Crystec Technology Trading GmbH

PEM Electrolyzer / Acidic Electrolyzer

The Proton Exchange Membrane Electrolyzer, also known as Proton Exchange Membrane or Polymer Electrolyte Membrane, is a technology for producing hydrogen by splitting water in an acidic environment. It differs from alkaline electrolysis, where the reaction takes place in a basic medium. One major advantage of PEM electrolysis lies in the higher ion mobility of hydrogen ions (H⁺) compared to hydroxide ions (OH^-), which allows faster reaction rates. Furthermore, the technology enables high hydrogen purity of up to 99.999% and is used in numerous applications.

Operating Principle of PEM Electrolysis

The principle of PEM electrolysis is based on the use of a proton exchange membrane. This semi-permeable membrane allows protons (H⁺) to pass through while preventing the gas exchange of oxygen (O₂) and hydrogen (H₂). At the anode, water is split into oxygen, electrons, and protons through the catalytic effect of noble metal-coated electrodes (platinum, molybdenum sulfide). The protons diffuse through the membrane to the cathode, where they combine with electrons to form hydrogen. The resulting gases are collected and discharged through special channel structures.

The decomposition of water can be described by the following reaction equations:

HER (Hydrogen Evolution Reaction):	4 H+ + 4 e- ⟶ 2 H2
OER (Oxygen Evolution Reaction):	H2O ⟶ 4 H+ + 4 e- + O2

The Proton Exchange Membrane is the core of this electrolysis technology. It consists of a solid polymer, which ensures corrosion resistance and low maintenance. The electrodes in direct contact with the membrane are often made of noble metals such as platinum (anode) and iridium or ruthenium oxide (cathode). Current collectors ensure electrical contact with the electrodes and conduct the current. One of the technological innovations lies in the structure of the PEM electrolysis stack, which consists of multiple layers including electrodes, current collectors, and seals — all contributing to high hydrogen generation efficiency.

Our partner company SHANDONG SAIKESAISI uses a CCM membrane (Catalyst-Coated Membrane), produced through a patented hot-pressing process. This membrane enables stable, efficient, and long-lasting hydrogen production. The design and materials of the electrolysis cells have been optimized to achieve high current densities, low electrolysis voltages, and a long service life (up to 15 years).

Our PEM electrolyzers can be delivered in customized container systems, offering a flexible, safe, and efficient solution for hydrogen production.

Technical Specifications (Example Model) Hydrogen Purity up to 99.999%; dew point: -65°C Power Range 50 mL/h to 260 Nm3/h (depending on model) Operating Temperature 5 – 65 °C Startup Behavior Fast startup possible Modular Design Stack-based scalability Container Design Includes electrical control, cooling, safety zones Monitoring Integrated sensors (pressure, temperature, H₂ leak, humidity) Certification CE-Certification

Advantages of PEM Electrolysis

• Fast startup – flexible and quick response to fluctuating power input (e.g. PV/Wind)
• High purity – up to 99.999%, ideal for electronics or fuel cell applications
• High efficiency – faster proton mobility compared to hydroxide ions allows higher rates and pressures
• Partial load operation – stable operation possible at only 5% load
• Low corrosion and maintenance due to solid polymer membrane
• Modular and scalable – easily expandable by adding modules

PEM electrolysis systems are modular and often installed in container structures, offering compact and flexible solutions. The container is divided into separate rooms — electrical control, electrolysis, and cooling — ensuring compliance with safety and explosion protection standards. Each compartment is isolated to guarantee safe and efficient operation.

Alkaline Electrolyzer

In alkaline electrolysis (AEL), the electrodes are made of metal and offer very high long-term stability. Typically, Dimensionally Stable Anodes (DSA) made of iron or titanium are used. On these conductive electrodes, a porous catalyst layer with a large surface area — called the Electrochemical Active Surface Area (ECSA) — is applied. This layer may consist of precious metal oxide or Raney nickel. A permeable diaphragm serves as the membrane. In earlier “cell gap” designs, the electrodes were placed a few millimeters to centimeters apart from the membrane to allow gas escape. In modern AEL electrolyzers, the “zero gap” design is used, where the electrodes are placed directly on the membrane to reduce resistance and enable higher current densities. The produced gas escapes through pores in the electrodes. A liquid electrolyte is still required for operation.

This method allows significantly higher gas flows compared to PEM electrolysis, making alkaline electrolyzers particularly suitable for large-scale plants. Reaction speed depends mainly on two factors: the higher the temperature, the faster the reaction and the lower the required voltage. However, excessive temperatures are difficult to manage, so our systems operate around 85°C. Secondly, the reaction speed is influenced by the ions used in the electrolyte — potassium ions offer significantly better mobility than sodium ions. Adding potassium hydroxide solution (KOH) produces an electrolyte that conducts much better than pure water, leading to rapid gas separation at the electrodes.

Thus, water splitting occurs in a basic environment and can be described by the following reaction equations:

HER (Hydrogen Evolution Reaction):	4 H2O + 4 e- ⟶ 2 H2 + 4 OH-
OER (Oxygen Evolution Reaction):	4 OH- ⟶ 2 H2O + 4 e- + O2

The electrodes are separated by a permeable membrane (diaphragm) that allows hydroxide ions (OH^-) to pass through but prevents oxygen and hydrogen gas exchange. To allow ion diffusion in the aqueous solution, the membrane must be hydrophilic. This is achieved by combining hydrophobic polymers such as PTFE or polysulfone with hydrophilic ceramics like potassium titanate or zirconium oxide. Such membranes are chemically and mechanically stable and allow electrolyte-filled pores. When DC voltage is applied, oxygen forms at the anode and hydrogen at the cathode.

Alkaline hydrogen production technology is well established and characterized by low production costs. Our alkaline electrolyzers currently enable hydrogen generation from 5 Nm³/h to 2000 Nm³/h at operating pressures of ≤16 bar. Partial load operation between 30–100% is possible. The separating membrane is not perfect; gas crossover depends on concentration rather than total gas volume, meaning unwanted mixing has a stronger effect at lower loads.

Our alkaline electrolyzers are available in modular container systems, providing a cost-efficient, robust, and sustainable solution for large-scale hydrogen production.

Technical Specifications (Example Model) Hydrogen Purity 99.999%; dew point: -70°C Capacity Range 5 Nm3/h to 2000 Nm3/h Gas Flow Utilization Flexible between 30–100% Operating Temperature 85 °C Operating Pressure ≤ 16 bar Installation Simple enclosure Cost Low operating costs Certification CE Certification

Required Water Quality

Good water quality is essential for all types of electrolyzers. Based on your water analysis data, we can optionally integrate a water treatment unit into our systems.

Hydrogen Purification and Drying

After both alkaline and PEM electrolysis, residual moisture remains in the produced hydrogen gas. The required drying process is already integrated into our systems. Oxygen and most of the water are returned to the tank and removed from the system by an oxygen pump. Hydrogen passes through a water separator for primary separation of hydrogen and small amounts of water. After this stage, the raw hydrogen enters the system’s integrated purification unit, where drying and cleaning occur.

This gas drying can be achieved by cooling the gas and using a swing adsorption dryer (SAD), based on either temperature swing adsorption (TSA) or pressure swing adsorption (PSA). Such systems use three columns filled with molecular sieves (silicate or alumina), alternating between adsorption and regeneration cycles by changing temperature or pressure. This process increases hydrogen purity up to 99.999%. Numerous sensors (pressure, H₂ leak, water flow, etc.) continuously monitor system parameters to ensure safe and reliable generator operation.

Applications

The high purity of the produced hydrogen enables a wide range of applications:

• Hydrogen fuel cells for vehicles, hydrogen engines, and stationary energy systems
• Electronics industry for semiconductor and chip manufacturing
• Renewable energy: energy storage from wind or photovoltaic systems
• Nuclear power plants: For cooling and reduction in thermonuclear generators
• Chemical industry: Hydrogen for chemical reactions, e.g., in oil processing
• Medicine: Use of hydrogen molecules in medical research
• Military: Support of fuel cells in military applications such as submarines or weather sensors
• Ammonia production: The hydrogen generated is suitable for ammonia production, which facilitates transport in larger quantities as a hydrogen carrier. This can be easily split back into hydrogen elsewhere with the aid of an ammonia cracker.

Electrolysis technology offers a promising basis for the future hydrogen economy, which politicians and strategists see as a key technology for sustainable energy supply in the 21st century. Access to hydrogen from renewable energy sources makes it a virtually inexhaustible and environmentally friendly source of energy.

Crystec looks forward to building you a cost-effective system that meets your most stringent requirements.