Conclusion First

When choosing an electrolyzer, you should consider the following parameters

  1. Electrolysis Efficiency: This is one of the most important considerations. A more efficient electrolyzer can convert electrical energy into hydrogen energy more effectively, meaning higher energy returns and lower long-term operational costs.
  2. Cost: This includes both the initial purchase cost and long-term operational costs. While more efficient electrolyzers may have higher initial costs, they can be more economical due to lower operating costs. More durable and reliable equipment can reduce maintenance costs and downtime.
  3. Adaptability to Energy Sources: The energy efficiency of electrolyzers can vary depending on the type of power source used, such as renewable energy or grid electricity.
  4. Hydrogen Purity: This is especially important in commercial and industrial applications. Different electrolysis technologies vary in the purity of hydrogen they produce.
  5. Manufacturer’s Reputation and Support: The reliability and reputation of the manufacturer, as well as the customer service and technical support they offer, are also important considerations.

Electrolysis Efficiency

Higher electrolysis efficiency means less energy consumption, leading to lower long-term operating costs. Among the current four water electrolysis technologies, the efficiency ranking from high to low is: SOCE (85%~100%) > PEM (70%~90%) = AEM (60%~90%) > ALK (60%-75%).

In terms of electrolysis efficiency, compared to the other three technologies, the main issues with ALK are:

  • Electrolyte concentration leads to lower conductivity and higher internal resistance. Both PEM and AEM use solid electrolytes.
  • The thickness of the diaphragm is excessive, causing high electrical resistance. The difficulty in transporting OH- ions from the cathode to the anode results in lower electrolysis efficiency. However, the reasons for these issues are the use of cheaper materials and processes, finding the most balanced solution between durability and efficiency. For example, the current diaphragm thickness in ALK is around 500 μm, while for PEM and AEM it’s around 100μm, and expected to decrease in the future. Reducing ALK’s diaphragm thickness to 57μm could increase efficiency from 53% to 75% at 1 A/cm2, but this would greatly reduce the lifespan and increase costs due to higher manufacturing standards.

SOEC has the highest electrolysis efficiency among the four technologies, mainly due to temperature. High temperatures significantly improve the kinetics of water splitting reactions, reducing the energy needed for electrolysis and thus increasing efficiency. Moreover, at high temperatures, the entropy change of water electrolysis is reduced, meaning that more energy is released from the reaction, contributing to higher overall efficiency.


Initial Purchase Cost: SOEC > PEM > ALK

The cost of Solid Oxide Electrolyzer Cells (SOEC) is the highest because SOEC technology is relatively new, and many of its processes and materials are not yet mass-produced, leading to higher costs. Additionally, SOEC needs to operate at high temperatures, requiring materials that can withstand heat and complex manufacturing processes, keeping its production cost high.

Proton Exchange Membrane (PEM) electrolyzers, although the manufacturing of the middle Membrane Electrode Assembly (MEA) layer and the cost of precious metals involved are high, the process has become quite mature. It can even be specialized based on your application, making the costs relatively controllable. Furthermore, the recycling technology for platinum and iridium metals used in PEM is gradually maturing, which will reduce its unit cost over time.

Alkaline hydrogen generators have the lowest initial cost. Their design and technology have a long history and are very mature. You can even find many videos on YouTube teaching how to make alkaline hydrogen generators at home. Therefore, you can imagine that the materials are quite easy to obtain.

Anion Exchange Membrane (AEM) electrolyzers are not discussed in this article, as they are currently at the laboratory stage. Many of their costs and design processes are not yet ready for mass production. However, it is generally believed that their costs will be lower. But based on our and our partners’ understanding, the current costs are not low, primarily because the manufacturing technology for AEM’s anion-exchange membranes is not mature, leading to high prices per membrane. Of course, whether the costs will decrease in the future is still unknown. We hope they will be able to significantly reduce costs in the future.

Long-Term Maintenance Costs: ALK > SOEC > PEM

The maintenance cost of Alkaline (ALK) electrolyzers is quite high because the high-concentration alkali solution can cause significant damage to steel materials and other components. There is a frequent need for cleaning rust and adjusting the concentration of the alkali solution. Often, the entire ALK electrolyzer needs to be disassembled for cleaning and maintenance, and even the reaction layer in the middle might need replacement. Regular thorough cleaning, which requires re-adding solutions like KOH (potassium hydroxide) or NAOH (sodium hydroxide), is both time-consuming and labor-intensive for the user, with NAOH representing an additional expense.

ALK corroded
ALK corroded

The main maintenance tasks for Solid Oxide Electrolyzer Cells (SOEC) are sealing maintenance, necessary cleaning, and temperature monitoring. As SOECs have relatively high tolerance to pollutants, they only require simple, regular cleaning. However, the key aspect is the maintenance of sealing, as they operate at high temperatures, and the materials used need to withstand high temperatures and chemical corrosion. Over time, this can lead to the degradation of these sealing components, necessitating regular inspections, maintenance, and replacements.

Proton Exchange Membrane (PEM) electrolyzers have the simplest maintenance. They require only simple adsorption of impurities in the circulating water to ensure its purity. PEM electrolyzer technology is less susceptible to contaminants. After a considerably long period of operation, only the inspection and replacement of the proton exchange membrane are needed.

Adaptability to Energy Sources

The focus here is specifically on renewable energy sources with high variability and high-temperature energy systems (such as nuclear energy and factories with a lot of waste heat) suitable for combined heat and power (CHP) projects. Most other situations involve a stable power supply and ambient temperatures, so only these two special cases are discussed.

  1. Renewable Energy: Due to the high variability of renewable energy sources, some countries even prohibit them from connecting to the national grid. For hydrogen electrolyzers, the ability to quickly respond to load changes and to start and stop rapidly is required. This makes Proton Exchange Membrane (PEM) hydrogen electrolyzers the only choice.
  2. Combined Heat and Power (CHP) Projects: Only Solid Oxide Electrolyzer Cells (SOEC) can withstand and utilize high temperatures to improve hydrogen production efficiency.

Hydrogen Purity

SOEC ≥ PEM > ALK. Different electrolysis technologies vary in the purity of the hydrogen they produce, which may affect their suitability for specific applications. Particularly for ALK (alkaline electrolyzers), due to technical reasons, the products available on the market are generally a mixture of hydrogen, oxygen, water vapor, and alkali mist. This is also referred to as HHO, but generally, HHO only refers to a mixture of hydrogen and oxygen gases (Brown’s gas). If you want pure hydrogen, an additional separation and purification device is required. SOEC, due to its high electrolysis efficiency and high temperatures, can theoretically produce hydrogen of quite high purity. However, the specific purity levels depend on the equipment and operating conditions, as the technology is not yet fully mature. PEM electrolyzers, on the other hand, can produce hydrogen with a purity of up to 99.999% by simply adding a drying process to remove excess water vapor.

Manufacturer Reputation and Support

When choosing a hydrogen electrolyzer, selecting a manufacturer with a good reputation is crucial. SENZA is a manufacturer with a good reputation in the hydrogen electrolyzer industry. Our verified Proton Exchange Membrane (PEM) and Alkaline electrolyzers are more reliable.

  • We also have extensive industry experience, a good reputation, and positive customer feedback.
  • We respond quickly to customer needs, resolve their queries, and provide excellent after-sales service.
  • We offer comprehensive and detailed operational training and educational resources to help customers better understand and use hydrogen electrolyzers, thereby improving electrolysis efficiency and safety.
  • Our continuous investment in research and development ensures that our technology remains at the forefront of the industry.

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