The hydrogen that powers fuel cells comes overwhelmingly from fossil fuels. Nearly 47% of global hydrogen production relies on natural gas, 27% comes from coal, and 22% is a byproduct of oil refining. Only about 4% is produced by splitting water with electricity, the method most people picture when they think of “clean” hydrogen. Here’s how each of these sources works and what it means for the fuel in your fuel cell vehicle or power system.
Natural Gas: The Dominant Source
Almost half the world’s hydrogen starts as methane, the main component of natural gas. The production method, called steam methane reforming, has been the industry standard for decades. In a high-temperature reactor (700°C to 1,000°C), steam strips hydrogen atoms away from methane molecules. The immediate products are hydrogen gas and carbon monoxide.
A second reaction then converts that carbon monoxide into carbon dioxide while releasing additional hydrogen. Finally, the mixed gas passes through a purification step that filters out the carbon dioxide and other impurities, leaving behind nearly pure hydrogen. The entire process requires significant heat input, which is typically supplied by burning more natural gas. For every unit of hydrogen produced, a substantial amount of CO2 goes into the atmosphere. This is commonly called “grey hydrogen.”
Coal Gasification
Coal accounts for roughly a quarter of hydrogen production worldwide, particularly in countries with large coal reserves. Instead of reacting with steam at moderate temperatures, coal is heated to extreme temperatures (1,200°C to 1,700°C) with steam and oxygen. This breaks the solid carbon down into a synthetic gas mixture containing hydrogen, carbon monoxide, and methane, along with contaminants like hydrogen sulfide and ammonia.
That raw gas then goes through extensive cleaning to remove particles and toxic byproducts before the hydrogen is separated out using techniques like pressure-swing adsorption or membrane filtration. Coal gasification produces more CO2 per unit of hydrogen than natural gas reforming, making it the most carbon-intensive production route. It also generates solid waste like ash and slag, though newer high-temperature methods can convert some of these residues into glassy construction materials.
Blue Hydrogen: Fossil Fuels With Carbon Capture
“Blue hydrogen” uses the same natural gas reforming process but adds carbon capture technology to trap CO2 before it reaches the atmosphere. On paper, capture systems are designed to remove over 94% of emissions. In practice, no commercial-scale facility has achieved even 80%. The best-performing project to date, located in Alberta, Canada, captured about 68% of its CO2.
Part of the gap comes from the fact that steam methane reforming produces CO2 in two separate streams, and most existing plants only capture one of them. Proponents argue that future facilities designed to capture both streams will perform better. But scaling up carbon capture has consistently proven more difficult and more expensive than projected, so the real-world carbon intensity of blue hydrogen remains significantly higher than its theoretical potential.
Green Hydrogen: Splitting Water
The cleanest established method produces hydrogen by running an electric current through water, separating it into hydrogen and oxygen. When the electricity comes from renewable sources like wind or solar, the result is “green hydrogen” with essentially zero carbon emissions during production.
Two main types of electrolyzers do this work. Alkaline electrolyzers are the older, more proven technology. Proton exchange membrane (PEM) electrolyzers are newer, more compact, and better at responding to the variable output of wind and solar farms. Both accomplish the same basic chemistry: electricity in, hydrogen and oxygen out. To officially qualify as renewable hydrogen under international standards like the EU’s Renewable Energy Directive, producers must demonstrate that their electricity actually came from renewable generation, not just from the general grid.
Green hydrogen currently makes up only about 4% of global production because it costs more than fossil-based methods. That share is growing as renewable electricity gets cheaper and governments invest in electrolyzer capacity, but the transition is still in its early stages.
What’s Inside the Fuel Cell Itself
The hydrogen is the fuel, but the fuel cell stack that converts it into electricity is built from its own set of materials. In the most common type (PEM fuel cells, used in vehicles like the Toyota Mirai), hydrogen flows across a specialized polymer membrane called Nafion. Platinum serves as the catalyst that helps split hydrogen molecules into protons and electrons, generating the electric current.
The structural plates that channel gases through the cell are traditionally made from graphite, though manufacturers also use stainless steel and nickel-rich alloys to reduce cost and weight. Composite versions blend graphite powder into plastic resins. These materials need to resist corrosion in the acidic environment inside the cell while still conducting electricity, which is why material selection remains one of the key engineering challenges in making fuel cells affordable.
Hydrogen Found Underground
A newer possibility is skipping production entirely and mining hydrogen straight from the earth. Naturally occurring “geologic hydrogen” forms underground through chemical reactions between water and iron-rich minerals. For decades, scientists assumed these deposits were too small or too scattered to matter. That view is changing.
In 2024, the U.S. Geological Survey released the first national map of potential geologic hydrogen deposits. It identified promising regions across the mid-continent (Kansas, Iowa, Minnesota, Michigan), the Four Corners states (Arizona, Colorado, New Mexico, Utah), the California coast, and parts of the Eastern seaboard. These areas have the right combination of hydrogen-generating rock, porous reservoir layers to hold the gas, and cap rock seals to trap it.
The catch: much of this hydrogen is likely too deep, too far offshore, or in pockets too small to extract economically. No commercial geologic hydrogen wells exist yet. But if even a fraction of these deposits prove recoverable, they could provide a low-cost, low-carbon hydrogen source that bypasses the energy-intensive production methods used today.