The colors of hydrogen offer a clear, visual way to understand how hydrogen is produced and its impact on the environment. While hydrogen itself is a colorless gas, “hydrogen colors” refer to the various production methods, each with unique environmental footprints. This brief guide details the hydrogen color spectrum and explains why these distinctions are crucial for the transition to clean energy.
What Does “Colors of Hydrogen” Mean?
Hydrogen is the most abundant element in the universe but is rarely found in its pure form on Earth. Instead, it must be produced from other resources – such as water, fossil fuels, biomass, or through nuclear processes. The colors of hydrogen make it easy to identify how hydrogen is sourced and how clean the process is: each color represents a different production process, resource, and environmental impact.
The Hydrogen Color Spectrum
Gray Hydrogen
Gray hydrogen is produced from natural gas (methane) through a process called steam reforming. In this method, methane reacts with high-temperature steam to produce hydrogen along with carbon monoxide (CO) and carbon dioxide (CO2). The greenhouse gases made in the process are not captured.
Most of the hydrogen produced for industrial use today is gray. In fact, the unabated natural gas route dominates, accounting for around two-thirds of the total hydrogen production.
Black and Brown Hydrogen
Black hydrogen is produced from anthracite or black coal through a process called gasification. Brown hydrogen follows the exact same process but is made from lignite or brown coal. Brown and black hydrogen are recognized as the most environmentally damaging, as substantial carbon emissions are released during the gasification process.
Blue Hydrogen
Blue hydrogen aims to address the emissions problem of gray hydrogen by coupling the steam methane reforming (SMR) process with carbon capture and storage (CCS) technology. In this approach, hydrogen is still produced from natural gas, but the CO2 byproduct is captured and permanently sequestered underground or used in other industrial processes.
Since emissions are captured and not dispersed in the atmosphere, blue hydrogen is more environmentally friendly than gray hydrogen and is often referred to as a “low carbon” hydrogen.
Green Hydrogen
Green hydrogen is produced from water using clean energy from renewable energy sources, such as solar, wind, or hydroelectric power. Through a process called electrolysis, water molecules (H2O) are split into hydrogen and oxygen. While hydrogen is extracted and stored, oxygen is simply released into the atmosphere without any negative impact on the environment.
Using electricity from renewable sources, green hydrogen is considered a truly clean, zero-emission fuel. While today’s global production of hydrogen is still primarily derived from fossil fuels, green hydrogen is expected to rise as the cost of renewables falls: according to IRENA, 94% of hydrogen will be based on renewable energy by 2050.
Turquoise Hydrogen
Turquoise hydrogen is produced through a process called methane pyrolysis, which uses high temperatures to split methane (CH4) into hydrogen and solid carbon. This method eliminates the need for CCS technologies, as the produced carbon is solid and doesn’t need to be captured. If the thermal process is powered with renewable energy and the carbon is permanently stored and used, turquoise hydrogen can be considered a low-emission type of hydrogen.
Pink, Red and Purple Hydrogen
These three colors have in common that they use nuclear energy to generate hydrogen from water. While the energy source is the same (nuclear), they differ in terms of production process: pink hydrogen is made through electrolysis, red through thermolysis (high-temperature catalytic splitting of water), and purple through a combination of electrolysis and thermolysis (a process called thermochemical electrolysis).
Yellow Hydrogen
Yellow hydrogen typically refers to hydrogen produced through solar-powered water electrolysis. However, it is sometimes used also when a mix of renewable and nuclear power sources are used.
Gold and White Hydrogen
Gold hydrogen – sometimes referred to as white, geological, or natural hydrogen – is a naturally occurring gas found in underground reservoirs, just like oil and natural gas. Unlike other types of hydrogen that are industrially produced, this form of hydrogen is created by natural geological processes. Gold hydrogen naturally accumulates in subsurface deposits, from where it can be extracted using drilling technologies.
Why the Colors of Hydrogen Matter
Identifying the colors of hydrogen is essential because not all hydrogen is environmentally friendly. Fossil fuel-based hydrogen (grey, black, brown) can be 9 to 18 times more carbon-intensive than green hydrogen. As nations move toward net-zero emissions by 2050, clean hydrogen (particularly green and blue) is set to become the dominant forms for a sustainable future. According to McKinsey, all new hydrogen production coming online after 2025 is in fact expected to be clean, supporting the gradual phase out of grey hydrogen and the shift to low-carbon hydrogen.
Enabling the Hydrogen Economy
Even as low-carbon and green hydrogen production rises, many challenges need to be tackled to enable the hydrogen economy — most notably, safe, efficient storage and transportation. Hydrogen’s low volumetric density requires advanced solutions to avoid inefficiency and high costs. Traditional storage methods involving compression or liquefaction have been incrementally improved over the past decades, but are still overall expensive and inefficient.
At H2MOF, we are developing a transformative, solid-state technology based on reticular materials for the safe and efficient storage of hydrogen at low pressure and near-ambient temperature. Learn more on our technology here!