Dear Snahasish Bhowmik There are various reasons for detaching the Cat from the electrode surface, such as high positive/negative voltage, bubbling etc. Also, it depends on ink film dispersion on the electrode surface due to different physisorption properties of the material and ionomer ratio. A possible solution could be, that you should know what is your exact potential window, try different ionomer/catalyst ratios, and try to make a very uniform thin film.
Following reference could be more useful to optimize the ink film formation.
Article Impact of film drying procedures on RDE characterization of ...