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Author Topic: Large Salt water battery ideas and questions  (Read 56495 times)

profitis

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Re: Large Salt water battery ideas and questions
« Reply #30 on: August 15, 2013, 01:06:14 PM »
it all boils down to the electron-sucking power of the cathode @sea monkey,thats why the lead-acid system is so good with its solid oxidizer PbO2,an extremely powerful oxidizing agent in acid solution:E=1.6v (ph1). Air in seawater: E=0.8v (ph8).hydrogen ion in seawater: E=0.4v (ph8)(2H+ + 2e- = H2 bubbles).also theres no gases involved with the lead-acid system thus minimal polarization of  electrodes but if mungo can get the air cathode art worked out we may see real improvements.

Mungo

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Re: Large Salt water battery ideas and questions
« Reply #31 on: August 15, 2013, 04:04:33 PM »
SeaMonkey is your objection to these batteries power density or is it that the hydrogen envelopment of the cathode ultimately shuts down production?  My application is rather specific, my energy needs fairly low, and I really don't care if I have to have 30 cells or if i wind up with two batteries ten times the size of a lead acid to do the same work.

So here's my thinking at the moment:  The next prototype will be a near full sized mockup, using narrow gauge copper tubing bundles as the cathode and bundles of aluminum box beam as the anode.  Both will be etched in muriatic acid beforehand to increase surface area.  The Anode will be completely submerged, the cathode about half so.  I'm going to prep to do the airstone idea to oxygenate the electrolyte and hopefully clear some of the H2 off of the cathode.  I will also prep some absorbent medium and try bundling that with the cathode to see how that works.  If that functions, Ill connect that through and inverter to a load and see how long that runs, how the electrodes perform, and what kind of changes we see in the electrodes and the electrolyte. (using a 1.030 sg salt solution).  I know this thing will produce the voltage, but Im curious what kind of current I can produce with it.  Ideas?  Suggestions?

Mungo

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Re: Large Salt water battery ideas and questions
« Reply #32 on: August 15, 2013, 04:11:06 PM »
I am curious about a couple of my initial test results:  The voltage output of the aluminum anode was less than that of the zinc (okay, galvanized mild steel), and due to their electrochemical potential, shouldn't that have been the other way 'round? 

Im also curious if a cathode of plates set very close together, angled slightly so that the gap was slightly wider at the top than the bottom, might force the hydrogen bubbles upward as they formed, clearing the plates and creating a mild current (fluid, not electrical) between them.  As we're talking microns here Im not sure I have the toys to do it, but it's an interesting idea.

Mungo

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Re: Large Salt water battery ideas and questions
« Reply #33 on: August 15, 2013, 04:14:26 PM »
but if mungo can get the air cathode art worked out we may see real improvements.

I was really liking this phrase until I realized you probably meant "air cathode PART" :) Maybe Art might actually be a better term :o

profitis

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Re: Large Salt water battery ideas and questions
« Reply #34 on: August 15, 2013, 04:49:29 PM »
tis indeed an artform to get batteries into practical gear.ive been doing it for years although my research has centred more around concentration cells and finding ways to maintain their concentration gradients with no expenditure of energy(ive had plenty success here believe it or not).if you used smooth aluminum it wouldve formed a slow-dissolving aluminum hydroxide layer and that would hamper voltage so its important to etch aluminum and get that surface area.zinc on the other hand tends to dissolve more smoothly into saltwater as zinc chloride but you are going to have to renew the saltwater at some stage because its ph will gradualy become alkaline as galvanic reaction proceeds and start precipitating zinc hydroxide on its surface.you must remember that many aluminum and zinc objects are alloys thus their rates of reaction will differ,its just a matter of trial and error to get the right anode.the cathode is the tough part because we want those H2 bubbles to self-discharge on contact with air on the cathode surface: H2 + O= H2O,your copper acting as catalyst

profitis

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Re: Large Salt water battery ideas and questions
« Reply #35 on: August 15, 2013, 05:07:51 PM »
if you adjust the ph of your saltwater by adding some muriatic acid you should get better results.if you adjust the ph to extreme alkaline by throwing in caustic soda or washing soda even better,then it becomes a classic zinc-air system and H2 bubbles will cling less hard due to wetting ability of alkali.throw in some caustic soda and see what happens.take caustic soda supply with you on the boat trip.

Mungo

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Re: Large Salt water battery ideas and questions
« Reply #36 on: August 15, 2013, 05:10:48 PM »
So the trick becomes how to bring more air to the cathode surface ....hmmmm...of course, since this is to be a marine application, there will be a constant degree of low level agitation of the electrolyte solution, which will probably help a bit.  I wonder if I could mechanically amplify that to move the cathode a bit from time to time.

I always tend toward the mechanical, but then, thats how my head works.


Mungo

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Re: Large Salt water battery ideas and questions
« Reply #37 on: August 15, 2013, 05:11:50 PM »
if you adjust the ph of your saltwater by adding some muriatic acid you should get better results.if you adjust the ph to extreme alkaline by throwing in caustic soda or washing soda even better,then it becomes a classic zinc-air system and H2 bubbles will cling less hard due to wetting ability of alkali.

so basically Im throwing in soap to break down the surface tension....

profitis

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Re: Large Salt water battery ideas and questions
« Reply #38 on: August 15, 2013, 05:16:35 PM »
yes but dont throw in soap as it will form scum on the anode.throw in caustic soda,it will dissolve zinc hydroxide.

profitis

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Re: Large Salt water battery ideas and questions
« Reply #39 on: August 15, 2013, 05:29:26 PM »
caustic soda will drasticly increase power output of aluminum anodes also,dont throw in too much.

Mungo

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Re: Large Salt water battery ideas and questions
« Reply #40 on: August 15, 2013, 06:26:23 PM »
 
yes but dont throw in soap as it will form scum on the anode.throw in caustic soda,it will dissolve zinc hydroxide.
I meant that metaphorically, but I take your meaning.  ;)

Mungo

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Re: Large Salt water battery ideas and questions
« Reply #41 on: August 15, 2013, 06:37:21 PM »
Anyone have any idea how much of a problem the O2 content of the electrolyte might be?  Is surface absorption of atmospheric O2 adequate, or will it eventually be exhausted by the anode?

profitis

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Re: Large Salt water battery ideas and questions
« Reply #42 on: August 15, 2013, 06:49:14 PM »
if you use caustic soda you may just be able to not even worry about air anymore @mungo because of the drastic increased wetting ability at the cathode,the H2 bubbles should seperate at a steady enough pace to give steady current.your copper pipes must stand totaly upright to allow bouyency to lift bubbles up and away.the voltage will be around 1.1-1.5 in this setup and should be quite stable.play with raising and lowering the copper to half-submerged and fully submerged to see if power improves.

Mungo

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Re: Large Salt water battery ideas and questions
« Reply #43 on: August 15, 2013, 07:05:53 PM »
these tests may have to go youtube in the future ???

profitis

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Re: Large Salt water battery ideas and questions
« Reply #44 on: August 15, 2013, 07:05:55 PM »
dont use brass as your cathode.brass is 40% zinc.use pure copper