Three mechanisms for power generation in the absence of
fuel were considered. The corresponding reactions at the anode
have been illustrated in Figure 3. The first hypothesized
mechanism is the oxidation of vanadium oxide when the fuel
supply is interrupted. To assess this possible origin of the
charge transfer in the absence of fuel, high-resolution XPS
spectra of the vanadium oxide anode were acquired from three
identical fuel cells operated in different conditions. Spectra were
acquired with a PHI VersaProbe II instrument using a
monochromatic Al K α source. The probe size was 50 μm
with a power of 12.5 W. The pass energy was 11.75 eV. The
spectra were charge-corrected for the main component of the
O1s peak set at 530.0 eV.