- We observed that the electrochemical active surface area (ECSA, m2/g) fully disappeared after some cycles of cyclic voltammetry in acidic media.
- The CV measurement (Potential window = -0.2 ~ 1.0 V vs. Ag/AgCl) was performed after N2 purging (3-electrode system)
- The currents for PtO reduction and proton sorption fully disappeared, resulting in showing only the EDLC area.
- By ex-situ measurements, we found that the Pt electrocatalyst still remained.
- Why was the ECSA diminished even if the Pt remained?
Hi David,
From where the Pt dissolved? I guess you mean from Pt/C electrode? loading?
It is normal for Pt/C, metal partially dissolve also agreggation is formed by submit to several CV (in this window, 1 to 1.2 vs RHE) Hydrogen as well as oxide reduction areas must be consequently decrease with time. Then, your ECSA similarly decrease. However, it not desapear completely (till be equal to EDLC area). Factors as loading, support and so on, influences as well on diminishing those areas.
Which ex-situ measurements are you using for measure remain Pt?
If Pt agreegates, you probably have same loading but lower ECSA (not only by dissolution)
If you are cycling in mentioned window potential, How you suggest to pasivate Pt to PtO? Both species are formed according anodic-cathodic way in acidic media, in Pt/C electrodes.
Here are a couple publications than maybe can help to understand ECSA lose phenomena
DOI: 10.1016/j.apcatb.2013.11.043
DOI: 10.1016/j.jpowsour.2011.03.064
Obviously, has a lot of publications related with. Just search
Regards and go ahead
José
no, PtOx can't passivate the Pt surface in acidic media.
In your case, the decrease of ECSA may be from the loss of surface active sites, such as Pt surface comtimination, particle ripening etc.
PtOx can't passivate the Pt surface in acidic media, but indeed it depends on the potential you applied. above 1.1V, the dissolution is reduced.
This might be due to the loss of active surface area of Pt due to agglomeration of Pt particles on the substrate and formation of edges difficult to access. Or may be the Pt shell is too thin to completely cover the core, which leads to core dissolution and loss of activity. But Pt-oxide formation will not passivate the surface.
Hi David again,
Probably your catalysts are suffering a rearrangement... from core to shell and an alloy is surface formed. For instance, if Ru is in core (i don´t know which one is yours) it let out meanwhile Pt go in, after several CV. Finally you get an alloy in surface. Also aggregation happens, no forget.
Afterwards the CV profile looks like more at PtRu alloy than single Pt.
However you wont passivate the Pt surface to PtOx to avoided as above answers. Other question is if your reference electrode does not influences in your particles, because chlorides adsorbs strongly on Pt surface:
Journal of The Electrochemical Society. 04/2010; 157(5):B621-B627
Could you try with other reference electrode?
Regards and go ahead
José
I quite agree with José.
If core/shell structures, the ECSA decline would quite depend on the core materials and particle size. If transition metals like Ni, Fe, Co or alloyed transition metals are in core and particle size is below 10-15 nm, basically particle growth will be prevented during potential cycling as transition metal segregation-oxidation-dissolution is relatively easier than Pt oxidation-dissolution. However, if your core metal has high affinity for oxygen (hydroxyle species) but stable in acidic media, then your ECSA loss could be due to the surface atomic rearrangement during cycling as mentioned by José.
Thank you for your valuable comments and I really appreciate it. I will go ahead on the basis of your comments. Thank you all again.
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