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suman suhag's avatar

When hydrogen is made from natural gas by partial oxidation it is a fossil fuel, because it is just the hydrogen that was in the CH4-molecule which constitutes natural gas.

CH4 + O2 -> CO2 + 2H2

When hydrogen is made from natural gas by steam reforming it is only partially a fossil fuel, because the hydrogen is partially from the CH4 and partially from the water steam. Most hydrogen is produced this way.

CH4 + 2 H2O -> CO2 + 4H2

When hydrogen is made from coal and water it is actually not a fossil fuel, because the hydrogen all comes from the water.

C + 2H2O -> CO2 + 2H2

But in all those cases you use energy that is stored in the fossil fuel to produce hydrogen, so in this regard it is a fossil fuel in any case. Note, that in all those cases CO2 is released. So, like every fossil fuel, hydrogen is not carbon neutral. The difference to conventional fossil fuel is that the CO2 is formed when you produce the hydrogen, not when you burn it.

Hydrogen made from biomass, water electrolysis, water photolysis or water thermolysis is not a fossil fuel and therefore potentially carbon neutral.

EDIT: You also can make hydrogen by pyrolysis of natural gas.

CH4 + energy (72 kJ/mol) -> C + 2H2

In this case hydrogen is a fossil fuel, but potentially carbon neutral, because no CO2 is formed, it only produces hydrogen and high purity solid carbon, which can be used for steel making.

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