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(a) DOO variation in catalytic activity, (the onset potential of ORR), with respect to reversible hydrogen electrode (RHE). The degree of the oxidation parameter DOO is defined by the integrated peak intensity for the (1 11 0) diffraction of and the (1 1 0) diffraction of TaCN. (b) Atomic fraction of Ta in phase in partially oxidized Ta–CNO particles, estimated by using XRD intensity simulation. The transmission electron micrograph shows a cross-section image of the Ta–CNO particles. The surface layer consists of . The inset shows a typical XRD pattern of the core-shell particles.
XAS Spectra for particles. (a) CEY-XAS XANES spectra. (b) XANES spectra taken in transmission mode. (c) Fourier transforms of EXAFS (CEY mode). (d) Fourier transforms of EXAFS (transmission mode). The FT amplitude for CEY-XAS for below is rather small due to the presence of the Ta–C or Ta–N bonds, while in the DOO range from 0.15 to 0.96, the radial structure functions have a -like characteristic with a peak near 1.6 Å corresponding to the Ta–O bonds. However, the maximum amplitude is slightly smaller than those of (stoichiometric ).
Fourier transforms of EXAFS for Ta–CNO particles with and . The solid lines are the simulated radial structure functions assuming a simplified model.
Coordination numbers and bond lengths for Ta–O first shells. Some of the Ta–O bonds were further merged for the simulation as listed.
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