Degradation of Carbon Supports in PEFC Cathode Investigated by Electrochemical STM: Effects of Platinum and Oxygen on Enhanced Carbon Corrosion

摘要

The corrosion of highly oriented pyrolytic graphite (HOPG) model electrodes' surfaces with Pt nanoparticles and oxygen molecules in an aqueous solution was investigated using electrochemical scanning tunneling microscopy in order to understand the degradation of carbon supports found in polymer electrolyte fuel cells (PEFCs) cathode. Structural changes of HOPG surfaces with Pt nanoparticles and oxygen due to the corrosion were observed directly at atomic levels under potentiostatic control between 0.6 to 1.2 V vs. RHE. The STM observations revealed that the graphite surface oxide formation due to corrosion of the HOPG surfaces with Pt nanoparticles occurred initially at step edge sites, i.e., at defect sites and then grew toward terraces. This indicates that Pt particles and oxygen on the HOPG surface accelerated the corrosion. Surface oxygen species formed through the partial oxidation of water and the dissociative adsorption of oxygen molecules likely enhance the oxidation rate of graphitic oxide species.