In this study, we use density functional theory to investigate the catalytic activity of graphene (G), single vacancy defective graphene (G SV ), quaternary N-doped graphene (NG Q ), and pyridinic N-doped graphene (NG py , 3NG py , and 4NG py ) on Co(0001) substrate for an oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). The results show pyridinic N-doped graphene on a Co support exhibited better performance than the NG Q on a Co support and free-standing systems. According to the results, ORR intermediates (*OOH, *O, and *OH) become more stable due to the presence of a Co substrate. The single pyridinic (3NG py ) layer placed on Co(0001) is the most active site. The overpotential for Co/3NG py is rather higher compared to pure Pt( 111) catalyst (0.65 V). Therefore, pyridinic N-doped graphene with a cobalt support could be a promising strategy to enhance the ORR activity of N-doped graphene in PEMFCs.
High-temperature oxidation processes
of carbon microparticles Vulcan XC72 coated with platinum nanoparticles
(Pt/C) were studied by thermogravimetric analysis (TGA) and differential
scanning calorimetry (DSC). The presence of different specific temperature
ranges in the oxidation of carbon support was shown to be due to both
the peculiarities of granulometric composition of carbon black microparticles,
different size, and uneven spatial distribution of platinum nanoparticles
in the pores and on the surface of the carbon support. The correlation
between the length of a section in the thermograms and the fraction
of carbon microparticles poorly coated with platinum can be used to
analyze the uniformity of Pt nanoparticle spatial distribution in
the metal–carbon catalysts and therefore to select electrocatalysts
with optimal microstructure. This analysis is expected to be effectively
utilized in order to assess the uniformity of platinum distribution
on carbon microparticles and also to provide additional information
about granulometric composition of carbon supports.
The aim of this work was to investigate the morphology, average size, and the electrochemical behavior of platinum nanoparticles electrodeposited from water and mixed water-ethylene glycol solutions of the electrolyte of H 2 PtCl 6 and H 2 SO 4 at a rotating disk electrode coated with Vulcan XC-72 carbon powder. Cyclic voltammetry and linear sweep voltammetry were used to determine the electrochemically active surface area (ESA) and oxygen reduction reaction (ORR) activity of the prepared Pt/C materials, respectively. XRD and scanning electron microscopy were used to study the influence of the electrodeposition methods applied on the morphology of platinum particles deposited in water and mixed waterethylene glycol solutions. The average size of Pt crystallites was in the range of ca. 6-10 nm, and the average size of deposited Pt particles was in the range of ca. 30-150 nm. It was found that the presence of ethylene glycol in the electrolyte solution increased the overpotential of electrodeposition and it also strongly affected the morphology of Pt deposits when constant current electrodeposition was employed. Moreover, it was shown that pulse current electrodeposition is a more effective method compared to constant current electrodeposition method for the preparation of the Pt/Vulcan electrode with high ESA of Pt and enhanced catalytic activity toward ORR. The results obtained concerning the morphology and the spatial distribution of platinum particles electrodeposited on the surface of carbon support at different conditions demonstrate new possibilities to improve synthesis of Pt/C by electrodeposition methods.
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