Hydrogen gas

Hydrogen gas (H₂) is a fuel that when burned, produces no pollution and no carbon emissions - only water vapor (H₂O).

There are no natural resources of hydrogen gas(...)( except in rare and extremely small quantities, not a viable way to supply energy in any meaningful amount ). To make hydrogen gas, you need to use some other energy source. In this way, hydrogen can be understood as a form of energy storage.

Production

Electrolysis

Electricity can turn water (H₂O) into hydrogen gas (H₂) and oxygen gas (O₂). This process is called electrolysis.

The electricity could come from renewable sources such as solar, wind, hydro, or geothermal. But even we manage to scale up those energy sources, there is still an issue with scaling up the electrolysis itself: the need for rare metals in the electrolyzers.

From fossil fuels

Currently most hydrogen is produced from natural gas via steam reforming, but this emits just as much CO₂ as burning the natural gas itself.

There's another (similar) process called methane cracking which takes in natural gas, and produces hydrogen gas + solid carbon (not CO₂). The main problem is that it's a net loss of energy (...)( it takes a lot more energy than you ultimately get by burning the hydrogen gas ). In theory, it doesn't have to be. [''']Chemistry equations:
CH₄ → C + 2 H₂ (endothermic: 74.850 kJ/mol)
2 H₂ + O₂ → 2 H₂O (exothermic: 285.820 kJ/mol)

Usage

Most hydrogen gas today is used in making fertilizer. However, there are other things that could be done with hydrogen if production was scaled up enough:

• Hydrogen gas can be burned.
  • This could be useful for heating and cooking.
  • It might be possible for some existing natural gas infrastructure be retrofitted for hydrogen gas.^{[RESEARCH needed]}
    • If so, gas stoves could run on hydrogen.
• Hydrogen gas can be used for making electricity, using a fuel cell.
  • However, to use this in energy storage systems is quite lossy:
    • "electricity → hydrogen gas → back to electricity" is at best only 40% to 48% efficient(...)( This is the combined energy-efficiency. The electrolyzers are about 80% efficient, and the fuel cells are about 50% to 60% efficient. ).

In this way, fuel cell vehicles are not as efficient as battery electric vehicles. At least they're still more efficient than hydrogen combustion vehicles.

Color terminology

Hydrogen is a colorless gas, but people sometimes name it with colors to indicate how it was produced:

• Grey hydrogen is made from natural gas (steam reforming) - high greenhouse gas emissions. Currently the vast majority of hydrogen is produced this way.
• Blue hydrogen is made from natural gas the same way, but with carbon capture. This is supposed to reduce emissions, but in practice it doesn't help much.
• Pink hydrogen is made from electrolysis using nuclear energy.
• Green hydrogen is made from electrolysis using renewable energy.