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Assertion: Hydrogen can be produced with acceptable, minimal hydrogen leakage

The production of green hydrogen has an estimated emissions rate of 0.3% to 9%.1 This means that for every unit of hydrogen produced, 0.3% to 9% of that hydrogen is released into the atmosphere during the electrolysis process. Leakage occurs during two stages of the electrolysis process: venting and purging.2

Venting refers to the release of oxygen produced during electrolysis. Electrolyzers consist of a cathode and anode on either side of a membrane. Hydrogen is produced at the cathode, and oxygen at the anode, with the membrane separating the two gasses. However, some hydrogen passes through the membrane and reaches the anode, where it is released alongside the oxygen vented out of the electrolyzer. Up to 0.15% of hydrogen can leak during the venting process.3

Purging during purification is the primary source of hydrogen leakage in the electrolysis process. After production, hydrogen must be purified of impurities such as leftover water and oxygen. The purification process uses hydrogen as a purge gas to remove absorbed moisture and other contaminants, but this also releases the purged hydrogen into the atmosphere. Some studies claim up to 10% of hydrogen leaks during this process, though most estimate the leakage rate to be closer to 3-4%.4

Hydrogen emissions from venting and purging can be reduced to nearly zero if producers reoxidize the vented hydrogen. This involves redirecting the vented and purged hydrogen to a recombining catalyst, which converts it back into water.5 Policymakers can promote this strategy through regulations or financial incentives that encourage hydrogen producers to implement practices that reduce hydrogen leakage.

Hydrogen losses from all other parts of the electrolysis process are minimal and likely significantly below 1%.6

Sources:​

Footnotes​

  1. Arrigoni, A. & Bravo Diaz, L. (2022). Hydrogen emissions from a hydrogen economy and their potential global warming impact, EUR 31188 EN, Publications Office of the European Union. ↩

  2. Frazer-Nash Consultancy. (2022). Fugitive hydrogen emissions in a future hydrogen economy. UK Government. ↩

  3. Ibid. ↩

  4. Ibid. ↩

  5. Ibid. ↩

  6. Ibid. ↩