Your guide to electrolysis: the tech behind the green hydrogen revolution

In an era marked by growing environmental concerns and the urgent need to transition towards cleaner and more sustainable energy sources, electrolysis has emerged as a transformative technology with the potential to revolutionize the energy landscape. It is the technology that facilitates the creation of green hydrogen.

Electrolysis is a process that harnesses electrical energy to split water molecules into hydrogen and oxygen gases. When the process is powered by renewable energy, it can be used to create green hydrogen. That green hydrogen can then, in turn, be used as a clean energy carrier.

The potential of green hydrogen to decarbonize hard-to-abate industries — shipping, aviation, steel, cement and petrochemical production — is vast. In fact, these industries account for roughly 30% of all greenhouse gas emissions.

Here’s everything you need to know about the technology responsible for the green hydrogen revolution.

Electrolysis will provide these sectors with green hydrogen

Transportation
Green hydrogen can be used in fuel cell vehicles, providing a zero-emission alternative to traditional internal combustion engines. Green ammonia and e-methanol, which are derivatives of green hydrogen, are currently being explored as key solutions in decarbonizing the world's industrial-scale transportation industries. This is particularly relevant in the global shipping industry, where there are projects set to be tested and developed as early as 2024.

Industry
Steel, cement and chemical production are among the industries with the highest level of emissions and, unfortunately, have the most difficulty in decarbonizing. This is partly due to the fact that many of the manufacturing processes across these industries require a large amount of energy to produce the high temperature heat needed for production. Luckily, these energy intensive processes can use green hydrogen as a substitute, opening up the possibility to produce products such as ‘green steel’ — where green hydrogen is used to generate heat and takes the place of coal and natural gas in facilitating chemical processes.

Energy storage
Green chemicals can also serve as energy storage mediums, allowing excess renewable energy from wind and solar to be stored and later converted back to electricity when needed. This helps stabilize the grid and supports the integration of intermittent renewable sources.

3 types of electrolysis: what you need to know
Electrolysis is primarily achieved through three types of industrial technologies: high-temperature Solid-Oxide Electrolysis Cell (SOEC); low-temperature alkaline electrolysis; and low-temperature polymer electrolyte membrane (PEM) electrolysis. With alkaline and PEM electrolysis, water is supplied as a liquid, whereas SOEC electrolysis uses steam due to its high temperatures.

PEM electrolysis
PEM electrolysis uses a solid polymer electrolyte membrane to separate the hydrogen and oxygen gases. This membrane allows for high proton conductivity, a key process in the creation of green hydrogen, while preventing the mixing of gases. It operates at relatively low temperatures, between 50-80°C, and is known for its rapid response time.

PEM electrolysis systems are compact, modular and well-suited for intermittent renewable energy sources like wind and solar. They can quickly adjust their output to match fluctuations in energy supply.

PEM electrolysis systems tend to be more expensive due to the cost of the membrane material. The market for PEM electrolysis is well established, particularly in applications requiring high purity hydrogen, such as fuel cell vehicles for pipelines. The market is expected to grow as renewable energy adoption expands.

SOEC electrolysis
SOEC electrolysis employs a solid oxide ceramic electrolyte that operates at high temperature, typically around 675°C to 825°C. At these temperatures, the water electrolysis reaction is easier to drive, which in turn results in a lower power consumption per unit of hydrogen produced.

SOEC offers higher efficiency than PEM and alkaline electrolysis, and can make use of waste heat from industrial processes or concentrated solar power. It is well-suited to large-scale hydrogen production with uses including steel, ammonia and chemicals production and refining.

The International Renewable Energy Agency (IRENA) estimate that SOEC electrolyzers are between 10-26% more efficient (by kWh per kg of hydrogen produced) than alkaline and PEM technologies.

SOEC electrolysis is a relatively nascent technology compared to PEM and alkaline for many applications. However, the technology holds promise for industrial and energy storage applications, especially where high-temperature heat sources and high heat-waste emissions are available.

Alkaline electrolysis
Alkaline electrolysis uses an alkaline electrolyte solution, usually potassium hydroxide, to facilitate the ion exchange process that makes hydrogen. It operates at moderate temperatures and has been used for decades in industrial applications.

Alkaline electrolyzers are cost-effective and have a long history of commercial use. However, Alkaline electrolysis systems are less efficient and slower to respond to load changes compared to PEM electrolysis.

Alkaline electrolysis remains competitive in certain industrial sectors but may face challenges in terms of efficiency and adaptability to renewable energy integration.

The opportunity of electrolysis
A green energy economy will not be enabled through any one single idea or technology. However, electrolyzers will be instrumental in creating green transitions for some of the world’s most carbon-intensive industries.

Green hydrogen is the bridge between a wind turbine, or a solar panel, to fuels we use in our everyday lives, in planes, in cars or in ships — and electrolysis makes that happen.

The emerging green hydrogen economy presents substantial economic prospects, fostering job creation and driving innovation and investment in clean energy technologies, and bolsters energy security.

Continued research, innovation and investment in electrolysis is essential — it is a major opportunity that will reap dividends for those who act fast and for the planet itself.

This was originally published on World Economic Forum's website 25 September 2023. You can see it here.