Large Salt water battery ideas and questions

[profitis]

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]

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]

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]

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

[profitis]

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