H2Tech editorial coverage includes the entire "spectrum" of hydrogen production—encompassing different types, or "colors," of H₂, as commonly referenced in industry jargon and further defined by the editorial team of H2Tech.

A summary of the commonly referenced colors of H₂ follows, in order from renewable feedstock types to non-renewable types:

Green H₂:

Produced via water electrolysis that is powered by renewable electricity, making the process carbon-neutral.

Pink H₂:

Produced via water electrolysis that is powered by nuclear energy, making the process carbon-neutral.

Red H₂:

Produced via biomass gasification, a process in which heat, steam and O₂ inputs are used to convert biomass to H₂ and other products in a controlled, non-combustion process. Feedstocks include forestry and agricultural crops and residues, animal residues, municipal solid waste and other biomasses. The process is associated with low CO₂ emissions.

Olive H₂:

Produced via algal or bacterial photosynthesis, via a bioreactor. Green microalgae or cyanobacteria provide enzymatic pathways, while water and sunlight provide power for the reaction. Although not a commercially viable technology pathway at this time, it holds promise for future large-scale, eco-friendly H₂ production as a carbon-neutral process.

Yellow H₂:

Produced via water electrolysis that is powered by mixed-origin grid energy (i.e., renewable energy and fossil fuels), associating it with low CO₂ emissions.

Blue H₂:

Produced via reforming of natural gas or gasification of coal, with added carbon capture, storage and utilization (CCUS). These processes are associated with low CO₂ emissions when CCUS is employed.

Turquoise H₂:

Produced via methane pyrolysis and grouped with low-carbon H₂ production processes. Results in a solid carbon byproduct.

Gray H₂:

Produced via reforming of natural gas (no CCUS). Accounts for 70% of present H₂ production, and results in medium CO₂ emissions. 

Brown H₂:

Produced via gasification of lignite coal. Results in high CO₂ emissions, and is highly polluting.

Black H₂:

via gasification of bituminous coal. Results in high CO₂ emissions, and is highly polluting.

White/Clear H₂:

Generated by raising the temperature of oil reservoirs, or naturally occurring in underground rocky deposits. Few viable H₂ exploitation strategies exist, although one company injects O₂ into spent oilfields to generate H₂ and other gases and then extracts H₂ via a wellbore, with the use of a proprietary downhole filter. The process is thought to be associated with low/no CO₂ emissions.

 A handy legend for the colors of H₂ production also appears below for industry reference. For questions about these classifications, please email Editors@H2-Tech.com.