2 research outputs found
Depth-Dependent Scanning Photoelectron Microspectroscopy Unravels the Mechanism of Dynamic Pattern Formation in Alloy Electrodeposition
Fascinating spatiotemporal
patterns forming during the electrodeposition
of some alloys have attracted the interest of the scientific communities
dealing with electrochemical materials science and dynamic processes.
Notwithstanding extensive experimental work and recently achieved
theoretical insights, several aspects of the physical chemistry of
these dynamic structures are still elusive. In particular, the analytical
methods employed so far to characterize these structures invariably
failed to pinpoint any chemical or structural patterns correlated
to those perceived by the naked eye or with a light microscope. In
this work, we have made systematic use of the extreme surface sensitivity
provided by synchrotron-based scanning photoelectron microspectroscopy,
combined with progressive erosion by precisely controlled Ar<sup>+</sup> sputtering, to achieve quantitative 3D understanding of the compositional
and chemical-state distribution of an Ag–In electrodeposited
layer, following the key elements Ag, In, and O. The results revealed
that the pattern is present only in the topmost region (ca. 100 nm)
of the layer and exhibits a regular distribution of the alloying elements
in certain chemical states. Specifically, pattern formation in Ag–In
electrodeposits is crucially controlled by the space distribution
of surface In<sup>3+</sup> oxi-/hydroxides, deriving from reaction-diffusion
processes taking place during alloy growth, and this pattern disappears
in depth because of the delayed reduction of In<sup>3+</sup> present
in this film to elemental In, followed by intermetallic formation
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