After 1000 cycles CV test, I find there are Pt nanoparticles on the working electrode. Are the Pt nanoparticles from the dissolvation of Pt wire, then electrolytic deposition on the working electrode?
reference electrode: Ag/AgCl, counter eletrode: Pt wire, working eletrode: Glassy Carbon Electrode, electrolyte: 0.5M H2SO4. under air atmosphere.
Question
Can Pt wire be dissolved under CV test during 0 to -0.6 V(Ag/AgCl) in 0.5 M H2SO4?
All Answers (26)
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Well friend, its possible. I observed such thing particular in the presence of halides . certainly pt oxidized in H2SO4 but some what higher potential vs Ag reference.
Please refer this paper ,
doi:10.1088/2043-6254/1/2/025013 -
Hi,
everything depends on your environment, but i don't think so.
I work with Pt wire in a H2SO4 1moll-1, in a set of tree electrodes in a range of -0,1 - 0,78V and everything runs all right.
And my boos have worked with over than 1000 cycles, at this same set and it is possible to be done. If something wrong happened, it might be based in your work electrode, or at the condition that you are handling them.
Wish you luck! -
The reference electrode (RE) Ag/AgCl is a source of ion chloride that can contaminate the H2SO4 solution, specially if the RE is close to WE by the lugging capillar. -
Thank friends！I carry out hydrogen evolution reaction test. I use r-GO as active material. After 10000 CV cycles , the hydrogen production potential is similar with Pt. HRTEM and EDS results confirm the Pt nanoparticles on r-GO. I don't know why Pt can be synthesized on the working electrode from Pt wire (counter electrode). Pt is usually stable at this condition. -
Hi,
I think it will possible, but not in a chemical way. Cyling at potentials of hydrogen evolution/H+ discharge, adsoption/ desorption under high current density may lead to desintegration of the Pt-metal along the grain sizes. -
I have never studied systems after 1000 cycles of CV. But I have long term experience with standard CV investigations of various organic and organometallic compounds, inclluding chlorides, on various electrodes, including Pt, in various media, including concentrated H2SO4 and I never observed any dissolution of Pt. In addition to this, the eventual dissolution should appear also during the exhaustive electrolysis and I never heard about generation of Pt-salts or complexes in the solution. I think, the electrolytic dissolution of Pt as such is impossible.
Do you work under inert atmosphere? Pt is known that forms with oxygen surface oxides and hxdrated oxides. Are not your "nanoparticles" the surface oxides? -
The hydrogen evolution should happen on the working eletrode. The counter eletrode (Pt wire) should have the oxidizing reaction. Is it possible that the Pt is oxidized, then be dissolved by H2SO4, at last be electrolytic deposited on the working eletrode?
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Pt should not really dissolve into H2SO4 solutions
with chlorides this is different, because they form Chlorine which will relatively easily attack Pt.
Although I know from some of my kollegues that it is at least not normally a desaster, even if you have a lot of chlorides
You scan to cathodic direction and back so you won't evolve chlorine on the working electrode
Also regarding the mentioned paper one thing as you also have: Some eventual chloride contamination. Use Hg/Hg2SO4 or a more environmentally friendly electrode the Ag/Ag2SO4 electrode (which is not so common)
http://www.consultrsr.com/resources/ref/refpotls.htm
Furthermore in that paper: No meaningful supporting electrolyte concentration at very high current densities (for a µm sized electrode). This can produce all kinds of weird things
Possible alternative interpretation of the mentioned paper: with increased conductivity of the H2SO4 solution you get smaller iR drop, that's why it has some influence.
In this region were the peak is there are usually some surface oxidation reactions, but usually Pt doesn't corrode
And there isn't either a conlusion like "Pt dissolves" in that paper. Neither are there appropriate mechanistic studies
For surface oxidation of Pt there are better papers than that, where you have also supporting electrolytes
(REF numer 19 and 20 from that paper)
I guess that what happened, was the following: small counter electrode (Pt wire) big working electrode == high anodic current densities and Cl-. You get chlorine evolution and dissolve Pt from the Counter that redeposits on the working electrode
(anodic reaction happens on the counter electrode when you scan to cathodic direction on your working electrode)
Liquid bridge or agar bridge might help as well if bigger Counter doesn't help and you don't want to buy other REF -
Platinum dissolves in aqua regia because of the Strong Reduction-Oxidation battle going on between F- and NO3- at the Pt surface, Sulfuric doesn't have a reduction component. strong bases can dissolve Pt., if there are enough Cl- ions present in solution, they are a potential source for redox, in that case small amounts could be deposited on the other electrode. The solution you have is very low concentration and shouldn't have any effect. I would look for other sources of contamination. -
Perhaps you should check the purity of platinum. I have found an alloy of platinum / nickel marketed as pure platinum which is dissolved in sulfuric acid under anodic polarization.
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I agree this seems a very strange result and very unusual for conventional voltammetry at low current densities. The cell design and proper isolation of the electrodes are likely important factors that can relate to contamination after many cycles. Are you reducing both H+ and oxygen under this cathodic condition?
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During cycling of your working electrode in cathodic direction, from 0 towards -0.6 V vs. Ag/AgCl, at counter electrode you will have oxygen evolution and disolving of Pt which will be redeposited at your working electrode.
This is probably main reason why you see nanoparticles of Pt. -
I have not performed the CV with 1000 cycles but I have used Pt electrode in 0.5 M H2SO4. I have never experienced/observed dissolution of Pt. Even I've used Pt in presence of KCl as supporting electrolyte. But the potential region -0.6 V Vs Ag/AgCl where evolution of Oxygen occurs might affect the system. Did u confirm the particles with EDX? -
what you carried out is a normal active processing of glassy carbon electrode. while a strange result you get. have you confirm these particles? Pt, or other metal? the purity of H2SO4 and Pt electrode should be confirmed. -
So far I have not experienced any dissolution of Pt counter electrode in mild electrolyte. It might dissolve (oxidized) if the electrolyte is a mixture of concentrated HCl plus nitric acid with very high applied potential. The best way to confirm it is to do elemental analysis of the 'Pt nanoparticles' you think appeared at your working electrode. -
I think it is not necesary to worry about this problem。
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In addation，there might be two explainations: the pt wire is oxided in the air or the pt nanoparticle is spurting physically by the evoluted hydrogen.
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Thanks very much for all friends' help.
According to all comments, the possible reasons are summarized.
1. possible Ag/AgCl release some Cl-, then react with Pt wire.
2. the current or voltage are too high. there are a mass of bubble on the Pt wire and working electrode. possible the Pt is oxygenated.
I think I need use memebranes and reduce the CV voltage. Because I carry out HER test. If there is a little of Pt, the Hydrogen production potential will reduce too much. -
No. It won't dissolve in sulfuric acid at 0.5 M concentration when your applying the potential up to 1.0 V vs Ag/AgCl.
So, you can use it for CV studies in acidic medium. -
Other hypothesis: You can follow the potential ramp using an external recorder (i.e osciloscope) with high impedance. Check that programing of potential is clean. Why?. I remember several year ago, that using a potentiostat we verify that potential programm was not clean. We can observe the appereance the some peak of potential during ramp, between delay time, etc. Could be a problem of the electronic of the device!!!
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Some comments on
>No. It won't dissolve in sulfuric acid at 0.5 M concentration when your applying the potential up to 1.0 V vs Ag/AgCl.
>So, you can use it for CV studies in acidic medium.
Usually SO4 based REF electrodes are not available and many people use AgAgCl instead then, including me ;-((
However, better practise is to use a REF with the same anion of the acid that you use, when possible
Nano particles are really small, why did you analyse this in the first place?
It might be maybe normal.
I have no idea about what would be equilibirum concentration of Pt in H2SO4 solutions??
At least a very very small number, but I guess not 0.
So is it enough to form nanoparticles on glassy carbon??? (Whose amount in moles is very small, so you don't need very much) On the other hand limiting currents are very small as well if you have small Pt concentrations.
That's why I would still guess Chlorides are the problem, or you have some other contamination source
What is your reaction that you study? You probably don't study oxydation or reduction of glassy carbon...
Maybe there is some answer when you tell what is your redox couple that you study (present at about mM level?)
Cl- ions are quite mobile compared to HSO4- so also "electroatraction" will help to move the chloride to the counter electrode (anodic (+) while scanning to cathodic direction on the working electrode)
>2. the current or voltage are too high. there are a mass of bubble on the Pt wire and working electrode. possible the
>Pt is oxygenated.
agree with Ivan Suarez Suarez,
I think there are two possibilities:
a) Your REF is clogged and your potentiostate goes wild, because it cannot measure the potential of the reference... (Measure its impedance). Quite probable.
a2) something is wrong with your potentiostat, or use some lower bandwidth (if you can set that) and it is far beyond 10 kHz
in both cases--> Your resulting CV looks maybe also very awfull
check the potentiostat's potential output with an oscilloscope (if you have one) and the reference electrode and all your electrode connections and cables are ok.
That your electrolyte is "boiling" next to your electrodes is quite common if REF potential cannot be read or if the electrodes or cables are not very well connected
b) Your wire is very small and the current at the glassy carbon very big
Normally you should have a small working electrode and a counter electrode which is much bigger in proportion -
check Inzelt et al. http://iupac.org/publications/pac/83/2/0269/
dissolution of platinum after cycling
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Hi,
Pt wire is 'stable' in this conditions. You have to cause a transition from the 'free' to oxidised surface (or vice versa) in order to start the dissolution. You can check my paper in the attachment. The experiments are made in 0.1 M HClO4, but the behaviour is the same in sulphuric acid (the result will be published soon).
cheers
Angel -
In my opinion, the dissolution of Pt electrode can still be realized if the electrolyte contains chloro ions such as perchlorate and chloride. These ions are needed to capture and stabilize the ionization products, [PtCl6]2- ions.
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Hi Roto Roto,
I've made also several series with chloride containing solutions also. Up to my experience: the Cl- can enhance the dissolution at certain conditions (to be published soon also ;-), but doesn't change the general statement from above. e.g. If you don't cause oxidation or reduction of the platinum surface, you won't get dissolution in the mentioned above conditions (when I say no dissolution: I mean no detectable one. We have a detection limit of our ICP-MS for Pt in region of 5-10ppt, which allows quantification of dissolution amounts in sub-monolayer region)
Cheers
Angel
