Green hydrogen is an increasingly critical component of the shift toward cleaner, renewable energy sources, and is generated through a process called electrolysis, which splits water into hydrogen and oxygen using electricity. When powered by renewable energy sources like wind, solar, or hydropower, this process produces zero emissions, making green hydrogen an environmentally friendly alternative to fossil fuels.
Here’s a Haush look at the various methods of producing green hydrogen, along with an overview of experimental approaches and technologies under development.
Overview of Electrolysis
Electrolysis is the key process for producing green hydrogen. This method splits water molecules (H₂O) into hydrogen (H₂) and oxygen (O₂) using an electric current. An electrolyser, the device that performs this function, typically consists of an anode (positive electrode) and a cathode (negative electrode), separated by a membrane or an electrolyte. When a voltage is applied, water molecules break apart: hydrogen is collected at the cathode, and oxygen is released at the anode.
Different Types of Electrolysis Methods
Each electrolyser type differs in efficiency, scalability, operational temperature, and cost. The main methods of electrolysis include:
Alkaline Electrolysis
- Invented: Alkaline electrolysis dates back to the 1920s and is one of the oldest methods of water electrolysis.
- Pioneers: Early alkaline electrolysis can be attributed to pioneering work in electrochemistry by Michael Faraday in the 19th century. Faraday’s laws of electrolysis laid the groundwork for electrolysis, leading to the development of alkaline electrolysers.
- Commercialisation: Alkaline electrolysers were first used commercially in the 1920s, with Norwegian scientists Kristian Birkeland and Sam Eyde contributing to large-scale industrial electrolysis. Companies such as Norsk Hydro further developed the technology for industrial hydrogen production in the early 20th century.
- Process: Alkaline electrolysers use a liquid alkaline solution, usually potassium hydroxide (KOH) or sodium hydroxide (NaOH), as the electrolyte. When electricity is applied, hydrogen is produced at the cathode, and oxygen is released at the anode. A diaphragm separates the two electrodes to prevent recombination.
- Pros:
- Mature and widely used, with proven reliability.
- Generally, less expensive due to well-understood technology.
- Good for large-scale hydrogen production.
- Cons:
- Operates at relatively low current densities, which can affect efficiency.
- Takes time to reach optimal production levels, making it less suitable for variable renewable energy inputs.
- Limited tolerance to partial loads (i.e., it’s less efficient when not running continuously).
- Limitations: Lower efficiency compared to more modern electrolyser types, and the need for caustic chemicals (alkaline solutions) and poses handling challenges.
- Availability: AWE systems are widely available and used in various industrial sectors across Europe and the UK. Companies like McPhy, INEOS, NEL Norsk Hydro and Thyssenkrupp are significant players in this space.
Proton Exchange Membrane (PEM) Electrolysis
- Invented: Developed in the 1960s but commercially used for hydrogen production since the early 2000s.
- Inventor: General Electric (GE) researchers Thomas Grubb and Leonard Niedrach developed the first PEM electrolysis system in the 1960s. They initially designed PEM cells for NASA’s Gemini space missions, where a compact, efficient method of generating oxygen and hydrogen was required.
- Commercialisation: GE’s advancements eventually led to PEM electrolysis being adopted in various applications. Companies like Siemens Energy and Cummins have continued to innovate and commercialize PEM technology for green hydrogen production today.
- Process: PEM electrolysers use a solid polymer electrolyte (the proton exchange membrane) instead of a liquid electrolyte. Water is fed to the anode side, where it splits into oxygen, protons, and electrons. The membrane allows protons to pass through to the cathode, where they combine with electrons to form hydrogen.
- Pros:
- Fast response time, making it ideal for intermittent renewable energy sources.
- High-purity hydrogen output.
- Compact design allows for modular scaling and efficient use in smaller spaces.
- Cons:
- High cost due to expensive membrane materials and noble metals (platinum or iridium) used as catalysts.
- Limited lifespan of PEM materials under high-pressure or high-temperature conditions.
- Limitations: The high cost of materials and components can be a barrier to large-scale adoption. Recycling and replacing expensive catalysts also add to operational costs.
- Availability: PEM electrolysis is gaining traction across the UK and Europe, with companies like ITM Power, Hyfindr,Siemens Energy, H-Tec (QuestOne MAN Group) and Cummins investing heavily in PEM technology. It is currently being deployed in various pilot projects, particularly in conjunction with renewable energy sources.
Solid Oxide Electrolysis (SOE)
- Invented: Initially developed in the early 1980s and has since been the subject of extensive research, though still largely in the experimental stage.
- Pioneers: Solid oxide electrolysis builds on advances in solid oxide fuel cells (SOFCs), with research beginning in the 1970s and 1980s. Early work in SOFCs and SOE was carried out by scientists like Zbigniew G. Łodzianaand George H. Völzke.
- Research and Development: The United States Department of Energy (DOE) and European research initiatives have driven most modern SOE research, with companies like Sunfire in Germany and FuelCell Energy in the U.S. taking on commercial SOE technology development.
- Process: SOE operates at very high temperatures (700–1000°C), which enables the electrolyser to use both electricity and heat to split water, resulting in higher overall efficiencies. The high temperatures allow for the efficient breakdown of water into hydrogen and oxygen, with the help of a solid ceramic electrolyte.
- Pros:
- High efficiency, especially when integrated with industrial processes that generate waste heat.
- Potentially lower energy requirement due to the thermal component.
- Cons:
- High operating temperatures necessitate specialised, expensive materials that can withstand thermal stress.
- Startup and shutdown cycles are slow, making it less suitable for intermittent renewable energy.
- Limitations: Still primarily in the research and pilot stages. Materials that can endure high temperatures without degrading remain a challenge, as do the high costs and engineering challenges for commercial use.
- Availability: Solid oxide electrolysis is still in the developmental stage, with fewer commercial applications compared to AWE and PEM. However, companies like Sunfire in Germany are leading efforts to bring this technology to market, particularly for industrial applications. SOE is expected to reach commercialisation around 2030, primarily for industrial applications where waste heat or high-temperature processes are readily available.
Experimental Processes and Emerging Technologies
Anion Exchange Membrane (AEM) Electrolysis
- Development Status: A relatively recent innovation, AEM electrolysis is still in the experimental and pilot stages.
- Inventor: AEM electrolysis is a more recent technology without a single inventor. However, pioneering contributions came from researchers like Dr. Thomas J. Schmidt and Dr. Peter Strasser in the early 2000s, who explored anion-conducting polymers for low-cost electrolysis.
- Development: Research institutions and companies like Enapter and Ohmium are at the forefront of AEM technology today, developing commercially viable AEM electrolysers.
- Process: AEM electrolysers use an alkaline anion-conducting membrane, combining features of both alkaline and PEM electrolysis. This membrane enables the device to operate without requiring expensive noble-metal catalysts.
- Potential Advantages:
- Lower cost than PEM electrolysis due to cheaper materials.
- Can operate at lower temperatures, reducing material strain.
- Challenges:
- Membrane stability and durability are still problematic.
- Limited power density and efficiency compared to mature technologies like PEM and SOE.
- Future Prospects: If these technical challenges are resolved, AEM electrolysis could become a cost-effective alternative, bridging the gap between alkaline and PEM technologies.
- Availability: AEM is currently in the pilot phase, with companies such as Enapter and H2Pro pushing the technology forward. It has significant potential but is still a few years away from large-scale deployment.
- Timelines: AEM technology is expected to become commercially viable between 2025 and 2030, with large-scale deployment dependent on overcoming efficiency and durability challenges.
Photocatalytic and Solar-Thermal Electrolysis
- Development Status: Still primarily in the research stage, with some pilot projects.
- Pioneers: Photocatalytic electrolysis research began with Fujishima-Honda effect in 1972, discovered by Akira Fujishima and Kenichi Honda at the University of Tokyo. They found that titanium dioxide (TiO₂) could be used to split water under UV light.
- Further Research and Development: Subsequent researchers, including Michael Grätzel of the Swiss Federal Institute of Technology, contributed to the development of efficient photocatalytic materials. Solar-thermal electrolysis has seen contributions from institutions like Sandia National Laboratories with its Sunshine to Petrol (S2P) program, which seeks to harness concentrated solar power for high-temperature hydrogen production.
- Process:
- Photocatalytic Electrolysis: Utilizes sunlight directly to activate a catalyst, which then splits water into hydrogen and oxygen.
- Solar-Thermal Electrolysis: Concentrated solar power heats water to temperatures where hydrogen production is more energy-efficient. This method combines both thermal and electrical energy to boost efficiency.
- Potential Advantages:
- Direct use of sunlight could theoretically offer higher energy efficiencies and lower costs.
- Reduces reliance on electricity by directly utilising solar energy.
- Challenges:
- Photocatalytic materials are not yet efficient or stable enough for large-scale applications.
- Solar-thermal systems require large, high-cost installations, which can limit adoption.
- Future Prospects: With advancements in material science, photocatalytic and solar-thermal electrolysis could offer viable, renewable hydrogen production with minimal infrastructure.
Comparison of Methods: Key Metrics
| Method | Efficiency | Cost | Scalability | Renewable Compatibility | Current Use Stage |
| Alkaline Electrolysis | Moderate | Low | High | Moderate | Commercial |
| PEM Electrolysis | High | High | Moderate | High | Commercial |
| Solid Oxide Electrolysis | Very High | Very High | Low | Low | Pilot/Experimental |
| AEM Electrolysis | Moderate | Moderate | Potentially High | High | Experimental |
| Photocatalytic/Solar-Thermal | Potentially High | Potentially Low | Low | High | Research |
Green hydrogen is a critical clean energy technology that could dramatically reduce global carbon emissions if scalable, cost-effective solutions are implemented. Each electrolysis method has unique benefits and challenges:
- Alkaline electrolysis is reliable and cost-effective but less adaptable to renewable energy.
- PEM electrolysis is suitable for intermittent renewable energy but costly due to expensive catalysts.
- SOE promises high efficiency when integrated with industrial waste heat but requires costly, heat-resistant materials.
- AEM electrolysis and photocatalytic processes are emerging as potentially game-changing, cost-effective alternatives if technical challenges can be overcome.
With advances in materials science, catalysis, and renewable integration, green hydrogen is likely to play a central role in the clean energy transition, enabling large-scale decarbonisation across industries and energy sectors.
The post Green Hydrogen: How is it produced? first appeared on Haush.