Best cathode for magnesium cell

[large_ghostman]

High I am making a magnesium cell using magnesium ribbon as the Anode, I will be using sodium chloride as the electrolyte but wondered if there was anything better than carbon/graphite for the cathode?

 

[Externet]

...anything better than carbon/graphite for the cathode?

-No-
If money does not come out of your ears, try stainless steel 316. It's cheap.

----> https://en.wikipedia.org/wiki/Galvanic_series

And come back with results / more questions, as I have been itching on making exactly that for a while. Canibalized magnesium rods of discarded water heaters, but found them crumbling old. They want too much for new ones.
Wondering if carbon fibre would work, got some, to try some day. Cinema arc rods should work. (surplus)

Been working on a jfet circuit to step-up the voltage too. (sort of thief circuit). D you live by a seashore ?

 

[large_ghostman]

I do indeed live by the sea! The magnesium part proved easy to sort out, now I am after a Cathode. I might try some carbon based material thats almost like cotton, I prepare the magnesium ribbon carefully and use several lengths stacked on top of each other. I used a vacuum chamber with gloves to take the oxide layer off, I am amazed how much you can get out of the tiny cells.
I am also working on a lithium cell but its truly a PITA, trying to get lithium out of a battery in a vacuum chamber while not shorting it out is a nightmare!
I am about to run out of time so might have to give the lithium a miss for the exhibition.

 

[Externet]

OK. Small scale project on yours...

Am 'lending' you my treasured best link on the subject; you deserve it. Hit "Power supply" on the left column :
----> http://www-odp.tamu.edu/publications/191_IR/chap_03/chap_03.htm

And come back with progress.

 

[large_ghostman]

Thats really interesting! Its also exactly the opposite of what I have been doing , I have been boiling out the oxygen and doing my best to ensure no calcium was in the system. I will make some Calcium chloride from sea shells (dissolve the Carbonate of the shell with Conc Hydrochloric acid).
I can simulate agitation to prevent build up of deposits. I would love to try this side by side with Sodium chloride, I found table salt was no good because of the additives. So far my top voltage has been 3.2V but no matter how I try and replicate this I cant!! There is a commercial toy in the form of a motorbike that uses two of these cells, I will try and find the link to it.

 

[Externet]

Just get a bucket of seawater from the shore, and be happy with around 2 Volts.

There is newer ICs for the DC conversion task, like ----> https://www.linear.com/parametric/energy_harvesting

The toys are here ----> https://duckduckgo.com/?q=toy+runs+salt+water&t=canonical

Drool here ----> https://www.intelligentliving.co/salt-water-powered-car-gets-european-approval/

 

[Overclocked]

I actually did this Years ago. I started out with An aluminum Air battery..with just salt, then I mixed the Following together:

Sodium Hydroxide (Very Caustic!)
Potassium Chloride
Sodium Chloride
Water

You only need Small Amounts of these chemicals (About a teaspoon). All of those chemicals are fine together, they just end up exchanging ions in the end. Carbon Fiber is Key to making it small and powerful. On a 1x1 Square, I managed to power a single LED from a joule thief for over 24hrs. I used An Aluminum Plate and Carbon fiber in a small jar. Magnesium Would have given me a better output, but the cheapness of Aluminum Cant be beat.

 

[Externet]

The carbon fiber you used, is it the plain "fiberglass substitute" cloth style like
----> http://www.sino-composites.com/up_product/big/2012-8-4-1051387464.jpg ?

How did you secure an electrode terminal ? Crimping ? Riveting ? Sandwiching ?

 

[large_ghostman]

The car thing is great except its not green energy in reality, a bit like wind power all looks green until you add in the footprint for production etc. The other bit that kind of grinds a little is the description of some sites that its a saltwater battery.
The salt water is just the electrolyte and the elctrons flow from the magnesium eventually using it up by transforming it to an oxidation state.
Minor points I guess, I have converted the really tiny ride on mower (8HP) to use an ethanol mix with bio oil for lube. As its now winter I cant do any more work on it for now. I was using a home built solar still for the ethanol, I have got really good at alginate immobilization of yeast and using grass cutting as the feed stock. Dad has a Gas Chromatograph for work and the ethanol is distilled pure enough via the panel, but you wouldnt want to drink all the lower alcohols in the raw mix before distilling!
The other thing we have done is switch over to recovering waste mineral oil for the heating system, we use a 22,000G centrifuge system and filtration to clean up the oil, its pretty good and although dark it shows little contamination from metals and water. The heater has been running fine all winter and the flue gas is cleaner than kerosene according to the boiler man.
We have a good source of free waste oil and get around 700 litres a month (Tractor repair place). from that we get around 630 useable oil, I dont bother heating it any more I just spin it for longer.
Been loads happening around here. I want to make a small demo voltaic cell from scratch but having trouble getting DECENT info.
I got a really great bargain on ebay months ago with a good vacuum pump (twin vane type) and a older pump (rough work), its really opened up what I can make and cast.
Dads science program for primary aged kids has finally been given the go ahead so he is going to start a kick starter campaign to raise the rest of the cash.

 

[Externet]

Can you manage/ask your dad's 22000G and find if seawater becomes less salty by the surface layer than at the bottom after a good spin ?

 

[large_ghostman]

Can you manage/ask your dad's 22000G and find if seawater becomes less salty by the surface layer than at the bottom after a good spin ?

Sure, I have already spun up saltwater for other things, its a real eyeopener how much crud is in sea water lol.
Do want the SG from different layers? The tube length for the sample is a max of 110mm, I have two options for configuration.
!) Fixed 45 degree tube
2) moving tube where its angel is dependent on the force, I normally use this as it prevents and spills from the tube

Finally any particular temperature? its a heated/cooled centrifuge so I can spin anywhere from a temperature of -32C to +130C

 

[jbeng]

The old-style carbon-zinc batteries have an anode made of a carbon rod (hence the name). I have removed and used them on several occasions for various purposes. They're usually just sealed into the top of the cell with a tar-like compound. The anode rod in a standard D-type cell is about 6-7 mm in diameter and about 5 cm long. I expect the ones in a square 6 volt lantern-type battery would be between 8 and 10 cm long.

 

[Externet]

Sure, I have already spun up saltwater for other things, its a real eyeopener how much crud is in sea water lol.
Do want the SG from different layers? The tube length for the sample is a max of 110mm, I have two options for configuration.
!) Fixed 45 degree tube
2) moving tube where its angel is dependent on the force, I normally use this as it prevents and spills from the tube

Finally any particular temperature? its a heated/cooled centrifuge so I can spin anywhere from a temperature of -32C to +130C

SG ?? ... salinity gradient ?? Yes, at every cm would be very good.
100 mm is OK.
Angle dependent on force
Ambient temperature.
The part I cannot suggest is the method to measure salinity or conductivity without creating any stirr (remixing) after centrifuged so layers stay as separate as possible. Perhaps pulling out layers with a pipette and measuring in separate.
----> The point is finding down to which level seawater becomes 'drinkable' after the spin.
Thanks

====================================================

6V 'lantern' batteries have four 'C' cells inside.

 

[large_ghostman]

SG = specific gravity, you wont remove all chloride ions simply because water and sodium chloride form an azeotrope, you can reduce it and alter the specific gravity but you wont get it potable, the contents dont tend to mix back after you spin (no idea why) and separating them is easy enough with a pipette. Having said all that I will see how salt free I can get it, but I am gonna guess there is enough of an azeotrope for it to not be drinkable.
Oil can have particles smaller than 1 micron removed by G Force, but you always get a dark taint no matter what, its proved better to leave some the dark colour anyway.
The only time its an issue is if the vehicle is fitted with an optical fuel line sensor (so I am told). Dad can use a much more powerful centrifuge at work I might get him to try on that.

 

[jpanhalt]

This thread has used a couple of confusing terms that seem to be getting intertwined. According to Michael Faraday the term "anode" in an electrochemical cell applies to the electrode at which oxidation occurs. In terms of positive and negative of a battery, it is the negative terminal. Similarly, the cathode of a battery is the positive terminal. Wikipedia makes the distinction that those labels apply during discharge. Presumably, the magnesium cell you are working on will be a primary cell, so recharging is not an issue.

LG properly named the magnesium ribbon in his proposed cell the "anode." But others (e.g., post#12) have referred to the positive terminal (carbon rod) as the anode. That is a common misuse of the term, and I have even seen it is Wikipedia. I don't find using the term "anode" for the negative terminal of a primary battery at all confusing, but perhaps calling the terminals negative or positive, as appropriate, would avoid confusion.

... you wont remove all chloride ions simply because water and sodium chloride form an azeotrope, you can reduce it and alter the specific gravity but you wont get it potable..

I was unaware the water and NaCl formed an azeotrope. I think a citation is needed for that conjecture. Distillation of salt waters is an established means of creating potable water. It is by a similar process that we get rain.

John

 

[large_ghostman]

This thread has used a couple of confusing terms that seem to be getting intertwined. According to Michael Faraday the term "anode" in an electrochemical cell applies to the electrode at which oxidation occurs. In terms of positive and negative of a battery, it is the negative terminal. Similarly, the cathode of a battery is the positive terminal. Wikipedia makes the distinction that those labels apply during discharge. Presumably, the magnesium cell you are working on will be a primary cell, so recharging is not an issue.

LG properly named the magnesium ribbon in his proposed cell the "anode." But others (e.g., post#12) have referred to the positive terminal (carbon rod) as the anode. That is a common misuse of the term, and I have even seen it is Wikipedia. I don't find using the term "anode" for the negative terminal of a primary battery at all confusing, but perhaps calling the terminals negative or positive, as appropriate, would avoid confusion.


I was unaware the water and NaCl formed an azeotrope. I think a citation is needed for that conjecture. Distillation of salt waters is an established means of creating potable water. It is by a similar process that we get rain.

John

Hi John your correct in terms of distillation only weak azeotropic bonding is present and the heat easily breaks the bond, the same isnt so true for separation by centrifuge, BUT I dont know how true this is over 22G as I have never tried.
Azeotrope is a bit misleading in this context, similar to the cell and anode I guess.
If you look at the mid Atlantic conveyor where salt and fresh water are under high pressure and form a layer, the layer isnt exactly salt/freshwater, there is a tiny layer at the interface where they meet, this layer isnt as salty as the water above it and isnt as fresh as the water below it.
I offered to try and get dad to spin some up at work on the beast they have, I am sure there will be a point where you could separate it out, but for sure its above 22,000g as I have tried this, I have also tried to clear used engine on the work machine and it does kind of clear, but it rips things apart and the oil isnt as good after. I asked how high it could go but dont have a answer, apparently you have to be precise on the set up before you get an answer to that, I know on my machine it has to be carefully weighed and balanced on all sides when spun over 500G or it cuts out.
The length of tube etc etc etc all make a difference on the bigger machines as to how high they can go, Common sense would say if the tube was long enough and you could spin it up fast enough you will get a fresh and salt water layer,but from a practical lets try it point of view it becomes less simple.
The other point with Azeotropes is most can be broken, for example Ethanol and water can be broken by magnesium sulphate and the final drop of water removed with sodium wire. But distillation alone will not break ethanol and water, I am not entirely convinced that going as high as you can speed wise is the best way. it could well be that over a certain force it becomes counter productive, I will look for a paper that might help but I am not sure there will be much on it.
Most will deal with water and salt distillation and there is no problem separating that way. The best I can do is try it on a better machine, I cant use the bigger one as its in a sealed room etc etc due to safety if it breaks apart!
My first one went upto 12,000G and when the spindle broke it wrecked the case as well. The much much bigger machines at his uni are far more dangerous if parts give out, I do know the tubes cost over £35 each for tests over 35,000G.

The anode, cathode thing is utterly confusing so I tried to use the chemistry excepted way of the anode being the magnesium etc. But it is one area I get confused on a great deal! our fishing boat has a zinc sacrificial anode, but to my thinking its actually a cathode! Maybe this is one case where plus and minus are better terms

 

[alec_t]

According to Michael Faraday the term "anode" in an electrochemical cell applies to the electrode at which oxidation occurs. In terms of positive and negative of a battery, it is the negative terminal. Similarly, the cathode of a battery is the positive terminal.

Hmmm. According to the Oxford English Dictionary an anode is "a positively-charged electrode".

 

[jpanhalt]

Faraday had naming rights. There is no doubt what he wrote. The same confusion exists in the US. A "positively charged electrode" can mean a lot of things. I am a little surprised that O.E. D , doesn't have more to say on the subject. Unfortunately, I no longer have access to it.

Here, we are talking about electrochemical cells -- batteries specifically. We all know that in a typical circuit, the more positive side of a device (e.g., a diode) is called the anode. But that device is not supplying current itself. When Faraday's convention is applied to a battery in a circuit, the battery can be interpreted as being in series with the rest of the circuit. So far as I know, analysis of a circuit from that perspective works just fine.

It can be confusing, which is why I prefer to refer to positive and negative to avoid confusion.

John

 

[jpanhalt]

Hi John your correct in terms of distillation only weak azeotropic bonding is present and the heat easily breaks the bond, the same isnt so true for separation by centrifuge, BUT I dont know how true this is over 22G as I have never tried.
Azeotrope is a bit misleading in this context, similar to the cell and anode I guess.
If you look at the mid Atlantic conveyor where salt and fresh water are under high pressure and form a layer, the layer isnt exactly salt/freshwater, there is a tiny layer at the interface where they meet, this layer isnt as salty as the water above it and isnt as fresh as the water below it.
I offered to try and get dad to spin some up at work on the beast they have, I am sure there will be a point where you could separate it out, but for sure its above 22,000g as I have tried this, I have also tried to clear used engine on the work machine and it does kind of clear, but it rips things apart and the oil isnt as good after. I asked how high it could go but dont have a answer, apparently you have to be precise on the set up before you get an answer to that, I know on my machine it has to be carefully weighed and balanced on all sides when spun over 500G or it cuts out.
The length of tube etc etc etc all make a difference on the bigger machines as to how high they can go, Common sense would say if the tube was long enough and you could spin it up fast enough you will get a fresh and salt water layer,but from a practical lets try it point of view it becomes less simple.
The other point with Azeotropes is most can be broken, for example Ethanol and water can be broken by magnesium sulphate and the final drop of water removed with sodium wire. But distillation alone will not break ethanol and water, I am not entirely convinced that going as high as you can speed wise is the best way. it could well be that over a certain force it becomes counter productive, I will look for a paper that might help but I am not sure there will be much on it.
Most will deal with water and salt distillation and there is no problem separating that way. The best I can do is try it on a better machine, I cant use the bigger one as its in a sealed room etc etc due to safety if it breaks apart!
My first one went upto 12,000G and when the spindle broke it wrecked the case as well. The much much bigger machines at his uni are far more dangerous if parts give out, I do know the tubes cost over £35 each for tests over 35,000G.

The anode, cathode thing is utterly confusing so I tried to use the chemistry excepted way of the anode being the magnesium etc. But it is one area I get confused on a great deal! our fishing boat has a zinc sacrificial anode, but to my thinking its actually a cathode! Maybe this is one case where plus and minus are better terms

That is mostly gibberish. The mid-Atlantic conveyor and your subsequent statements have nothing to do with clarifying what you mean by terms such as, "weak azeotropic bonding" and a water-NaCl azeotrope. Can you give a source for that fancy phrase and your claim that NaCl and water form an azeotrope?

This is the definition I was taught:

Source: **broken link removed**

An azeotrope (pronounced /əˈzi.ətroʊp/ ə-ZEE-ə-trope) is a mixture of two or more liquids in such a ratio that its composition cannot be changed by simple distillation. This occurs because, when anazeotrope is boiled, the resulting vapor has the same ratio of constituents as the original mixture.

I am willing to allow that a solid at room temperature with a high vapor pressure, say naphthalene, might be considered part of an azeotrope with water, but NaCl per se has an extremely low vapor pressure and is a different case.

John

 

[large_ghostman]

Ok what would you call it? The mid Atlantic conveyor I think has everything to do with it, you are also not dealing with normal pressure if your spinning something at 22,000G??? I doubt Azeotrope is correct in this sense, but I have no idea how to describe why I dont think I can separate Salt and water with only 22,000G.
The only thing I came up with was a similar situation with the water layers in the Atlantic. The water dosnt go salty/fresh there is a small area where the concentration is constantly shifting, the best person to ask for detail on this is pro bally Nigel and his daughter.
This is way more chemistry than anything else, you are dealing with water at a high pressure and sodium chloride, where they meet there is interaction between the molecules, would agree or not with this?
Now if you apply this to spinning salt water up you have a similar situation except you have a much smaller space, I dont think at those G's you could induce enough force over 100mm to separate the two. I willingly accept I could be wrong above this speed as I have never done it and have never had a reason to look into it.
I didnt ask the question I simply gave an answer based on what I did know and what I thought would happen based on something that is similar in the real world.
Vapour pressure isnt really anything to do with it. You can take much crap out of used oil if you spin it high enough, but try and use a tube say 15mm long and you dont get the same separation (No idea why exactly but I tried with smaller tubes).
So I guess until someone clued up on chemistry can give an opinion I will stick with you cant separate salt and water at 22,000g over a 100mm.
But disregarding the increase in pressure at room temp or not isnt valid.
The conditions in the Atlantic are what I would expect if you spin the tube up higher, but I still doubt it would separate completely.
I will ask though over at a chemistry forum, maybe someone there can explain it properly.


EDIT

Ok I was wrong on one thing for sure, there is no chemical bonding with salt and water!! (I learnt something new there), BUT I dont have an answer on the centrifuge yet except its unlikely...............
I will also ask over at science madness they are pretty good over there

Only thing I found even remotely close was this
**broken link removed**

sea water separation by centrifuge is apparently a not possible But I want to know why so disregard that answer until I have an explanation from him