Electrolyzer for the production of hydrogen and oxygen.

Electrolyzer, Hydrogen Generator
Crystec Technology Trading GmbH

Electrolyzer for the Production of Hydrogen

An electrolyzer is used to produce high-purity hydrogen. By applying an electric current, water (H2O) undergoes a chemical decomposition (dissociation) into hydrogen (H2) and oxygen (O2). Since only renewable resources are required for production, electrolyzers represent a green technology.

In water electrolysis, a distinction can be made between PEM and Alkaline electrolysis:

PEM Electrolyzer / Acid Electrolyzer

The Proton-Exchange-Membran-Electrolyser (PEM) 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 environment. A key advantage of PEM electrolysis lies in the faster ion mobility of hydrogen ions (H+) compared to hydroxide ions (OH-), which enables higher speeds. In addition, the technology enables a high hydrogen purity of up to 99.999% and is used in numerous areas.

Functioning Principle of PEM Electrolysis

The principle of PEM electrolysis is based on the use of a proton exchange membrane. This semipermeable 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 by the catalytic action 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 gases produced are collected and transported out of the cell via special channel structures.

The decomposition of water can be described here with the following reaction equations.

HER (Hydrogen evolution reaction, hydrogen evolution reaction):    4 H+ + 4 e- arrow 2 H2
OER (Oxygen evolution reaction, oxygen evolution reaction): H2O arrow 4 H+ + 4 e- + O2

PEM Electrolysis

The Proton Exchange Membrane is the heart of this electrolysis technology. It consists of a solid polymer, which guarantees corrosion resistance and low maintenance requirements. The electrodes, which are in direct contact with the membrane, are often made of noble metals such as platinum at the anode and iridium or ruthenium oxide at the cathode. Current collectors ensure the contact of the electrodes and conduct the electric current. One of the technological innovations lies in the design of the PEM electrolysis stack. This consists of multiple layers, including electrodes, current collectors, and seals, which ensure the high efficiency of hydrogen production.

Our partner company SHANDONG SAIKESAISI uses a CCM membrane (Catalyst-Coated-Membrane) for its systems, which is manufactured using 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 ensure high current densities, low electrolysis voltages, and a long service life (up to 15 years).

PEM Cell Structure

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

            
PEM Electrolyzer (SHANDONG SAIKESAISI)
  • Hydrogen purity of 99.999%; dew point: -65°C
  • Fast start-up
  • No corrosion
  • Low maintenance
  • High degree of automation
  • Single-tank hydrogen gas flows between 50 mL/h and 260 Nm3/h
  • Operating temperature: 5-65°C
  • Easy installation through housing
  • Full CE certification
PEM-Elektrolyseur

PEM electrolysis systems are modular in design and are often installed in container structures to provide a compact and flexible solution. The container is divided into several separate rooms to meet safety and explosion protection requirements. This structuring consists of an electrical control room, an electrolysis room, and a cooling room. Each room is strictly separated to ensure safe and efficient operation.

Advantages of PEM Electrolysis

Alkaline Electrolyzer

In alkaline electrolysis (AEL), the electrodes are made of metal and have very high long-term stability. As a rule, dimensionally stable anodes (DSA) made of iron or titanium are used. A porous catalyst layer with a large surface area, called ECSA (Electrochemical active surface area), is applied to this electrically conductive electrode. This can consist of, for example, noble metal oxide or Raney nickel. A permeable diaphragm is used as a membrane. In earlier designs, the so-called cell gap design, the electrodes were attached to the membrane with a small gap to allow the escaping gas to escape. The distance varied between a few centimeters and millimeters. In modern AEL electrolyzers, on the other hand, the zero gap design is used. Here, the electrodes are placed directly on the membrane to reduce electrical resistance and enable higher current densities. The gas produced escapes through pores in the electrodes in this design. A liquid electrolyte is also necessary for this design. With this method, significantly higher gas flows can be achieved than, for example, with PEM electrolysis. An alkaline electrolyzer is therefore particularly recommended for very large plants.
The speed of the reaction depends primarily on two factors. The higher the temperature, the faster the reaction and the less voltage is required. On the other hand, too high temperatures are difficult to handle. Therefore, our systems operate at a temperature of about 85° C. Secondly, the speed is influenced by the type of ions in the electrolyte. Potassium shows significantly better ion mobility than, for example, sodium. By adding potassium hydroxide (KOH), an electrolyte is created that conducts much better than water. This results in rapid gas separation at the electrodes. The splitting of hydrogen thus takes place in a basic medium and can be described by the following reaction equation:

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

The electrodes are separated by a permeable membrane (diaphragm). This allows the transport of hydroxide ions (OH-) but prevents the exchange of the resulting gases, oxygen and hydrogen, both in dissolved form and as gas bubbles. To enable the diffusion of ions in aqueous solution, the membrane must have hydrophilic properties. This is achieved today by a combination of hydrophobic organic plastics such as PTFE or polysulfone as a carrier material and hydrophilic ceramics such as potassium titanate or zirconium oxide. Such membranes are chemically and mechanically stable and allow the pores to be filled with electrolyte. By applying a direct current, oxygen is produced at the anode and hydrogen at the cathode.


Alkaline Electrolysis

Alkaline hydrogen production technology is mature and characterized by low production costs. Currently, our alkaline electrolyzers allow hydrogen production of 5 Nm³/h-2000Nm³/h. The operating pressure of such a system is =16 bar. A partial load operation of 30-100% is possible. The separating membrane is not perfect. The proportion of gases passed through depends only on the concentrations, not on the amounts of gas produced. Therefore, unwanted mixing of the gases in the lower partial load range has a greater effect than in full operation.

                                                
Alkaline Electrolyzer (SinoHy)
                                                                         
                     
                                                          
  • Hydrogen purity of 99.999%; Dew point: -70°C
    •        
  • Low cost
    •        
  • Gas flows between 5 Nm³/h and 2000 Nm³/h
    •        
  • Flexible gas flow load: 30-100%
    •        
  • Operating temperature: 85°C
    •        
  • Operating pressure: =16 bar
    •        
  • Easy installation through housing
    •        
  • Full CE certification
    •      
    		                                                                             
      Alkali-Electrolyzer
               

Required Water Quality

For all types of electrolyzers, good water quality is a prerequisite. Based on your water analysis data, we can optionally integrate a water treatment system into our plants.

Hydrogen Purification and Drying

Both after alkaline electrolysis and after PEM electrolysis, residual moisture remains in the produced hydrogen gas. The necessary drying is already integrated into our systems. The oxygen and most of the water are returned to the water tank after electrolysis and are removed from the system by an oxygen pump. The hydrogen enters a hydrogen-water separator for the initial separation of hydrogen and a small amount of water. After this primary separation, the raw hydrogen is fed into the integrated purification unit of the system, which takes over the drying and purification.

This gas drying can be achieved by cooling the gas and by using a pressure swing adsorption dryer (PSA). Such a system consists of three columns filled with molecular sieves based on silicate or aluminum oxide, which absorb or regenerate moisture in a three-cylinder cycle. The switching from adsorption to regeneration takes place through an induced temperature or pressure change. Through this system, the purity of the raw hydrogen is increased to up to 99.999%. In addition, numerous sensors such as pressure, hydrogen leak, and water flow sensors are integrated throughout the system, which constantly monitor the operating parameters and ensure smooth operation of the generator.

Applications

The high purity of the produced hydrogen enables versatile applications:

Electrolysis technology offers a promising foundation for the future hydrogen economy, which is seen by politicians and strategists 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 energy source.

Crystec is looking forward to building a cost-effective system for you that meets your highest standards.