O hydrogen is a highly versatile chemical element, widely used as a fuel and raw material in various industries. Under normal conditions, it is found in the form of a colorless, odorless and highly flammable gas.
In recent years, hydrogen has gained relevance as a clean energy alternative, especially in the context of the energy transition to reduce greenhouse gas emissions. Hydrogen production can be classified by “colors”, according to the energy source and the method used.
Gray hydrogen
Gray hydrogen is the most common type that is traditionally produced from natural gas, primarily through the steam methane reforming process.
In this process, natural gas is subjected to high temperatures and pressure, resulting in the release of hydrogen and carbon dioxide (CO₂).
The downside of grey hydrogen is that it generates a significant amount of CO₂ emissions, one of the main greenhouse gases.
As a result, although it is a cheap way to produce hydrogen, grey hydrogen is considered less sustainable and faces criticism due to its environmental impact.
Blue hydrogen
Blue hydrogen is also produced from fossil fuels, such as natural gas, but with one important difference: the carbon dioxide generated during the process is captured and stored using carbon capture and storage (CCS) technologies.
This prevents CO₂ from being released into the atmosphere, making blue hydrogen less polluting compared to gray.
While blue hydrogen is considered a more sustainable alternative, it still relies on fossil fuels and may have limitations depending on the efficiency and scale of carbon storage.
green hydrogen
Green hydrogen is considered the cleanest and most sustainable form of hydrogen, as it is produced through water electrolysis, a process that uses electricity to separate water molecules into hydrogen and oxygen.
When the electricity used comes from renewable sources such as solar, wind or hydropower, the resulting hydrogen is completely carbon-free.
This approach makes green hydrogen an ideal option for combating climate change and reducing carbon footprint.
However, this technology is still expensive and depends on the availability of large-scale renewable energy to become economically viable.
Turquoise hydrogen
Turquoise hydrogen is an emerging technology produced through methane pyrolysis, which breaks methane into hydrogen and solid carbon instead of carbon dioxide.
This means there are no direct CO₂ emissions, making the process less polluting. Turquoise hydrogen is promising, but the technology is still in development and not widely commercialized.
Other colors: yellow, white and pink
Yellow hydrogen is produced by electrolysis, but uses electricity from a variety of sources, such as nuclear power. White hydrogen refers to hydrogen that occurs naturally in underground deposits, although it is rare and difficult to exploit.
Pink hydrogen is produced by electrolysis with electricity from nuclear power plants, which also does not generate direct carbon emissions.
In short, the “colors” of hydrogen reflect the different technologies and energy sources used in its production. Green hydrogen holds the most promise for a sustainable future, but gray, blue and other hydrogen variants still play important roles in the global energy transition.
As technologies evolve and costs decrease, hydrogen can become a key part of the global energy mix, promoting a cleaner economy that is less dependent on fossil fuels.
The production of green hydrogen is possible thanks to a process called electrolysis, which separates water (H₂O) into hydrogen (H₂) and oxygen (O₂) using electricity.
This process is central to the development of a sustainable, low-carbon hydrogen economy, as it does not release polluting emissions when the electricity used is from renewable sources.
How does water electrolysis work?
In electrolysis, a device known as a electrolytic cell, which consists of two electrodes (cathode and anode) immersed in water or a conductive aqueous solution, the electrolyte.
When electricity passes through the electrodes, it causes a chemical reaction that splits water molecules.
The process occurs in stages:
- Application of electric current: An electrical power source is connected to the electrodes, creating a potential difference. The cathode is the negative electrode, and the anode is the positive electrode.
- Separation of ions: When current passes through water, it splits the water molecules into hydrogen (H⁺) and hydroxide (OH⁻) ions.
- Reactions at the electrodes:
- At the cathode, a reduction reaction occurs: H⁺ ions receive electrons, forming hydrogen gas (H₂);
- At the anode, an oxidation reaction occurs: OH⁻ ions lose electrons, releasing oxygen gas (O₂) and forming water.
- Gas Production: Hydrogen gas is formed and released at the cathode, while oxygen gas is released at the anode. This hydrogen can be captured and stored for use as a fuel or in industrial processes.
Importance and challenges of electrolysis
Electrolysis is a promising technology for the production of green hydrogen, because when the electricity is from renewable sources, the process is entirely carbon-free.
However, the process is energy intensive, which increases its costs and requires innovations to increase efficiency and economic viability.
As the costs of renewables fall and electrolysis technology advances, green hydrogen is becoming an increasingly viable alternative to decarbonize sectors such as heavy transport, chemical industries and power generation.
Thus, electrolysis is a key piece for the future of hydrogen and the global energy transition.
The production of green hydrogen can help store excess energy from renewable sources, promoting greater integration of these sources and contributing to a more sustainable and resilient energy matrix.
