Green, blue and grey hydrogen

A fuel cell is only as clean as the hydrogen you feed it. That's why people tag hydrogen with colors — they're a shorthand for how it was made, and therefore how much carbon it carries.

The main colors

Grey hydrogen. Made from natural gas by steam-methane reforming, releasing carbon dioxide. It's the cheapest and most common today — and the least clean.
Blue hydrogen. Same process as grey, but paired with carbon capture and storage to trap much of the CO₂. Cleaner than grey; how clean depends on the capture rate and any upstream methane leaks.
Green hydrogen. Made by splitting water with an electrolyzer powered by renewable electricity. The only by-product is oxygen, so it can be essentially carbon-free. It's the gold standard — and, for now, the most expensive.

You'll also hear about pink (electrolysis powered by nuclear) and turquoise (methane pyrolysis that yields solid carbon instead of CO₂). The colors aren't official chemistry — they're a useful way to talk about lifecycle emissions.

Why it matters. "Hydrogen is clean" is only half true. Hydrogen is an energy carrier, not an energy source — it's exactly as clean as the energy used to make it. The whole climate case for fuel cells rides on getting green (and credible blue) hydrogen cheap enough to scale.

Where it's heading

Electrolyzer costs have been falling and projects are scaling up worldwide. The honest near-term picture: green hydrogen is still pricier than grey, so the first big wins are in places where clean hydrogen is uniquely valuable — heavy industry, long-duration storage, and hard-to-electrify transport.

About the author — George Howell Ward is a long-time clean-energy advocate and early adopter, not a licensed engineer, energy professional, or scientist. He holds a B.S. in Civil Engineering from the University of California, Berkeley, and writes here as an enthusiast and technologist. These guides are educational, draw on legitimate science only, and avoid debunked claims. His interest goes back over a decade: he was an early hydrogen fuel-cell enthusiast who promoted the technology through hands-on demonstrations — including hydrogen fuel-cell model cars — and attended a multi-day fuel-cell seminar hosted by UC Irvine's National Fuel Cell Research Center. (Mentioning the Center is descriptive only — it does not imply the Center endorses George, this site, or its content.)

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