Hi Horace, Your alternative explanation for the device doesn't work, see my comments in your text below.
2009/11/23 Horace Heffner <hheff...@mtaonline.net>: > > On Nov 23, 2009, at 2:48 AM, Michel Jullian wrote: > >> See: http://sci-toys.com/scitoys/scitoys/echem/fuel_cell/fuel_cell.html >> >> I had no idea an ultraclean rechargeable battery could be done so simply! >> >> Supplies: >> <<- One foot of platinum coated nickel wire, or pure platinum wire. >> Since this is not a common household item, we carry platinum coated >> nickel wire in our catalog. >> - A popsickle stick or similar small piece of wood or plastic. >> - A 9 volt battery clip. >> - A 9 volt battery. >> - Some transparent sticky tape. >> - A glass of water. >> - A volt meter.>> > > It seems to me a small amount of lye would help the reaction along. No > matter, the intent is apparently not to create a working cell, i.e. generate > power, it is merely to generate a voltage. > > I see they sell the wire for $14.41 plus shipping. A bulk source for wire > and mesh might be: > > http://www.gerarddaniel.com/ > > > >> H2 and O2 are produced by short electrolysis runs, after which the >> bubbles clinging to the electrodes are catalytically recombined by the >> electrode surface material (platinum) to generate electricity :) >> >> 1/ The article features nice "explanations" of how it works, but how >> does it _really_ work? In particular, in the generating (fuel cell) >> phase, they don't say what makes the positive hydrogen ions climb >> "uphill" from the negative electrode to the positive one, anyone can >> explain this miracle? ;-) >> >> 2/ It seems to me a much higher capacity (and perhaps even practical) >> rechargeable battery could be made by using a hydrogen >> absorbing/desorbing material e.g. Pd for the negative electrode, and >> by making gaseous oxygen available at the anode. Storing the latter is >> not required of course, O2 from the air is fine... maybe a floating >> support which would keep a grid or flat serpentine shaped positive >> electrode at the surface of the water or just below? >> >> Michel > > The explanation looks bogus to me. I think the cell works by reversible > reactions, not recombination. > Bockris states that conduction in an electrochemical cell in the volume > between the interface layers is almost entirely due to concentration > gradients. Gradients of charged particle concentration translate as E field. > That is because almost all the potential drop is in the interface > layers themselves. The E field in the bulk of the cell is very small. True, but it is non-null and has a direction, which would have to be (and indeed, is, I believe) the "wrong direction" IF indeed protons are travelling in the bulk from the (-) to the (+) electrode in the generating phase, agreed? > I expect the cell actually operates by creating even *more* bubbles, not > consuming the gas already there in the form of bubbles. > > In the course of the brief electrolysis by battery, the volume of water > around the anode (+) is filled with H3O+ ions, and the volume around the > cathode (-) > is filled with OH- ions. **Correct** (polarities added by me, to clarify things since polarities don't switch when switching from electrolysis to generating mode, contrary to anode/cathode names) > This can actually be viewed by use of a dilute > electrolyte, plus a pH indicator like phenolphthalein, which is colorless in > acidic electrolytes, and pink in basic solutions. To do this first add the > (liquid) phenolphthalein to distilled water. To view the creation and > migration of OH- ions: before connecting the battery add a little bit of > hydrochloric acid to the water, and stir until it just turns pink. Adding acid can't make it turn pink (pink=basic), I guess you meant lye > When the > battery is connected the volume around the cathode (- electrode) will turn > clear. If it turns clear (=acidic), then it must be the water around the (+) electrode, where H3O+ ions are appearing. You see it's all the wrong way round, including the paragraph below, and if you put it back the right way round (as it was where I commented "**Correct**" above) you'll see that your explanation below for the scitoy device doesn't hold. > To view the creation and migration of H3O+ > ions: before connecting the battery add a little bit of lye to the water, > and stir. When the battery is connected the volume around the anode (+ > electrode) will turn pink. It can take a little fooling around with > concentrations to get the effect to work quickly and dramatically. The > diffusion occurs slowly but at a clearly visible pace. ... > In any case I doubt it is actually recombination that causes the potential > at the electrodes. It is the presence of the high concentration of ions in > solution that makes the residual potential when the battery is disconnected. > The H3O+ ions take on electrons through the wire originally releasing > hydrogen at the site where the hydrogen was generated, the anode, thus > making *more* hydrogen bubbles. Similarly, the OH- ions donate electrons to > make H2O2 and *more* O2 at the site where O2 was generated prior. > > The meter is probably a 10 megohm meter, meaning registering the 2 V > potential requires generating 0.2 microamps of current, and thus 0.4 > microwatts of power. Not much of a fuel cell! That's what is consumed by the meter but we don't know how much the cell is actually capable of producing, plus the power can probably be improved by increasing the surface area of the electrodes (my scheme 2 above would work nicely with a codeposited cathode, which would also lower the cost compared to bulk Pd), and reducing the distance between them. Cheers, Michel
