Hydrogen is now seen as a key player in the global transition to clean energy. As a carbon-free fuel, hydrogen has the potential to reduce greenhouse gas emissions when used in transportation, energy storage, and industrial processes. Hydrogen is classified based on the production methods and its carbon footprint.

• Grey Hydrogen
  Grey hydrogen is primarily produce through Steam Methane Reforming (SMR), a process where natural gas (methane, CH4) is reacted with steam (H2O) at high temperatures ( to produce hydrogen and carbon monoxide. The carbon monoxide is the then further reacted with steam in a water shift reaction, producing carbon dioxide (CO2) and additional hydrogen.
  
  Grey hydrogen is the most widely used form of hydrogen today due to the abundance of natural gas and the relatively low production cost, but it is highly carbon-intensive.
  
  
• Blue Hydrogen
  Blue hydrogen is produced similarly to grey hydrogen via Steam Methane Reforming (SMR), but with a crucial difference: the carbon dioxide (CO₂) emissions are captured and stored using Carbon Capture and Storage (CCS) technology. This reduces the environmental impact by preventing the CO₂ from being released into the atmosphere.
The captured CO₂ can be stored in geological formations or used in industries like enhanced oil recovery or industrial carbonation.
  
  
• Green Hydrogen
  Green hydrogen is produced through electrolysis, which splits water (H₂O) into hydrogen (H₂) and oxygen (O₂) using renewable electricity from sources like solar, wind, and hydropower. Since no fossil fuels are used in the process, there are zero carbon emissions, making green hydrogen the most environmentally sustainable hydrogen option.
  
  
• Pink Hydrogen
  Pink hydrogen is also produced by electrolysis, but the electricity used is derived from nuclear power. Nuclear energy provides a reliable, carbon-free source of electricity, making pink hydrogen a low-emission alternative. Pink hydrogen production can also utilize high-temperature electrolysis in some cases, which is more efficient than conventional methods.
  
  
• Turquoise Hydrogen
  Turquoise hydrogen is produced through methane pyrolysis, a process that splits methane (CH₄) into hydrogen (H₂) and solid carbon (C) at high temperatures, typically in the absence of oxygen. Methane pyrolysis does not generate CO₂, making it a cleaner alternative to SMR. The challenge lies in managing the solid carbon byproduct effectively.
Some companies are exploring ways to use solid carbon for materials like carbon black (used in tires, plastics, and pigments) or graphite (used in batteries).
  
  
• Yellow Hydrogen
  Yellow hydrogen is produced through electrolysis powered specifically by solar energy. It is a subcategory of green hydrogen but distinguishes itself by the exclusive use of solar power as the renewable energy source. This method has the advantage of being directly tied to solar farms, integrating hydrogen production with solar electricity generation.
  
  
• White Hydrogen
  White hydrogen refers to naturally occurring hydrogen found in underground reservoirs. This form of hydrogen requires minimal or no extraction processes beyond tapping into the hydrogen source. White hydrogen is a rare but naturally occurring gas, often found in geothermal or volcanic activity zones.
Extraction methods for white hydrogen are still in their early stages and face technical challenges.