Synthesis, studies and fuel cell performance of “core–shell” electrocatalysts for oxygen reduction reaction based on a PtNix carbon nitride “shell” and a pyrolyzed polyketone nanoball “core”

This report describes a new class of "core-shell" electrocatalysts for oxygen reduction reaction (ORR) processes for application in Proton Exchange Membrane Fuel Cells (PEMFCs). The electrocatalysts are obtained by supporting a "shell" consisting of PtNix alloy nanoparticles embedded into a carbon nitride matrix (indicated as PtNix-CN) on a "core" of pyrolyzed polyketone nanoballs, labeled 'STp'. ST(p)s are obtained by the sulfonation and pyrolysis of a precursor consisting of XC-72R carbon nanoparticles wrapped by polyketone (PK) fibers. The ST(p)s are extensively characterized in terms of the chemical composition, thermal stability, degree of graphitization and morphology. The "core-shell" ORR electrocatalysts are prepared by the pyrolysis of precursors obtained impregnating the STp "cores" with a zeolitic inorganic-organic polymer electrolyte (Z-IOPE) plastic material. The electrochemical performance of the electrocatalysts in the ORR is tested "in situ" by single fuel cell tests. The interplay between the chemical composition, the degree of graphitization of both PtNix-CN "shell" and STpS "cores", the morphology of the electrocatalysts and the fuel cell performance is elucidated. The most crucial preparation parameters for the optimization of the various features affecting the fuel cell performance of this promising class of ORR electrocatalysts are identified

Electrochemical behaviour of the β(II)-Ni(OH)2/β(III)-NiOOH redox couple upon potentiodynamic cycling conditions

International audienceThe electrochemical behaviour of pure and Co-doped Ni(OH)2 powders is investigated under potentiodynamic cycling conditions. Evolution of some β-Ni(OH)2 physical properties as a function of the oxidation state is followed by ex situ Surface Enhanced μ-Raman Spectroscopy and in situ Ellipsometry. Effects related to the first and second reduction steps, as well as to the sweeping rate, are qualitatively studied. When compared to the results that have been recently obtained under galvanostatic conditions [S. Deabate, F. Henn, Electrochim. Acta 50 (2005) 2823], the present work confirms that the second reduction process is strongly associated to the occurrence of a reduced phase, i.e. NiO2H2−var epsilon, with 0 < var epsilon < not, vert, similar0.3, at the surface of the active mass grains. This reduced phase exhibits spectroscopic features very similar to the initial hydroxide which is known to be highly insulating in regards to both electrons and protons transfer

Structural modifications and electrochemical behaviour of the beta(II)-Ni(OH)(2)/beta(III)-NiOOH redox couple upon galvanostatic charging/discharging cycling

International audienceAmong the various crystallographic phases of nickel hydroxide, the β-form is the most widely used as the active mass of the positive electrode of nickel-based secondary cells. However, the exact electrochemical and structural behaviour of the redox system upon cycling and ageing remains to be clarified. This work reports the electrochemical behaviour under galvanostatic conditions of two non-doped Ni(OH)(2) samples having different initial crystallography and morphology. The evolution of these features is investigated as a function of the cycling conditions and more particularly as a function of the reduction state achieved on discharge. Electrodes cycled at the 1st discharge plateau show that charged/discharged active materials are very similar. However, when discharge is continued down to the so-called 'second discharge plateau', drastic changes are observed as an increase of the crystallisation degree and of the compactness of the Ni(OH)(2) powder. Some insights into the nickel electrode redox behaviour are given. It appears that the nickel electrode operates, upon charge, as a single-phase or as a mixed-phase system depending on the depth of discharg

Caractérisations physico-chimiques et électrochimiques d'hydroxydes de nickel synthétisés par électrodialyse

MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF