Abstract
Understanding the lateral variations in the elemental and chemical state of constituents induced by electrochemical reactions at nanoscales is crucial for the advancement of electrochemical materials science. This requires in situ studies to provide observables that contribute to both modeling beyond the phenomenological level and exactly transducing the functionally relevant quantities. A range of X-ray coherent diffraction imaging (CDI) approaches have recently been proposed for imaging beyond the diffraction limit with potentially dramatic improvements in time resolution with chemical sensitivity. In this paper, we report a selection of ptychography results obtained in situ during the electrodeposition of a metal–polymer nanocomposite. Our selection includes dynamic imaging during electrochemically driven growth complemented with absorption and phase spectroscopy with high lateral resolution. We demonstrate the onset of morphological instability feature formation and correlate the chemical state of Mn with the local growth rate controlled by the current density distribution resulting from morphological evolution.
Highlights
Manganese oxides are popular non-precious oxygen reduction reaction (ORR) catalysts for metal/air batteries [1] owing to their low cost, adequate electrochemical stability and good catalytic activity towards the decomposition of hydrogen peroxide, produced by the ORR 2epathway, typical for alkaline solutions [2,3,4]
Notwithstanding their electrocatalytic appeal, the practical application of Mn-Co oxides is impaired by their poor electrical conductivity: high-conductivity materials can be fabricated by composite synthesis routes, e.g., by dispersing the metal oxide particles into a polypyrrole (PPy) matrix
The electrocatalytic activity of Mn-Co/PPy samples towards ORR was evaluated by linear sweep voltammetric (LSV) measurements in O2 -saturated (SIAD 6.0) 0.1 M KOH electrolyte under quasi-steady-state conditions (5 mV·s−1 ) at different Rotating Disk Electrode (RDE) rotation speeds
Summary
Manganese oxides are popular non-precious oxygen reduction reaction (ORR) catalysts for metal/air batteries [1] owing to their low cost, adequate electrochemical stability and good catalytic activity towards the decomposition of hydrogen peroxide, produced by the ORR 2epathway, typical for alkaline solutions [2,3,4]. Transition metal additions to manganese oxides, binary Mn-Co-Ox spinels [10,19,20,23] and MnOx /CoOx mixtures [21,22] have been the most extensively studied as ORR catalysts in alkaline solutions, because of their high catalytic activity and good corrosion stability with respect to the pure components Notwithstanding their electrocatalytic appeal, the practical application of Mn-Co oxides is impaired by their poor electrical conductivity: high-conductivity materials can be fabricated by composite synthesis routes, e.g., by dispersing the metal oxide particles into a polypyrrole (PPy) matrix. We extend this approach to the growth of mixed-oxide/PPy composites, in particular concentrating on an in situ dynamic description of the morphochemical development of the composite material during electrodeposition, based on complementary electrochemical and soft-X ray absorption and fluorescence microspectroscopies
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