Re: [Vo]:DIY electrolytic cell / fuel cell rechargeable battery
On Nov 26, 2009, at 6:55 AM, Michel Jullian wrote: Horace, 2009/11/26 Horace Heffner hheff...@mtaonline.net: snip Here is the original explanation, less the garbled indicator test information: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ... 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. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Still looks right to me, despite the fact I remain dizzy! snip Well no, the site where the hydrogen was generated (which was the cathode BTW, not the anode, Oh yes. That was a typo. I actually do know hydrogen is generated at the cathode in an electrolytic cell! 8^) let's call it the negative electrode rather, as anode and cathode names switch sides when current direction is reverted) was surrounded by OH- ions, and the site where O2 was generated prior (which was the anode, let's call it the positive electrode from now on) was surrounded by H3O+ ions. Therefore it can't be a case of more H2 where H2 was already bubbling and more O2 where O2 was already bubbling, agreed? Michel Agreed! For my scenario to be a valid explanation the polarity shown at the meter would have to change. It doesn't change. Interesting! So it appears there there has to be a reversal of ion flow in the electrolyte, the ions meeting in the middle and recombining. The H3O+ leaving the interface frees up electrons trapped on the other side of the electrolytic cell cathode interface. It remains a source of electrons for the meter. Similarly, the OH- leaving the vicinity of the electrolytic cell anode essentially leaves a net positive charge there to accept electrons. It would be interesting to see what an indicator like phenolphthalein would show when the battery is disconnected. There would be an immediate current in the correct direction due to a roughly 0.2 F/m^2 capacitance of the double layer. I don't know what size the wire is, but guessing at 0.5 mm diameter, that is 1.57 mm circumference, by 130 mm height, that's 1.99x10^-4 m^2 per wire or about 4x10^-4 m^2 total area, and thus (4x10^-4 m^2) (0.2 F/m^2) = 8x10^-5 F, which at 9V can only support a charge of 7.2x10^-4 coulombs. I estimated the need to drive 2 microamps current to register 2 V on the meter, which is about (7.2x10^-4 coulombs)/(2x10^-6 coulombs/sec) = 360 seconds. It looks like interface capacitance discharge may actually account for the current. The cell could be merely acting as a capacitor. It would be interesting to see what the charging time is - i.e. to compare discharge time to charge time. I'd like to see what happens to the bubbles when the battery is disconnected. If it really is a fuel cell it should be possible to bubble O2 and H2 (from another cell) around the separate wires and get a sustained current. It would also be interesting to connect two half cells together by an electrolyte bridge and remove the bridge prior to disconnecting the battery. No current should flow at all except for a brief rebalancing of charges due to the 9 V potential difference. This looks like an interesting high school science project. Best regards, Horace Heffner http://www.mtaonline.net/~hheffner/
Re: [Vo]:DIY electrolytic cell / fuel cell rechargeable battery
2009/11/27 Horace Heffner hheff...@mtaonline.net: I'd like to see what happens to the bubbles when the battery is disconnected. If it really is a fuel cell it should be possible to bubble O2 and H2 (from another cell) around the separate wires and get a sustained current. A very good idea, seems quite easy to implement with a couple of tubings going from the electrolytic cell to the fuel cell, this reminded me I had seen similar bubbling of an external gas on an electrode in articles on reference electrodes ( see e.g.: http://en.wikipedia.org/wiki/Standard_hydrogen_electrode ). Reference electrodes are probably quite relevant to the present discussion, in that they seem capable to maintain a reference voltage as long as you keep bubbling the gas, without any additional energy input! This looks like an interesting high school science project. Indeed, and it might even allow practical clean batteries for low power devices. Michel
Re: [Vo]:DIY electrolytic cell / fuel cell rechargeable battery
On Nov 25, 2009, at 1:05 PM, Michel Jullian wrote: Horace, My comments below, some things are still wrong 2009/11/25 Horace Heffner hheff...@mtaonline.net: Gad. It still isn't right! Corrections below. I have vertigo at the moment and can't think straight. I've actually done half of this experiment, though decades ago, and it is interesting how the concentration gradient wanders, it doesn't follow what you would expect for any kind of E field. 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. 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. 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 preferentially filled with H3O+ ions, as the OH- ions release their electrons and form O2 and H2O2, and the volume around the *cathode* is filled with OH- ions as the H3O+ ions present at the cathode surface are electrolyzed. 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. Connect the battery. To view the creation and migration of OH- ions: add a little bit of boric acid to the water, and stir. Repeat the process until you can see the electrolyte turns pink in the vicinity the *cathode* (- electrode) once the electrolyte settles down. Boric acid was chosen because it is commonly available from pharmacies. To view the creation and migration of H3O+ ions add a little bit of lye to the water and stir. Repeat the process until you can see the electrolyte is pink, but when the electrolyte settles down you can see the volume around the *anode* (+ electrode) gradually turing clear. 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. I agree with the above paragraph now, but putting it right has broken your explanation for the generating phase two paragraphs below. This is the same principle I had in my original explanation. Here is the original explanation, less the garbled indicator test information: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - I think the cell works by reversible reactions, not recombination. 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. You can demonstrate the reversibility of the reactions by reversing the battery. Note, however, that the diffusion occurs in a somewhat
Re: [Vo]:DIY electrolytic cell / fuel cell rechargeable battery
Horace, 2009/11/26 Horace Heffner hheff...@mtaonline.net: snip Here is the original explanation, less the garbled indicator test information: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ... 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. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Still looks right to me, despite the fact I remain dizzy! snip Well no, the site where the hydrogen was generated (which was the cathode BTW, not the anode, let's call it the negative electrode rather, as anode and cathode names switch sides when current direction is reverted) was surrounded by OH- ions, and the site where O2 was generated prior (which was the anode, let's call it the positive electrode from now on) was surrounded by H3O+ ions. Therefore it can't be a case of more H2 where H2 was already bubbling and more O2 where O2 was already bubbling, agreed? Michel
Re: [Vo]:DIY electrolytic cell / fuel cell rechargeable battery
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
Re: [Vo]:DIY electrolytic cell / fuel cell rechargeable battery
Michel, here I'll take another shot at getting things right. 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. 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. 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 *cathode* is filled with H3O+ ions, and the volume around the *anode* is filled with OH- ions. 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. Connect the battery. To view the creation and migration of OH- ions: add a little bit of boric acid to the water, and stir. Repeat the process until you can see the electrolyte turns pink in the vicinity the *anode* once the electrolyte settles down. Boric acid was chosen because it is commonly available from pharmacies. To view the creation and migration of H3O+ ions add a little bit of lye to the water and stir. Repeat the process until you can see the electrolyte is pink, but when the electrolyte settles down you can see the volume around the anode (+ electrode) gradually turing clear. 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. You can demonstrate the reversibility of the reactions by reversing the battery. Note, however, that the diffusion occurs in a somewhat random manner. It doesn't typically blossom out in a perfectly spherical or cylindrical manner (depending on the electrode shape). Reversing the reaction is thus not a perfect process either. I tried some of this decades ago in a feeble attempt to make a display technology. I got a nice red stream of ions coming from a copper anode in a basic solution. 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! It would be interesting to run the current for a while until a significant concentration
Re: [Vo]:DIY electrolytic cell / fuel cell rechargeable battery
Gad. It still isn't right! Corrections below. I have vertigo at the moment and can't think straight. I've actually done half of this experiment, though decades ago, and it is interesting how the concentration gradient wanders, it doesn't follow what you would expect for any kind of E field. 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. 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. 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 preferentially filled with H3O+ ions, as the OH- ions release their electrons and form O2 and H2O2, and the volume around the *cathode* is filled with OH- ions as the H3O+ ions present at the cathode surface are electrolyzed. 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. Connect the battery. To view the creation and migration of OH- ions: add a little bit of boric acid to the water, and stir. Repeat the process until you can see the electrolyte turns pink in the vicinity the *cathode* (- electrode) once the electrolyte settles down. Boric acid was chosen because it is commonly available from pharmacies. To view the creation and migration of H3O+ ions add a little bit of lye to the water and stir. Repeat the process until you can see the electrolyte is pink, but when the electrolyte settles down you can see the volume around the *anode* (+ electrode) gradually turing clear. 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. You can demonstrate the reversibility of the reactions by reversing the battery. Note, however, that the diffusion occurs in a somewhat random manner. It doesn't typically blossom out in a perfectly spherical or cylindrical manner (depending on the electrode shape). Reversing the reaction is thus not a perfect process either. I tried some of this decades ago in a feeble attempt to make a display technology. I got a nice red stream of ions coming from a copper anode in a basic solution. 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*
Re: [Vo]:DIY electrolytic cell / fuel cell rechargeable battery
Horace, My comments below, some things are still wrong 2009/11/25 Horace Heffner hheff...@mtaonline.net: Gad. It still isn't right! Corrections below. I have vertigo at the moment and can't think straight. I've actually done half of this experiment, though decades ago, and it is interesting how the concentration gradient wanders, it doesn't follow what you would expect for any kind of E field. 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. 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. 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 preferentially filled with H3O+ ions, as the OH- ions release their electrons and form O2 and H2O2, and the volume around the *cathode* is filled with OH- ions as the H3O+ ions present at the cathode surface are electrolyzed. 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. Connect the battery. To view the creation and migration of OH- ions: add a little bit of boric acid to the water, and stir. Repeat the process until you can see the electrolyte turns pink in the vicinity the *cathode* (- electrode) once the electrolyte settles down. Boric acid was chosen because it is commonly available from pharmacies. To view the creation and migration of H3O+ ions add a little bit of lye to the water and stir. Repeat the process until you can see the electrolyte is pink, but when the electrolyte settles down you can see the volume around the *anode* (+ electrode) gradually turing clear. 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. I agree with the above paragraph now, but putting it right has broken your explanation for the generating phase two paragraphs below. You can demonstrate the reversibility of the reactions by reversing the battery. Note, however, that the diffusion occurs in a somewhat random manner. It doesn't typically blossom out in a perfectly spherical or cylindrical manner (depending on the electrode shape). Reversing the reaction is thus not a perfect process either. I tried some of this decades ago in a feeble attempt to make a display technology. I got a nice red stream of ions coming from a copper anode in a basic solution. 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
[Vo]:DIY electrolytic cell / fuel cell rechargeable battery
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. 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
Re: [Vo]:DIY electrolytic cell / fuel cell rechargeable battery
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. 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. 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. 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. When the battery is connected the volume around the cathode (- electrode) will turn clear. HCl can be obtained from some bathroom tile cleaners, which are simply hydrochloric acid, HCl. 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. You can demonstrate the reversibility of the reactions by reversing the battery. Note, however, that the diffusion occurs in a somewhat random manner. It doesn't typically blossom out in a perfectly spherical or cylindrical manner (depending on the electrode shape). Reversing the reaction is thus not a perfect process either. I tried some of this decades ago in a feeble attempt to make a display technology. I got a nice red stream of ions coming from a copper anode in a basic solution. 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! Best regards, Horace Heffner http://www.mtaonline.net/~hheffner/
