I'm not a chemist/physicist, but if I had to guess it's because it takes more energy to break apart the water into Hydrogen than what you will get by burning the Hydrogen to power the motor.
this post was submitted on 14 Feb 2024
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Your guess is accurate.
The other side of the issue is that "water" is rarely only water. There are tons of other shit floating in the water that cause problems with the splitting process, so you usually have to clean the water first which takes even more energy/resources.
Correct. Splitting hydrogen from water is quite energy intensive. Burning hydrogen into oxygen to make water releases energy, but not as much energy as it takes to split the hydrogen off in the first place. The reason to use hydrogen fuel cells is that the extra energy needed to generate the hydrogen is still far better than the carbon output and costly materials needed for making and charging a battery. Batteries need rare earth metals, and they lose their charging ability over time. Splitting water into hydrogen creates "potential energy" from the later creation of water again, making it a useful, clean way to store electricity.
Same as the plans for using cranes stacking concrete bricks to store electricity. It takes more electric to stack them than is produced by unstacking them. But it's a clean way to store potential energy, and far more efficient and sustainable than a battery.
The reason to use hydrogen fuel cells is that the extra energy needed to generate the hydrogen is still far better than the carbon output and costly materials needed for making and charging a battery.
This is just absolutely a false statement. Hydrogen is a carbon fuel, because all of it for practical purposes comes from natural gas. Although it is possible to get hydrogen through electrical hydrolysis, this simply is not where hydrogen as a fuel source comes from today.
If you see or hear hydrogen being discussed, translate the word hydrogen to mean 'natural gas' or fossil fuels, because that's what you are actually talking about. We do not currently get hydrogen as a fuel by splitting. We currently get hydrogen as a fuel by splitting hydrogen from natural gas. You would likely be better off just driving a gas car than a hydrogen powered if your goal is overall emissions reductions. Batteries represent an actual renewable technology because right now (not hypothetically) we can and do power the electrical networks that charge them with renewables. In as far as renewable hydrogen is concerned, there basically is none, because it costs so much more so to produce in this manner than it does to get hydrogen from fossil fuels.
Correct. Green hydrogen is expensive and energy intensive, and is not as cost effective as getting it from natural gas. So currently most hydrogen comes from natural gas.
But, unless we find ways to make batteries without rare earth metals, we will be better suited to moving towards fuel cell, once we have the excess electricity from renewables needed to split hydrogen from water. For now, batteries are the better option.
Yep. Just wanted to get it out there because there are active propagandists promoting H2 as it's an extant carbon neutral technology ( I expect Hypx to show up any moment). I'm not arguing against potential but trying to ground the conversation in material reality.
Sodium-ion batteries appear promising. Like, the energy density by weight of the current market offerings is absolutely too low to be useful for vehicles, but there's hope that can be improved in a relatively short timescale. Prices should be pretty good when factories finish tooling up, and most chemistries use no rare earth metals. Current densities seem great for grid storage, which is where hydrogen has the most potential right now (imo).
I still like the idea of hydrogen for some forms of transportation (freight trains, container ships, possibly aircraft if energy density could be increased or aircraft weight decreased somehow) and as a strategic emergency energy reserve. It'd be great to have more grid resilience as the environment continues to decay. I just worry about the energy costs that come with transporting hydrogen for cars and individual transport. Pipelines seem like they'd be challenging, and trucking it around seems a bit wasteful. In-situ generation would be ideal if power and water are available and hydrolysis can be made more efficient and compact, but that's not possible everywhere.
I dunno. I'm glad it's not my job to figure out the actual energy cost of everything, but I'm really hoping grid-scale sodium-ion batteries will become a reality sooner rather than later, and that we'll see sodium-ion batteries in cars within the next 10-15 years.
As a lot of people have already said, breaking water down into hydrogen and O2 requires more energy than that produced by running a car on hydrogen.
Luckily, there's some promising research underway, on solar panels that converts water vapour in the air into hydrogen. Last I read, they're approaching kilowatt scale, but it takes a big system to produce just 500 grams of hydrogen in a day. Which will only produce around 2kW of output power.
Assuming they can somehow make all of that much smaller, and produce much, much more hydrogen from that smaller system, there's the secondary problem of storing and pressurizing the hydrogen produced, for use in a vehicle. That will take more energy again.
"Hydrogen powered" generally means burning hydrogen in oxygen to make water: 2(HH) + OO -> 2(HHO). To run a car on water as you say is a lot like trying to make a fire out of ash, rather than wood. You can't burn the ash because it has already been burned.
Technically speaking, no one outside of college demonstration engines are burning hydrogen. Almost all hydrogen powered EVs use fuel cell stacks that mediate the proton exchange through an electrolyte. This allows the capture of far more energy than could be possible by just letting the hydrogen burn, as in a internal combustion engine, for example.
True, but this is basically a battery.
Technically speaking, no one outside of college demonstration engines are burning hydrogen
Toyota has made various working prototype hydrogen combustion engines, so it's not impossible these could end up in production in the nearish future (they've done a hydrogen version of at least the GR Yaris/Corolla engine, a V6, and a V8).
They specifically said they were R&D units and never intended any to go to production. Sometimes they do that to gather data. Hydrogen combustion simply isn't efficient enough for a production vehicle. You'll be surprised by the amount of crazy tests car manufacturers do. This includes methanol/ethanol cars, natural gas ICE engines, solar panels, all sort of crazy experimental batteries.
Where does the energy to break down the water in the car come from?
Iirc the energy required to break down water into hydrogen and oxygen is greater than what burning the mixture produces, but in theory solar power might be a viable option to a certain extent.
Efficiency/viability would probably be nonexistent without some sort of miracle catalyst for the breakdown process.
Kinda like internal combustion, you can probably use a battery or something to start it and then use part of the energy from the motor to further continue the process, but yeah lol this seems wishful thinking🤷🏼♂️
That would be a perpetual motion machine, and violate the first law of thermodynamics.
The amount of energy you get by burning hydrogen (creating water) is exactly the same as you spent to split water into hydrogen and oxygen.
assuming no losses
Which in practice there absolutely would be.
Water is the exhaust product. Once you have water, the potential energy in the original chemical mix has already been released.
H~2~ + O --> H~2~O + energy (in the form of heat or electric potential)
To break down water you have to reverse the reaction and put that energy back in. That's how electrolysis works:
H~2~O + energy (in the form of electric potential) --> H~2~ + O
And since no thermodynamic process is 100% efficient, you will lose some of the energy each time you go back and forth between these reactions.
Out of curiosity, would you end up with the same resultant amount of water before and after hydrolysis? I'm aware some energy would be lost, but would hydrolysis actually decrease the amount of water? (sorry if this a dumb question, but I haven't actually seen it explicitly answered before)
Mass is conserved. If you split water into hydrogen and oxygen, then combine them back into water, you will have the same amount of water as when you started.
That's assuming you don't have leaky equipment in your lab, of course.
OK, thanks for the answer, it been bugging me for a bit and I couldn't definitively answer it. I've heard the argument that something hydrolysis would result in fresh water being decreased, good to know my first feeling (that that argument was bs) is true.
Because it will always take more energy to break the water than you will get burning the Hydrogen in Oxygen back into water - it's basic thermodynamics.
You will lose some energy as heat that you cannot get back*.
You can't power a car from a process that loses energy. Even if you use a battery to donate the lost energy, then you might as well just cut out the lossy middleman and just run off the battery or generate the Hydrogen elsewhere - which is what we currently do.
It is better to think of Hydrogen as an energy transporter than as a fuel, as you'd need to generate the Hydrogen somewhere that has abundant energy (ideally renewable), then transport I where needed, such as a Hydrogen powered generator.
*Interestingly the fact that all processes generate waste heat means the only theoretically 100% energy efficient process is heat generation itself, as all forms of energy eventually degrade to heat (as it is essentially the universe's waste energy).
Electric heaters aren't 100% efficient, because some of the energy is wasted altering the resistive material chemistry and emitting other electromagnetic radiation, and even sound, that doesn't heat the air inside your house (right away). Still at a perfect 100% efficiency, it takes 1 joule to raise your house temperature by 1 joule, ideally. Heat pumps, which are just an AC unit running in reverse, are more efficient than electric heaters. Some heat pumps have a coefficient of 3. Meaning they take 1 joule to heat the air in your house by 3 joules. Because they don't try to heat the air, they move heat to the air from outside, and they can achieve this even if outside is freezing.
That's the theoretically part - there are processes that will capture the energy generated that would've otherwise become heat, but that only affects the timeliness. Given enough time, all workable energy generated by a heater would become heat, even if you had to wait for the matter itself to decay trillions of years from now when all the stars have long since breathed their last breath.
Also has somebody watched Technology Connections by any chance?
Heat pumps are so cool - if you showed onw to someone even a hundred years ago, even knowing what electricity was, they'd think it was magic.
What you're asking for is, as far as my basic college understanding of physics goes, pretty much impossible. You're asking for a perpetual engine, looping electrolysis and catalyzing hydrogen and oxygen, creating energy at a net positive. This is impossible in terms of the laws of energy conservation. Energy can neither be created nor destroyed. It can only be converted from one form into another. Basically, you will only ever get what you put into it. Moreover, in real world applications, you will lose energy to things like heat runoff.
The reason hydrogen works as a fuel source is because of its potential energy. Hydrogen really wants to bond with things. Same thing with oxygen and so they have a high potential energy. However, combine hydrogen and oxygen into water and you've got a basically inert molecule that then takes a lot of energy to break back apart. That energy is then converted back into potential energy. The problem again is that this relies on your engine being a perfect system, which can't exist in practical, real world applications. You WILL lose energy in the reaction in any real world scenario. Meaning you will alway need to put more energy into the system. Thus, always returning a net loss.
That's kinda why we haven't gotten fusion reactors working quite yet. Solve that problem and you've solved the world's energy crisis.
It takes a certain amount of energy for water to exist as water, a certain amount of energy for oxygen to exist as oxygen, and a certain amount of energy for hydrogen to exist as hydrogen
The amount of energy it takes for water to keep being water is less than the sum total of the energy it takes for oxygen and hydrogen to keep being themselves.
When you burn hydrogen, it combines with oxygen in the air and makes water. But that requires less energy to exist, so where does the excess energy go? It's released as heat.
To split water back into hydrogen and oxygen, you have to re-add that same amount of energy again.
Hydrogen as a fuel isn't so much a source of energy as a store of energy. A battery doesn't make energy. You charge it with energy so that you can retrieve that energy later. Similarly, a big power plant electrolyses a bunch of water and makes a bunch of hydrogen. Later, you can use that hydrogen in your car without having to be connected to the big power plant that made it.
this is all probably largely wrong and you should ignore it chemistry SUCKS
Water contains two elements, hydrogen (very explosive) and oxygen, which can make almost anything burn. You'd think tossing a match into a body of water would end all life, for the amount of stored Oxygen and Hydrogen. It won't because it is essentially ash. Inert. It takes a large amount of energy to separate the Oxygen and Hydrogen from each other, before either could be used again. That is the problem. That's why we don't pour a gallon of water into a tank and head across country.
Think of hydrogen-power as more of a battery.
Batteries have to be charged with energy from an energy source. And hydrogen has to be produced with energy from an energy source.
2nd principle of thermodynamic, no machine has an efficiency above 100% the energy you get by burning H2 in water, is at best equivalent to the enrgy spent to break down water in H2 + 02.
You just invented a fuel cell vehicle. Creating hydrogen from water requires a lot of energy, though, so that's not feasible to do in a car. Theoretically you could use solar panels but then you'd need a truck for all the equipment and a couple of days of collecting sunlight for a tank full.
You should probably look into the chemistry needed to do 2 H~2~O -> 2H~2~ + O ~2~
Obviously the biggest problem is making sure you have an even number of water molecules.
Hint: It’s not because this idea never occurred to any of the scientists and engineers involved in hydrogen power.
You can. You break down water in a station, vent the o2 and put the h2 in the vehicle.