There are various ways to activate a Pt electrode. Although cleanliness is important, it is nearly impossible to avoid impurity adsorption unless the entire process is conducted in a sealed high vacuum chamber where the surface is cleaned by ion or electron bombardment. To preserve the cleaned surface, it is necessary to transfer the electrode to a cell containing the solution in the vacuum chamber. Not an easy task and one that requires specialized equipment and training. One method in the laboratory is to repetitively CV cycle the Pt electrode from –0.2 V to +1.0 V vs. Ag/AgCl reference electrode in 1 M H2SO4 until well-defined H-adsorption waves appear. High purity water must be used for making solutions and for best results, the solution degassed by purging with pure N2 or argon to remove oxygen, and maintaining a flow of the gas above the solution during experiments.
Just remember, when you use solid electrodes like Pt, the surface chemistry can greatly affect what you see for the electrochemistry of the analyte.