Standard cell potential

  1. I am using NiSO4 aqueous solution, Pt anode, Cu cathode coated with Au for Ni electroplating (at 3 V DC) on Au. Cu is not exposed to solution.
    To calculate cell potential should I consider Cu/Pt or Au/Pt. If I replace Pt with graphite, whether for same 3 V DC supply Ni plating would be possible? Your suggestion will be very useful.
  2. jcsd
  3. Borek

    Staff: Mentor

    If you are electroplating with Ni, your system is Ni(II)/Ni.

    Out of curiosity - please show what you mean by calculating cell potential with Au/Pt.
  4. I am not using Ni electrode...

  5. Borek

    Staff: Mentor

    Yes you do. You start with something else, but your reaction is Ni2+ -> Ni. Even if the first layer is deposited on something else, every next layer is deposited on the nickel electrode. There will be some small difference between the deposition of the first layer and deposition of next layers, but I doubt you will be able to observe it - try to estimate amount of nickel required to cover your Au or Pt electrode with monoatomic layer of Ni. How long does it take?
  6. Thanks...I never thought like that....

  7. But would your electrode be covered with monoatomic layer?

    You have 4 competing reactions, all under the same voltage of the whole electrode:
    1) Ni2+ -> Ni on Ni electrode, once formed
    2) H+ -> H2 on Ni electrode
    3) H+ -> H2 on whatever your base electrode is
    4) Ni2+ -> Ni on the underlying non-Ni surface, initiating new Ni crystals.

    All 4 have different kinetic barriers. And what exactly the barriers 3 and 4 are depends on what the base electrode is.

    For example, if you attempt to cover an electrode with Ni, and your electrode happens to have very low kinetic barrier for H2 production, then you could be producing hydrogen and getting no Ni deposition because of your choice of electrode.

    Furthermore I see no reason why you should succeed in electroplating. If the kinetic barrier on initiating new Ni crystals on the base electrode is high compared to kinetic barrier on depositing Ni on existing Ni surface, then you may well get a few dendrite Ni crystals on your electrode, and the rest of your base electrode uncovered and unplated.

    So... what is necessary to get a successful electroplated monoatomic Ni cover instead of H2 or a few Ni dendrite crystals?
  8. Borek

    Staff: Mentor

    I took the question at face value - and as it asked about Ni electroplating on gold, I assumed OP uses a recipe for Ni electroplating on gold. Such recipes are designed to ensure Ni deposition and to eliminate competing reactions. You are right system can be much more complicated and it doesn't have to yield a monoatomic Ni as a first phase, but once you have enough Ni (even as dendrites) and no competing reactions, potential is still defined by the Ni(II)/Ni. Monoatomic Ni was intended rather as an example of how fast the situation can change, not as a description of what really happens, perhaps I should be more clear about it.

    As far as I know it depends on the electrode material. I have a gut feeling Ni will deposit nicely on Au, but that's just an intuition.

    What I do know is that often the best recipe for electroplating with Ni is to first electroplate with a thin copper layer (which is relatively easy on most metals), and then to proceed with nickel electroplating. Trying to deposit nickel directly - especially on steel/iron - is a serious PITA. OP clearly stated that while the copper is present, it is below gold and not exposed, so we are dealing with Ni on Au.
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