Methane cracking

Methane cracking(...)( Note: the word 'cracking' has nothing to do with physical cracks in any material. ) is a process that converts methane (usually from natural gas) into hydrogen gas and solid carbon. The hydrogen can be burned for energy, and the carbon could be buried in the ground or used for something else. The carbon does not become CO₂ (unlike normal combustion of methane).

Energy viability

Not viable - but could work in theory

Every methane-cracking method invented so far is a net loss of energy. Meaning that it takes more energy to crack the methane than you ultimately get from burning the hydrogen.

But in theory, this need not be true:

Cracking the methane:

CH₄ → C + 2 H₂     (energy in:endothermic reaction   74.850 kJ/mol)

Burning the hydrogen:

2 H₂ + O₂ → 2 H₂O   (energy out:exothermic reaction 571.640 kJ/mol)

Hydrogen production efficiency comparison

Type	Method	Energy out / energy in
Methane cracking	Theoretical best case	764% [''']from the chemistry equations above
Not methane cracking	Electrolysis of water	80%
Methane cracking	Best technologies so far	. . .   [''']To be filled in soon. It's almost certainly less than 80%.
Not methane cracking	Heat -> turbine -> electrolysis of water	25%

There have been some green initiatives to use non-fossil-fuel energy to crack methane to make hydrogen gas. However, this is only worthwhile if the efficiency is better than non-methane-cracking ways to make hydrogen (see table).

Above 100%, you don't need any non-fossil-fuel energy for it to be green. Just burn some of the hydrogen to keep cracking the methane. Sadly, this has never been achieved.

In the ideal case, fossil fuels could power the entire world with zero carbon emissions. At least, until oil and gas reserves run out.