Seawater electricity

[CDK]

Originally Posted by Paul No Boat

Could a boats hull or at least the keel be made into a battery by sheathing it with dissimilar metels or paints based on disimilar metals (copper paint stipes between aluminum paint stripes) and then produce usable current to charge a battery while sitting in water? and how long would the metal plates last before deteriorating to a non usable surface? I know there are a million by products to this. I just want to know if it would work.

One very good reason why doing that would be 100% senseless:

Batteries are stacked to obtain a usable output voltage, like 3 cells in a flashlight, 6 cells in a 12 V car battery. To achieve that, individual cells are connected + to -. Dissimilar metals dangling in the sea have a common electrolyte, hence the voltage is limited to that of a single cell.

[capt vimes]

Originally Posted by Dave Gudeman

Fanie, that is not possible. Burning hydrogen produces water. It produces exactly the same amount of water that you originally disassociated to get the hydrogen and it produces exactly the same energy that was used to disassociate the hydrogen. The reaction works like this:

2 H2O --(E)--> 2 H2 + O2

2 H2 + O2 --(-E)--> 2 H2O

The number in parentheses represents the energy put into the system. When you disassociate water into hydrogen and oxygen, you have to put energy E into the system to break the chemical bonds. The energy depends only on the bonds and does not depend at all on what process you use to break the bonds. You can't weaken the bonds without putting in a proportional amount of energy. You can't just make the bonds go away. The molecule is in a low-energy state and in order to put it in a higher-energy state you have to supply the energy. When you burn H2 in O2 to get water, it releases exactly the same energy back.

This is a classic closed system and if you could make it work then you would be violating the principle of conservation of energy.

you are right... in theory...
the energy which goes in - comes out... but you are not able to convert this energy to a 100%....
you will have losses when splitting the water... resistance, thermal losses and such which will force you to but more energy than needed to it...
and you will have losses when you burn H2 to water again... giving you less _consumeable_ energy back than there actually is generated... far less by the way...
remember - a combustion, piston engine works with not even 35% of efficency...

[Dave Gudeman]

Originally Posted by capt vimes

you are right... in theory...
the energy which goes in - comes out... but you are not able to convert this energy to a 100%....

True. Neither the energy that you put in to get hydrogen nor the energy that you get out from the hydrogen would be 100% efficient. You would have losses on both ends.

[Boston]

ok so Im a little rusty on all this but two dissimilar metals in an electrolyte produce a charge

electrolyte being a abundance of free hydrogen

ends up producing oxides
ok

so why do they use lead oxide paste over a grid to produce the modern lead acid battery

now Im confused

B

[CDK]

A lead acid battery has different chemistry. When discharged, all plates are covered with PbSO4 and the H2SO4 acid has weakened. Charging returns the SO4 to the acid and changes the plates into Pb (+) and PbO2 (-).

Starting with pure lead plates and charging was the old way to make batteries, using PbO2 produces so-called dry charged cells, saving a lot of time.

[Boston]

hmmmm

so in essence you could burn lithium and aluminum instead of fuel and buy lithium instead of diesel

hmmmmm
I wonder how that works out in terms of $ per mile

[capt vimes]

you are definetely not "burning" (wasting) lithium!
this stuff is so sparse on this farking planet that nobody wants to just burn it off...
i do not understand duracell i.e. bringing some one-way, unrechargeable lithium batteries to the market when one could produce high power rechargeables with lithium...
hell - i never understood economy... it just makes no sense if you think about it....

why is lithium so good?
it has the lowest electronegativity of all known elements and - as CDK has already pointed out - the voltage you get from any electrical source where you simply connect 2 different conductors is based on the materials electronegativity... there is no better stuff known than lithium...

you do not wanna burn that and dump it in a bin!

[Boston]

sooooo
how would you go about recovering the lithium once the reaction has taken place and wouldnt that end up taking more energy than it gave up ( yes )
basically how expensive is lithium and is it worth it to either manufacture an artificial alternative or produce a non rechargeable battery

just kicking around some ideas

B

[mcollins07]

The U.S. government has been funding the development of fuel cells for many years. These are a type of battery where the plates are a catalyst, the liquid is something like alcohol. The alcohol reacts with the catalyst producing electricity as a battery would, but instead of recharging it, you add more fuel. I do not know the state of the art on this, perhaps someone else does?

[capt vimes]

there are various types of fuel cells...
http://en.wikipedia.org/wiki/Fuel_cell

what they have all in common:
low efficency and low voltage... (0.6-0.7 V for 50% efficency)
and than there is this nasty behaviour: the stronger the current you draw from the cell, the lower the voltage you get and decreasing efficency even further...

[Dave Gudeman]

Originally Posted by Boston

sooooo
how would you go about recovering the lithium once the reaction has taken place and wouldnt that end up taking more energy than it gave up ( yes )
basically how expensive is lithium and is it worth it to either manufacture an artificial alternative or produce a non rechargeable battery

just kicking around some ideas

B

Warning: the following is all guesswork.

You could probably burn lithium in a boiler to run a steam engine. I guess you could melt it and run it through an internal combustion engine of some sort, but I doubt it would be much like current IC engines since I doubt the burning properties of liquid lithium are similar to the burning properties of hydrocarbons and alcohols. Also, the main byproduct of burning lithium is lithium oxide which melts at 2858 degrees F so I doubt very much of it would go away in the exhaust. You would have to find some way to flush it out of the system (hint for researchers: it does dissolve very rapidly in water).

I assume you could recover lithium from the lithium oxide by some process, but I don't know how.

However, if you want to use lithium as a fuel, I would guess that you could do it more efficiently by going electric and using the lithium in a lithium-air fuel cell than by actually burning it.

By the way, lithium is not at all a rare element and it is used in lots of other applications besides batteries.

[Boston]

I was using the term figuratively

someone had said that the reaction results in the loss of metal

by burning lithium what I meant was using it up in the fuel cell

so if lithium is cheap then why not just build a number of cells in series and provide for replacing the aluminum and lithium from time to time

or would that end up substantially heavier than typical batteries

[Dave Gudeman]

Originally Posted by Boston

so if lithium is cheap then why not just build a number of cells in series and provide for replacing the aluminum and lithium from time to time

or would that end up substantially heavier than typical batteries

No, it would be substantially lighter than typical batteries for the same energy storage. The main problem is that currently you can't recharge lithium air batteries, you have to recycle them.

Also, they might be more expensive. I don't know if commercial ones are available or how much they would cost. Lithium is cheap, but so is hydrogen, and hydrogen fuel cells are expensive because they need a very expensive catalyst (usually platinum).

Still, I expect that the next big jump in battery energy density will come from metal air fuel cells. Or, to be more precise, you can already get metal air fuel cells that have much better energy density than normal types of cell, but they have various disadvantages to overcome before they can replace batteries in certain applications like running laptop computers and boats.

[Boston]

could you use a solar cell to run the thing backwards and electroplate the metals back into position on the plates

sorta a passive recharging system