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Hydrogen gas: Difference between revisions
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Hydrogen gas ( | Hydrogen gas (H<sub>2</sub>) is a fuel that when burned, produces no pollution and no [[climate change|carbon emissions]] - only water vapor (H<sub>2</sub>O). | ||
To make hydrogen gas, you need to use some other [[energy]] source. | There are '''no''' natural resources of hydrogen gas{{x|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== | ==Production== | ||
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===Electrolysis=== | ===Electrolysis=== | ||
Electricity can turn water ( | Electricity can turn water (H<sub>2</sub>O) into hydrogen gas (H<sub>2</sub>) and oxygen gas (O<sub>2</sub>). This process is called [[electrolysis]]. | ||
The electricity could come from renewable sources such as [[solar]], [[wind]], or [[ | 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: [[electrolysis#need for catalyst metals|the need for rare metals]] in the electrolyzers.<!-- TODO: say more decisively whether this scaling is viable or not: but first there are questions to resolve on the [[electrolysis]] page --> | ||
==== | ===From fossil fuels=== | ||
Currently most hydrogen is produced from [[natural gas]] via [//wikipedia.org/wiki/Steam_reforming steam reforming], but this emits just as much CO<sub>2</sub> 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 CO<sub>2</sub>). The main problem is that it's a ''net loss'' of energy {{x|it takes a lot more energy than you ultimately get by burning the hydrogen gas}}. In theory, it doesn't have to be. | |||
{{p|Chemistry equations:<br />CH<sub>4</sub> → C + 2 H<sub>2</sub>   (endothermic: 75 kJ/mol)<br />2 H<sub>2</sub> + O<sub>2</sub> → 2 H<sub>2</sub>O (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.{{rn}} | |||
*** 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{{x|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.<!-- TODO: cite that article I found awhile ago --> | |||
* | * [[Pink hydrogen]] is made from electrolysis using [[nuclear]] energy. | ||
* [[Green hydrogen]] is made from electrolysis using renewable energy. | |||