Deposition of Pt nanoparticles on electrochemically functionalized carbon black electrode for potential application in polymer membrane electrolyte fuel cells was realized with in situ ion-exchange method. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis show that carboxylic acid groups are introduced on the carbon black through electrochemical functionalization. The ion-exchange mechanism is confirmed. Scanning electron microscope and transmission electron microscope images show that Pt nanoparticles are highly dispersed on the surface of carbon black, with an average size of 4.1 nm, which is consistent with the particle size calculated through X-ray diffraction method. The electrochemical surface area is greatly increased and the Pt utilization is greatly enhanced on the ion-exchanged electrode (electrode made by in situ ion exchange method), which is 96.6%, 2.42 times that of the conventional one (39.9%). The increase in electrochemical surface area and Pt utilization is attributed to the specific structure of the ion-exchanged electrode. (c) 2006 The Electrochemical Society.