ammonia synthesis: a new perspective on the role of nitrogen scaling relations. ChemSusChem 8, 2180–2186 (2015). This paper presents insights from DFT calculations that describe limitations on the low-temperature electrocatalytic production of NH3 from dinitrogen.

    Article  Google Scholar 

  72. Skúlason, E. et al. A theoretical evaluation of possible transition metal electro-catalysts for N2 reduction. Phys. Chem. Chem. Phys. 14, 1235–1245 (2012).

    Article  Google Scholar 

  73. Rostamikia, G., Maheshwari, S. & Janik, M. J. Elementary kinetics of nitrogen electroreduction to ammonia on late transition metals. Catal. Sci. Technol. 9, 174–181 (2019).

    Article  Google Scholar 

  74. Andersen, S. Z. et al. A rigorous electrochemical ammonia synthesis protocol with quantitative isotope measurements. Nature 570, 504–508 (2019). This letter provides a rigorous protocol from which the source of activated nitrogen can be determined.

    ADS  Article  Google Scholar 

  75. Suryanto, B. H. R. et al. Challenges and prospects in the catalysis of electroreduction of nitrogen to ammonia. Nat. Catal. 2, 290–296 (2019).

    Article  Google Scholar 

  76. Wang, P. et al. Breaking scaling relations to achieve low-temperature ammonia synthesis through LiH-mediated nitrogen transfer and hydrogenation. Nat. Chem. 9, 64–70 (2017). This study designs a two active-centre strategy using TM(N)–LiH composite catalysts to create an energy-efficient pathway that allows NH3 synthesis under mild conditions.

    Article  Google Scholar 

  77. Schwalbe, J. A. et al. A combined theory–experiment analysis of the surface species in lithium-mediated NH3 electrosynthesis. ChemElectroChem 7, 1542–1549 (2020).

    Article  Google Scholar 

  78. Lazouski, N., Chung, M., Williams, K., Gala, M. L. & Manthiram, K. Non-aqueous gas diffusion electrodes for rapid ammonia synthesis from nitrogen and water-splitting-derived hydrogen. Nat. Catal. 3, 463–469 (2020).

    Article  Google Scholar 

  79. Lazouski, N., Schiffer, Z. J., Williams, K. & Manthiram, K. Understanding continuous lithium-mediated electrochemical nitrogen reduction. Joule 3, 1127–1139 (2019).

    Article  Google Scholar 

  80. Andersen, S. Z. et al. Increasing stability, efficiency, and fundamental understanding of lithium-mediated electrochemical nitrogen reduction. Energy Environ. Sci. 13, 4291–4300 (2020).

    Article  Google Scholar 

  81. McEnaney, J. M. et al. Ammonia synthesis from N2 and H2O using a lithium cycling electrification strategy at atmospheric pressure. Energy Environ. Sci. 10, 1621–1630 (2017).

    Article  Google Scholar 

  82. Kim, K. et al. Lithium-mediated ammonia electro-synthesis: effect of CsClO4 on lithium plating efficiency and ammonia synthesis. J. Electrochem. Soc. 165, F1027 (2018).

    Article  Google Scholar 

  83. Hattori, M., Iijima, S., Nakao, T., Hosono, H. & Hara, M. Solid solution for catalytic ammonia synthesis from nitrogen and hydrogen gases at 50 °C. Nat. Commun. 11, 2001 (2020).

    ADS  Article  Google Scholar 

  84. Davy, H. The Bakerian Lecture, on some chemical agencies of electricity. Philos. Trans. R. Soc. Lond. 97, 1–56 (1807).

    ADS  Google Scholar 

  85. Rayleigh, L. XIII. — Observations on the oxidation of nitrogen gas. J. Chem. Soc. Trans. 71, 181–186 (1897).

    Article  Google Scholar 

  86. Boucher, D. L., Davies, J. A., Edwards, J. G. & Mennad, A. An investigation of the putative photosynthesis of ammonia on iron-doped titania and other metal oxides. J. Photochem. Photobiol. A Chem. 88, 53–64 (1995).

    Article  Google Scholar 

  87. Shipman, M. A. & Symes, M. D. A re-evaluation of Sn(II) phthalocyanine as a catalyst for the electrosynthesis of ammonia. Electrochim. Acta 258, 618–622 (2017).

    Article  Google Scholar 

  88. Licht, S. et al. Retraction. Science 369, 780 (2020).

    ADS  Article  Google Scholar 

  89. Du, H.-L., Gengenbach, T. R., Hodgetts, R., MacFarlane, D. R. & Simonov, A. N. Critical assessment of the electrocatalytic activity of vanadium and niobium nitrides toward dinitrogen reduction to ammonia. ACS Sustain. Chem. Eng. 7, 6839–6850 (2019).

    Article  Google Scholar 

  90. Choi, J. et al. Promoting nitrogen electroreduction to ammonia with bismuth nanocrystals and potassium cations in water. Preprint at https://doi.org/10.26434/chemrxiv.11768814.v1 (2020).

  91. Yang, X. et al. Quantification of active sites and elucidation of the reaction mechanism of the electrochemical nitrogen reduction reaction on vanadium nitride. Angew. Chem. 131, 13906–13910 (2019).

    Article  Google Scholar 

  92. Bao, D. et al. Electrochemical reduction of N2 under ambient conditions for artificial N2 fixation and renewable energy storage using N2/NH3 cycle. Adv. Mater. 29, 1604799 (2017).

    Article  Google Scholar 

  93. Hao, Y.-C. et al. Promoting nitrogen electroreduction to ammonia with bismuth nanocrystals and potassium cations in water. Nat. Catal. 2, 448–456 (2019).

    Article  Google Scholar 

  94. Smeets, M. A. M. et al. Odor and irritation thresholds for ammonia: a comparison between static and dynamic olfactometry. Chem. Senses 32, 11–20 (2007).

    Article  Google Scholar 

  95. Dabundo, R. et al. The contamination of commercial 15N2 gas stocks with 15N-labeled nitrate and ammonium and consequences for nitrogen fixation measurements. PLoS ONE 9, e110335 (2014). This paper shows that commercial isotope-labelled 15N2 contains significant contamination across lot numbers and different manufacturers.

    ADS  Article  Google Scholar 

  96. Giordano, L. et al. PH dependence of OER activity of oxides: current and future perspectives. Catal. Today 262, 2–10 (2016).

    Article  Google Scholar 

  97. Shinagawa, T., Garcia-Esparza, A. T. & Takanabe, K. Insight on Tafel slopes from a microkinetic analysis of aqueous electrocatalysis for energy conversion. Sci. Rep. 5, 13801 (2015).

    ADS  Article  Google Scholar 

  98. Limaye, A., Zeng, J. S., Willard, A. & Manthiram, K. Bayesian data analysis reveals no preference for cardinal tafel slopes in CO2 reduction electrocatalysis. Nat. Commun. 12, 703 (2021).

    ADS  Article  Google Scholar 

  99. Neyerlin, K. C., Gu, W., Jorne, J. & Gasteiger, H. A. Determination of catalyst unique parameters for the oxygen reduction reaction in a PEMFC. J. Electrochem. Soc. 153, A1955 (2006).

    Article  Google Scholar 

  100. Choi, J. et al. Identification and elimination of false positives in electrochemical nitrogen reduction studies. Nat. Commun. 11, 5546 (2020). This perspective assesses a wide range of electrocatalytic nitrogen reduction reports identifying false positives and providing an experimental protocol for ensuring rigorous ammonia quantification in upcoming works.

    ADS  Article  Google Scholar 

  101. Wei, C. et al. Recommended practices and benchmark activity for hydrogen and oxygen electrocatalysis in water splitting and fuel cells. Adv. Mater. 31, 1806296 (2019).

    Article  Google Scholar 

  102. Ledezma-Yanez, I., Díaz-Morales, O., Figueiredo, M. C. & Koper, M. T. M. Hydrogen oxidation and hydrogen evolution on a platinum electrode in acetonitrile. ChemElectroChem 2, 1612–1622 (2015).

    Article  Google Scholar 

  103. Raccichini, R., Amores, M. & Hinds, G. Critical review of the use of reference electrodes in Li-ion batteries: a diagnostic perspective. Batteries 5, 12 (2019).

    Article  Google Scholar 

  104. Ren, Y. et al. Is it appropriate to use the Nafion membrane in electrocatalytic N2 reduction? Small Methods 3, 1900474 (2019).

    Article  Google Scholar 

  105. Liu, H., Zhang, Y. & Luo, J. The removal of inevitable NO species in catalysts and the selection of appropriate membrane for measuring electrocatalytic ammonia synthesis accurately. J. Energy Chem. 49, 51–58 (2020).

    Article  Google Scholar 

  106. Hongsirikarn, K., Goodwin, J. G., Greenway, S. & Creager, S. Influence of ammonia on the conductivity of Nafion membranes. J. Power Sources 195, 30–38 (2010).

    ADS  Article  Google Scholar 

  107. Halseid, R., Vie, P. J. S. & Tunold, R. Influence of ammonium on conductivity and water content of Nafion 117 membranes. J. Electrochem. Soc. 151, A381 (2004).

    Article  Google Scholar 

  108. Lindley, B. M., Appel, A. M., Krogh-Jespersen, K., Mayer, J. M. & Miller, A. J. M. Evaluating the thermodynamics of electrocatalytic N2 reduction in acetonitrile. ACS Energy Lett. 1, 698–704 (2016).

    Article  Google Scholar 

  109. Guo, J. et al. Lithium imide synergy with 3d transition-metal nitrides leading to unprecedented catalytic activities for ammonia decomposition. Angew. Chem. Int. Ed. Engl. 54, 2950–2954 (2015).

    Article  Google Scholar 

  110. Kitano, M. et al. Ammonia synthesis using a stable electride as an electron donor and reversible hydrogen store. Nat. Chem. 4, 934–940 (2012).

    Article  Google Scholar 

  111. Ma, Z., Zhao, S., Pei, X., Xiong, X. & Hu, B. New insights into the support morphology-dependent ammonia synthesis activity of Ru/CeO2 catalysts. Catal. Sci. Technol. 7, 191–199 (2017).

    Article  Google Scholar 

  112. Wu, S. et al. Removal of hydrogen poisoning by electrostatically polar MgO support for low-pressure NH3 synthesis at a high rate over the Ru catalyst. ACS Catal. 10, 5614–5622 (2020).

    Article  Google Scholar 

  113. Searle, P. L. The berthelot or indophenol reaction and its use in the analytical chemistry of nitrogen. A review. Analyst 109, 549 (1984).

    ADS  Article  Google Scholar 

  114. Zhao, Y. et al. Ammonia detection methods in photocatalytic and electrocatalytic experiments: how to improve the reliability of NH3 production rates? Adv. Sci. 6, 1802109 (2019).

    Article  Google Scholar 

  115. Zhou, L. & Boyd, C. E. Comparison of Nessler, phenate, salicylate and ion selective electrode procedures for determination of total ammonia nitrogen in aquaculture. Aquaculture 450, 187–193 (2016).

    Article  Google Scholar 

  116. Giner-Sanz, J. J., Leverick, G. M., Pérez-Herranz, V. & Shao-Horn, Y. Salicylate method for ammonia quantification in nitrogen electroreduction experiments: the correction of iron III interference. J. Electrochem. Soc. 167, 134519 (2020).

    ADS  Article  Google Scholar 

  117. Murray, E. et al. A colorimetric method for use within portable test kits for nitrate determination in various water matrices. Anal. Methods 9, 680–687 (2017).

    Article  Google Scholar 

  118. Hayashi, M. Temperature–electrical conductivity relation of water for environmental monitoring and geophysical data inversion. Environ. Monit. Assess. 96, 119–128 (2004).

    Article  Google Scholar 

  119. Bruker. What is NMR? 145–158 (Bruker BioSpin, 2010).

  120. Hodgetts, R. Y. et al. Refining universal procedures for ammonium quantification via rapid 1H NMR analysis for dinitrogen reduction studies. ACS Energy Lett. 5, 736–741 (2020). This paper assesses the sensitivity of NMR towards the detection of NH3 in solutions with different proton concentration.

    Article  Google Scholar 

  121. Nielander, A. C. et al. A versatile method for ammonia detection in a range of relevant electrolytes via direct nuclear magnetic resonance techniques. ACS Catal. 9, 5797–5802 (2019). This paper reports a frequency-selective pulse NMR method for the accurate determination of NH3.

    Article  Google Scholar 

  122. Mooney, E. F. & Winson, P. H. Nitrogen magnetic resonance spectroscopy. Annu. Rep. NMR Spectrosc. 2, 125–152 (1969).

    Article  Google Scholar 

  123. Giddey, S., Badwal, S. P. S. & Kulkarni, A. Review of electrochemical ammonia production technologies and materials. Int. J. Hydrog. Energy 38, 14576–14594 (2013).

    Article  Google Scholar 

  124. Seh, Z. W. et al. Combining theory and experiment in electrocatalysis: insights into materials design. Science 355, eaad4998 (2017).

    Article  Google Scholar 

  125. Choi, J. et al. Electroreduction of nitrates, nitrites, and gaseous nitrogen oxides: a potential source of ammonia in dinitrogen reduction studies. ACS Energy Lett. 5, 2095–2097 (2020).

    ADS  Article  Google Scholar 

  126. Li, J. & Wu, N. Semiconductor-based photocatalysts and photoelectrochemical cells for solar fuel generation: a review. Catal. Sci. Technol. 5, 1360–1384 (2015).

    Article  Google Scholar 

  127. Kisch, H. Semiconductor photocatalysis — mechanistic and synthetic aspects. Angew. Chem. Int. Ed. 52, 812–847 (2013).

    Article  Google Scholar 

  128. Chen, X., Shen, S., Guo, L. & Mao, S. S. Semiconductor-based photocatalytic hydrogen generation. Chem. Rev. 110, 6503–6570 (2010).

    Article  Google Scholar 

  129. Kibsgaard, J., Nørskov, J. K. & Chorkendorff, I. The difficulty of proving electrochemical ammonia synthesis. ACS Energy Lett. 4, 2986–2988 (2019).

    Article  Google Scholar 

  130. Turner, C., Španěl, P. & Smith, D. A longitudinal study of ammonia, acetone and propanol in the exhaled breath of 30 subjects using selected ion flow tube mass spectrometry, SIFT-MS. Physiol. Meas. 27, 321–337 (2006).

    Article  Google Scholar 

  131. Tao, H. et al. Nitrogen fixation by Ru single-atom electrocatalytic reduction. Chem 5, 204–214 (2019).

    Article  Google Scholar 

  132. Xiong, W. et al. Facile, cost-effective plasma synthesis of self-supportive FeSx on Fe foam for efficient electrochemical reduction of N2 under ambient conditions. J. Mater. Chem. A 7, 19977–19983 (2019).

    Article  Google Scholar 

  133. Suryanto, B. H. R. et al. MoS2 polymorphic engineering enhances selectivity in the electrochemical reduction of nitrogen to ammonia. ACS Energy Lett. 4, 430–435 (2019).

    Article  Google Scholar 

  134. Li, X. et al. Boosted electrocatalytic N2 reduction to NH3 by defect-rich MoS2 nanoflower. Adv. Energy Mater. 8, 1801357 (2018).

    Article  Google Scholar 

  135. Chen, G.-F. et al. Ammonia electrosynthesis with high selectivity under ambient conditions via a Li+ incorporation strategy. J. Am. Chem. Soc. 139, 9771–9774 (2017).

    Article  Google Scholar 

  136. Song, Y. et al. A physical catalyst for the electrolysis of nitrogen to ammonia. Sci. Adv. 4, e1700336 (2018).

    ADS  Article  Google Scholar 

  137. Zhou, F. et al. Electro-synthesis of ammonia from nitrogen at ambient temperature and pressure in ionic liquids. Energy Environ. Sci. 10, 2516–2520 (2017).

    Article  Google Scholar 

  138. Tsuneto, A., Kudo, A. & Sakata, T. Lithium-mediated electrochemical reduction of high pressure N2 to NH3. J. Electroanal. Chem. 367, 183–188 (1994).

    Article  Google Scholar 

  139. Tsuneto, A., Kudo, A. & Sakata, T. Efficient electrochemical reduction of N2 to NH3 catalyzed by lithium. Chem. Lett. 22, 851–854 (1993).

    Article  Google Scholar 

  140. Zhang, L. et al. A Janus Fe–SnO2 catalyst that enables bifunctional electrochemical nitrogen fixation. Angew. Chem. Int. Ed. 59, 10888–10893 (2020).

    Article  Google Scholar 

  141. Hirakawa, H., Hashimoto, M., Shiraishi, Y. & Hirai, T. Photocatalytic conversion of nitrogen to ammonia with water on surface oxygen vacancies of titanium dioxide. J. Am. Chem. Soc. 139, 10929–10936 (2017).

    Article  Google Scholar 

  142. Comer, B. M. et al. The role of adventitious carbon in photo-catalytic nitrogen fixation by Titania. J. Am. Chem. Soc. 140, 15157–15160 (2018).

    Article  Google Scholar 

  143. Medford, A. J. & Hatzell, M. C. Photon-driven nitrogen fixation: current progress, thermodynamic considerations, and future outlook. ACS Catal. 7, 2624–2643 (2017).

    Article  Google Scholar 

  144. Wang, Z. et al. Recent developments in polymeric carbon nitride-derived photocatalysts and electrocatalysts for nitrogen fixation. ACS Catal. 9, 10260–10278 (2019).

    Article  Google Scholar 

  145. Lv, C. et al. Defect engineering metal-free polymeric carbon nitride electrocatalyst for effective nitrogen fixation under ambient conditions. Angew. Chemie Int. Ed. 57, 10246–10250 (2018).

    Article  Google Scholar 

  146. Hu, B., Hu, M., Seefeldt, L. & Liu, T. L. Electrochemical dinitrogen reduction to ammonia by Mo2N: catalysis or decomposition? ACS Energy Lett. 4, 1053–1054 (2019).

    Article  Google Scholar 

  147. Liu, Q. et al. Photocatalytic N2 reduction: uncertainties in the determination of ammonia production. ACS Sustain. Chem. Eng. 9, 560–568 (2021).

    Article  Google Scholar 

  148. Bielawa, H., Hinrichsen, O., Birkner, A. & Muhler, M. The ammonia-synthesis catalyst of the next generation: barium-promoted oxide-supported ruthenium. Angew. Chem.Int. Ed. 40, 1061–1063 (2001).

    Article  Google Scholar 

  149. Hagen, S. et al. New efficient catalyst for ammonia synthesis: barium-promoted cobalt on carbon. Chem. Commun. 11, 1206–1207 (2002).

    Article  Google Scholar 

  150. Kojima, R. & Aika, K. Cobalt molybdenum bimetallic nitride catalysts for ammonia synthesis Part 2. Kinetic study.pdf. Appl. Catal. A Gen. 218, 121–128 (2001). This article presents a typical kinetic study for thermo-catalytic NH3 synthesis, including the measurement conditions, the derivation process of the equations and the calculations.

    Article  Google Scholar 

  151. Hagen, S. Ammonia synthesis with barium-promoted iron–cobalt alloys supported on carbon. J. Catal. 214, 327–335 (2003).

    Article  Google Scholar 

  152. Aika, K. Role of alkali promoter in ammonia synthesis over ruthenium catalysts — effect on reaction mechanism. Catal. Today 286, 14–20 (2017).

    Article  Google Scholar 

  153. Holzman, P. R., Shiflett, W. K. & Dumesic, J. A. The importance of ammonia pressure in the kinetics of ammonia synthesis over supported Ru. J. Catal. 62, 167–172 (1980). This study compares the results of apparent activation energies measured at constant NH3 pressure and at constant flow rate, demonstrating the importance of NH3 partial pressure for reaction kinetics.

    Article  Google Scholar 

  154. Ye, T.-N. et al. Vacancy-enabled N2 activation for ammonia synthesis on an Ni-loaded catalyst. Nature 583, 391–395 (2020).

    ADS  Article  Google Scholar 

  155. Tang, Y. et al. Metal-dependent support effects of oxyhydride-supported Ru, Fe, Co catalysts for ammonia synthesis. Adv. Energy Mater. 8, 1801772 (2018).

    Article  Google Scholar 

  156. Kobayashi, Y. et al. Titanium-based hydrides as heterogeneous catalysts for ammonia synthesis. J. Am. Chem. Soc. 139, 18240–18246 (2017).

    Article  Google Scholar 

  157. Cao, Y. et al. Vanadium hydride as an ammonia synthesis catalyst. ChemCatChem. 13, 191–195 (2020).

    Article  Google Scholar 

  158. Kammert, J. et al. Nature of reactive hydrogen for ammonia synthesis over a Ru/C12A7 electride catalyst. J. Am. Chem. Soc. 142, 7655–7667 (2020).

    Article  Google Scholar 

  159. Gao, W., Guo, J. & Chen, P. Hydrides, amides and imides mediated ammonia synthesis and decomposition. Chin. J. Chem. 37, 442–451 (2019).

    Article  Google Scholar 

  160. Peterson, A. A., Abild-Pedersen, F., Studt, F., Rossmeisl, J. & Nørskov, J. K. How copper catalyzes the electroreduction of carbon dioxide into hydrocarbon fuels. Energy Environ. Sci. 3, 1311–1315 (2010).

    Article  Google Scholar 

  161. Sundararaman, R., Goddard, W. A. & Arias, T. A. Grand canonical electronic density-functional theory: algorithms and applications to electrochemistry. J. Chem. Phys. 146, 114104 (2017).

    ADS  Article  Google Scholar 

  162. Kastlunger, G., Lindgren, P. & Peterson, A. A. Controlled-potential simulation of elementary electrochemical reactions: proton discharge on metal surfaces. J. Phys. Chem. C 122, 12771–12781 (2018).

    Article  Google Scholar 

  163. Govender, A., Curulla Ferré, D. & Niemantsverdriet, J. W. A density functional theory study on the effect of zero-point energy corrections on the methanation profile on Fe(100). Chemphyschem 13, 1591–1596 (2012).

    Article  Google Scholar 

  164. Sholl, D. S. & Steckel, J. A. Density Functional Theory: A Practical Introduction Ch. 5 113–130 (Wiley, 2009). This book chapter covers zero-point energy and entropy/enthalpy energy terms and provides a good overview of the theory.

  165. Sprowl, L. H., Campbell, C. T. & Árnadóttir, L. Hindered translator and hindered rotor models for adsorbates: partition functions and entropies. J. Phys. Chem. C 120, 9719–9731 (2016).

    Article  Google Scholar 

  166. Comer, B. M. & Medford, A. J. Analysis of photocatalytic nitrogen fixation on rutile TiO2(110). ACS Sustain. Chem. Eng. 6, 4648–4660 (2018).

    Article  Google Scholar 

  167. Núñez, M., Lansford, J. L. & Vlachos, D. G. Optimization of the facet structure of transition-metal catalysts applied to the oxygen reduction reaction. Nat. Chem. 11, 449–456 (2019). This paper shows trade-offs between activity and stability.

    Article  Google Scholar 

  168. Goldsmith, B. R., Sanderson, E. D., Bean, D. & Peters, B. Isolated catalyst sites on amorphous supports: a systematic algorithm for understanding heterogeneities in structure and reactivity. J. Chem. Phys. 138, 204105 (2013).

    ADS  Article  Google Scholar 

  169. Wexler, R. B., Qiu, T. & Rappe, A. M. Automatic prediction of surface phase diagrams using ab initio grand canonical monte carlo. J. Phys. Chem. C. 123, 2321–2328 (2019).

    Article  Google Scholar 

  170. Shimanouchi, T. ‘Molecular vibrational frequencies’ in NIST chemistry WebBook in NIST Standard Reference Database Number 69 (NIST, 2018).

  171. Makepeace, J. W. et al. Reversible ammonia-based and liquid organic hydrogen carriers for high-density hydrogen storage: recent progress. Int. J. Hydrog. Energy 44, 7746–7767 (2019).

    Article  Google Scholar 

  172. Service, R. F. Liquid sunshine. Science 361, 120–123 (2018).

    ADS  Google Scholar 

  173. Christensen, C. H., Johannessen, T., Sørensen, R. Z. & Nørskov, J. K. Towards an ammonia-mediated hydrogen economy? Catal. Today 111, 140–144 (2006).

    Article  Google Scholar 

  174. Kerru, N., Gummidi, L., Maddila, S., Gangu, K. K. & Jonnalagadda, S. B. A review on recent advances in nitrogen-containing molecules and their biological applications. Molecules 25, 1909 (2020).

    Article  Google Scholar 

  175. Chen, C. et al. Coupling N2 and CO2 in H2O to synthesize urea under ambient conditions. Nat. Chem. 12, 717–724 (2020).

    Article  Google Scholar 

  176. Nielander, A. C. et al. Readily constructed glass piston pump for gas recirculation. ACS Omega 5, 16455–16459 (2020).

    Article  Google Scholar 

  177. Tang, C. & Qiao, S.-Z. How to explore ambient electrocatalytic nitrogen reduction reliably and insightfully. Chem. Soc. Rev. 48, 3166–3180 (2019).

    Article  Google Scholar 

  178. Kang, C. S. M., Zhang, X. & MacFarlane, D. R. High nitrogen gas solubility and physicochemical properties of [C4mpyr][eFAP]-fluorinated solvent mixtures. J. Phys. Chem. C. 123, 21376–21385 (2019).

    Article  Google Scholar 

  179. Shi, R., Zhang, X., Waterhouse, G. I. N., Zhao, Y. & Zhang, T. The journey toward low temperature, low pressure catalytic nitrogen fixation. Adv. Energy Mater. 10, 2000659 (2020).

    Article  Google Scholar 

  180. Munter, T. R., Bligaard, T., Christensen, C. H. & Nørskov, J. K. BEP relations for N2 dissociation over stepped transition metal and alloy surfaces. Phys. Chem. Chem. Phys. 10, 5202 (2008).

    Article  Google Scholar 

  181. Yu, W. et al. Cathodic NH4+ leaching of nitrogen impurities in CoMo thin-film electrodes in aqueous acidic solutions. Sustain. Energy Fuels 4, 5080–5087 (2020).

    Article  Google Scholar 

  182. Chen, Y. et al. Revealing nitrogen-containing species in commercial catalysts used for ammonia electrosynthesis. Nat. Catal. 3, 1055–1061 (2020). This paper shows that various commercially sold pure metals contain significant nitrogen-containing contamination, and provides a way to measure these contaminants.

    Article  Google Scholar 

  183. Schlesinger, W. & Hartley, A. A global budget for atmospheric NH3. Biogeochemistry 15, 191–211 (1992).

    Article  Google Scholar 

  184. Vojvodic, A. et al. Exploring the limits: a low-pressure, low-temperature Haber–Bosch process. Chem. Phys. Lett. 598, 108–112 (2014).

    ADS  Article  Google Scholar 

  185. Spinelli, J. B., Kelley, L. P. & Haigis, M. C. An LC-MS approach to quantitative measurement of ammonia isotopologues. Sci. Rep. 7, 10304 (2017).

    ADS  Article  Google Scholar 

  186. Liu, Y. et al. Facile all-optical method for in situ detection of low amounts of ammonia. iScience 23, 101757 (2020).

    ADS  Article  Google Scholar 

  187. Mou, S., Wang, H. & Sun, Q. Simultaneous determination of the three main inorganic forms of nitrogen by ion chromatography. J. Chromatogr. A 640, 161–165 (1993).

    Article  Google Scholar 

  188. Andersen, S. Z. Electrochemical Nitrogen Reduction under (Near) Ambient Conditions (Technical Univ. of Denmark, 2020).

  189. Timmer, B. H., van Delft, K. M., Otjes, R. P., Olthuis, W. & van den Berg, A. Miniaturized measurement system for ammonia in air. Anal. Chim. Acta 507, 137–143 (2004).

    Article  Google Scholar 

  190. Sato, K. et al. A low-crystalline ruthenium nano-layer supported on praseodymium oxide as an active catalyst for ammonia synthesis. Chem. Sci. 8, 674–679 (2017).

    Article  Google Scholar 

  191. Kim, K., Yoo, C.-Y., Kim, J.-N., Yoon, H. C. & Han, J.-I. Electrochemical synthesis of ammonia from water and nitrogen in ethylenediamine under ambient temperature and pressure. J. Electrochem. Soc. 163, F1523–F1526 (2016).

    Article  Google Scholar 

  192. Kitano, M. et al. Low-temperature synthesis of perovskite oxynitride-hydrides as ammonia synthesis catalysts. J. Am. Chem. Soc. 141, 20344–20353 (2019).

    Article  Google Scholar 

  193. Kitano, M. et al. Self-organized ruthenium–barium core-shell nanoparticles on a mesoporous calcium amide matrix for efficient low-temperature ammonia synthesis. Angew. Chem. Int. Ed. 57, 2648–2652 (2018).

    Article  Google Scholar 

  194. Wang, Y. et al. Generating defect-rich bismuth for enhancing the rate of nitrogen electroreduction to ammonia. Angew. Chem. Int. Ed. 58, 9464–9469 (2019).

    Article  Google Scholar 

  195. Kong, J. et al. Electrochemical synthesis of NH3 at low temperature and atmospheric pressure using a γ-Fe2O3 catalyst. ACS Sustain. Chem. Eng. 5, 10986–10995 (2017).

    Article  Google Scholar 

  196. Shi, M.-M. et al. Au sub-nanoclusters on TiO2 toward highly efficient and selective electrocatalyst for N2 conversion to NH3 at ambient conditions. Adv. Mater. 29, 1606550 (2017).

    Article  Google Scholar 

  197. Zhang, N. et al. Refining defect states in W18O49 by Mo doping: a strategy for tuning N2 activation towards solar-driven nitrogen fixation. J. Am. Chem. Soc. 140, 9434–9443 (2018).

    Article  Google Scholar 

  198. Wang, S. et al. Light-switchable oxygen vacancies in ultrafine Bi5O7Br nanotubes for boosting solar-driven nitrogen fixation in pure water. Adv. Mater. 29, 1701774 (2017).

    Article  Google Scholar 

  199. Jang, Y. J., Lindberg, A. E., Lumley, M. A. & Choi, K. S. Photoelectrochemical nitrogen reduction to ammonia on cupric and cuprous oxide photocathodes. ACS Energy Lett. 5, 1834–1839 (2020).

    Article  Google Scholar 

  200. Zhu, D., Zhang, L., Ruther, R. E. & Hamers, R. J. Photo-illuminated diamond as a solid-state source of solvated electrons in water for nitrogen reduction. Nat. Mater. 12, 836–841 (2013).

    ADS  Article  Google Scholar 

  201. Wang, X. et al. Insight into dynamic and steady-state active sites for nitrogen activation to ammonia by cobalt-based catalyst. Nat. Commun. 11, 653 (2020).

    ADS  Article  Google Scholar 

  202. Ogura, Y. et al. Efficient ammonia synthesis over a Ru/La0.5Ce0.5O1.75 catalyst pre-reduced at high temperature. Chem. Sci. 9, 2230–2237 (2018).

    Article  Google Scholar 

  203. Hargreaves, J. S. J. Heterogeneous catalysis with metal nitrides. Coord. Chem. Rev. 257, 2015–2031 (2013).

    Article  Google Scholar 

  204. Krauth, O., Fahsold, G. & Lehmann, A. Surface-enhanced infrared absorption. Surf. Sci. 433, 79–82 (1999).

    ADS  Article  Google Scholar 

  205. Yao, Y., Zhu, S., Wang, H., Li, H. & Shao, M. A spectroscopic study on the nitrogen electrochemical reduction reaction on gold and platinum surfaces. J. Am. Chem. Soc. 140, 1496–1501 (2018).

    Article  Google Scholar 

  206. Yao, Y., Wang, H., Yuan, X. Z., Li, H. & Shao, M. Electrochemical nitrogen reduction reaction on ruthenium. ACS Energy Lett. 4, 1336–1341 (2019).

    Article  Google Scholar 

  207. Matsui, T. et al. In situ attenuated total reflection infrared spectroscopy on electrochemical ammonia oxidation over Pt electrode in alkaline aqueous solutions. Langmuir 31, 11717–11723 (2015).

    Article  Google Scholar 

  208. Abdiaziz, K., Salvadori, E., Sokol, K. P., Reisner, E. & Roessler, M. M. Protein film electrochemical EPR spectroscopy as a technique to investigate redox reactions in biomolecules. Chem. Commun. 55, 8840–8843 (2019).

    Article  Google Scholar 

  209. Bajada, M. A. et al. A precious-metal-free hybrid electrolyzer for alcohol oxidation coupled to CO2-to-syngas conversion. Angew. Chem. Int. Ed. 59, 15633–15641 (2020).

    Article  Google Scholar 

  210. Joris, G. G. & Taylor, H. S. Exchange reactions of nitrogen isotopes on iron and tungsten surfaces. J. Chem. Phys. 7, 893–898 (1939).

    ADS  Article  Google Scholar 

  211. Urabe, K. Activation of nitrogen by alkali metal-promoted transition metal II. Isotopic exchange in molecular nitrogen over potassium-promoted ruthenium–carbon catalyst. J. Catal. 32, 108–113 (1974).

    Article  Google Scholar 

  212. Urabe, K. Activation of nitrogen by alkali metal-promoted transition metal VI. Hydrogen effect on isotopic equilibration of nitrogen and rate-determining step of ammonia synthesis on potassium-promoted ruthenium catalysts. J. Catal. 42, 197–204 (1976).

    Article  Google Scholar 

  213. Hunter, S. M. et al. A study of 15N/14N isotopic exchange over cobalt molybdenum nitrides. ACS Catal. 3, 1719–1725 (2013).

    Article  Google Scholar 

  214. Hargreaves, J. S. J. Nitrides as ammonia synthesis catalysts and as potential nitrogen transfer reagents. Appl. Petrochem. Res. 4, 3–10 (2014).

    Article  Google Scholar 

  215. Shannon, S. L. & Goodwin, J. G. Characterization of catalytic surfaces by isotopic-transient kinetics during steady-state reaction. Chem. Rev. 95, 677–695 (1995).

    Article  Google Scholar 

  216. Nwalor, J. Steady-state isotopic transient-kinetic analysis of iron-catalyzed ammonia synthesis. J. Catal. 117, 121–134 (1989).

    Article  Google Scholar 

  217. Nwalor, J. U. & Goodwin, J. G. Isotopic tracing study of K promotion of NH3 synthesis on Ru. Top. Catal. 1, 285–293 (1994).

    Article  Google Scholar 

  218. McClaine, B. Isotopic transient kinetic analysis of Cs-promoted Ru/MgO during ammonia synthesis. J. Catal. 210, 387–396 (2002).

    Article  Google Scholar 

  219. McClaine, B. C. & Davis, R. J. Importance of product readsorption during isotopic transient analysis of ammonia synthesis on Ba-promoted Ru/BaX catalyst. J. Catal. 211, 379–386 (2002).

    Article  Google Scholar 

  220. Siporin, S. Isotopic transient analysis of ammonia synthesis over Ru/MgO catalysts promoted by cesium, barium, or lanthanum. J. Catal. 222, 315–322 (2004).

    Article  Google Scholar 

Download references

Acknowledgements

Y.S.-H acknowledges support by Toyota Research Institute through the Accelerated Materials Design and Discovery Program. H.I. acknowledges support from the Imperial–MIT Department of Materials Exchange Program. S.Z.A. and I.C. acknowledge funding by Villum Fonden, part of the Villum Center for the Science of Sustainable Fuels and Chemicals (V-SUSTAIN grant 9455) and Innovationsfonden (E-ammonia grant 9067-00010B). P.C. and X.Z. were supported by the National Natural Science Foundation of China (Grant Nos 21633011 and 21988101). The material based upon work by A.J.M. and B.M.C. was supported by the National Science Foundation under Grant No. 1943707. I.E.L.S. and J.B. acknowledge financial support from the Engineering and Physical Sciences Research Council (EP/M0138/1), the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 866402) and the National Research Council Canada through the Materials for Clean Fuels Challenge Program. The authors thank M. Hatzell and Z. J. Xu for insightful discussion regarding N2 oxidation, and V. Shadravan for helpful advice on thermochemical catalysis. The authors acknowledge J. Montoya for providing data on the vibrational frequencies and free energy calculations for N2 reduction on Ru(211) for Fig. 9a.

Author information

Authors and Affiliations

Authors

Contributions

Introduction (H.I., S.Z.A. and Y.S.-H.); Experimentation (S.Z.A., H.I., X.Z., J.B., P.C., I.E.L.S., I.C. and Y.S.-H.); Results (S.Z.A., H.I., X.Z., B.M.C., J.B., P.C., I.C., A.J.M. and Y.S.-H.); Applications (H.I. and S.Z.A.); Reproducibility and data deposition (H.I. and I.C.); Limitations and optimizations (S.Z.A.); Outlook (H.I., S.Z.A., J.B., X.Z. and I.E.L.S.); Overview of the Primer (H.I., S.Z.A. and Y.S.-H.). All authors discussed and edited the full manuscript.

Corresponding authors

Correspondence to Ping Chen, Andrew J. Medford, Ifan E. L. Stephens, Ib Chorkendorff or Yang Shao-Horn.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Peer review information

Nature Reviews Methods Primers thanks D. Gao, M. Symes and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Publisher’s note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Glossary

Faradaic efficiency

The efficiency at which charge, in the form of electrons, participates in a specific electrochemical reaction.

Activation barriers

The minimal amounts of energy required for reactants to undergo a chemical reaction. These are the energy difference between the reactant and the transition state.

Standard potentials

The potentials (V) of a reversible electrode at standard state with ions at an effective 1 M concentration at a pressure of 1 atm.

Electrochemical half-cell reactions

Either oxidation reactions on the anode electrode where an electron is lost or reduction reactions on the cathode electrode where an electron is gained.

Electric arc-generated hot plasma

A discharge of electric current across a spatial gap, sustained by the presence of a thermally ionized plasma, which allows for the flow of said current.

Density functional theory

(DFT). A computational quantum mechanical modelling method used to investigate the electronic structure of many-body systems.

Reaction orders

The power dependence of the rate on the concentration of each reactant, which is an experimentally determined parameter that can have fraction values.

Tafel analysis

A method used to determine an electrochemical systems transfer coefficient via voltammograms, thereby providing information about the electrochemical mechanism and catalytic activity.

Ohmic correction

Accounting for the ohmic resistance of the media to accurately determine the potential at the surface of the electrode.

Quantum yield

Determining the number of times a specific event occurs per absorbed photon by the system in question.

Zero-point energy

The lowest possible energy that a quantum mechanical system contains, which includes fluctuations in the lowest energy state from the Heisenberg uncertainty principle.

Pareto-optimal frontier

A curve that contains physically possible optimal trade-offs between activity and stability.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Iriawan, H., Andersen, S.Z., Zhang, X. et al. Methods for nitrogen activation by reduction and oxidation. Nat Rev Methods Primers 1, 56 (2021). https://doi.org/10.1038/s43586-021-00053-y

Download citation

  • Accepted:

  • Published:

  • DOI: https://doi.org/10.1038/s43586-021-00053-y

Search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing