Responses

Energy-related

Response to

Du, HL., Chatti, M., Hodgetts, R.Y. et al. Electroreduction of nitrogen at almost 100% current-to-ammonia efficiency. Nature (2022). https://doi.org/10.1038/s41586-022-05108-y https://www.nature.com/articles/s41586-022-05108-y

This could be a breakthrough for fertilizer. Electricity could convert nitrogen gas (N₂) to ammonia (NH₃) at nearly 100% efficiency - unlike any previous attempts. Lithium is a catalyst for the reaction.

Best case scenario

Farmers could produce all their ammonia fertilizer locally, powered by solar panels. The solar panels would cover less than 0.01% of their farm land:

(This estimate assumes the chemistry equation: 6 H₂O + 2 N₂ → 4 NH₃ + 3 O₂)

ammonia.production

150 million tonnes / year

Global production of ammonia

Ammonia production worldwide 2021 - Statista
www.statista.com › Chemicals & Resources › Chemical Industry
Using data from 2021

ammonia.eof

-46.190 kJ/mol

Enthalpy of formation of NH3

Molar Enthalpy of Formation of Various Substances - Ohio University
www.ohio.edu › thermo › property_tables › combustion › Enth_Formation

water.eof

-285.820 kJ/mol

Enthalpy of formation of H2O

Molar Enthalpy of Formation of Various Substances - Ohio University
www.ohio.edu › thermo › property_tables › combustion › Enth_Formation

crop_land

15000000 km^2

Agricultural land used for growing crops - global total

sunlight_average

200 watts per m^2

Solar irradiance, averaged over a whole year INCLUDING nights, cloudy days, etc.

Note: This varies by region.
https://www.newport.com/t/introduction-to-solar-radiation
http://www.ftexploring.com/solar-energy/insolation.htm

solar_panel.efficiency

17%

Efficiency of an average solar panel

Some solar panels are more efficient than this, but they tend to be expensive and contain more rare metals.

ammonia.production * (4 ammonia.eof - 6 water.eof) / ((12 hydrogen + 6 oxygen + 4 nitrogen) g/mol) % crop_land (sunlight_average solar_panel.efficiency) (calculation loading) Or, in American units: 0.0086897109 % square(feet) per acre (calculation loading)

Questions left to answer

The hydrogen atoms can come from water, I assume? Or does the system require hydrogen gas as an input?

How much lithium would be needed (per unit of ammonia output rate)?

• Some clues: the article mentions "stabilised ammonia yield rates of 150±20 nmol s-1 cm-2" but that's per unit of electrode surface area. The lithium is in the electrolyte, not the electrodes.

What would be the lifespan of the system? How would it eventually wear out? At that point, how hard would it be to re-use the lithium in new construction of the same system?

Are there any other catalysts involved? Do the electrodes have to be made of rare metals, for example? How expensive are all the reagents involved (per unit of ammonia output rate)?