The electrochemical synthesis of ammonia from nitrogen under mild conditions using renewable electricity is an attractive alternative1,2,3,4 to the energy-intensive Haber–Bosch process, which dominates industrial ammonia production. However, there are considerable scientific and technical challenges5,6 facing the electrochemical alternative, and most experimental studies reported so far have achieved only low selectivities and conversions. The amount of ammonia produced is usually so small that it cannot be firmly attributed to electrochemical nitrogen fixation7,8,9 rather than contamination from ammonia that is either present in air, human breath or ion-conducting membranes9, or generated from labile nitrogen-containing compounds (for example, nitrates, amines, nitrites and nitrogen oxides) that are typically present in the nitrogen gas stream10, in the atmosphere or even in the catalyst itself. Although these sources of experimental artefacts are beginning to be recognized and managed11,12, concerted efforts to develop effective electrochemical nitrogen reduction processes would benefit from benchmarking protocols for the reaction and from a standardized set of control experiments designed to identify and then eliminate or quantify the sources of contamination. Here we propose a rigorous procedure using 15N2 that enables us to reliably detect and quantify the electrochemical reduction of nitrogen to ammonia. We demonstrate experimentally the importance of various sources of contamination, and show how to remove labile nitrogen-containing compounds from the nitrogen gas as well as how to perform quantitative isotope measurements with cycling of 15N2 gas to reduce both contamination and the cost of isotope measurements. Following this protocol, we find that no ammonia is produced when using the most promising pure-metal catalysts for this reaction in aqueous media, and we successfully confirm and quantify ammonia synthesis using lithium electrodeposition in tetrahydrofuran13. The use of this rigorous protocol should help to prevent false positives from appearing in the literature, thus enabling the field to focus on viable pathways towards the practical electrochemical reduction of nitrogen to ammonia.
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The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.
Shipman, M. A. & Symes, M. D. Recent progress towards the electrosynthesis of ammonia from sustainable resources. Catal. Today 286, 57–68 (2017).
Jewess, M. & Crabtree, R. H. Electrocatalytic nitrogen fixation for distributed fertilizer production? ACS Sustainable Chem. Eng. 4, 5855–5858 (2016).
Nørskov, J. et al. Sustainable Ammonia Synthesis – Exploring the Scientific Challenges Associated with Discovering Alternative, Sustainable Processes for Ammonia Production. https://doi.org/10.2172/1283146 (United States Department of Energy, 2016).
Ye, L., Nayak-Luke, R., Bañares-Alcántara, R. & Tsang, E. Reaction: “green” ammonia production. Chem 3, 712–714 (2017).
Singh, A. R. et al. Electrochemical ammonia synthesis—the selectivity challenge. ACS Catal. 7, 706–709 (2017).
Skúlason, E. et al. A theoretical evaluation of possible transition metal electro-catalysts for N2 reduction. Phys. Chem. Chem. Phys. 14, 1235–1245 (2012).
Sclafani, A., Augugliaro, V. & Schiavello, M. Dinitrogen electrochemical reduction to ammonia over iron cathode in aqueous medium. J. Electrochem. Soc. 130, 734–736 (1983).
Zhang, Z., Zhong, Z. & Liu, R. Cathode catalysis performance of SmBaCuMO5+δ (M=Fe, Co, Ni) in ammonia synthesis. J. Rare Earths 28, 556–559 (2010).
Lan, R., Irvine, J. T. S. & Tao, S. Synthesis of ammonia directly from air and water at ambient temperature and pressure. Sci. Rep. 3, 1145 (2013).
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).
Greenlee, L. F., Renner, J. N. & Foster, S. L. The use of controls for consistent and accurate measurements of electrocatalytic ammonia synthesis from dinitrogen. ACS Catal. 8, 7820–7827 (2018).
Chen, G.-F. et al. Advances in electrocatalytic N2 reduction—strategies to tackle the selectivity challenge. Small Methods 1800337 (2018).
Tsuneto, A., Kudo, A. & Sakata, T. Efficient electrochemical reduction of N2 to NH3 catalyzed by lithium. Chem. Lett. 22, 851–854 (1993).
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).
Hager, T. The Alchemy of Air (Harmony Books, 2008).
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. Chem. 88, 53–64 (1995).
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).
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).
Schlesinger, W. & Hartley, A. A global budget for atmospheric NH3. Biogeochemistry 15, 191–211 (1992).
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).
Song, Y. et al. A physical catalyst for the electrolysis of nitrogen to ammonia. Sci. Adv. 4, e1700336 (2018).
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).
Wang, H. et al. Ambient electrosynthesis of ammonia: electrode porosity and composition engineering. Angew. Chem. Int. Ed. 57, 12360–12364 (2018).
Tsuneto, A., Kudo, A. & Sakata, T. Lithium-mediated electrochemical reduction of high pressure N2 to NH3. J. Electroanal. Chem. (Lausanne) 367, 183–188 (1994).
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).
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).
Kong, J. et al. Electrochemical synthesis of NH3 at low temperature and atmospheric pressure using a γ-Fe2O3 catalyst. ACS Sustainable Chem. Eng. 5, 10986–10995 (2017).
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).
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).
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).
Čoćli, V. et al. Experimental aspects in benchmarking of the electrocatalytic activity. ChemElectroChem 2, 143–149 (2015).
Gritzner, G. Standard electrode potentials of M+|M couples in non-aqueous solvents (molecular liquids). J. Mol. Liq. 156, 103–108 (2010).
Brass, M., Pritzel, T., Schulte, E., and Keller, J. U. Measurements of vapor–liquid equilibria in the systems NH3–H2O–NaOH and NH3–H2O–KOH at temperatures of 303 and 318 K and pressures 0.1 MPa<p<1.3 MPa. Int. J. Thermophys. 21, 883–898 (2000).
Ma, L. et al. In situ DRIFTS and temperature-programmed technology study on NH3-SCR of NOx over Cu-SSZ-13 and Cu-SAPO-34 catalysts. Appl. Catal. B 156–157, 428–437 (2014).
Ma, L. et al. Characterization of commercial Cu-SSZ-13 and Cu-SAPO-34 catalysts with hydrothermal treatment for NH3-SCR of NOx in diesel exhaust. Chem. Eng. J. 225, 323–330 (2013).
Cook, R. L. & Sammells, A. F. Ambient temperature gas phase electrochemical nitrogen reduction to ammonia at ruthenium/solid polymer electrolyte interface. Catal. Lett. 1, 345–349 (1988).
Furuya, N. & Yoshiba, H. Electroreduction of nitrogen to ammonia on gas-diffusion electrodes modified by Fe-phthalocyanine. J. Electroanal. Chem. Interfacial Electrochem. 263, 171–174 (1989).
Furuya, N. & Matsui, K. Electroreduction of carbon dioxide on gas-diffusion electrodes modified by metal phthalocyanines. J. Electroanal. Chem. Interfacial Electrochem. 271, 181–191 (1989).
Kordali, V., Kyriacou, G. & Lambrou, C. Electrochemical synthesis of ammonia at atmospheric pressure and low temperature in a solid polymer electrolyte cell. Chem. Commun. 1673–1674 (2000).
Pospíšil, L. et al. Electrochemical conversion of dinitrogen to ammonia mediated by a complex of fullerene C60 and γ-cyclodextrin. Chem. Commun. 2270–2272 (2007).
Xu, G., Liu, R. & Wang, J. Electrochemical synthesis of ammonia using a cell with a Nafion membrane and SmFe0.7Cu0.3−xNixO3 (x = 0−0.3) cathode at atmospheric pressure and lower temperature. Sci. China Ser. B 52, 1171–1175 (2009).
Kugler, K., Luhn, M., Schramm, J. A., Rahimi, K. & Wessling, M. Galvanic deposition of Rh and Ru on randomly structured Ti felts for the electrochemical NH3 synthesis. Phys. Chem. Chem. Phys. 17, 3768–3782 (2015).
Li, S.-J. et al. Amorphizing of Au nanoparticles by CeOx –RGO hybrid support towards highly efficient electrocatalyst for N2 reduction under ambient conditions. Adv. Mater. 29, 1700001 (2017).
Chen, S. et al. Electrocatalytic synthesis of ammonia at room temperature and atmospheric pressure from water and nitrogen on a carbon-nanotube-based electrocatalyst. Angew. Chem. Int. Ed. 56, 2699–2703 (2017).
Marnellos, G. & Stoukides, M. Ammonia synthesis at atmospheric pressure. Science 282, 98–100 (1998).
Murakami, T., Nohira, T., Goto, T., Ogata, Y. H. & Ito, Y. Electrolytic ammonia synthesis from water and nitrogen gas in molten salt under atmospheric pressure. Electrochim. Acta 50, 5423–5426 (2005).
Wang, B. H., De Wang, J., Liu, R., Xie, Y. H. & Li, Z. J. Synthesis of ammonia from natural gas at atmospheric pressure with doped ceria–Ca3(PO4)2–K3PO4 composite electrolyte and its proton conductivity at intermediate temperature. J. Solid State Electrochem. 11, 27–31 (2006).
Köleli, F. & Kayan, D. B. Low overpotential reduction of dinitrogen to ammonia in aqueous media. J. Electroanal. Chem. 638, 119–122 (2010).
Amar, I. A. et al. Electrochemical synthesis of ammonia based on doped-ceria-carbonate composite electrolyte and perovskite cathode. Solid State Ionics 201, 94–100 (2011).
Amar, I. A., Lan, R., Petit, C. T. G., Arrighi, V. & Tao, S. Electrochemical synthesis of ammonia based on a carbonate-oxide composite electrolyte. Solid State Ionics 182, 133–138 (2011).
Amar, I. A. et al. Electrochemical synthesis of ammonia from N2 and H2O based on (Li,Na,K)2CO3–Ce0.8Gd0.18Ca0.02O2−δ composite electrolyte and CoFe2O4 cathode. Int. J. Hydrogen Energy 39, 4322–4330 (2014).
Licht, S. et al. Ammonia synthesis by N2 and steam electrolysis in molten hydroxide suspensions of nanoscale Fe2O3. Science 345, 637–640 (2014).
Lan, R., Alkhazmi, K. A., Amar, I. A. & Tao, S. Synthesis of ammonia directly from wet air at intermediate temperature. Appl. Catal. B 152–153, 212–217 (2014).
Amar, I. A., Lan, R. & Tao, S. Electrochemical synthesis of ammonia directly from wet N2 using La0.6Sr0.4Fe0.8Cu0.2O3−δ-Ce0.8Gd0.18Ca0.02O2−δ composite catalyst. J. Electrochem. Soc. 161, H350–H354 (2014).
Amar, I. A., Lan, R., Petit, C. T. G. & Tao, S. Electrochemical synthesis of ammonia based on Co3Mo3N catalyst and LiAlO2–(Li,Na,K)2CO3 composite electrolyte. Electrocatalysis 6, 286–294 (2015).
Cui, B. et al. Electrochemical synthesis of ammonia directly from N2 and water over iron-based catalysts supported on activated carbon. Green Chem. 19, 298–304 (2017).
Van Tamelen, E. E. & Akermark, B. Electrolytic reduction of molecular nitrogen. J. Am. Chem. Soc. 90, 4492–4493 (1968).
Becker, J. Y., Avraham (Tsarfaty), S. & Posin, B. Nitrogen fixation: Electrochemical reduction of titanium compounds in the presence of catechol and N2 in MeOH or THF. J. Electroanal. Chem. Interfacial Electrochem. 230, 143–153 (1987).
Köleli, F. & Röpke, T. Electrochemical hydrogenation of dinitrogen to ammonia on a polyaniline electrode. Appl. Catal. B 62, 306–310 (2006).
Kim, K. et al. Communication—electrochemical reduction of nitrogen to ammonia in 2-propanol under ambient temperature and pressure. J. Electrochem. Soc. 163, F610–F612 (2016).
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).
Dong, G., Ho, W. & Wang, C. Selective photocatalytic N2 fixation dependent on g-C3N4 induced by nitrogen vacancies. J. Mater. Chem. A 3, 23435–23441 (2015).
Banerjee, A. et al. Photochemical nitrogen conversion to ammonia in ambient conditions with FeMoS-chalcogels. J. Am. Chem. Soc. 137, 2030–2034 (2015).
Li, J., Li, H., Zhan, G. & Zhang, L. Solar water splitting and nitrogen fixation with layered bismuth oxyhalides. Acc. Chem. Res. 50, 112–121 (2017).
Liu, J. et al. Nitrogenase-mimic iron-containing chalcogels for photochemical reduction of dinitrogen to ammonia. Proc. Natl Acad. Sci. USA 113, 5530–5535 (2016).
Hu, S. et al. Effect of Cu(I)–N active sites on the N2 photofixation ability over flowerlike copper-doped g-C3N4 prepared via a novel molten salt-assisted microwave process: the experimental and density functional theory simulation analysis. ACS Sustain. Chem. Eng. 5, 6863–6872 (2017).
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).
This work was supported by the Villum Foundation V-SUSTAIN grant 9455 to the Villum Center for the Science of Sustainable Fuels and Chemicals. 400 MHz and 800 MHz NMR spectra were recorded on the spectrometers of the NMR Center at the Technical University of Denmark supported by the Villum Foundation. We acknowledge the contribution of Albert Kravos in setting up the analytical methods to detect ammonia.
Nature thanks Lauren Greenlee, Mark Symes and the other anonymous reviewer(s) for their contribution to the peer review of this work.
The authors declare no competing interests.
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Extended data figures and tables
All measurements were performed three times; the top of the bars show the mean, the errors show the standard deviation. The following were tested for contamination: a, new and treated Nafion membranes; b, new Celgard membrane; c, 2 ml of 0.1 M solutions or MilliQ H2O left open overnight; d, 2 ml 0.1 M KOH, into which one person had breathed 3 l of air through a glass straw.
Spectra were acquired using a Bruker AVANCE III HD 800 MHz spectrometer equipped with a 5 mm TCI CryoProbe. Solutions contain equal concentrations of 14NH4+ and 15NH4+ from NH4Cl. a, Spectrum of a solution of 600 µl 0.1 M KOH, acidified with 0.5 M H2SO4 to a pH of 1. CH3OH (200 μM) was added as an internal reference. b, Integrated peak areas from a for both 14NH4 and 15NH4. c, Spectrum of a solution of 500 µl 0.1 M LiClO4 in THF and ethanol with a ratio of 99:1, respectively, with 2 µl 4 M HCl and 50 µl THF-d8. d, Integrated peak areas from c for both 14NH4 and 15NH4. The variation of chemical shift of the NMR peaks is due to slight differences in the pH, volume, and/or temperature of the samples. e, Magnified view of the samples in a that contain the lowest concentrations of 14NH4+ and 15NH4+. f, Spectra of samples with the same concentrations as those in a, using a Bruker AVANCE III HD 400 MHz spectrometer equipped with a 5 mm Prodigy probe.
Extended Data Fig. 3 Gas phase Fourier-transform infrared spectra of labelled and unlabelled ammonia.
Spectra were acquired on a Nicolet iS50 spectrometer fitted with a 2-m path length gas cell heated to 135 °C. The total volume of the vaporized sample was 100 μl. The ammonia concentration was 1,000 p.p.m. in H2O before vaporization.
Extended Data Fig. 4 The set-up for gas (15N2, 14N2, Ar or 10% H2 in Ar) circulation through the electrochemical cell.
a, Schematic of the set-up. b, Photograph of the set-up with the components labelled. The pump that circulates the gas through the set-up is situated behind the metal panel, and its position is outlined by the white dashed rectangle.
Spectra were acquired using a Bruker AVANCE III HD 800 MHz spectrometer equipped with a 5-mm TCI CryoProbe. No 15NH4+ was seen in the measurements.
a–e, Three sequentially repeated measurements of the concentrations of: ammonia (using the indophenol method) without cleaning the gas stream (a); ammonia (using the indophenol method) with the described cleaning procedure (b); nitrite concentration without cleaning the gas stream (c); nitrite concentration with the described cleaning procedure (d); and hydrazine without cleaning the gas stream (e).
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Andersen, S.Z., Čolić, V., Yang, S. et al. A rigorous electrochemical ammonia synthesis protocol with quantitative isotope measurements. Nature 570, 504–508 (2019). https://doi.org/10.1038/s41586-019-1260-x
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