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...
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.
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.
> 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...
Yes, I know the name of the process, but the level of details usually provided - including in this article - isn't quite enough for what I'm looking for.
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.
Surely this is the other way round: plug-in electric vehicles are starting to take off on batteries, having the upper hand in the short term. While hydrogen hasn't quite taken off because of the handling difficulties.
I think it's more likely we'll see a renewables-to-methanol/ethanol solution than a hydrogen economy. There are various proposed processes for this, including the USAF's nuclear-to-jetfuel one which claims $6/USgal amortised cost.
Renewables to methane probably makes more sense. Methane is cheap and easy to produce. Using it skips the additional step of methane to methanol conversion. There are already plenty of methane powered cars on the road in Europe and a few on the road in the US. Renewable production of methane is already being done at scale by BioSNG in Sweden.
This claims that it is not yet competitive with untaxed natural gas from fossil fuels though:
Methane still forces you to run on the Otto cycle or a variant thereof, not the more efficient Diesel cycle, so unless engine makers get HCCI right, renewables-to-diesel would still be a better choice.
The only thing that matters for adoption of renewables in transportation is $/mile. The efficiency of the heat engines is irrelevant.
Natural gas is cheaper to make in a renewable manner than diesel (Europe is already mass producing natural gas from biomass) and has higher energy densities in J/g, which makes it suitable for transportation. The lower combustion temperatures do lower efficiency, but they also lower NOx emissions, which are a difficult problem for diesel.
As far as aviation is concerned, natural gas could be more efficient not only due to the lower weight, but also due to the fuel being "precooled" in its liquid state:
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.
> 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.
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.
I would love to get some kind of hybrid vehicle. But I really want to talk to someone who has had one for a period of time, in the real world, before I commit to it. I have no clue what maintenance is like, or more importantly costs. Can you replace components, or do you have to buy entire assemblies when something breaks?
Most if not all of the EV car manufacturers offer long warranties. Components are replaced. The better companies like Telsa do recalls over efficiency improvements, and over the air software upgrades.
The two issues I see with pure battery solutions are weight and recharge time. As density increases we can solve the weight issue which is a serious negative currently but the issue with more density/etc is that charging systems may evolve beyond the point of being installed anywhere but dedicated facilitates.
Has anyone calculated the maximum in KW/H or such that a normal house hold could sustain from standard street connections?
> Has anyone calculated the maximum in KW/H or such that a normal house hold could sustain from standard street connections?
I don't feel like this is very relevant. The number of people who can't charge their daily need within 8 hours on a 10kW connection is on the order of one in every 10'000, if not less.
Or maybe you assume people charges at home in the same pattern as how they fill gasoline? I.e., they only charge when the battery is down to like 30%? That's probably not gonna be the case. If you have the option to charge at home, there's no reason not to plug it in every night.
A significant number of people will need to drive long distance 2 or more days in a row, every once in a while, so that has to be solved by rapid charging stations.
We will end up with ~350kW rapid chargers (the rough physical limit with water cooled cables), which is almost fast enough that it'd feel like filling gasoline does. But yeah, that will be dedicated facilities with grid storage scale batteries to smooth power consumption.
Yup in ~2 years of EV ownership only time I've every wanted faster charging at home(~15kW) was once after ~7 hours of driving with 5% left when I finally got home.
Just ended up taking the other car we had, if I needed to I could have just hung out at the supercharger for another 15 minutes.
What's the charging limit on the car end of the cables limit it to 350kW. If it's a purpose built charge-station then why not superconducting cabling, or pumped liquid nitrogen, or ... that would push to the limit of the car/battery.
In the US the 'standard' service for new household installations is 100 amps, but there isn't anything unusual about 200 amp service.
So with the larger panel, a bit more than 40 kW.
And maybe 15 kW with the smaller panel if you want to be able to run other stuff. So 6.5 hours is enough to fully charge the biggest Tesla packs using a normal connection. Install a bigger service and you can do 200 kW in that time (I guess charging might slow down, but that's the facile napkin math).
It's also likely to be acceptable to only add 500 miles of range in the first night of charging.
There's toy investment in hydrogen and quite a lot of vehicles on the road using LNG. I don't think it is really a blind alley, it's just that fuel cells exist so they get talked about.
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.
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.
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.
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.
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
34 comments
[ 3.3 ms ] story [ 69.1 ms ] threadCan somebody describe how - and why - oppositely charged particles get separated?
https://en.wikipedia.org/wiki/Fuel_cell#Types_of_fuel_cells....
Very tricky system.
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.
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.
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...
https://en.wikipedia.org/wiki/Alkaline_fuel_cell
Then you add platinum which you get from the contract with the devil.
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.
I think it's more likely we'll see a renewables-to-methanol/ethanol solution than a hydrogen economy. There are various proposed processes for this, including the USAF's nuclear-to-jetfuel one which claims $6/USgal amortised cost.
It has better energy density than ethanol and absorbs less water than ethanol and is not as good a solvent as ethanol (so engine parts last longer).
This claims that it is not yet competitive with untaxed natural gas from fossil fuels though:
http://www.biosng.com/fileadmin/biosng/user/documents/report...
Presumably, the taxes in Sweden are sufficient to make it feasible.
Natural gas is cheaper to make in a renewable manner than diesel (Europe is already mass producing natural gas from biomass) and has higher energy densities in J/g, which makes it suitable for transportation. The lower combustion temperatures do lower efficiency, but they also lower NOx emissions, which are a difficult problem for diesel.
As far as aviation is concerned, natural gas could be more efficient not only due to the lower weight, but also due to the fuel being "precooled" in its liquid state:
https://en.m.wikipedia.org/wiki/Precooled_jet_engine
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.
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.
There could be niche usecases though, such as long range trucks or buses - if energy density is more important than fuel cost.
Has anyone calculated the maximum in KW/H or such that a normal house hold could sustain from standard street connections?
I don't feel like this is very relevant. The number of people who can't charge their daily need within 8 hours on a 10kW connection is on the order of one in every 10'000, if not less.
Or maybe you assume people charges at home in the same pattern as how they fill gasoline? I.e., they only charge when the battery is down to like 30%? That's probably not gonna be the case. If you have the option to charge at home, there's no reason not to plug it in every night.
A significant number of people will need to drive long distance 2 or more days in a row, every once in a while, so that has to be solved by rapid charging stations.
We will end up with ~350kW rapid chargers (the rough physical limit with water cooled cables), which is almost fast enough that it'd feel like filling gasoline does. But yeah, that will be dedicated facilities with grid storage scale batteries to smooth power consumption.
Just ended up taking the other car we had, if I needed to I could have just hung out at the supercharger for another 15 minutes.
So with the larger panel, a bit more than 40 kW.
And maybe 15 kW with the smaller panel if you want to be able to run other stuff. So 6.5 hours is enough to fully charge the biggest Tesla packs using a normal connection. Install a bigger service and you can do 200 kW in that time (I guess charging might slow down, but that's the facile napkin math).
It's also likely to be acceptable to only add 500 miles of range in the first night of charging.
It's not as safe as diesel, but no worse than gasoline, or even large Lithium batteries.
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.
Today I learned.
https://en.wikipedia.org/wiki/Hydrogen_internal_combustion_e...