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Quasi-in-Situ Single-Grain Photoelectron Microspectroscopy of Co/PPy Nanocomposites under Oxygen Reduction Reaction
This paper reports an investigation
into the aging of pyrolyzed cobalt/polypyrrole (Co/PPy) oxygen reduction
reaction (ORR) electrocatalysts, based on quasi-in-situ photoelectron
microspectroscopy. The catalyst precursor was prepared by potentiostatic
reverse-pulse coelectrodeposition from an acetonitrile solution on
graphite. Accelerated aging was obtained by quasi-in-situ voltammetric
cycling in an acidic electrolyte. Using photoelectron imaging and
microspectroscopy of single Co/PPy grains at a resolution of 100 nm,
we tracked the ORR-induced changes in the morphology and chemical
state of the pristine material, consisting of uniformly distributed ∼20
nm nanoparticles, initially consisting of a mixture of CoÂ(II) and
CoÂ(III) oxidation states in almost equal amounts. The evolution of
the Co 2p, O 1s, and N 1s spectra revealed that the main effects of
aging are a gradual loss of the Co present at the surface and the
reduction of CoÂ(III) to CoÂ(II), accompanied by the emergence and growth
of a N 1s signal, corresponding to electrocatalytically active C–N
sites