Decarbonisation Technology August 2025 Issue

+ – AEC

+ – AEM

+ – PEM

+ – SOE

Notes: – In the AEC, AEM and PEM, lye or water ow from the electrolyser cell with the oxygen and/or hydrogen gases. These liquids are mixed and recirculated to the electrolyser. – Air is used to purge the SOE anode to avoid oxygen accumulation which may present a hazard at the high operating temperature. – Bipolar plates made of stainless steel (titanium for PEM) are used to stack adjacent cells in each electrolyser type.

H (plus CO)

Air plus O

HO as water

Air

HO as steam (plus CO)

Alkaline Electrolysis Cell AEC

Anion Exchange Membrane / Alkaline Electrolyte Membrane AEM

Polymer Electrolyte Membrane / Proton Exchange Membrane PEM/PEMEC

Solid Oxide Electrolysis Cell SOE/SOEC

Electrode material

– Cathode: Ni, Co or Fe – Anode: Ni

– Cathode: Ni/Ni alloys – Anode: Fe, Ni, Co oxides

– Cathode: Pt/Pd – Anode: IrO/RuO

– Cathode: Ni – Anode: La/Sr/MnO (LSM) or La/Sr/Co/FeO (LSCF) Zirconium Oxide with ~8% Yttrium Oxide Up to 0.5 A/cm Hydrogen (or syngas if fed with steam and CO) ~25% heat from steam, ~75% electrical power

Lye: 25-30% Potassium Hydroxide solution in water

Electrolyte

Anion Exchange ionomer (e.g. AS-4)

Fluoropolymer ionomer (e.g. Naon, a DuPont brand)

100% electrical power

Energy source

100% electrical power

Up to 0.5 A/cm

Current density Hydrogen or syngas product

0.2–1 A/cm Hydrogen

Up to 3 A/cm Hydrogen

Hydrogen

Gas outlet pressure

Up to 40 bar

Up to 35 bar H, 1 bar O

Up to 40 bar

Close to atmospheric

~80 ˚C

~60 ˚C

~750 to 850 ˚C

Cell temperature

Figure 7 Electrolysers: AEC, AEM, PEM, and SOE for hydrogen (and syngas) production

Will these membrane-free electrolysers and their innovators be sustainable? Will this be the first category of electrolysers to fall by the wayside? Innovation is not about taking unnecessary risk. Safety must be prioritised as innovations are screened through to higher maturity levels, where the investment requirements will grow, and the stakes will escalate in all dimensions. Compounding incremental innovations There is no single silver bullet behind Electric Hydrogen’s ultra-high current-density PEM stack. Its innovation is breaking the PEM paradigm and challenging the reputation of PEM as an expensive electrolyser technology choice (see Figure 6 ). This breakthrough involved integrating a number of smart, synergistic innovations at component level to make the stack and associated system more cost-effective. But its magic was to look at the components and build-up.

Similar things can be said about Fortescue Zero’s rectangular pressurised alkaline stack, which has not yet been commercialised and may, unfortunately, never see the light of day. This broke the trend for this class of electrolyser, which historically used round stacks. As with the electric hydrogen case, the high current density of Fortescue Zero’s stack (which led to its small size) was achieved through cumulative component-level innovations. De Nora’s new Dragonfly pressurised alkaline electrolyser also has a rectangular stack. A key innovation is its use of in-cell cooling of the bipolar plate component. This decouples thermal management through lye cooling from lye recirculation for electrochemical reasons. This, in turn, reduces the lye recirculation rate, which results in an associated reduction in the size, cost, and parasitic power draw of BOP equipment. While these three players are all working on compelling innovations, there is no guarantee