I performed PEIS in an organic electrolyte system (1MHz to 1kHz, 10mV amplitude).

Working electrode: carbon felt loaded with Pt/C catalyst

Counter electrode: blank carbon felt

Reference electrode: Ag/AgCl

System: 0.2M TBAPF6, 3mM cobaltocene in MeCN

The image in the attachment shows that the voltage was set to +300mV vs. cobaltocene standard potential. The results of the test at around 0V are not much different.

Even more strange is that I performed similar PEIS measurements in aqueous solution (perchloric acid) and replaced the carbon felt electrode with platinum mesh, and I also observed capacitive behavior (or artifacts) in the high frequency region.

Does anyone have any idea how this capacitive behavior in HF region come from.