  Hydrogen peroxide (H2O2) formation rates in a proton exchange membrane (PEM)
fuel cell anode and cathode were estimated as a function of humidity and
temperature by studying the oxygen reduction reaction (ORR) on a rotating ring
disc electrode (RRDE). Fuel cell conditions were replicated by depositing a
film of Pt/Vulcan XC-72 catalyst onto the disk and by varying the temperature,
dissolved O2 concentration and the acidity levels in hydrochloric acid (HClO4).
The HClO4 acidity was correlated to ionomer water activity and hence fuel cell
humidity. The H2O2 formation rates showed a linear dependence on oxygen
concentration and square dependence on water activity. The H2O2 selectivity in
ORR was independent of oxygen concentration but increased with decrease in
water activity (i.e., decreased humidity). Potential dependent activation
energy for the H2O2 formation reaction was estimated from data obtained at
different temperatures.
