- We observed that the electrochemical active surface area (ECSA, m2/g) fully disappeared after some cycles of cyclic voltammetry in acidic media. The active material was a core-shell composite (Pt=shell)
- 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 TEM analysis, we found that the Pt electrocatalyst still remained.
- Why was the ECSA diminished even if the Pt remained?
This might be due to the loss of active surface area of Pt due to aggregation 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 rearrangement of your core-shell model and loss of activity. But Pt-oxide formation will not passivate the surface.
Explanation given by Hatem M A Amin may be true, since presence of Pt should show the characteristic CV response that is generally become prominent by successive cycling; opposite of the observation mentioned.
Confirmation of presence of Pt on the substrate with TEM analysis is not rational, I think. In addition, no information about substrate and binder (if any) used. However, study may be conducted with more thicker Pt shell to justify the matter.
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