At present, technologies that are prevalent in the market include Alkaline, Proton Exchange Membrane (PEM), Solid Oxide Electrolysis Cell (SOEC) and Anion Exchange Membrane (AEM). Some are in pre-commercial phase and some have already commercialized. Almost two-thirds of production capacity today is for alkaline electrolysers and a fifth for PEM electrolysers. IEA estimates that under Net-Zero emissions scenario, 850 GW of total electrolyser capacity needs to be deployed by 2050.
Alkaline electrolysers are a more mature technology than PEM, with a long history of deployment in the chlor-alkali industry. However, for hydrogen production, both technologies are at the same readiness level, both being commercially available. At the same time, both technologies require policy support and improvements to stay competitive. SOEC is a technology under demonstration. AEM electrolyser is in very earlier stages of development.
Alkaline electrolysis (AE) is a mature and commercial technology. However, the technology is yet to be scaled up and reach market maturity due to rapid scale up of competing sources of energy as well as sources of Hydrogen (Eg: Natural Gas/SMR Process). AE technology is characterized by lower CAPEX compared to other technologies, primarily because they do not require precious metal inputs. However, need for further purification of hydrogen for fuel cell applications and slow ramping response are some of the challenges to long term viability of AE for integration with variable renewable energy (VRE) technologies. Cost of alkaline electrolysers is estimated to range from USD 500 to 1000/KW . However, the cost is highly contingent upon the scale, with electrolysers in excess of 10 MW capacity estimated to cost below USD 500/KW.11
PEM electrolysis is a relatively newer technology, developed in 1960s in response to the operational limitations of AE. PEM electrolysers holds several advantages over AE such as use of high purity water as an electrolyte solutions obviating the need for recovery and recycling of Potassium Hydroxide solution used in AE: better operational flexibility more suitable for integration with VRE and providing balancing & ancillary frequency control support in power applications. Further, PEM electrolysers have an added advantage of producing highly compressed hydrogen (up to 100 bar as opposed 30 bar for AE), making them suitable for decentralized production and storage. However, requirement of precious metals such as platinum (estimated to be about 300 Kg/GW)1 and iridium (estimated to be about 700 KG/GW) increase CAPEX and are potential supply chain bottlenecks. The current cost of PEM electrolyser (without balance of plant cost) is around USD 1100/KW.
Solid Oxide Electrolysis Cell (SOEC) technology is still in development/pilot phase. SOEC technology has the potential to achieve lower CAPEX with scaling up due to lower material costs due to use of ceramics as the electrolyte. Further, high electrical efficiency, high operating temperature, and use of steam make SOEC an ideal candidate for combined heat and power applications as well as production of synthetic fuels. Further, the fact that SOEC may be operated in reverse mode as fuel cells make them ideal prospect for stationary applications such as balancing services, thus potentially increasing their utilisation rate as well.
Anion exchange membrane (AEM) electrolysis is the electrolysis of water that utilizes a semipermeable membrane that conducts hydroxide ions (OH−) called an anion exchange membrane. Like a proton-exchange membrane (PEM), the membrane separates the products, provides electrical insulation between electrodes, and conducts ions. Unlike PEM, AEM conducts hydroxide ions. The major advantage of AEM water electrolysis is that a high-cost noble metal catalyst is not required, low-cost transition metal catalyst can be used instead. AEM electrolysis is similar to alkaline water electrolysis, which uses a non-ion-selective separator instead of an anion-exchange membrane.
|Type of Electrolyser||AWE (Alkaline Water Electrolyser)||PEM (Proton Exchange Membrane)||SOEC (Solid Oxide Electrolyser)||AEM (Anion Exchange Membrane Electrolyser)|
|Key Technology||Microporous separator||Proton exchange membrane (PEM)||Protonic ceramic electrochemical cell||Anion exchange membrane (AEM)|
|Most common electrolyte/membrane||Na– or KOH (usually Aqueous KOH of 20–40 wt.%)||Proton conductive polymer (e.g. Nafion®) membrane||Ceramic: Solid, nonporous metal oxide (usually Y2O3- stabilized ZrO2)||Anion exchange ionomer (e.g. AS-4) + optional dilute caustic solution|
|Reactant||Water (liquid)||Water (liquid)||Water (gas)||Water (liquid)|
|Most common electrodes (cathode)||Ni & Ni-Mo alloys||Pt & Pt-Pd||Perovskite electrodes||Ni & Ni-Mo alloys|
|Most common catalyst||Pt and Ru, but also Mn and W||Pt black, Ir, Ru, Rh||ZrO2||Pt and Ru, but also Mn and W|
|Minimum load (% of design capacity)||15–40, 5 (state of the art)||0–10 ~5 (typical)||>3||10-20|
|Operating temperature (deg C)||50–80||60–200||800–1000||50–60|
|Average system efficiency (HHV) (%)||68–77||70–80||80–90.8||<=74|
|H2 purity (%)||99.5– 99.99998||99.9–99.9999||~99.99||99.99|
|Estimated stack lifetime (h)||~60,000– 100,000||~50,000– 90,000||~20,000– 90,000||~30,000|
|Estimated system lifetime (years)||20–30||20–30||10–20||<20|
|Approximate investment cost (USD/kW)||800–1,500||1,400–2,100||>2,000|
|System size range (kW)||1.8–5,300||100–1,300||1.5–200||>100|
|H2 production per stack (Nm3 /h)||<760||<400||<10|
|Technological maturity||Mature TRL 9||Commercial TRL 7-8||R&D TRL 5-7||R&D TRL 2-5|