Importance of Catalyst Stability vis-\`a-vis Hydrogen Peroxide Formation Rates in PEM Fuel Cell Electrodes

TL;DR

This study investigates how catalyst stability influences hydrogen peroxide formation and membrane durability in PEM fuel cells, revealing that certain alloy catalysts with higher H2O2 selectivity do not necessarily cause more membrane degradation.

Contribution

It demonstrates that catalyst stability, rather than H2O2 formation rates alone, is crucial for membrane durability in PEM fuel cells, highlighting the importance of alloy catalysts like PtIrCo.

Findings

PtIrCo shows the least membrane degradation despite higher H2O2 selectivity.

H2O2 formation rates do not directly correlate with membrane degradation.

Catalyst stability significantly impacts PEMFC membrane durability.

Abstract

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.