Electrolyzer

Electrolyzer: key component in the renewable energy system

An electrolyser breaks down water into its basic components, hydrogen (H₂) and oxygen (O₂), through the process of electrolysis.

Electrolysis  

Water electrolysis, the electrochemical splitting of water into hydrogen and oxygen using electricity, currently only accounts for around 0.1% of global hydrogen production. However, with announced and planned projects, global electrolyzer capacity could reach between 175 and 420 GW by 2030.

Types of electrolyzers

Types of Electrolyzers

Electrolyzers play a crucial role in producing green hydrogen, especially when powered by renewable energy sources like wind or solar. There are several types of electrolyzers, including:

1. Alkaline Electrolyzer – Uses an alkaline solution as the electrolyte.

2. Proton Exchange Membrane (PEM) Electrolyzer – Utilizes a solid proton exchange membrane to transport protons (H+) from the anode to the cathode.

3. Solid Oxide Electrolyzer (SOEC) – Operates at high temperatures using a solid ceramic as the electrolyte.

These technologies are essential to advancing hydrogen as a clean energy carrier.

Market Development

As of the end of 2022, 60% of installed electrolyzer capacity consisted of alkaline electrolyzers, followed by proton exchange membrane (PEM) electrolyzers, which accounted for around 30%. This distribution is expected to shift over the coming years, with PEM electrolyzers likely gaining market share relative to alkaline electrolyzers. This forecast is based on numerous project announcements, although many future projects have not yet decided or disclosed which electrolyzer technology they will use. Solid oxide electrolyzers (SOECs) currently play a minor role, with less than 1% of installed capacity. In terms of geographical distribution, by the end of 2022, one-third of global installed capacity was in China, another third in Europe, and the United States and Canada together accounted for around 10%.

Alkaline Electrolysis (AEL)

Alkaline electrolysis (AEL) is one of the longest-established methods for hydrogen production and plays a vital role in the energy transition. As a key technology for green hydrogen generation, it offers numerous advantages, particularly due to its proven technology and durability in large-scale industrial applications.

What is Alkaline Electrolysis?

Alkaline electrolysis is a process that splits water into hydrogen and oxygen. In this process, an electric current is passed through an aqueous solution of water and a basic electrolyte, such as potassium hydroxide (KOH) or sodium hydroxide (NaOH). AEL has proven robust and efficient, having been used in industry for decades. It offers a relatively simple design, long lifespan, and can be operated at large scales, making it particularly suitable for industrial-scale hydrogen production.

How Alkaline Electrolysis Works

The electrolysis process involves two primary reactions: oxidation at the anode and reduction at the cathode.

1. Anodic reaction (water oxidation): At the positively charged anode, hydroxide ions (OH−) from the electrolyte are oxidized, releasing oxygen gas, water, and electrons. The reaction is as follows:

4OH⁻→O₂+2H₂O+4e− 

1. Cathodic reaction (water reduction): At the negatively charged cathode, water molecules are reduced by the incoming electrons, producing hydrogen gas and regenerating hydroxide ions that return to the electrolyte: 

4H₂O+4e⁻→2H₂+4OH⁻

Advantages of Alkaline Electrolysis

Alkaline electrolysis offers several advantages that make it one of the most widely used technologies for hydrogen production:

• High Reliability and Durability: AEL technology is particularly durable and reliable due to its robust design and proven materials. AEL electrolyzers can operate continuously over long periods with minimal performance loss.
• Cost Efficiency: The cost of AEL electrolyzers is relatively low compared to other electrolysis technologies, such as PEM electrolysis. Large-scale production facilities benefit from AEL's economic efficiency.
• Industrial Scale Applications: AEL systems can produce large quantities of hydrogen, making them attractive for industrial applications such as steel production, the chemical industry, and other energy-intensive sectors.
• Proven Technology: AEL is a well-tested technology with a long history and a track record of successful large-scale industrial use, making it a reliable choice for hydrogen generation.

Challenges of Alkaline Electrolysis

Despite its numerous benefits, alkaline electrolysis faces certain challenges that necessitate further development and optimization:

• Lower Efficiency Compared to PEM: Compared to proton exchange membrane electrolysis (PEM), AEL has slightly lower energy efficiency due to higher electrical resistance and slower electrochemical reactions in the alkaline environment.
• Greater System Complexity: AEL requires additional components for electrolyte management due to the use of liquid electrolytes, increasing system complexity and maintenance requirements.
• Limited Flexibility with Renewable Energy: AEL is slower to respond to fluctuating energy inputs, as seen with renewable energy sources like solar and wind. This limits its integration into hybrid energy systems, which need quick adaptation to varying power sources.

Research and Development: Optimizing AEL Technology

In recent years, research has focused intensively on improving the efficiency and performance of alkaline electrolysis. Key areas of research include innovative materials and new design approaches:

1. Improved Electrode Materials: New electrode materials can increase reaction rates at the electrodes, improving the overall performance of AEL. Nanostructured materials and advanced catalysts offer promising approaches for enhancing AEL efficiency.
2. Membrane Development: Researchers are working to optimize membranes used in AEL systems, aiming to improve ion conductivity and reduce electrical resistance, which could boost system performance.
3. System Integration: Another research focus is integrating AEL with hybrid energy systems powered by renewable sources. Developing smart control systems and adapting AEL to variable energy inputs could further increase the efficiency of hydrogen production.

Applications of Alkaline Electrolysis

The flexibility and robustness of alkaline electrolysis make it suitable for a variety of applications:

• Industrial Hydrogen Production: Due to its capacity for high hydrogen output, AEL is widely used in steel production, the chemical industry, and other energy-intensive industries.
• Green Hydrogen: In combination with renewable energy, AEL can produce green hydrogen, which is used in sectors such as mobility, energy storage, and industrial processes.
• Energy Storage: Hydrogen produced by AEL can serve as energy storage in hybrid energy systems, storing excess energy generated by renewable sources for later use.

Future Outlook for Alkaline Electrolysis

Alkaline electrolysis has established itself as one of the most important technologies for hydrogen production, especially for large-scale industrial applications. With ongoing research and development, AEL's efficiency is expected to improve, and costs are expected to decrease.

In particular, the combination of AEL with renewable energy offers great potential for producing green hydrogen on a large scale, contributing significantly to the decarbonization of the industrial and energy sectors. Advances in material science and system integration will be crucial in the coming years for the continued adoption of AEL technology.

PEM-Electrolysis

What is PEM Electrolysis?

PEM (Proton Exchange Membrane) electrolysis has emerged as a promising technology for efficient and sustainable hydrogen production. As renewable energy gains importance and global efforts to reduce carbon emissions intensify, PEM electrolysis is increasingly seen as a key technology for producing green hydrogen. PEM electrolysis is a hydrogen production process where water (H₂O) is split into hydrogen (H₂) and oxygen (O₂) using electrical energy. A proton exchange membrane (PEM) is used as the electrolyte. This membrane is permeable to protons but impermeable to electrons, allowing for efficient separation of hydrogen and oxygen.

How PEM Electrolysis Works

PEM electrolysis is based on an electrochemical process divided into two main reactions:

1. Anodic reaction (water oxidation): At the anode, the positively charged electrode, water is oxidized and decomposed into oxygen, protons, and electrons. The reaction equation is:
2. Cathodic reaction (water reduction): At the cathode, the negatively charged electrode, protons (H⁺) are conducted across the PEM membrane and reduced with electrons flowing through the external circuit to form hydrogen: 

2H_2​O→O₂​+4H⁺+4e⁻

4H⁺+4e^-→2H₂​

The hydrogen produced in this process is then collected and can be used in various applications, such as in mobility, industry, or for energy storage.

Advantages of PEM Electrolysis

Compared to other electrolysis technologies like alkaline electrolysis, PEM electrolysis offers several advantages:

• High Efficiency: The proton exchange membrane enables high efficiency in hydrogen production.
• Quick Response Times: PEM technology responds very quickly to fluctuations in electricity supply, making it ideal for use with renewable energy sources like wind and solar.
• Compact Design: PEM electrolyzers are more compact and require less space than other technologies, making integration into existing systems easier.
• High Purity of Hydrogen: The hydrogen produced is of very high purity, which is particularly important for specific industrial applications.

Challenges of PEM Electrolysis

PEM electrolysis faces several challenges, especially as it scales up to meet the demands of green hydrogen production:

• Catalysts: PEM electrolyzers rely on catalysts, typically made from platinum group metals (PGMs) such as platinum and iridium. These materials are not only expensive but also scarce, which raises both the capital cost and limits large-scale deployment.
• Electrolyzer Stack: The stack, which contains multiple cells, requires costly components that can withstand acidic environments and high currents.
• Catalyst and membrane degradation: PEM electrolyzers operate in highly corrosive acidic environments, which can degrade catalysts over time, especially on the anode.  Also, the proton-exchange membrane can degrade under high voltage and fluctuating load conditions, impacting efficiency and system lifespan.
• Water purity requirements: PEM electrolyzers require highly purified water, as impurities, such as ions or particulates, can accumulate on the membrane or poison the catalysts, reducing efficiency and lifespan. Additional purification steps or systems add to the operational complexity and cost. 

Research and Development: Advances in PEM Electrolysis

Research and Development (R&D) in PEM electrolysis is focused on overcoming existing technical and economic challenges, as well as improving efficiency, durability, and scalability for hydrogen production. Here are key R&D questions that scientists and engineers are exploring:

• Reducing PGM loading in catalysts: Research aims to develop alternative catalysts that are less costly and more abundant, like non-PGM or reduced-PGM catalysts, while maintaining or even improving the efficiency and stability.
• Membranes with enhanced proton conductivity and durability: New membrane materials or composite designs allowing high proton conductivity and resist degradation.
• Use of low-cost materials in PEM electrolyzer construction: Beyond catalysts, reducing costs associated with other components like bipolar plates, and end plates, making PEM electrolysis more economically viable.
• System design and integration: PEM electrolyzer adaptation for dynamic load operation with renewable energy sources and integration with storage and fuel cell technologies.
  
   

Applications of PEM Electrolysis

The flexibility and efficiency of PEM electrolysis make it ideal for a wide range of applications:

• Green Hydrogen: Combined with renewable energy, PEM electrolysis can produce green hydrogen, a zero-emission energy carrier.
• Hydrogen Storage: The energy generated by PEM electrolysis can be stored as hydrogen and later converted back to electricity, balancing fluctuations in renewable energy supply.
• Industrial Applications: Hydrogen is required in numerous industrial processes, such as in the chemical industry and steel production. PEM electrolysis provides a sustainable method to meet this demand.

High-Temperature Electrolysis: Efficient Hydrogen Production through Thermochemical Processes

High-temperature electrolysis (HTEL) represents a promising technology for hydrogen production. Unlike other electrolysis methods, high-temperature electrolysis utilizes elevated temperatures to reduce the energy required for water splitting and to enhance process efficiency. Particularly when combined with renewable energy sources or industrial waste heat, high-temperature electrolysis has significant potential to make hydrogen production more sustainable and cost-effective.

What is High-Temperature Electrolysis?

 

High-temperature electrolysis is a hydrogen production process in which water (H₂O) is split into hydrogen (H₂) and oxygen (O₂) at temperatures between 700 and 1000 °C. By supplying thermal energy, the energy demand for the electrochemical process is reduced, enabling a higher efficiency than that of other electrolysis methods, such as alkaline or PEM electrolysis.

How High-Temperature Electrolysis Works

This process involves two reactions:

1. Cathodic reaction (water reduction): At the cathode (negatively charge electrode), steam is reduced to produce hydrogen gas and oxygen ions. The reaction is:

H₂O(g)+2e⁻→H₂+O₂⁻

1. Anodic reaction (water oxidation): At the anode (positively charged electrode), the oxygen ions that have migrated through the electrolyte combine and release electrons to produce oxygen gas:

2O₂⁻→O₂+4e⁻

 

Advantages of High-Temperature Electrolysis

Compared to other electrolysis methods, high-temperature electrolysis offers a range of advantages, making it especially appealing for industrial applications and large-scale hydrogen production:

• Higher Efficiency: By utilizing thermal energy, HTEL achieves a significantly higher efficiency than other methods. This leads to more efficient use of energy sources, especially when waste heat from industrial processes is used.

• Reduced Electricity Consumption: As a substantial portion of the energy for water splitting is provided as heat, the electrical energy consumption in high-temperature electrolysis is lower than in conventional methods, resulting in lower operating costs. 

• Potential for Industrial Integration: HTEL can be effectively integrated into industrial processes that generate large amounts of waste heat, such as steel plants, chemical facilities, or power plants. Using this waste heat for hydrogen production enhances the overall energy efficiency of these industries.

• Use of Renewable Energy: When combined with renewable energy sources like solar thermal or geothermal, HTEL is an emission-free hydrogen production technology.

Challenges of High-Temperature Electrolysis

Despite its many advantages, high-temperature electrolysis faces several technical and economic challenges:

• High Material Requirements: The extreme temperatures required place high demands on the materials used. In particular, the electrodes and ceramic membranes acting as electrolytes must be thermally stable and corrosion-resistant to ensure long-term operation.

• Complex System Design: Integrating thermal and electrochemical processes requires complex system design. Efficient use of thermal energy and cooling of the electrolysis cells present technological challenges that complicate the development and implementation of HTEL systems.

• Scalability and Cost: Although high-temperature electrolysis offers great potential for large-scale hydrogen production, production and operating costs remain relatively high due to the complex technology. Further technological advancements and cost reductions are needed to enable widespread adoption.

Research and Development: Advances in High-Temperature Electrolysis

Research in HTEL focuses primarily on improving the materials used and optimizing system integration. The most promising research approaches include:

1. Material Development: Developing new, thermally stable, and corrosion-resistant materials for electrodes and electrolytes is a central research area. 

2. System Integration: Efficient use of thermal energy sources, such as coupling high-temperature electrolysis with industrial waste heat or renewable energy sources, is another research focus. The goal is to reduce system complexity and maximize efficiency.

3. Optimization of Operating Conditions: Through simulation and optimization of operating conditions such as temperature, pressure, and current density, the efficiency of high-temperature electrolysis can be further enhanced. This helps to lower operating costs and make the technology more economically attractive.