Hi,
The main possible reasons for the degradation in such case are the loss of Pt and carbon corrosion. 2.2 V is a high potential. At this potential, carbon is thermodynamically unstable and can be oxidised (C + 2H2O → CO2 + 4H+ + 4e– , Eθ = 0.207 V vs. SHE), leading to severe carbon corrosion (especially poorly crystalline carbon such as carbon black). The consequences may include the detachment/aggregation of Pt catalyst, or in more extreme cases, the collapse of the entire carbon structure.
Hi,
The main possible reasons for the degradation in such case are the loss of Pt and carbon corrosion. 2.2 V is a high potential. At this potential, carbon is thermodynamically unstable and can be oxidised (C + 2H2O → CO2 + 4H+ + 4e– , Eθ = 0.207 V vs. SHE), leading to severe carbon corrosion (especially poorly crystalline carbon such as carbon black). The consequences may include the detachment/aggregation of Pt catalyst, or in more extreme cases, the collapse of the entire carbon structure.
Hi,
as pham wrote, thermodynamics allow carbon oxidation already at potentials as low as ~0.2V. That we can use it in a fuel cell cathode is only possible because the corrosion kinetics are extremely sluggish. Hence, at 80°C you can use non-graphitized carbon blacks (e.g. Ketjen or Vulcan) up to 0.9 - 1 V (vs. the RHE). A graphitized carbon black (more corrosion stable) will be corroded strongly only above 1.4 V.
There is a lot of data in the literature about the effects of potential, RH and temperature on the carbon corrosion rate.
Take-home message: do not expose carbon electrode to potentials higher than 1 V.
Cheers, Philipp
Hi, I agree.
Just to add to the story:Although holding the electrode at high potential result in sever losses, cycling to the same potential results in even higher losses per unit time.
Cheers, Gustav
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