High-pressure electrolysis (HPE) is the

electrolysis of water Electrolysis of water, also known as electrochemical water splitting, is the process of using electricity to decompose water into oxygen and hydrogen gas by electrolysis. Hydrogen gas released in this way can be used as hydrogen fuel, or remi ...

by decomposition of water (H₂O) into oxygen (O₂) and

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...

gas (H₂) due to the passing of an electric current through the water. The difference with a standard proton exchange membrane electrolyzer is the compressed hydrogen output around at 70 °C. By pressurising the hydrogen in the electrolyser the need for an external

hydrogen compressor A hydrogen compressor is a device that increases the pressure of hydrogen by reducing its volume resulting in compressed hydrogen or liquid hydrogen. Traditionally, applications for hydrogen compressors included Chlorine electrolyser and many che ...

is eliminated, the average energy consumption for internal differential pressure compression is around 3%.

Approaches

As the required compression power for water is less than that for hydrogen-gas the water is pumped up to a high-pressure, in the other approach

differential pressure Pressure measurement is the measurement of an applied force by a fluid (liquid or gas) on a surface. Pressure is typically measured in units of force per unit of surface area. Many techniques have been developed for the measurement of pressur ...

is used. There is also an importance for the electrolyser stacks to be able to accept a fluctuating electrical input, such as that found with

renewable energy Renewable energy is energy that is collected from renewable resources that are naturally replenished on a human timescale. It includes sources such as sunlight, wind, the movement of water, and geothermal heat. Although most renewable energy ...

. This then enables the ability to help with

grid balancing Grid balancing ensures that electricity consumption matches electricity production of an electrical grid at any moment. Electricity is by its nature difficult to store and has to be available on demand, so the supply shall match the demand very clo ...

and

energy storage Energy storage is the capture of energy produced at one time for use at a later time to reduce imbalances between energy demand and energy production. A device that stores energy is generally called an accumulator or battery. Energy comes in ...

Ultrahigh-pressure electrolysis

Ultrahigh-pressure electrolysis is high-pressure electrolysis operating at .XI.13 High-Efficiency, Ultra-High Pressure Electrolysis with Direct Linkage to Photovoltaic Arrays (Phase II Project)
Available here
Accessed 2008-08-9.) At ultra-high pressures the water solubility and cross-permeation across the membrane of H₂ and O₂ is affecting

hydrogen purity Hydrogen purity or hydrogen quality describes the presence of impurities in hydrogen when used as a fuel gas. Impurities in hydrogen can interfere with the proper functioning of equipment that stores, distributes, or uses hydrogen fuel. Hydrogen ...

, modified PEMs are used to reduce cross-permeation in combination with catalytic H₂/O₂ recombiners to maintain H₂ levels in O₂ and O₂ levels in H₂ at values compatible with

hydrogen safety Hydrogen safety covers the safe production, handling and use of hydrogen, particularly hydrogen gas fuel and liquid hydrogen. Hydrogen possesses the NFPA 704's highest rating of 4 on the flammability scale because it is flammable when mixed eve ...

requirements.

Research

The US DOE believes that high-pressure electrolysis, supported by ongoing research and development, will contribute to the enabling and acceptance of technologies where hydrogen is the energy carrier between renewable energy resources and clean energy consumers.Alkaline, High Pressure Electrolysis
Available here
Accessed 2008-08-9.) High-pressure electrolysis is being investigated by the DOE for efficient production of hydrogen from water. The target total in 2005 is $4.75 per gge H₂ at an efficiency of 64%.2005 DOE H2 Program Review Alkaline, High Pressure Electrolysis.
Available here
Accessed 2008-08-9.) The total goal for the DOE in 2010 is $2.85 per gge H₂ at an efficiency of 75%. As of 2005 the DOE provided a total of $1,563,882 worth of funding for research. Mitsubishi is pursuing such technology with its

High-pressure hydrogen energy generator In science and engineering the study of high pressure examines its effects on materials and the design and construction of devices, such as a diamond anvil cell, which can create high pressure. By ''high pressure'' is usually meant pressures of th ...

(HHEG) project.Mitsubishi Monitor August and September 2004
available here
Accessed 2008-08-9.) The Forschungszentrum Jülich, in Jülich Germany is currently researching the cost reduction of components used in high-pressure

PEM electrolysis Polymer electrolyte 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 ...

in the EKOLYSER project. The primary goal of this research is to improve performance and gas purity, reduce cost and volume of expensive materials and reach the alternative energy targets set forth by the German government for 2050 in the Energy Concept published in 2010. ThalesNano Energy released a lab-scale high pressure (100 bar) hydrogen generator as a replacement for hydrogen cylinders in chemistry laboratories.

Commercial Products

Honda installed its Smart Hydrogen Station (SHS) in Los Angeles for use by fuel cell automobiles.

References

External links

High pressure electrolyzerEC-supported STREP program on high pressure PEM water electrolysis
{{DEFAULTSORT:High Pressure Electrolysis Hydrogen technologies Electrolysis Hydrogen production