Influence of the addition of nanoparticles on the oxygen reduction reaction characteristics of FeNC catalysts and the impact on the stability

Abstract

Hydrogen peroxide is known to have a detrimental effect on the stability of FeNC catalysts, as previously concluded from the comparison of differently prepared FeNC catalysts. However, beside the release of hydrogen peroxide, the iron composition as well as the carbon morphology changes. Different iron species might cause varying degrees of demetallation (associated with Fenton reaction and reactive oxygen species), whereas the carbon morphology is characteristic of the ability to persist under oxidative conditions. Thus, the true effect of H2O2 is difficult to understand from the comparison of different FeNC catalysts. To overcome this, we explored the relation between H2O2 formation and FC performance for an FeNC catalyst and a series of catalysts obtained by modification of this catalyst with different precious group metal (PGM) nanoparticles (Pd, Ag, Ir, Au). At two catalyst loadings, we performed detailed electrochemical investigations to identify changes in the oxygen reduction reaction pathway induced by accelerated stress tests mimicking the load cycle conditions. Moreover, hydrogen peroxide oxidation and reduction experiments were used to identify changes in the kinetics before and after load cycles. The results were compared to FC activity and short stability tests. While all modified catalysts exhibited a higher degree of H2O2 formation, the addition of small quantities of PGM nanoparticles improved the stability in FC. The latter effect can be associated with an enhanced HPRR kinetic.