AWE (Alkaline Water Electrolysis)

AWE is the most established technology for electrolysis with relatively low capital costs.

At the cathode side, two molecules of water reacts with electrons to form the hydrogen and hydroxyl ions ($OH^-$) .Hydroxyl ions transfer through the porous diaphragm to the anode,resulting in half molecule of oxygen (O2) and one molecule of water (H2O).

(Image Credit: S.Shiva Kumar & V.Himabindu ^2)

The following reactions take place:

Anode: $$2 OH^- --> 0.5 O_2 + H_2O + 2 e^-$$

Cathode: $$2 H_2O+ + 2 e^- --> H_2 + 20H^-$$

Full reaction : $$H_20 --> H_2 + 1/2O_2$$

The first AWE water electrolysis was introduced by Troostwijk and Diemann in 1789 ^2. AWE operates at lower temperatures such as 30-80 C with aqueous solution (KOH/NaOH) as the electrolyte. Nickel materials are used for the electrodes and asbestos were used for diaphragm. However a new approach in the alkaline electrolysis is under development of anion exchange membranes (AEM) made up of polymers with anionic conductivity instead of asbestos diaphragm ^2.

The cost of hydrogen production from AWE given by IRENA in 2017 is around 3.5 EUR/kg of H2 (via alkaline electrolyser in Denmark) ^3. Alkaline CAPEX cost is expected to decrease from EUR 750/kW (2017) to EUR 480/kW (2025) ^3 which gives a CAPEX in 2020 of 581.25 EUR/kW.

Alkaline electrolyser OPEX costs are 2 - 3 % of CAPEX excluding electricity ^4.

The lifetime of an alkaline electrolyser is around 25 years and the construction delay is around 1 year ^5. Reported electrical efficiency for alkaline electrolyzer is around 60% with a possible improve around 70% ^5.

As alkaline electrolysers are the most mature electrolysis technology, they dominate the market, especially for large-scale projects. In 2020, the global electrolysis capacity is 200 MW ^6. Assuming 8000 yearly load hours, the global production of electrolysis is around 1.6 TWh. The PEM hydrogen production is of 0.24TWh per year (see PEM documentation) and others electrolysis technologies are not yet commercialized. Then we assume that AWE world production in 2020 is 0.76 TWh.

Alkakine electrolysers is the lowest efficient electrolysis technology we assume that no investments have been made during the past years.

^1: Flexible combined production of power, heat and transport fuels from renewable energy sources,FLEXCHX, deliverable report of European Union Horizon 2020 research (2018).

^2: Hydrogen production by PEM water electrolysis - A review, S. Shiva Kumar, V. Himabindu, Materials Science for Energy Technologies (2019).

^3: Renewable power-to-hydrogen, innovation landscape brief, IRENA (2019)

^4: Techno-economic feasibility of hydrogen production via polymer membrane electrolyte electrolysis for future power-to-x systems,M. Lappalainen, Master of Science Thesis, Tampere University (2019)

^5: David, M., Ocampo-Martínez, C. and Sánchez-Peña, R., 2019. Advances in alkaline water electrolyzers: A review. Journal of Energy Storage, 23, pp.392-403.