Hydrogen gas

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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 gasexcept 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 if 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:   75 kJ/mol)
2 H2 + O2 → 2 H2O (exothermic:   572 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% efficientThis 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: