Water electrolysis for hydrogen production is currently progressing and several major electrolysis technologies have been developed and optimised for practical applications. They mainly include alkaline electrolytic water (ALK), proton exchange membrane electrolytic water (PEM), high-temperature solid oxide electrolytic water (SOEC) and anion exchange membrane electrolytic water (AEM). Each of these technologies has its own advantages and disadvantages, as well as different development status:
- Alkaline electrolytic water (ALK)
Technology maturity: Alkaline electrolytic water technology is relatively mature and has been widely used for industrial hydrogen production.
Efficiency: The efficiency is low, especially at high current density. Oxygen will diffuse to the cathode, reducing the electrolysis efficiency and posing a safety hazard.
Cost: Due to the use of liquid alkaline electrolyte (e.g. KOH or NaOH), the cost of this technology is relatively low, and it is the most cost-advantageous way of hydrogen production at present.
Disadvantages: It is difficult to achieve high current density and requires high corrosion resistance of the equipment.
- Proton exchange membrane water electrolysis (PEM)
Technical features: PEM uses a solid polymer membrane as the electrolyte and pure water as the raw material, with high energy density, high purity of hydrogen production, and adapts to the dynamic load input of renewable energy.
Efficiency: Higher efficiency and higher current density, low tank pressure and high electrolysis efficiency.
Application advantages: Compact, high hydrogen purity, particularly suitable for distributed hydrogen production applications.
Disadvantages: High cost, especially the use of proton exchange membranes and precious metal catalysts (platinum, iridium, etc.) makes PEM electrolysers expensive to manufacture.
Prospects: With the improvement of technology, the precious metal catalyst is gradually reduced, which is expected to reduce the overall cost.
- High-temperature solid oxide electrolytic water (SOEC)
Operating temperature: SOEC operates at high temperatures (700-1000°C), which reduces electrical energy requirements by providing heat energy and makes hydrogen production more efficient.
Efficiency: Highest theoretical efficiency, up to 90%, suitable for efficient hydrogen production with industrial waste heat.
Advantages: High energy conversion efficiency, part of the electrolysis process can be used with industrial waste heat, which helps to save energy.
Disadvantages: High temperature puts high demands on materials, equipment is easy to age, durability still needs to be further optimised.
Application Scenario: It has good potential to be applied in industrial environments with waste heat resources or cogeneration.
- Anion exchange membrane water electrolysis (AEM)
Stage of development: AEM is a relatively new technology aimed at combining the advantages of alkaline electrolysis and PEM electrolysis, using non-precious metal catalysts and low-cost alkaline solid electrolytes.
Advantages: Reduced cost by eliminating the need for precious metal catalysts; compact and suitable for renewable energy power supply.
Technical Challenge: At this stage, there are problems such as low conductivity and poor stability of membrane materials, and the lifetime and alkaline resistance of membranes need to be improved.
Development potential: With the development of non-precious metal catalysts and high-performance membrane materials, it is expected to become a high-efficiency and low-cost hydrogen production technology.
Overall trend
As the proportion of renewable energy increases and carbon neutrality targets are pushed forward, hydrogen production from electrolytic water is receiving more and more attention, especially in the direction of more environmentally friendly and efficient technologies such as PEM and AEM.
Current technologies are improving in terms of cost reduction, efficiency and durability, and the development of new materials (e.g. high efficiency catalysts, low or non-precious metal catalysts) is an important breakthrough for the future.
Companies and organisations around the world are investing more, and some of the new water electrolysis technologies are expected to achieve significant cost reductions in the next few years, leading to scaled-up commercial applications.