Anion exchange membrane electrolysis is an electrolysis technology that combines the compact design of PEM with the low cost of alkaline electrolysis. It is very recent and still in an experimental stage, but is already mobilizing several projects, such as Enapter and Gen-Hy.
What is anion exchange membrane electrolysis?
As with other water electrolysis processes, the aim here is to produce hydrogen from water. However, the process is a bit special.
The heart of the anion exchange membrane electrolyser is composed of two electrodes between which a membrane is located. On the anode side (where the water comes from) comes a 1% solution of potash (KOH, potassium hydroxide), which will soak the membrane. On contact with the cathode, the water in the solution will react with electricity and release hydrogen and OH- ions.
Hydrogen Evolution Reaction (HER) : 4H2O + 4e- → 4OH- + 2H2.
The gas produced contains 99.9% dihydrogen. Back through the membrane, the ions produced will react with the anode and produce water, oxygen and electrons.
Oxygen evolution reaction (OER): 4OH- → 2H2O + O2 + 4e-
A performance of 74% could be recorded in the laboratory, at 1000 mA cm -2 , 1.9 V and 60 °C. (1)
The advantages of anion exchange membrane electrolysis
The proton exchange membrane is supposed to have the benefits of the two main current technologies: alkaline electrolysis and proton exchange membrane electrolysis:
A non-acidic environment, which allows the use of base metals for the electrodes A very compact design
The membrane itself, a polymer with quaternary alluminium salts, is reportedly not very expensive and reacts little with CO2. Thus, it is hoped that it will work just as well at a lower cost.
According to an article published in the journal Scientific Reports, this technology is currently less efficient than conventional technologies.
Enapter claims to be able to produce 1Nm3 of 99.9% pure hydrogen at 35bars from 4.8kWh.
To go further:
- Vincent, I., Lee, EC. & Kim, HM. Étude complète de l’impédance de l’électrolyse à membrane échangeuse d’anions à faible coût pour la production d’hydrogène à grande échelle. Sci Rep 11 , 293 (2021). https://doi.org/10.1038/s41598-020-80683-6
- Leng, Y. et al. Solid-state water electrolysis with an alkaline membrane. J. Am. Chem. Soc. 134, 9054–9057 (2012).
- Parrondo, J. et al. Degradation of anion exchange membranes used for hydrogen production by ultrapure water electrolysis. RSC Adv. 4, 9875 (2014).
- Vincent, I., Kruger, A. & Bessarabov, D. Development of efficient membrane electrode assembly for low cost hydrogen production by anion exchange membrane electrolysis. Int. J. Hydrogen Energy 42, 10752–10761 (2017).
- Miller, H. A. et al. Green hydrogen from anion exchange membrane water electrolysis: A review of recent developments in critical materials and operating conditions. Sustain. Energy Fuels 4, 2114–2133 (2020).
- Vincent, I. & Bessarabov, D. Low cost hydrogen production by anion exchange membrane electrolysis: A review. Renew. Sustain. Energy Rev. 81, 1690–1704 (2018).