A Technical Insight into Benefits and Drawbacks of Electrolyser Technologies for Green Hydrogen Production

Green hydrogen has emerged as a pivotal element in the transition to a sustainable energy future. Electrolyser technologies play a crucial role in producing green hydrogen by splitting water into hydrogen and oxygen using renewable electricity. Different electrolyser technologies—Alkaline Electrolysers, Proton Exchange Membrane (PEM) Electrolysers, Anion Exchange Membrane (AEM) Electrolysers, and Solid Oxide Electrolysers (SOEC)—offer various advantages and drawbacks. Understanding the strengths and weaknesses of each technology is critical for scaling up green hydrogen production.

1. Alkaline Electrolysers

Overview: Alkaline electrolysers are one of the oldest and most established technologies for hydrogen production. This technology relies on a liquid electrolyte, typically potassium hydroxide (KOH) or sodium hydroxide (NaOH), to facilitate the splitting of water molecules. The electrodes in alkaline electrolysers are typically made of inexpensive materials like nickel.

Benefits:

• Mature Technology: Alkaline electrolysers are the most mature and commercially deployed technology. This long history of use means they are well understood, reliable, and widely available.
• Lower Installed Cost: Due to their mature status, alkaline electrolysers benefit from relatively low upfront capital costs, making them attractive for large-scale installations.
• Durability: Alkaline electrolysers have a long operational lifespan, often exceeding 60,000 hours, making them highly durable and cost-effective over time.

Drawbacks:

• Low Operating Pressure: Alkaline electrolysers generally operate at low pressures, usually between 1 and 30 bar. As a result, the produced hydrogen requires additional multi-stage compression to reach higher pressures, which adds cost and energy consumption to the process.
• Long Ramp-Up Time: Alkaline electrolysers have slower response times to power fluctuations, making them less suitable for variable renewable energy sources like solar or wind power.
• Lower Energy Efficiency: Compared to other technologies like PEM and SOEC, alkaline electrolysers tend to be less energy-efficient, with energy losses during operation.

2. PEM Electrolysers

Overview: Proton Exchange Membrane (PEM) electrolysers are a newer and more advanced technology than alkaline electrolysers. PEM electrolysis uses a solid polymer electrolyte that conducts protons from the anode to the cathode, where hydrogen is produced.

Benefits:

• Higher Operating Pressure: One of the key advantages of PEM electrolysers is their ability to operate at higher pressures (up to 50–60 bar), reducing the need for post-electrolysis hydrogen compression. This reduces energy consumption and system complexity.
• Faster Response Times: PEM electrolysers offer rapid startup and shutdown times, making them more compatible with intermittent renewable energy sources such as solar or wind.
• Smaller Footprint: PEM systems are more compact and have a smaller physical footprint compared to alkaline systems. This makes them suitable for space-constrained installations like urban hydrogen refueling stations or small-scale industrial applications.

Drawbacks:

• Higher Cost: PEM electrolysers are more expensive than alkaline systems due to the use of precious metals like platinum and iridium in the catalyst layers and expensive membrane materials.
• Shorter Lifespan: PEM electrolysers tend to have shorter lifetimes, with typical operational durations of around 40,000 hours. This reduces their cost-effectiveness over the long term compared to alkaline systems.
• Membrane Sensitivity: The polymer membrane used in PEM electrolysers is sensitive to contamination and degradation, requiring high-purity water and meticulous operational control to prevent damage.

3. AEM Electrolysers

Overview: Anion Exchange Membrane (AEM) electrolysers represent an emerging and promising technology for hydrogen production. AEM electrolysis combines some of the advantages of both alkaline and PEM systems, using a solid-state membrane like PEM electrolysers but operating under alkaline conditions.

Benefits:

• Lower Costs: Unlike PEM electrolysers, AEM systems do not rely on precious metals as catalysts. This can significantly reduce the costs of materials and make AEM a more cost-effective solution for hydrogen production.
• Potential for High Efficiency: AEM electrolysers have the potential to achieve high energy efficiency comparable to or even better than PEM electrolysers, making them an attractive option for future applications.
• Simpler System Requirements: AEM electrolysers can operate with less stringent water purity requirements compared to PEM systems, reducing the need for costly water purification processes.

Drawbacks:

• Early-Stage Development: AEM electrolysers are still in the early stages of development and commercialization. As a result, their deployment is limited, and much work is required to improve system robustness and scale.
• Membrane Durability: One of the key challenges facing AEM technology is membrane durability. Current AEM membranes suffer from shorter lifetimes compared to alkaline and PEM systems, which limits their commercial viability.
• Gas Purity Issues: AEM electrolysers can have issues with gas crossover, leading to lower hydrogen purity. This issue must be addressed through further research and development.

4. SOEC Electrolysers

Overview: Solid Oxide Electrolysis Cells (SOECs) operate at high temperatures (typically around 700–1000°C) to split water into hydrogen and oxygen. This high-temperature operation allows SOECs to achieve very high electrical efficiencies.

Benefits:

• Highest Electrical Efficiency: SOECs offer the highest efficiency among all electrolyser technologies, with electrical efficiencies reaching 85–90%. This makes SOECs potentially the most energy-efficient method for producing green hydrogen.
• Potential for Co-Electrolysis: SOEC technology can also be used to co-electrolyze water and carbon dioxide, enabling the production of syngas, which can be used as a feedstock for synthetic fuels and chemicals.
• High Integration Potential: The high operating temperatures of SOECs make them well-suited for integration with industrial processes that produce excess heat, such as steelmaking or chemical manufacturing.

Drawbacks:

• Immature Technology: SOECs are still in the early stages of commercialization and development. While they hold great potential, the technology has not yet been proven at scale, and there are significant challenges related to system durability and long-term reliability.
• Material Degradation: The high operating temperatures of SOECs lead to faster degradation of materials, particularly the electrolyte and electrodes. This reduces the operational lifespan of the system and increases maintenance costs.
• High Capital Cost: Due to their current developmental status, SOEC systems are expensive to produce and install. Further research and innovation are needed to bring costs down to commercially competitive levels.

5. General Considerations for Electrolyser Selection

When selecting an electrolyser technology for green hydrogen production, several key factors must be taken into account, including the cost of electricity, electrolyser cost, flexibility, durability, and system design.

• Cost of Renewable Electricity: The cost of electricity is the dominant factor in the economics of green hydrogen production. All electrolyser technologies benefit from cheap and abundant renewable energy sources.
• Electrolyser Cost: While renewable electricity cost is crucial, electrolyser costs must also come down through economies of scale and technological innovation. AEM and SOEC electrolysers show promise for future cost reductions.
• Flexibility: Electrolyser flexibility is important for integrating with variable renewable energy sources like solar and wind. PEM electrolysers are currently the most flexible, while alkaline systems are less adaptable to fluctuating power supply.
• Durability and Lifetime: Durability is key to ensuring long-term economic viability. Alkaline electrolysers offer the longest lifetimes, while PEM and AEM systems need further development to match this durability.
• System Design and Integration: The overall system design, including the balance of plant components, plays a major role in the efficiency and cost of hydrogen production. Proper integration with renewable energy sources and industrial processes is essential for optimizing electrolyser performance.

6. Research and Development Needs

The future of green hydrogen production depends on continued research and development in electrolyser technologies. Each technology—whether mature like alkaline or still emerging like AEM and SOEC—requires further innovation to improve performance, reduce costs, and overcome technical challenges. Focus areas for R&D include:

• Materials Innovation: Development of new catalyst materials, membranes, and electrolytes can improve efficiency and reduce costs across all electrolyser types.
• Manufacturing Processes: Scaling up production and improving manufacturing techniques will help lower the cost of electrolyser systems, particularly for PEM and SOEC technologies.
• System Integration: Continued efforts to integrate electrolysers with renewable energy sources and industrial processes are crucial for reducing overall system costs and improving performance.

Conclusion

The transition to green hydrogen as a key energy carrier requires the deployment of efficient, cost-effective electrolyser technologies. Each electrolyser type—alkaline, PEM, AEM, and SOEC—has its own advantages and limitations, making them suited for different applications. As the hydrogen economy grows, ongoing research, technological advancements, and system integration will be vital in overcoming current challenges and driving the adoption of green hydrogen worldwide.