Model study on the stability of carbon support materials under polymer electrolyte fuel cell cathode operation conditions

The electrochemical oxidation and corrosion resistance of differently prepared and post-treated (graphitization, surface oxidation) carbon support materials, whose surface area and composition were characterized by adsorption measurements and X-ray photoelectron spectroscopy, were investigated in model studies performed under fuel cell cathode relevant potential conditions. These included also the abnormal cathode potentials (up to 1.5 V_RHE) occurring during start-up and shut-down procedures. Reversible surface oxidation, leading, e.g., to the formation of quinones/hydroquinones, and irreversible oxidation to CO₂ were discriminated by combining electrochemical and on-line mass spectrometry measurements. Oxygenated surface carbon species were found to affect the surface area normalized electrooxidation activity much more than the surface area and porosity of the material, with graphitized carbon with low porosity and low oxygen surface content being most resistant towards reversible oxidation and towards irreversible oxidation at high potentials. Trapped CO₂, formed upon carbon oxidation at high potentials, is proposed to be at least partly responsible for CO₂ release at low potentials, below the standard potential for electrochemical carbon oxidation.