Talk:Platinum black

Potential or overpotential?

Regarding section 3: "Potential of Pt black versus shiny platinum: In hydrogen saturated hydrochloric acid, the shiny platinum electrode is observed to assume positive potential versus that of platinum black (+ 340 mV at room temperature). With the temperature increasing to 70 °C, the difference in potentials dropped to zero.[2]" This is tasty info, but something about "assume positive potential" bothers me. Most of this article seems to refer to reference electrodes and reference electrode potential, to the point that the word "potential" tends to imply "equilibrium potential". Reference electrodes are used at equilibrium, i.e., zero current and no net production or consumption of the redox species. I thought the equilibrium potential of an electrode is independent of its area. (I'm tentatively assuming Pt-black is equivalent to Pt-shiny except having more active area. Also assuming the Cl- from HCl is passive.) So I would have thought the "potentials" were equal. Unfortunately I don't expect I can read the reference [2] right away to see its details, but I wonder if the 340mV difference was observed in some condition having a net consumption rate of hydrogen. (Atmospheric oxygen leaking in might have this effect.) If so, the 340mV is the difference in "overpotential for hydrogen production" rather than "potential". Low hydrogen overpotential is another common reason for using Pt-black, so it's very relevant on this page, but it might be more educational to add some admission of net current or production or reaction rate, if that's what the reference is talking about. I would be gratified if the author who inserted reference [2] would look there for an implicit reaction rate, and maybe put such detail into this section. I'd try it myself but I'm not real fast at finding books. I suppose it's possible that some unstated practical situation often causes this (e.g., O2 leak-in, or room light) without any specificly stated condition of non-zero reaction rate. jimswen (talk) 07:50, 24 May 2008 (UTC)[reply]

I added a page number to the reference, for the reader's convenience, quantification that that potential is at a zero net current, and (hopefully) uncontentious explanation that "the reason for this is not perfectly clear, although several explanations have been proposed." Personally, I like this summary:

Too often, this electrode (SHE) is treated as a thermodynamic instrument to be taken for granted. In the literature dealing with the hydrogen evolution reaction, there is a tendency to exclude important phenomena from consideration because "poisoning" has provided an easy way of dismissing them. (D.J.Ives, G.J. Janz, "Reference Electrodes, Theory and Practice", Academic Press, 1961, p.91)

You might also wish to see Glassy_carbon#Electrochemical_properties.

Hope this helps. Have a good Sunday. Stan J. Klimas (talk) 12:54, 24 May 2008 (UTC)[reply]

Platinised Platinum different to Platinum Black?

The article currently states, 'covering platinum electrodes with platinum black is called "platinization of platinum".' However, there are several papers (e.g. Mills, A., "Porous Platinum Morphologies: Platinised, Sponge and Black", Platinum Metals Review, 51, 1, Jan 2007) that state that platinised platinum is a different form to platinum black. Does the article therefore need either correcting or clarifying? AHDGraham (talk) 09:19, 2 July 2008 (UTC)[reply]

Good point. I tried to address this; see the most recent diffs to the article; please feel free to correct any imperfections you may see. Stan J. Klimas (talk) 23:15, 3 July 2008 (UTC)[reply]