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[[Category:Energy storage]]
[[Category:Energy storage]]


'''Hydrogen gas''' (H<sub>2</sub>) is a combustible fuel that leaves behind nothing but water vapor (H<sub>2</sub>O) when burned.
'''Hydrogen gas''' (H<sub>2</sub>) is a combustible fuel that leaves behind water vapor (H<sub>2</sub>O) when burned {{light|(no carbon)}}. <!--
<!-- TALK: Maybe this is wrong if NOx emissions can be emitted too? {{qn}} If so, how to rephrase while maintaining simplicity? -->
'''Hydrogen gas''' (H<sub>2</sub>) is a combustible fuel that leaves behind only water vapor (H<sub>2</sub>O) when burned {{x|when burned in pure oxygen at least. Note that when it's burned in plain air, there are still some nitrogen oxides produced as well - but in any case, no CO<sub>2</sub> is produced from the combustion}}. -->


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}}.
There are basically '''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]]'''.
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]]'''.




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==Platinum-group metals==
==Platinum-group metals==
{{sum|Problem in some cases}}
{{sum|Problem in some cases}}
'''Tl;dr:''' [[Fuel cell vehicles]] '''would''' be a problem. [[Wind]]-based hydrogen production would '''not''' be.


Both '''electrolysis''' and '''fuel cells''' need platinum-group metals (PGMs):
 
Both ''electrolysis'' and ''fuel cells'' need platinum-group metals (PGMs):
* '''[platinum, palladium, rhodium, ruthenium, iridium, osmium]'''
* '''[platinum, palladium, rhodium, ruthenium, iridium, osmium]'''
** Any of these metals will do, but all of them are extremely scarce (even more than gold), with platinum & palladium being the most available.
** Any of these metals will do, but all of them are extremely scarce (even more than gold), with platinum & palladium being the most available.
** These metals serve as ''catalysts'' in the reactions. They are not used up, but they need to ''be there'', in a thin layer plated onto the electrodes.
** These metals serve as ''catalysts'' in the reactions. They are not used up, but they need to ''be there'', in a thin layer plated onto the electrodes.
{{minor|Note: It ''is'' possible to build fuel cells and electrolysis systems without PGMs, but the energy-efficiency is much lower.{{qn}} There are scientists trying to overcome this,<sup>[LINKS needed]</sup> but there's no guarantee that it will be viable in the near future.}}
{{minor|Note: It ''is'' possible to build fuel cells and electrolysis systems without PGMs, but the energy-efficiency is much lower.{{qn}} There are scientists trying to overcome this,<sup>[LINKS needed]</sup> but there's no guarantee that it will be viable in the near future.}}
The supply of PGMs is limited to what we can mine from the Earth (mineral reserves / resources), so we have to be mindful of how much would be needed.


===How much would be needed, if hydrogen were scaled up?===
===How much would be needed, if hydrogen were scaled up?===
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<tab name="General principles" collapsed>
<tab name="General requirements" collapsed>
The supply of PGMs is limited to what we can mine from the Earth (mineral reserves / resources), so we have to be mindful of how much would be needed.
 
{{minor|The mass of PGMs needed is proportional to ''peak power'':}}
{{minor|The mass of PGMs needed is proportional to ''peak power'':}}
* For electrolysis systems, the maximum '''rate of hydrogen production''' {{light|is limited by the amount of PGMs}}.
* For electrolysis systems, the maximum '''rate of hydrogen production''' {{light|is limited by the amount of PGMs}}.
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** {{minor|But the vehicle can still achieve ''short bursts'' of higher horsepower if there's a battery or supercapacitor in parallel with the fuel cell.}}
** {{minor|But the vehicle can still achieve ''short bursts'' of higher horsepower if there's a battery or supercapacitor in parallel with the fuel cell.}}
</tab>
</tab>


'''Scenario 1:''' If hydrogen gas (from wind power) were to directly replace all fossil fuels (this implies that people would drive [[hydrogen combustion vehicles]]):
'''Scenario 1:''' If hydrogen gas (from wind power) were to directly replace all fossil fuels (this implies that people would drive [[hydrogen combustion vehicles]]):
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|electrolysis.pgm_by_power / electrolysis.efficiency / wind.capacity_factor * fossil_fuels.consumption
|electrolysis.pgm_by_power / electrolysis.efficiency / wind.capacity_factor * fossil_fuels.consumption
|% pgm.reserves
|% pgm.reserves
|a
|...
}}
}}
{{calc
{{calc
|a
|...
|years pgm.mine_production
|years pgm.mine_production
}}
}}
</tab>
</tab>


In other words, the amount of PGMs needed is pretty reasonable - but we'd have to start mining a lot faster than the status quo (and find some way to do it '''without''' exploitative [[labor]]).{{npn}}
The amount of PGMs needed is pretty reasonable (16% of mineral reserves) - but we'd have to start mining a lot faster than the status quo (and find some way to do it ''without'' exploitative [[labor]]). {{npn}}


And in fact, some{{x|about half, if calculated from the same datapoints used on this page}} of this mining could be avoided, as we could also recycle existing catalytic converters{{x|which also contain ''some'' PGMs, though nowhere near as much as fuel cell vehicles}} from the gasoline cars and diesel trucks that would no-longer be used.
To prevent NOx emissions ([[#NOx emissions|see section below]]), hydrogen combustion vehicles need ''catalytic converters'', just like gasoline or diesel vehicles do. Catalytic converters ''also'' contain some PGMs, which could be obtained by recycling old catalytic converters from fossil-fuel vehicles.




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|(toyota_mirai.pgm - catalytic_converter.pgm) * world.cars * commercial_factor
|(toyota_mirai.pgm - catalytic_converter.pgm) * world.cars * commercial_factor
|% pgm.reserves
|% pgm.reserves
|b
|...
}}
}}
{{calc
{{calc
|b
|...
|years pgm.mine_production
|years pgm.mine_production
|||Fuel-cell vehicles don't need catalytic converters, but a fuel cell contains far more PGMs than a catalytic converter.
}}
}}
</tab>
</tab>
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One benefit of fuel cell vehicles is that they're more energy-efficient than combustion vehicles (i.e. less hydrogen used per kilometer driven).
One benefit of fuel cell vehicles is that they're more energy-efficient than combustion vehicles (i.e. less hydrogen used per kilometer driven).


The problem is, fuel cells would need 7 times the PGMs of Scenario 1 {{light|(estimated)}}. Perhaps too much to be scalable. And this is true even though we factored in the recycling of old catalytic converters this time (which have less than 1/10th the PGMs of a hydrogen fuel cell vehicle, on average).
The problem is, fuel cells would need 7 times the PGMs of Scenario 1 {{light|(estimated)}}. Perhaps too much to be scalable. And this is true even though we factored in the recycling of old catalytic converters (which have less than 1/10th the PGMs of a hydrogen fuel cell vehicle, on average).
 
 
'''Verdict:'''
* If we're going to have hydrogen-powered vehicles, most of them will probably have to be combustion only (or some sort of hybrid with just a very small fuel cell).
* At least PGMs are not a limiting factor for wind-based hydrogen ''production''.


<tab name="More discussion / research needed">
<tab name="More notes on these estimates" collapsed>
<div style="font-size:70%;color:#333;margin:1em;border:1px dashed #CCC">
More musings about the calculations above:
More musings about the calculations above:
* All of this assumes that electrolyzers and fuel cells can be completely recycled at their end-of-life, with all PGMs recovered. If they can't, we're kind of screwed in the long run (at least for hydrogen).
* All of this assumes that electrolyzers and fuel cells can be completely recycled at their end-of-life, with all PGMs recovered. If they can't, we're kind of screwed in the long run (at least for hydrogen).
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* But in any case, we probably wouldn't actually use wind/hydrogen for everything anyway. [[Rooftop solar]] combined with [[the great battery challenge|batteries]] could probably be a better way to provide electricity whenever hydrogen need not be involved.
* But in any case, we probably wouldn't actually use wind/hydrogen for everything anyway. [[Rooftop solar]] combined with [[the great battery challenge|batteries]] could probably be a better way to provide electricity whenever hydrogen need not be involved.
* Since vehicle fuel cells use the biggest share of PGMs in this estimate, this is yet another reason to advocate for [[public transit]] and [[walkability]].
* Since vehicle fuel cells use the biggest share of PGMs in this estimate, this is yet another reason to advocate for [[public transit]] and [[walkability]].
</div></tab>
</tab>


===Verdict===
* If we're going to have hydrogen-powered vehicles, most of them will probably have to be combustion only (or some sort of hybrid with just a very small fuel cell).
* At least PGMs are not a limiting factor for wind-based hydrogen ''production''.


<!-- TODO: Uncomment this when done writing about PGMs above (a more immediate and important mention that should be on here first)
==Atmospheric losses==
{{sum|Probably minor}}
The concern would be that when hydrogen gas leaks to the atmosphere, it's so light that it ends up being lost into outer space via [//wikipedia.org/wiki/Jeans_escape Jeans escape]. At what point would this permanent loss of hydrogen affect ecosystems? Would it be on the scale of billions of years or millions of years or thousands? Per unit of energy, I bet there would actually be hydrogen loss than with [[nuclear fusion]]. {{rn}} {{pn|TODO: Estimate using the status-quo gas leak rate of natural gas.}} }}
-->


==Energy losses==
==Energy losses==
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*** Note however: For vehicles, this is outweighed by the fact that [[hydrogen combustion vehicles]] are less fuel-efficient than [[fuel cell vehicles]].
*** Note however: For vehicles, this is outweighed by the fact that [[hydrogen combustion vehicles]] are less fuel-efficient than [[fuel cell vehicles]].


{{pn|TODO: add calculation: knowing the losses, is there still enough [[land]] for wind-generated hydrogen gas were to directly replace all fossil fuels, in principle?}}
{{pn|TODO: Add calculation: Knowing the losses, is there still enough [[land]] for wind-generated hydrogen gas were to directly replace all fossil fuels, in principle?}}




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* {{pn|This section needs more safety-related info.}}
* {{pn|This section needs more safety-related info.}}


==NOx emissions==
{{sum|Manageable}}
Burning hydrogen gas in air produces nitrogen oxides (NOx) in the same amount as burning gasoline or any other fuel. This happens because air is 78% nitrogen gas and 21% oxygen gas - any high temperature will cause some of the nitrogen to react with the oxygen. NOx gases are [[greenhouse gases]].
For [[hydrogen combustion vehicles]], this problem can be solved the same way it is for gasoline or diesel combustion: The vehicle has a ''catalytic converter'' to convert these gases into harmless substances. This requires some platinum-group metals ([[#platinum-group metals|see section above]]).




==NOx emissions==
==Atmospheric losses==
{{sum|{{rn}} }}
{{sum|Very minor}}
{{empty|TALK: maybe change the intro to this page; remove the "nothing but" with regards to water vapor?}}
'''Concern:''' When hydrogen gas leaks into the atmosphere, it's so light that it ends up being lost forever into outer space via [//wikipedia.org/wiki/Jeans_escape Jeans escape]. If this goes on for ''long enough'', could Earth lose enough hydrogen that it would harm ecosystems or deplete the global water supply? How long would that take exactly?
 
'''Answer:''' If we assume:
* that hydrogen gas leaks would happen at about the '''same rate''' as natural gas,
* that losing '''0.1%''' of the world's oceans would be enough to be a problem,
* that hydrogen gas would be replacing '''all''' fossil fuels, by energy,
Then it would take a '''million''' years to have even a minor effect on the ecosystems:
 
<tab name="(see maths)">
{{dp
|natural_gas.leak_rate
|1.4%
|Percent of natural gas that is lost to leaks
|[https://www.bloomberg.com/features/2022-methane-leaks-natural-gas-energy-emissions-data/ As Natural Gas Booms, Methane Leaks Spark Climate Alarm - Bloomberg]
}}
{{dp
|water.hydrogen_by_mass
|(hydrogen*2)/(hydrogen*2+oxygen)
|How much of water's mass is hydrogen
|About 11%. Calculated using chemistry constants built into the calculator.
}}
{{dp
|oceans.volume
|1.35 billion km^3
|Total volume of all oceans on Earth
|https://hypertextbook.com/facts/2001/SyedQadri.shtml
}}
{{dp
|hydrogen_gas.energy_by_mass
|120 MJ/kg
|The ''specific energy'' of hydrogen gas
|"...hydrogen has an energy density of approximately 120 MJ/kg , almost three times more than diesel or gasoline. In electrical terms, the energy density of hydrogen is equal to 33.6 kWh of usable energy per kg, versus diesel which only holds about 12–14 kWh per kg." - Oct 2, 2019 - Run on Less with Hydrogen Fuel Cells - RMI - rmi.org › Blog
}}
{{calc
|0.1% oceans.volume * waterdensity * water.hydrogen_by_mass
|million years (natural_gas.leak_rate / hydrogen_gas.energy_by_mass * fossil_fuels.consumption)
}}
{{minor|Side note: For the same amount of energy, this is still a lot more hydrogen loss than [[nuclear fusion]] of hydrogen atoms.}}
</tab>




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