Dear All,
I understand that in PEM Fuel Cell, the electrocatalyst are evaluated by the ECSA, which is calculated by taking an appropriate "flat" baseline between 0.35 and 0.4V.
I was doing the durability study (by cycling between 0.6V and 1.2V) of the catalyst we had developed. Initially the CV had a flat capacitive region between 0.35 to 0.4, but as number of cycles increases, that region becomes slanted. I have 2 doubts pertaining to this
(1) Why the graph turns slanted in nature as cycles progress
(2) What appropriate baseline should be taken in case of baseline between 0.35 and 0.4 is not flat, but slanted. e.g. the attached graphs
PS: The attached graphs are full scan of CVs taken after: 0 cycles (initially), 100 cycles, 500 cycles, 2000 cycles, 5000 cycles, 15000 cycles and 30000 cycles
Dear Khantesh Agrawal ,
For ECSA integrate the charge of hydrogen evolution. The background you can take like linear fit between 0.35 and 0.4 V as you said if you want to do it still the same way and automatic. So it is correct. My background subtraction by "eye" is attached.
Double layer should be symmetrical around current 0. In your case it is not. It means that there is presence of hydrogen or oxygen which shift it up or down, respectively.
To answer your question exactly:
1) Oxygen impurities are more significant with time due to increase of amount of oxygen or because of your catalyst is weaker with time or both. Be that as it my, you ll see stronger oxygen reduction with time.
2) Maybe you can find the bump ("hydrogen desorption" region) and try to cut the background but the obtained data will be meaningless I think.
The solution might by to purge electrolyte properly by fresh one to get rid of oxygen and then measure CV. I cannot say more without knowing experimental setup.
I hope that it will be helpful for you.
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