  The role of catalyst stability on the adverse effects of hydrogen peroxide
(H2O2) formation rates in a proton exchange membrane fuel cell (PEMFC) is
investigated for Pt, Pt binary (PtX, X = Co, Ru, Rh, V, Ni) and ternary (PtCoX,
X = Ir, Rh) catalysts. The selectivity of these catalysts towards H2O2
formation in the oxygen reduction reaction (ORR) was measured on a rotating
ring disc electrode. These measured values were used in conjunction with local
oxygen and proton concentrations to estimate local H2O2 formation rates in a
PEMFC anode and cathode. The effect of H2O2 formation rates on the most active
and durable of these catalysts (PtCo and PtIrCo) on Nafion membrane durability
was studied using a single-sided membrane electrode assembly (MEA) with a
built-in reference electrode. Fluoride ion concentration in the effluent water
was used as an indicator of the membrane degradation rate. PtIrCo had the least
fluorine emission rate (FER) followed by PtCo/KB and Pt/KB. Though PtCo and
PtIrCo show higher selectivity for H2O2 formation than unalloyed Pt, they did
not contribute to membrane degradation. This result is explained in terms of
catalyst stability as measured in potential cycling tests in liquid electrolyte
as well as in a functional PEM fuel cell.
