PEM Electrolysers vs. Alkaline Electrolysers. Choosing the best hydrogen production technology for your project.  

Article main takeaways 

• Water Electrolysers split water into hydrogen and oxygen using electricity, a process central to green hydrogen production. 
• PEM Electrolysers offer efficiency and rapid response to power fluctuations but come with higher costs and maintenance demands.
• Alkaline Electrolysers are reliable, cost-effective, and widely used for industrial-scale hydrogen production.
• Comparison Table provides an overview of 10 key features to help readers select the right electrolyser for their needs. 
• Alternative Hydrogen Production Technologies: Beyond Alkaline and PEM, other technologies like SOEC and AEM are emerging.  
• Stargate Hydrogen’s Expertise: Available for consultation to help companies identify the best technology for their green hydrogen objectives. 

Introduction to electrolysers

With the growing focus on renewable energy, hydrogen became a choice of sustainable energy storage that can help reduce dependence on fossil fuels. Electrolyser technology is crucial in producing green hydrogen, and in this article, we will explore the two primary types—Alkaline and PEM (Proton Exchange Membrane) electrolysers—which offer distinct benefits and limitations.  

This article provides these technologies, their advantages, and where they fall short. Additionally, it includes a comparison table and explores alternative hydrogen production methods to offer a broader view of the landscape. 

What Is a Water Electrolyser for Hydrogen Production? 

Water electrolysers use electrical energy to split water into hydrogen and oxygen. The concept of electrolysis has been around since the 19th century, but it has gained renewed attention as green hydrogen production rises in importance. Unlike other hydrogen production methods, electrolysis doesn’t rely on fossil fuels, making it a key technology for renewable energy applications. By using electrolysers, industries can store excess renewable electricity in the form of hydrogen, which can then be utilized for power generation, transport, chemical processes and many other applications. 

A Brief History of PEM Electrolysis 

PEM technology has its roots in the space program. Initially, the Proton Exchange Membrane (or Polymer Electrolyte Membrane) was developed in the 1960s by NASA as a method for fuel cells to generate power on spacecraft. This early adoption stemmed from PEM's unique ability to produce pure hydrogen and oxygen in compact systems, making it ideal for the limited space and strict safety requirements of spacecraft. 

However, using PEM in water electrolysis for hydrogen production didn’t gain traction until the 1970s, when researchers saw its potential in creating clean energy. With the rise of the environmental movement, early-stage experiments explored PEM technology’s promise for industrial and energy applications, but commercial adoption remained slow due to high costs and limited availability of suitable materials, like the precious metals needed as catalysts. 

The 1990s brought significant breakthroughs, with advancements in membrane technology and increased production of precious metals, making PEM electrolysers more feasible for broader applications. Over the past two decades, global interest in hydrogen as a clean fuel has sparked further innovations in PEM electrolysis, improving the efficiency, durability, and affordability of these systems. By the early 2000s, PEM electrolysers were already proving valuable in high-purity hydrogen applications, such as laboratories and fuel cells. 

Today, PEM electrolysers are used for on-site hydrogen generation in industries, renewable energy storage, and fuel cell applications. The push for clean energy and hydrogen’s role as a sustainable fuel source continues to drive investments and research into PEM technology. 

PEM Electrolysers 

How PEM Electrolysers Work: An In-Depth Look 

PEM (Proton Exchange Membrane) electrolysers represent a relatively newer approach to hydrogen production. At their core, they rely on a solid polymer electrolyte that separates the two electrodes within the cell and facilitates proton movement during the electrolysis process. This membrane, made of specially designed polymers, allows only positively charged ions to pass through, blocking gases like oxygen and hydrogen to keep the system stable and efficient. Here’s a breakdown of how PEM electrolysis works, step-by-step: 

1. Electricity Supply: When direct current (DC) power is applied, typically sourced from renewable energy or grid power, it provides the energy needed to drive the chemical reaction in the electrolyser. The anode side of the cell, which is positively charged, attracts electrons to initiate the reaction. 
    

2. Water Molecule Splitting: Water (H₂O) enters the cell on the anode side, where the electrical current splits each water molecule into oxygen, protons (H⁺ ions), and electrons. This reaction produces pure oxygen gas as a by-product. 
    

3. Proton Movement Through the Membrane: The PEM (proton exchange membrane) allows the H⁺ ions (protons) to travel through the membrane to the cathode side of the cell. This selective permeability of the membrane is critical because it prevents oxygen and hydrogen gases from mixing, reducing the risk of explosions and enhancing purity. 
    

4. Hydrogen Production at the Cathode: On the cathode side, electrons from the electric current combine with the protons that have passed through the membrane, producing hydrogen gas (H₂). This hydrogen is collected and stored for various applications, from industrial uses to clean energy generation. 
    

5. Gas Collection and Purification: Both oxygen and hydrogen gases are separately collected, and in most cases, the hydrogen produced by PEM electrolysis is very pure (typically over 99.9%), which is ideal for applications requiring high-grade hydrogen, such as fuel cells. 

The solid PEM membrane is a key advantage in this process, allowing PEM electrolysers to start and stop quickly, respond well to fluctuations in electricity, and produce high-purity hydrogen with minimal impurities. 

Pros of PEM Electrolysers 

• High Efficiency: PEM electrolysers achieve high efficiency, making them suitable for applications requiring optimized energy use. 

• Fast Response Time: Their rapid startup and load adjustment capabilities make them well-suited for use with intermittent renewable energy sources. 

• Compact and Lightweight Design: Small size allows for installation in limited spaces, which can be advantageous for certain projects. 

• High-Purity Hydrogen Production: PEM technology produces high-purity hydrogen, minimizing the need for additional purification. 

• Lower Operational Temperatures: Lower temperatures reduce the degradation rate of materials, potentially extending equipment lifespan. 

Cons of PEM Electrolysers 

While PEM electrolysers offer some benefits, they also come with significant limitations that need to be carefully considered: 

• High Initial Cost: The complex materials needed, including precious metal catalysts (platinum and iridium), drive up the cost of PEM electrolysers, making them a larger investment than alkaline systems. 

• Limited Lifespan: Despite lower operational temperatures, PEM membranes and electrodes are more prone to wear and tear over time. This can result in a shorter operational life compared to alkaline electrolysers. 

• Expensive and Complex Maintenance: The intricate design of PEM electrolysers requires specialized knowledge for repairs and maintenance, often increasing long-term costs. 

• Dependence on Precious Metals: PEM electrolysers rely on platinum and iridium as catalysts, which are both costly and subject to market fluctuations. This can make scaling up PEM production financially challenging. 

• Limited Scalability: Scaling PEM electrolysers for large, industrial applications can be complex and expensive due to material costs and technical constraints. This restricts their suitability for high-volume hydrogen production. 

• Membrane Degradation Under Stress: While PEM electrolysers respond quickly to variable loads, the constant adjustment can accelerate membrane degradation, impacting lifespan and overall cost-effectiveness. 

Alkaline Electrolysers 

How Alkaline Electrolysers Work 

Alkaline electrolysers use an alkaline electrolyte solution—often potassium or sodium hydroxide—to enable the flow of ions between two electrodes. This approach, which typically operates at low temperatures (60–80°C), has been the standard for decades and is widely recognized for its robust design and affordability. 

Pros of Alkaline Electrolysers 

• Lower Production Costs: Due to simpler materials and designs, production costs for alkaline electrolysers are lower, making them more accessible. 

• Durability: Alkaline electrolysers are known for their longevity and consistent performance over time. 

• Proven Technology: Trusted in industrial hydrogen production, alkaline electrolysers are a well-known solution with a long operational history. 

• Ease of Maintenance: With fewer complex components, maintenance is simpler and requires less specialized expertise. 

• Scalability for Large-Scale Production: Alkaline electrolysers are well-suited to large setups where costs need to be controlled, allowing for efficient, steady hydrogen output. 

Cons of Alkaline Electrolysers 

• Lower Efficiency: Alkaline technology in some cases has lower energy efficiency, particularly at high current densities. 

• Longer Startup and Shutdown Times: Alkaline electrolysers are slower to start and adjust their output, which can limit their effectiveness in applications with variable energy sources. 

• Lower Hydrogen Purity: Compared to PEM electrolysers, alkaline electrolyser provide lower hydrogen purity. Additional purification steps may be required, especially for applications needing very high-purity hydrogen, adding to operational costs. 

Comparison Table – PEM Electrolysers vs. Alkaline Electrolysers 

* The values in the table above are an estimation based on the average specifications of each technology. 

Alternative technologies for hydrogen production 

While Alkaline and PEM electrolysers are the two most common types, alternative technologies are emerging that may meet specific production needs: 

1. Solid Oxide Electrolyser Cells (SOECs): 

1. Operation: SOECs operate at high temperatures (typically above 700°C), using a solid oxide or ceramic electrolyte. 

2. Pros: Superior efficiency thanks to heat reuse, making them ideal for industrial applications with access to excess heat. 

3. Cons: The high temperatures involved result in faster degradation of materials, increasing maintenance needs and limiting lifespan. 
    

2. Anion Exchange Membrane (AEM) Electrolysers: 

1. Operation: AEM electrolysers combine features of both alkaline and PEM technologies, using a polymer membrane that allows for anion transport. 

2. Pros: No need for precious metals as catalysts, making them potentially more affordable than PEM electrolysers. 

3. Cons: AEM technology is still in early stages of development and lacks the commercial maturity and reliability of PEM and Alkaline options. 
    

Choosing the right electrolyser technology 

When selecting the best hydrogen production technology, consider the specific needs of your application. Alkaline electrolysers offer a cost-effective, durable solution for large-scale, continuous hydrogen production. PEM electrolysers, on the other hand, are more suitable for smaller applications relying on energy sources that experience power fluctuations.  

Common myths about alkaline electrolyser technology 

Despite its proven performance and widespread industrial use, several myths persist around Alkaline electrolyser technology. Here are some common misconceptions that may discourage businesses from considering Alkaline electrolysers—along with explanations to set the record straight. 

1. Myth #1: Alkaline Electrolysers Are Not Suitable for Renewable Energy Sources 

Reality: While Alkaline electrolysers have a slower response time compared to PEM electrolysers, recent technological advancements have improved their ability to handle variable loads. Newer models are more adaptable to renewable energy sources like wind and solar, allowing Alkaline electrolysers to be used in settings with intermittent power. Solutions such as hybrid systems or energy storage can also help stabilize the power supply, making Alkaline electrolysers a viable option for renewables. 

2. Myth #2: Alkaline Electrolysers Are Outdated Technology 

Reality: Alkaline technology may have a long history, but it remains a reliable and cost-effective option for hydrogen production. Continuous improvements have increased the efficiency, lifespan, and scalability of Alkaline electrolysers, keeping them competitive with newer technologies. Many industries still rely on Alkaline systems because they offer durability and cost-efficiency that other technologies have yet to match at an industrial scale. 

3. Myth #3: Alkaline Electrolysers Produce Low-Purity Hydrogen 

Reality: Alkaline electrolysers produce hydrogen at a high enough purity for most applications. While they may require additional purification steps in applications that demand ultra-pure hydrogen, so do most PEM systems. Alkaline electrolysers are widely used in industries such as chemical manufacturing, where purity levels are up to 99.5% meeting production needs without costly extra processing. 

4. Myth #4: Alkaline Electrolysers Are Too Bulky and Not Scalable 

Reality: Although Alkaline systems are often larger than PEM systems, they are still scalable and adaptable to industrial setups, especially when space is available. Their robust design and simple maintenance requirements make them particularly well-suited for large-scale hydrogen production. In fact, Alkaline technology is the choice of many high-output production facilities due to its stability and scalability. 

5. Myth #5: Alkaline Electrolysers Are Inefficient Compared to PEM Electrolysers 

Reality: While it’s true that PEM electrolysers typically operate at a slightly higher efficiency, the efficiency difference is not as dramatic as often perceived. Alkaline electrolysers operate at competitive efficiency levels, and in many industrial settings, the cost savings associated with their simpler design and lower material costs outweigh minor efficiency differences. Advanced models are closing the efficiency gap further, allowing Alkaline electrolysers to perform well even under demanding conditions. 

6. Myth #6: Alkaline Electrolysers Have a Short Lifespan 

Reality: Alkaline electrolysers are known for their long operational lifespans, often outlasting PEM counterparts. This technology has a proven track record of durability, making it highly reliable for continuous operations. With regular maintenance, Alkaline systems can achieve a long service life, further enhancing their cost-effectiveness over time. 

7. Myth #7: Alkaline Electrolysers Require Hazardous Chemicals 

Reality: The alkaline electrolyte (usually a solution of potassium hydroxide) used in these electrolysers is indeed a caustic substance, but it is safely contained within the system. Modern Alkaline electrolysers are designed with advanced safety features to prevent leaks and contain the electrolyte, ensuring safe, low-risk operation in industrial environments. 

8. Myth #8: Alkaline Electrolysers Are Costly to Maintain 

Reality: Alkaline electrolysers are typically easier and less expensive to maintain than PEM electrolysers due to their simpler design and fewer specialized components. They do not rely on precious metal catalysts, making parts replacement more affordable. With regular inspections and basic upkeep, Alkaline electrolysers can operate for many years with minimal maintenance costs. 

9. Myth #9: Alkaline Electrolysers Can't Meet High Production Demand 

Reality: Alkaline electrolysers are highly scalable and can handle high-demand applications. They are often the go-to choice for large industrial hydrogen production facilities. The robust, modular design of modern Alkaline systems makes them well-suited to meet the continuous demand required by industries such as ammonia production and petroleum refining. 

10. Myth #10: Alkaline Electrolysers Are Inflexible and Lack Innovation 

Reality: Alkaline electrolysers have seen significant innovation, especially in recent years, with improvements in efficiency, adaptability, and durability. A good example is Stargate’s Hydrogen extensive R&D investments towards building upon the best aspects alkaline electrolysis technology and complement it with breakthrough materials for a completely new class of electrolysers: ceramics-based alkaline electrolysers, that have high current densities, and high efficiencies, yet contain no precious metals. This results in significantly lower hydrogen production costs and makes the electrolysers affordable for the end-users. 

Why Alkaline Electrolysers are a solid choice 

Despite these myths, Alkaline electrolysers offer compelling advantages, particularly in terms of cost-effectiveness, durability, and scalability. For companies with high hydrogen demands or established power infrastructure, Alkaline technology is a proven, reliable choice that can deliver efficient, sustainable results for green hydrogen production. 

For those interested in learning more, contact Stargate Hydrogen’s team of experts to help evaluate the best hydrogen production technology for your specific needs. Whether for renewable applications or large-scale industrial production, we can guide you through the options and support your goals for sustainable hydrogen production.