A structurally ordered phase of PdCu3 nanoparticles (NPs)/carbon black (CB), in which PdCu3 has a Cu3Au-type structure, was prepared by co-reduction of Pd and Cu precursors using ethylene glycol as a reducing agent and an annealing procedure. The obtained catalysts were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The XRD and STEM measurements enabled us to confirm the crystal structures of both atomically disordered Pd-Cu NPs/CB and ordered intermetallic PdCu3 NPs/CB. From the TEM and EDS measurements, it was found that PdCu3 NPs are uniformly dispersed on the CB surface and the atomic ratio of Pd to Cu is 25.3 : 74.7. DFT calculations suggested that the PdCu3 NPs have a uniformly ordered structure of Pd and Cu and that Cu-free surface-structured PdCu3 NPs, which are formed by so-called electrochemical dealloying, i.e., the dissolution of surface and sub-surface Cu in the ordered PdCu3 structure, exhibit superior electrocatalytic activity in the ORR in comparison with Pd NPs/CB. This catalytic activity can be explained reasonably on the basis of the measured value of the d-band center and theoretical calculations of catalyst-oxygen binding energies. Interestingly, the surface of electrochemically dealloyed PdCu3 has a lower oxygen binding energy than the Pt (111) surface (i.e., the oxygen binding energy of PdCu3 was significantly decreased by electrochemical dealloying). We have found a Pd-based catalyst of which the electrocatalytic activity in the ORR may exceed that of Pt-based catalysts according to DFT calculations. In addition, the potential of PdCu3 NPs/CB as a cathode catalyst in direct methanol fuel cells is discussed briefly.
Bibliographical noteFunding Information:
This work was nancially supported by the Iketani Science and Technology Foundation and JSPS KAKENHI Grant Number 16K05945. This work was also partially supported by the National Institute for Materials Science (NIMS) microstructural characterization platform as a program of the “Nanotechnology Platform” of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.
All Science Journal Classification (ASJC) codes
- Renewable Energy, Sustainability and the Environment
- Materials Science(all)