Ammonia from nitrogen and water

Ammonia is produced from dinitrogen and water at near-ambient temperature and pressure, in amounts that cannot be explained by contamination, without plating a metal to activate N₂ and without consuming a stoichiometric reductant.

Ammonia is the feedstock for fertilizer and a candidate hydrogen carrier. The industrial Haber–Bosch reaction, as Izelaar and co-workers state it, runs at 300–500 °C and 200–300 bar, and most of its emissions come from making hydrogen by reforming methane. A route that uses N₂, water, and electricity or H₂ near room temperature would let ammonia follow renewable power. The laboratory version of that claim has been crowded with false positives, so the grade is a rate, an efficiency, and an isotope balance together.

Izelaar and co-workers state that reported aqueous electrochemical rates were still extremely low, 0.003–14 nmol of ammonia per square centimetre per second. That range is their summary of the literature, not a champion catalyst they certified. At three electrons per ammonia and 96,485 C mol⁻¹, 14 nmol cm⁻² s⁻¹ is 4.05 mA cm⁻² if every electron made ammonia. Andersen and co-workers found that aqueous pure-metal electrodes produced no ammonia under a quantitative ¹⁵N₂ protocol. Lithium electrodeposition in tetrahydrofuran did, which is why metal plating is excluded here rather than ignored.

Two later metal-plating results sit outside this problem and are the reason the exclusion is explicit. Li, Zhou, Fu, and co-workers ran a lithium-mediated flow electrolyser for 300 h at 1 bar and room temperature, with a 25 cm² electrode, a current-to-ammonia efficiency of 64 ± 1%, and about 98% of the ammonia in the gas phase. The abstract couples nitrogen reduction to hydrogen oxidation in a chain-ether electrolyte. It is not water as the only proton source, and it is lithium-mediated. Goyal and co-workers report a magnesium-mediated cell at an ammonia faradaic efficiency of 25.28 ± 3.80% and a total current density of −45 mA cm⁻², which they convert to an ammonia partial current density of −11.30 ± 1.77 mA cm⁻², under 6 bar of N₂, with ethanol as the proton donor. That partial current is above this problem’s rate mark and still fails the pressure, the efficiency, the proton source, and the plating rule.

The reaction uses N₂ at a partial pressure of at most 1 bar and a temperature of at most 40 °C. The only proton source is water. The reductant is electrons or H₂. The geometric area is the projected area of the electrode in contact with the electrolyte, or, for a thermal bed, the internal cross section of the bed. It is written down before the run. It is not an electrochemical surface area.

The attempt reports a continuous run of at least 4 hours. Ammonia is quantified by two methods that agree within 20% relative: proton NMR of the ammonium salt in a non-exchanging solvent, and a colorimetric or ion-chromatographic assay. The figure of merit uses the average of the two assays after the blank subtraction below.

For an electrochemical cell the partial current density is 3 × 96,485 C mol⁻¹ × (blank-subtracted moles of ammonia) / (duration × geometric area). The faradaic efficiency is that ammonia, times three electrons, divided by the charge passed during the same 4 hours. Charge is not blank-subtracted. For a thermal reactor fed with H₂, the molar rate uses the same blank-subtracted moles, and the electron efficiency is 3 × moles of ammonia / (2 × moles of H₂ consumed). H₂ consumption is inlet flow minus outlet flow, both measured. If the consumed H₂ is less than 10% of the H₂ fed, the run is invalid, because the difference is then too small to support a 50% efficiency.

A catalytic claim requires that the blank-subtracted moles of ammonia be at least ten times the moles of transition metal in the catalyst charge. Plated lithium, sodium, magnesium, calcium, aluminium, or zinc does not count as that catalyst.

The blank-subtracted partial current density to ammonia is at least 10 mA per square centimetre of geometric area, or the thermal molar rate is at least 34.6 nmol cm⁻² s⁻¹ on the geometric area defined above, and the faradaic or electron efficiency is at least 50%, both averaged over the 4-hour run. The isotope controls pass, and the two assays agree within 20% relative.

These current, rate, efficiency, temperature, pressure, assay-agreement, and turnover figures are pass marks defined here. Ten milliamperes per square centimetre is 10 × 10⁻³ / (3 × 96,485) = 34.6 nmol cm⁻² s⁻¹, above the top of the aqueous range Izelaar and co-workers summarized. Fifty percent efficiency is a pass mark, not a cited record. The magnesium partial current of about 11 mA cm⁻² does not clear this threshold: it was measured at 6 bar with ethanol as the proton donor.

The controls follow the quantitative isotope protocol of Andersen and co-workers and the cautions of Choi and co-workers.

• The N₂ and argon feeds are scrubbed, and the residual ammonia and nitrogen oxides in the feed are measured before the run. They must be too small to account for the ammonia reported.
• An argon electrolysis, and a dinitrogen experiment at open circuit, each of the same duration, produce less than 10% of the ammonia measured in the N₂ run. The ammonia subtracted from the N₂ run is the ammonia found in the argon electrolysis, not the sum of the two blanks.
• A ¹⁵N₂ run, with the labeled gas itself assayed for labeled ammonia and nitrogen oxides before use, produces ¹⁵N-ammonia in an amount that agrees within 20% relative with the ¹⁴N₂ run under the same conditions. Qualitative appearance of a doublet, without that quantitative match, does not count.
• The ¹⁵N fraction in the ammonia matches the ¹⁵N fraction of the feed gas within the uncertainty of the NMR integral.
• Two further N₂ runs reproduce the rate within 20% relative.

Commercial ¹⁵N₂ can carry labeled ammonia. De Ras, Hollevoet, Martens, and co-workers measured about 73 ppm ¹⁵NH₃ in a commercial 98 atom% cylinder, and showed that the impurity alone can exceed typical reported aqueous yields. The feed assay is not optional.

Heterogeneous or molecular catalysts, including enzymes, provided the metal-turnover rule is met and water is the proton source. H₂ as the reductant in a thermal catalytic reactor inside the same temperature and pressure limits. A proton-exchange membrane whose only function is to separate the electrodes, if the proton inventory comes from water.

Lithium, sodium, magnesium, calcium, aluminium, or zinc metal as a stoichiometric reductant, and any cycle in which one of those metals is plated and then converts N₂ to a nitride, whether or not the metal is later regenerated. A proton source other than water, including ethanol. Nitrogen oxides, nitrate, or nitrite as the feedstock. A run shorter than 4 hours. A claim based on a single assay. Pressure above 1 bar of N₂, or temperature above 40 °C. Reporting a rate per electrochemical surface area in place of the geometric area.

All of the controls pass, the metal turnover is at least 10, the faradaic or electron efficiency is at least 20%, and the partial current density is at least 1 mA cm⁻², or the thermal rate is at least 3.46 nmol cm⁻² s⁻¹, averaged over 4 hours. Twenty percent, 1 mA cm⁻², and 3.46 nmol cm⁻² s⁻¹ are pass marks for this lesser bar. They show that the ammonia came from N₂ and that the process is catalytic. They are not a solution. One milliampere per square centimetre is still below the top of the range Izelaar and co-workers summarized, so this lesser bar is a cleanliness-and-catalysis bar, not a claim to have beaten that summary.

Aqueous pure-metal electrodes produced no ammonia under the quantitative ¹⁵N₂ protocol, while lithium electrodeposition in tetrahydrofuran did: Andersen and co-workers, Nature, 2019, 570, 504–508, doi:10.1038/s41586-019-1260-x (opens in a new tab). The same paper requires quantitative agreement between the ¹⁴N₂ and ¹⁵N₂ experiments. Choi and co-workers describe why a qualitative isotope spectrum is not enough: Nature Communications, 2020, doi:10.1038/s41467-020-19130-z (opens in a new tab). Izelaar and co-workers state the aqueous rate range and the Haber–Bosch conditions of 300–500 °C and 200–300 bar: ACS Energy Letters, 2023, 8, 3614–3620, doi:10.1021/acsenergylett.3c01130 (opens in a new tab). Labeled ammonia at about 73 ppm in commercial ¹⁵N₂: De Ras, Hollevoet, Martens, and co-workers, Green Chemistry, 2024, 26, 1302–1305, doi:10.1039/D3GC04272C (opens in a new tab). Lithium-mediated continuous operation at 64 ± 1% for 300 h: Li, Zhou, Fu, and co-workers, Nature, 2024, doi:10.1038/s41586-024-07276-5 (opens in a new tab). Magnesium-mediated partial current and conditions: Goyal, Gande, Bhawnani, Hamlyn, Farghaly, and Singh, Advanced Science, 2025, 12, 2504882, doi:10.1002/advs.202504882 (opens in a new tab). The 10 mA cm⁻², 34.6 nmol cm⁻² s⁻¹, 50%, 20% assay agreement, 4-hour, 40 °C, and 1 bar requirements are pass marks defined here. The conversion of 14 nmol cm⁻² s⁻¹ to 4.05 mA cm⁻², and of 10 mA cm⁻² to 34.6 nmol cm⁻² s⁻¹, is arithmetic on the Faraday constant, not a new measurement.