science

High-pressure electrolysis

High-pressure electrolysis is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand High-pressure electrolysis rather than just read about it. In short: High-pressure electrolysis (HPE) is the electrolysis of water by decomposition of water (H2O) into oxygen (O2) and hydrogen gas (H2) due to the passing of an electric current through the water. The difference with a standard proton exchange membrane (PEM) electrolyzer is the compressed hydrogen output around 12–20 megapascals (120–200 bar) at 70 °C.

Key takeaways

High-pressure electrolysis belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect High-pressure electrolysis to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of High-pressure electrolysis from memory before moving on to harder problems.

Reference excerpt

High-pressure electrolysis (HPE) is the electrolysis of water by decomposition of water (H2O) into oxygen (O2) and hydrogen gas (H2) due to the passing of an electric current through the water. The difference with a standard proton exchange membrane (PEM) electrolyzer is the compressed hydrogen output around 12–20 megapascals (120–200 bar) at 70 °C. By pressurising the hydrogen in the electrolyser the need for an external hydrogen compressor 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 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. This then enables the ability to help with grid balancing and energy storage.

Ultrahigh-pressure electrolysis Ultrahigh-pressure electrolysis is high-pressure electrolysis operating at 340–690 bars (5,000–10,000 psi). At ultra-high pressures the water solubility and cross-permeation across the membrane of H2 and O2 is affecting hydrogen purity, 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 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. 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%. 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 (HHEG) project. The Forschungszentrum Jülich, in Jülich Germany is currently researching the cost reduction of components used in high-pressure PEM electrolysis 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.

See also Regenerative fuel cell Electrochemical engineering High-temperature electrolysis

References

External links High pressure electrolyzer EC-supported STREP program on high pressure PEM water electrolysis

Illustrations

High-pressure electrolysis: High-pressure PEM electrolyser. — High-pressure PEM electrolyser.

Worked examples

Example 1 — a first encounter with High-pressure electrolysis

Start with the simplest possible case. Write down what High-pressure electrolysis claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to High-pressure electrolysis before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about High-pressure electrolysis ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of High-pressure electrolysis

In research: High-pressure electrolysis appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses High-pressure electrolysis in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: High-pressure electrolysis is common in secondary-school and first-year university syllabi. It links to neighbouring topics Electrolysis, Hydrogen production, Hydrogen technologies, so understanding it makes those chapters shorter.
In everyday life: Look for High-pressure electrolysis outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study High-pressure electrolysis in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what High-pressure electrolysis means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain High-pressure electrolysis out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is High-pressure electrolysis in simple terms?

Why does High-pressure electrolysis matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study High-pressure electrolysis?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on High-pressure electrolysis.