Hydragyrum - 13-5-2009 at 00:04
As is usual with me, I'm not 100% sure if this is the right forum for my question, so the usual apologies apply if I should have placed this
elsewhere.
I am about to embark on a great adventure in electrochemistry. I know a small amount of the theory (how to add two half-equations together to make an
overall voltage for a particular reaction, and maybe to add a small amount more of potential difference to that predicted to 'grease the wheels' of
the reaction in practice, and so on...).
What I don't know is what metal to use for an electrode in a given case.
For example, if I am expecting to evolve O2 at the anode, what should I use for the anode? Perhaps nickel?
On the other hand, I have read somewhere that if hydrogen is evolved (in a different reaction) then using Ni is not so good because hydrogen makes Ni
brittle. OK, if this is so, what should the electrode be made of in this case? Perhaps Cu?
Can anybody suggest a good reference where I can find all this written down? I'm sure it must be well-known, but I have had no luck so far finding the
information (to date, I have been confined to the internet as I find it tricky to get to a library at present - and nothing has jumped out at me so
far).
Any help will be welcome!
DJF90 - 13-5-2009 at 02:46
Platinum is best used 
However it is very expensive and graphite often offers a
good (and cheap) alternative. It all really depends on your electrolyte (you dont want your electrode to dissolve now do you). PbO2 electrodes may
have general use similar to graphite, and titanium can also be used in some circumstances.
Hydragyrum - 13-5-2009 at 03:45
OK, but can you tell me the best electrode material for a given reaction type? (or better, can you suggest a reference which gives a comprehensive
list of recommended electrodes based upon what will be done?).
DJF90 - 13-5-2009 at 04:21
You aren't being specific enough. There are loads of different electrodes that could possibly be used. Using graphite for the anode and cathode is
generally fine, unless you're making perchlorate or something (they can be used for chlorate but the graphite does wear quite fast according to some
and your product becomes contaminated with very fine carbon particles that are hard to remove. I'm not an electrochemist so it'll be interesting to
see what advice others can give.
.
Hydragyrum - 13-5-2009 at 05:13
DJF90, I do appreciate your replies. However, I have several plans in mind and am hoping that someone knows of a good reference which covers a wide
range of conditions.
For instance, I expect to do one experiment where O2 is evolved at the anode. I don't want the electrode to be consumed, so I need one which is
impervious to 'nascent' oxygen. I think even platinum may be degraded under such conditions (but maybe I'm wrong?). I have an impression that nickel
may be OK though, for O2 evolution, because it might be protected by a layer of oxide.
For reactions producing hydrogen, I think nickel is made brittle, and this is no good for an electrode you want to re-use; palladium absorbs H2 and is
thereby affected by it, so possibly platinum is no good either. Perhaps graphite is OK under these conditions? (I also plan to strip some batteries
for the carbon rods).
The thing is, I want to know in advance which substance to use as an electrode for a given set of conditions. I am lazy and love to have all
my information in one place! I have a fairly decent collection of materials: hafnium and platinum wire; niobium, tantalum, molybdenum, and tungsten
plate; titanium, nickel, and copper rods... so I do have variety. However, many of these items were not cheap to buy and I'd prefer to know the best
conditions for each material: what are their good points and bad points in relation to functioning as an impervious electrode? Before I commit an
expensive metal to the cauldron, I want to know it will not be degraded.
On the other hand, I have other metals like vanadium, chromium, manganese, cobalt, and zinc which I might like to use as dissolving anodes in order to
prepare some salts.
If there is a book on all this, a kind of encyclopaedia of electrode materials, then this is what I need. I want to be able to just look something up,
and then be able to pick and choose which metal to use in any given experiment.
If anybody knows of any reference book... or else has done heaps of experiments themselves and so they just know this through experience, then I want
to hear from you! We could make this an electrode information thread if people want to.
Phosphor-ing - 13-5-2009 at 05:21
Electrochemistry of Organic Compounds
The Manufacture of Chemicals by Electrolysis
Both these titles are in the library here just look.
Hydragyrum - 14-5-2009 at 03:30
Phosphor-ing, thanks for the suggestion of the books, I have been reading them.