Analysis of oxygen sources and reaction pathways of carbon support corrosion at the cathode in PEMFC using oxygen-18 DEMS

Oxygen gas, water used to humidify the gases, and surface oxides originated from the carbon black and catalyst preparation are the three possible oxygen sources contributing to carbon support corrosion (CSC) at the cathode in proton exchange membrane fuel cells (PEMFC). To discriminate among them, oxygen was isotopically labeled by replacing regular water with oxygen-18 (18O) enriched water (H218O, 98%) in differential electrochemical mass spectrometry (DEMS). The DEMS spectra of the cathode exhaust gases O2, O18O, 18O2, CO2, CO18O and C18O2 (m/z equal to 32, 34, 36, 44, 46 and 48 correspondingly), sampled by a mass spectrometer during cyclic voltammetry (potential cycled for 100–1400 mV at the rate of 10 mV s−1) and chronoamperometry, were analyzed to identify the sources of oxygen, identify mechanistic pathways, and classify the surface oxides on carbon for CSC.It was found that water is the main direct oxygen source for CSC. Water reacts with carbon to produce at least three types of carbon surface oxides, which are then further oxidized with water to produce CO2 in different potential ranges.