
How a Hydrogen Fuel Cell Engine Works - jonbaer
http://www.rybrook.co.uk/magazine/news/how-a-hydrogen-fuel-cell-engine-works/
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audunw
Has anyone tried to calculate roughly how cheap and energy dense batteries
have to get before hydrogen fuel cells become uncompetetive for small/medium
vehicles?

I figure, hydrogen's technological downside is a fuel that's hard to store and
handle (can't fill a portable tank and carry around like with gasoline, can't
fill at home like with batteries). Pure battery's downside is shorter range
and longer time to "fill". Hydrogen's economical downside is a more complex
system with more parts to assemble. Battery's downside is the cost of large
amounts of batteries.

In both cases it seems that hydrogen has the upper hand in the short term, if
they solve the cost of the fuel cell itself. But in both cases it seems to me
like pure batteries have downsides that are likely to improve over time.

It would be interesting to know where the break-even point is, given we have a
cheap fuel cell.

I'm worried that the hydrogen fuel cells are a bit of a blind alley for cars.
Heavy trucks and cargo ships is another matter though. But then maybe biofuels
aren't so bad if we can just combust them cleanly enough.

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ZeroGravitas
The consensus seems to be that hydrogen fuel cells have never been competitive
for cars, so any future reduction in battery costs and building out of
charging infrastructure is only going to make that worse. So it's interesting
that you think they have a short term advantage.

There's also plug-in hybrid cars which would fill the gaps that pure EV don't
yet cover better than fuel cells, by allowing short commutes or restricted
city centres to be pure electric with no emisions, while still allowing for
quick refuels on longer journies and defeating range anxiety.

~~~
audunw
> So it's interesting that you think they have a short term advantage.

I think you missed this part ", if they solve the cost of the fuel cell
itself. "

Until they solve the high cost of the fuel cell, no, they don't have an
advantage at all. But I feel like it's reasonable to assume that it can be
solved.

That is, I want to give hydrogen the benefit of doubt, but even then I see
issues.

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m_mueller
AFAIK even if the fuel cell was free it would still not be competitive. The
reason being that you need 2-3x more electrical energy to get the same kinetiv
energy if you store it in hydrogen rather than lithium based batteries. There
goes the entire price advantage you have over gasoline cars - in order to get
the mass market it needs to be cheaper both upfront and to run it, which only
batteries can achieve, safe some revolutionary new way to convert electricity
to hydrogen.

There could be niche usecases though, such as long range trucks or buses - if
energy density is more important than fuel cost.

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jgamman
Google for the fuel cell handbook from the DOE. Last I looked it was a clear
intro. Wrt charge balances and driving force you need to remember this is a 3
phase system- h2 splits, ions migrate, charge balances by electron flow.
Product is steam that wafts away so it is reasonable to think of a fuel cell
as a battery with replenishable fuel. It's been a long time. I walked away
from fuel cells in '02 or so. Nothing has changed and battery tech has
completely owned any large scale opportunity

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avmich
> 2\. Hydrogen molecules activated by the anode catalyst release their
> electrons.

Can somebody describe how - and why - oppositely charged particles get
separated?

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agumonkey
Since I'm no chemist I don't get the details, but the thin platinum anode
"forces" Hydrogen to split into H+ to go through it, while electrons cannot
traverse and thus will flow to the other output...

[https://en.wikipedia.org/wiki/Fuel_cell#Types_of_fuel_cells....](https://en.wikipedia.org/wiki/Fuel_cell#Types_of_fuel_cells.3B_design)

Very tricky system.

~~~
avmich
Thank you. My question is about how that "forcing to split" works.

An example of how a catalyst works can be presented in terms of energies. If a
set of atoms (like, two atoms of hydrogen) can be in several different states
(like, as a molecule or as two separate atoms), and there is an energy barrier
between those two states, then the system "sits" in a potential hole. In order
to get to another state, it has to increase energy to overcome the barrier.
Catalyst can help with that, providing a new path between two energy states
which doesn't require that high jump in energy.

However, when initial state (the molecule) has much lower energy than the
final state (two separate atoms), catalyst doesn't help. There can't be a "low
energy path to the top of the energy mountain".

Here we don't have splitting of neutral molecule into neutral atoms... but I'd
still listen to an explanation.

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wuschel
Hi,

I am afraid I won't dig into this now due to time reasons (I have to go back
and read up stuff), but I just would like to give a remark regarding the
concept you have sketched out:

The different states you describe do not have to be on different energy
levels. A catalyst provides an alternative reaction mechanism that might have
a different activation energy. It can result in a molecule of similar energy
state, and, yes, you can have a reaction towards an energetically higher
state.

I am sure there is many a publication that models the electronic transitions
that occurs when gas molecules react with metals. Funky stuff, which involves
number crunching with models of atomic/molecular orbitals or bands, and even
more funky spectroscopic real time measurements of reactions.

Chemistry has gone a long way since alchemy, and there are many abstraction
layers to get through if you want to have an explanation that would satisfy a
physicists. At the end, you will move from empirical knowledge towards a world
of quantum chemistry/physics. That is the beauty (or curse) of the discipline
that is chemistry.

Now, if you are curious how such a thing works, I suggest look up the
"Wilkenson catalyst" (a Rhodium based catalytic hydrogenation agent) as an
example. It gives you an idea how organometallic compounds work at various
levels of depth.

~~~
avmich
> and, yes, you can have a reaction towards an energetically higher state.

Where does that extra chemical energy come from? Other degrees of freedom of a
molecule?

In general, I'd expect the reaction H2 -> 2H+ + 2e- not to be anything like
dominant. It's the separation of charges which is the source of energy of the
cell, and the energy is released along the path of those charges recombining.
Or am I missing something here?

> there are many abstraction layers to get through if you want to have an
> explanation that would satisfy a physicists.

Yes, I'm interested in the actual physics of the process, not in the net
chemical result...

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lagadu
Huh. I always just assumed that hydrogen cars were internal combustion
engines, in which they filled a combustion chamber with H2 and burned it off.
I'm surprised it's nothing like that.

Today I learned.

~~~
alirazaq
Internal combustion engines tuned for hydrogen fuel also exist. However the
benefit of a fuel-cell vehicle is being able to recharge the batteries with
the fuel-cells, regenerative braking, or at a charging stations.

[https://en.wikipedia.org/wiki/Hydrogen_internal_combustion_e...](https://en.wikipedia.org/wiki/Hydrogen_internal_combustion_engine_vehicle)

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JATOimpala
Are people actually amenable to driving cars carrying substantial quantities
of pressurized hydrogen and oxygen? It's a bomb on wheels.

~~~
Pigo
I never considered that. Surely it'd be illegal if a car crash would cause a
massive explosion.

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achamayou
There's no pressurised oxygen, only hydrogen, the oxygen is extracted from
ambient air as needed. If you work out a safety valve system that's good
enough (which has presumably been done, since Toyota Mirais are driving around
where I live), rapid release should be reasonably safe. Hydrogen is much
lighter than air and will evaporate quickly.

It's not as safe as diesel, but no worse than gasoline, or even large Lithium
batteries.

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spsgtn
700 atm? I would never drive with a tank of any significant size held at that
pressure.

~~~
baldfat
I have a friend who has been working on Hydrogen and fuel cells since 1999. He
told me in 2001 that it was never going to happen for cars and that fuel cells
just are not going to pay off except for a few instances that aren't really
clear.

2016 he says the same thing. Fuel cells will never be the fuel for cars and no
clear viable application. The issue is that you can't just go with hydrogen
into a magical filter and split the hydrogen atoms and get energy without it
costing multiple more then gas or electric.

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eip
RIP Stan Meyer

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cowardlydragon
It magically gets the free hydrogen from a bearded white man in the sky...

Then you add platinum which you get from the contract with the devil.

