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Hydrogen Electrolysers Explained: A Practical Guide with Insights from PAC



The shift to cleaner energy is urgent, and hydrogen is set to play a significant role. As a clean fuel that emits only water when used, hydrogen can help decarbonise industries that electricity alone cannot reach. However, to make hydrogen truly green, it must be produced using clean methods. This is where electrolysers become essential.


Electrolysers are systems that use electricity to split water into hydrogen and oxygen, with no carbon emissions involved. In this guide, we explain how electrolysers work, why they are important, and what developments lie ahead. We also share insights from PAC, a team working to advance this technology to make it more efficient, reliable, and sustainable.


What Is a Hydrogen Electrolyser?

A hydrogen electrolyser is a device that uses electricity to separate water into its two components: hydrogen and oxygen. The process is relatively straightforward. When an electric current passes through water, the H₂O molecules split apart. Oxygen is released into the atmosphere, while hydrogen is collected and stored as a clean fuel source.


What makes hydrogen electrolysers particularly important is the cleanliness of the process. When powered by renewable energy sources such as wind or solar, the system emits no carbon dioxide. This is why electrolysers are considered essential for producing “green hydrogen.”


This clean hydrogen can be used to power trucks, heat buildings, run industrial processes, and store energy for future use. As the world accelerates efforts to cut carbon emissions and reduce reliance on fossil fuels, hydrogen electrolysers are becoming a key part of the solution. They are not just machines; they represent a path toward a cleaner energy future.



Types of Electrolysers

There are three key types of electrolysers used today:


Alkaline electrolysers are the most established and proven. They operate at moderate temperatures, typically between 60 and 80 degrees Celsius, using a potassium hydroxide solution and nickel-based electrodes. These units are affordable, reliable, and well-suited for steady, long-term operation. However, they respond more slowly to fluctuations in electricity supply.


PEM electrolysers use a solid polymer membrane, also known as a proton exchange membrane, and operate at approximately 50 to 80 degrees Celsius under higher pressure. They produce highly pure hydrogen, start up quickly, and integrate well with renewable sources like solar and wind. However, they are more expensive due to the use of noble-metal catalysts such as platinum and iridium.


SOECs (solid‑oxide electrolysers) operate at much higher temperatures, typically between 700 and 1000 degrees Celsius. This allows them to use thermal energy in addition to electricity, which increases their overall efficiency to as high as 85 to 90 percent. While still an emerging technology, SOECs are ideal for locations where industrial waste heat is available. They do face challenges, including material limitations and higher capital costs.


Quick comparison:

  • Alkaline: cost-effective and durable, best suited for large-scale, steady hydrogen production.

  • PEM: compact and flexible, ideal for use with renewables and suitable for off-grid or variable conditions.

  • SOEC: highly efficient and promising for industrial applications, but still in the development phase.


The right type of electrolyser depends on your priorities: whether that is scale, hydrogen purity, system responsiveness, or energy efficiency.


Key Components and How They Work

Electrolysers are made up of several essential parts:


1. Electrodes – These include the anode and cathode, typically made of metals like nickel in alkaline systems or platinum and titanium in PEM systems. These components are where the water-splitting reaction occurs


2. Membrane or separator – This component keeps the generated gases apart and conducts ions while preventing gas crossover. In PEM systems, the membrane also facilitates the transport of protons.


3. Power system – The Balance of Plant includes transformers and rectifiers that convert alternating current (AC) into direct current (DC) for the stack. The stability and quality of the power source significantly impact system efficiency and longevity.


4. Balance of Plant (BOP) – This includes auxiliary components such as pumps for water or electrolyte circulation, purification systems, heat exchangers, gas separators, and control systems. These parts influence system reliability, cooling performance, water quality, and overall uptime.


Why does efficiency and reliability matter?

Efficiency depends on factors such as membrane resistance, electrode catalytic performance, and operational load. For instance, PEM systems can handle high current densities ranging from 1 to 3 amperes per square centimetre. However, pushing these systems too hard can shorten their lifespan. Alkaline electrolysers are simpler and typically operate at lower current densities between 0.4 and 0.8 amperes per square centimetre, but their efficiency decreases outside optimal conditions.


When all components function well together, the system runs more efficiently, lasts longer, and delivers clean hydrogen consistently.


Real-World Applications

Electrolysers are already being used in practical applications across a variety of sectors. One key use is in grid balancing and energy storage. Electrolysers can absorb excess renewable power from sources like solar and wind and convert it into hydrogen. This hydrogen can then be stored long-term or reconverted into electricity through fuel cells, helping to stabilise grid frequency, voltage, and capacity.


They are also vital for industrial decarbonisation. Industries that require high-temperature heat or clean feedstocks, such as ammonia production, steelmaking, glass manufacturing, and chemical processing, are beginning to adopt electrolytic hydrogen as a zero-carbon alternative to fossil fuels. For example, Australia’s Yuri project uses hydrogen from electrolysers to produce green ammonia for fertiliser.


In transport, hydrogen produced via electrolysis powers fuel-cell vehicles, including heavy-duty trucks, buses, forklifts, and even trains. These vehicles refuel quickly, have longer ranges, and emit only water vapour. The unifying advantage is flexibility. Electrolysers connect renewable energy generation to industrial use, energy storage, and clean transportation, while also enhancing grid stability.


Electrolysers Are the Bridge to a Cleaner Tomorrow

Hydrogen electrolysers are not simply a new form of technology. They are a foundational element of the clean energy transition. Electrolysers enable the storage of renewable electricity, reduce industrial emissions, and power sustainable transport. Although challenges remain, companies like PAC are already delivering practical solutions. The path to a greener future is becoming clearer, and hydrogen electrolysers are helping to pave the way.


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