Characterization of Vulcan Electrochemically Oxidized under Simulated PEM Fuel Cell Conditions

Abstract

Electrochem. surface oxidn. of Vulcan XC-72, a carbon black commonly used in proton exchange membrane (PEM) fuel cells, was studied following potentiostatic treatments up to 120 h at potentials from 0.6 to 1.2 V at room temp. and 65°. Surface oxidn. was followed using cyclic voltammetry (CV), TGA coupled to online mass spectrometry (TGA-MS), XPS, and contact angle measurements. The anal. techniques all indicate significant surface oxidn. occurred during the 1st 16 h of 1.2 V potential bias holds at room temp. and a slow increase in surface oxide formation occurred thereafter. An identification of ether, carbonyl, and carboxyl surface oxide species was made by deconvolution of XPS spectra and assigning these functional groups to the obsd. TGA-MS CO2 evolution peaks (150 °C-750 °C). An increase in CO evolution ( > 800°C) detd. by TGA-MS was consistent with electrochem. CV data, which detected electroactive hydroquinone/quinone species; these electrochem. detected species were a minor fraction of the electrochem. generated surface oxides. Potential bias holds at 1.0 V at room temp. only resulted in slight oxidn. of Vulcan XC-72. However, expts. at 65 °C showed clear signs of surface oxidn. after only 16 h at potentials ≥0.8 V, verifying that surface oxides can be generated under simulated PEM fuel cell conditions. Overall, these results suggest that changes in component hydrophobicity, driven by carbon surface oxidn., are an important factor in detg. long-term PEM performance instability and decay. [on SciFinder(R)]