Electrolysis of water in an enclosed container
Discussion
So what happens then if you put water in a high pressure container, and then pass electricity through it to split it into hydrogen and oxygen.....does the splitting of the two components stop as the pressure in the container rises, or is it possible to end up with a highly explosive high pressure mixture with the same weight of the original water? It strikes me this would be an efficient way of storing power without a battery, as you could then use the hydrogen to run a fuel cell, or burn the mixture in an internal combustion engine. Basically you have a fuel tank you fill with water, pass electricity through it until the water has gone, then go and fit it to your car without needing to compress the gas in the first place. (???)
Hydrogen and oxygen under high pressure in a sealed container could probably be made to react by the passage of a stray cosmic ray or a self-generated static discharge - with catastrophic results. Electrolysis of water requires about 40 times the amount of energy put into it in comparison with the amount of energy you get out. Reacting hydrogen with atmospheric oxygen across an electron exchange membrane in a fuel cell is far more effective and much less likely to flatten your home!
Astronut said:
Hydrogen and oxygen under high pressure in a sealed container could probably be made to react by the passage of a stray cosmic ray or a self-generated static discharge - with catastrophic results. Electrolysis of water requires about 40 times the amount of energy put into it in comparison with the amount of energy you get out. Reacting hydrogen with atmospheric oxygen across an electron exchange membrane in a fuel cell is far more effective and much less likely to flatten your home!
due to the inefficiency of energy capture right? not claiming different energies are involved between separating water and making it again?My basic point being in all this is put put in x number of Joules to split the water in the first place, that is now stored in the oxygen hydrogen mix that you could then utilise. You have not had to use extra energy to compress the gas. If the conversion process is very inefficient- how does the energy appear thats not used breaking the bonds, heat?
R300will said:
due to the inefficiency of energy capture right? not claiming different energies are involved between separating water and making it again?
well, er, actually, they are, because there are activation energies required for the electrolysis of water (e.g. transfer of the electron from an electrode to H+). You are right that the energy difference between H2O and H2 and 0.5 O2 is the same in both directions (obviously), but to get the reaction going you have to put in a bit more energy. (electrochemically this is called the overpotential - name for the extra energy required for waffly and undefined 'other stuff' that has to happen before the reaction happens).blitzracing said:
So what happens then if you put water in a high pressure container, and then pass electricity through it to split it into hydrogen and oxygen.....does the splitting of the two components stop as the pressure in the container rises, or is it possible to end up with a highly explosive high pressure mixture with the same weight of the original water? It strikes me this would be an efficient way of storing power without a battery, as you could then use the hydrogen to run a fuel cell, or burn the mixture in an internal combustion engine. Basically you have a fuel tank you fill with water, pass electricity through it until the water has gone, then go and fit it to your car without needing to compress the gas in the first place. (???)
as the pressure increases you will observe a higher and higher energy requirement to drive the electrolysis. so for a given voltage eventually the electrolysis should stop.blitzracing said:
My basic point being in all this is put put in x number of Joules to split the water in the first place, that is now stored in the oxygen hydrogen mix that you could then utilise. You have not had to use extra energy to compress the gas. If the conversion process is very inefficient- how does the energy appear thats not used breaking the bonds, heat?
yep, the difference between the overpotential and the potential required according to the thermodynamics is normally released as heat.Use Psychology said:
as the pressure increases you will observe a higher and higher energy requirement to drive the electrolysis. so for a given voltage eventually the electrolysis should stop. because the pressure inside the closed system will increase as you make more H2 and O2 you need add extra energy to do the work of compressing the gas.
Use Psychology said:
as the pressure increases you will observe a higher and higher energy requirement to drive the electrolysis. so for a given voltage eventually the electrolysis should stop.
Perhaps the same concept as my theory that if you put enough smokers into a room, eventually the smoke will get so thick that (even with sufficient oxygen) the cigarattes will go out because the 'smoke pressure' matches that of the combustion ('latent smoke of tobacco')...Reckon if I'd been any good at maths I'd have a Nobel Prize by now
Use Psychology said:
as the pressure increases you will observe a higher and higher energy requirement to drive the electrolysis. so for a given voltage eventually the electrolysis should stop.
So effectively the DC resistance of the reaction would go up, and the current would drop then for a given voltage... so if you ramp the voltage up the required wattage would now go up if it takes X amps to keep the reaction running , and the waste heat generated would go up then. I just wonder how this compares just to the energy utilised to just compress hydrogen into a tank for say automotive use, (let alone produce it in the first place) where the heat generated must be huge, although obviously you would not bother compressing the oxygen in the first place as its freely available. I also wonder how electrolysis compares the the efficiency of charging a chemical battery as a energy storage medium. Being realistic if you say started with say 150kg of water and you could split it fairly efficiently could you get a usable amount of energy back or are the figures all wrong?most hydrogen is actually produced from hydrocarbons (water-gas shift reaction), producing hydrogen for use as a fuel by electrolysis of water is only really economical/practical/useful using electricity generated from renewable sources.
ultimately I think the solution will be photocatalysts which decomopose water using sunlight...
ultimately I think the solution will be photocatalysts which decomopose water using sunlight...
Use Psychology said:
plants do this but they don't make H2, of course.
copying - maybe. modifying - no. and making inorganic systems to do the same thing - definitely not too complex.
Not gaseous hydrogen, but if I recall my biochem correctly the H2 makes NADP into NADPH2 which then goes off and acts as a reducing agent in a cycle (TCA?) to make glucose.copying - maybe. modifying - no. and making inorganic systems to do the same thing - definitely not too complex.
R300will said:
Astronut said:
Hydrogen and oxygen under high pressure in a sealed container could probably be made to react by the passage of a stray cosmic ray or a self-generated static discharge - with catastrophic results. Electrolysis of water requires about 40 times the amount of energy put into it in comparison with the amount of energy you get out. Reacting hydrogen with atmospheric oxygen across an electron exchange membrane in a fuel cell is far more effective and much less likely to flatten your home!
due to the inefficiency of energy capture right? not claiming different energies are involved between separating water and making it again?Use Psychology said:
but it does take more energy (in practice) to separate water than you gain from burning h2 in o2.
True. The only part of the reaction that you can employ is heat (you get a bit of kinetic energy from the expansion of the product) and only a small percentage of that. If you could harvest the energy at 100% efficency, you would get out what you put in - energy is neither created nor destroyed...Hi guys. I am building a system to self pressurize. I was researching saftey valves ,check valves .pressure sensors .just a whole slew of saftey on saftey. But reading above and learning something new. So the voltage controls the limit of electrolysis under pressure ? I had thought the process just shut down at about 1100 psi. Which is way to high for my tanks .Is there a formula for this? Id like to see if i could use solar panels at the cabin . This is very interesting to me because i could possibly eliminate a pressure regulating switch by letting the solar load regulate the tank pressure. Basically im using large tanks low pressure. Thus using at the cabin. Lol. my goal is not necessarily fuelling my generator but having a system that can be drained by a generator and reloaded automatically. Something to add to the off grid system.
Thanks guys
Thanks guys
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