Technology

Technology2017-09-04T13:41:56+00:00

How does water-based electrolysis work ?

Hydrogen is the H in H2O. Hydrogen is extracted from water by heating up its atomic structure with electrolysis.
Electrolysis is a technique that uses a direct electric current (DC) to drive a chemical reaction. A DC is passed through an ionic substance, known as an electrolyte, this can be either a molten substance or something dissolved in a suitable solvent. The current produces chemical reactions at the electrodes and separation of materials. In water electrolysis, an electrolyser converts electrical energy into the chemical energy contained in hydrogen.

SEE ALSO : PEM Electrolyzer Product Line

PEM water electrolysis

In PEM electrolysis, we use a solid polymer electrolyte also called Proton Exchange Membrane. Protons flow constantly within the membrane whereas electrons travel along an external channel. Hydrogen is produced at the cathode.

Proton Exchange Membrane (PEM) electrolysis is the electrolysis of water in a cell equipped with a solid polymer electrolyte (SPE) that is responsible for the conduction of protons, separation of product gases, and electrical insulation of the electrodes.
The PEM electrolyser is designed to overcome the issues of partial load, low current, hydrogen density, and low pressure operation that handicap alkaline electrolysers. PEM Electrolysis is an important technology for producing hydrogen to be used as an energy carrier. It offers fast dynamic response times, large operational ranges, high efficiencies, and very high gas purities (99.999%).
The use of a PEM for electrolysis was first introduced during the Apollo Gemini project in the1960s, developed to overcome the drawbacks of alkaline electrolysis technology.

One of the major advantages of PEM electrolysis is its ability to operate at high-current densities with first-rate efficiencies. This results in reduced operational costs. The polymer electrolyte allows the PEM electrolyser to operate with a very thin membrane (~100-200μm) while still allowing high pressures and an electrochemical compression of the hydrogen output.

Nowadays electrolytic cells are stacked into units of up to 15 and even 20 Nm3/h hydrogen output. The active surface of the cells can reach up to 600 cm2, and the stacks can contain up to 100 cells.

Commercially-speaking, this is where PEM stands today.

To increase capacities and reach capabilities of power consumption above 1 MW (required from renewable energy storage perspectives), PEM electrolyser manufacturers work on increasing the active surface per cell, increasing current density (A/cm2) whilst still maintaining yields above 83% efficiency, and increasing the number of cell assembling capabilities.

Consequently, the higher the electrolysis capacities, the lower the cost per KW (or Nm3/h) installed. We are, however, still in the early stages of this technology today.

 

One of the other great advantages of PEM electrolysers, moreover, is their Balance of Plant (BOP) simplicity. Solid polymer membrane electrolysers are only fed with water and electrical power.
Consequently, the BOP downstream of the stacks is only involved in the drying stage of the produced gases.
At 30 Bar outlet pressure, drying hydrogen to 4 °C results in a -33°C dew point at atmospheric pressure.

The secret of running long-life PEM electrolysers lies in the water preparation and its quality control. Connected to the tap water network the water is deionized through a reverse osmosis system to ensure water conductivity below 0.1μS/cm. As long as membrane catalysts are not poisoned by ions, cell stack efficiency and lifetime can be ensured for over 60,000 hours. Critical applications such as space or military applications have shown that this technology is highly reliable.
By integrating this technology in traditional industrial electrolyser applications, such as cooling alternators in power plants, protective atmospheres in heat treatment or float-glass processes, industrial users are now given a new perspective on understanding on-site hydrogen production.

This equipment has become much simpler to handle and, above all, requires a lot less maintenance in comparison with traditional alkaline electrolysers. The BOP can be designed for a 20-year lifetime without the need to change valves or fittings and without the use or handling of corrosive chemical compounds. Maintenance becomes limited to mandatory regulations such as hydrogen detector calibration. As the water preparation upstream of the electrochemical process is critical, primary filters do need to be changed. Finally, water circulation in stacks is ensured by pumps that need yearly lubrication, and a bearing change every 5 years to achieve 98% availability.

Flexibility and cost-effectiveness are top priorities to ensure PEM electrolysers compete with other more established technologies in the industrial market.

The levels of flexibility and safety provided by this solution are without precedence.On-site hydrogen production is no longer perceived as a process that requires highly critical equipment, but one that is extremely productive, reliable and cost-effective.

PEM electrolysis is also a promising alternative for energy storage when coupled with renewable energy sources.
At long last, we have discovered a scalable means of producing hydrogen by electrolysis, i.e. PEM technology.

In PEM electrolysis, we use a solid polymer electrolyte also called Proton Exchange Membrane. Protons flow constantly within the membrane whereas electrons travel along an external channel. Hydrogen is produced at the cathode.

Proton Exchange Membrane (PEM) electrolysis is the electrolysis of water in a cell equipped with a solid polymer electrolyte (SPE) that is responsible for the conduction of protons, separation of product gases, and electrical insulation of the electrodes.
The PEM electrolyser is designed to overcome the issues of partial load, low current density, and low pressure operation that handicap alkaline electrolysers. PEM Electrolysis is an important technology for producing hydrogen to be used as an energy carrier. It offers fast dynamic response times, large operational ranges, high efficiencies, and very high gas purities (99.999%).
The use of a PEM for electrolysis was first introduced during the Apollo Getmini project in the1960s, developed to overcome the drawbacks of alkaline electrolysis technology.

One of the major advantages of PEM electrolysis is its ability to operate at high-current densities with first-rate efficiencies. This results in reduced operational costs. The polymer electrolyte allows the PEM electrolyser to operate with a very thin membrane (~100-200μm) while still allowing high pressures and an electrochemical compression of the hydrogen output.
Nowadays electrolytic cells are stacked into units up to 15 and even 20 Nm3/h. The active surface of the cells can reach up to 600 cm2, and the stacks can contain up to 100 cells.

Commercially-speaking, this is where PEM stands today.

To increase capacities and reach capabilities of power consumption above 1 MW (Required for renewable energy storage perspectives), PEM electrolyser manufacturers work on increasing active surface per cell, increasing current density (A/cm2) whilst still maintaining yields above 83% efficiency, and increasing the number of cell assembling capabilities.
Consequently, the higher electrolysis capacities, the lower the cost per KW (or Nm3/h) installed. We are, however, still in the early stages of this technology today. One of the other great advantages of PEM electrolysers, moreover, is their Balance of Plant (BOP) simplicity. Solid polymer membrane electrolysers are only fed with water and electrical power.
Consequently, the BOP downstream of the stacks is only involved in the drying stage of the produced gases.
At 30 Bar outlet pressure, drying hydrogen at 4 °C results in a -33°C dew point at atmospheric pressure.

The secret of running long-life PEM electrolysers lies in the water preparation and its quality control. Connected to the tap water network the water is deionized through a reverse osmosis system to ensure water conductivity below 0.1μS/cm. As long as membrane catalysts are not poisoned by ions, cell stack efficiency and lifetime can be ensured for over 60,000 hours. Critical applications such as space or military applications have shown that this technology is highly reliable.
By integrating this technology in traditional industrial electrolyser applications, such as on-site hydrogen production, cooling alternators in power plants, used as protective atmospheres in heat treatment or float-glass processes, industrial users are now given a new perspective on understanding on-site hydrogen production.

This equipment has become much simpler to handle and, above all, offer a much reduced requires a lot less maintenance in comparison with traditional alkaline electrolysers. As the development is KOH-free, the BOP can be designed for a 20-year lifetime without the need to change valves or fittings and without handling corrosive chemical compounds. Maintenance becomes limited to mandatory regulations such as hydrogen detector calibration. As the water preparation upstream of the electrochemical process is critical, primary filters do need to be changed. Finally, water circulation in stacks is ensured by pumps that need yearly lubrication, and a bearing change every 5 years based on 98% availability.

Flexibility and cost-effectiveness are top priorities, to convince industrial players of the relevancy of using PEM electrolysers.

The levels of flexibility and safety provided by this solution are without precedence and on-site hydrogen production is no longer perceived as a process that requires highly critical equipment, but one that is extremely productive, reliable and cost-effective.

PEM electrolysis is also a promising alternative for hydrogen energy storage coupled with renewable energy sources.
At long last, we have discovered a means of producing hydrogen by electrolysis, i.e. PEM technology.