J.R.C. Salgado

Electrocatalytic Properties of PtCo ∕ C and PtNi ∕ C alloys for the Oxygen Reduction Reaction in Alkaline Solution

The oxygen reduction reaction (ORR) was studied on carbon-dispersed Pt 3 Co, PtCo, and Pt 3 Ni alloys in KOH electrolyte. A detailed discussion of the enhancement of the O 2 reduction kinetics based on the physical and electronic properties of the catalysts is presented. The characterization techniques considered were high-resolution transmission electron microscopy, XRD (X-ray diffraction), in situ XANES (X-ray absorption near edge structure), and EXAFS (extended X-ray absorption fine structure) measurements. Cyclic voltammetry and steady-state polarization measurements for the ORR were conducted using a rotating ring-disk electrode. The XANES results at the Pt L 3 edge at anodic potentials showed lower oxide coverage on the PtCo/C catalysts, while at the Co and Ni K edges the results evidenced compositions that include Co or Ni metals and oxides. The XRD and EXAFS analyses showed a slight reduction of the Pt-Pt interatomic distance in the Pt alloys compared to Pt/C. The polarization curves indicated that the 4-electron mechanism is mainly followed for the ORR on all materials. The highest electrocatalytic activity was obtained for the PtCo/C alloy (1:1 atomic ratio), and this was attributed to less Pt-OH formation or faster Pt-O - electroreduction due to a lower Pt d-band center.

Carbon-Supported Pt-Ni Alloys Prepared by the Borohydride Method as Electrocatalysts for DMFCs

Carbon-supported Pt-Ni electrocatalysts in the Pt:Ni atomic ratio 90:10 and 70:30 were prepared by reduction at room temperature of Pt and Ni salts with sodium borohydride and tested for the first time in direct methanol fuel cells ~DMFCs! both as anode and as cathode materials. The performance of Pt-Ni as cathode in DMFC was higher than that of Pt-Ni as anode. Pt90Ni10 as cathode showed better performance than Pt both in terms of mass activity and specific activity. When used as an anode material, the cell performance increased with increasing nickel content in the material. The enhanced performance of Pt-Ni as a cathode is ascribed both to a better activity for the oxygen reduction ~electronic effect! and a better methanol-tolerance ~ensemble effect! than Pt, related mainly to the alloyed nickel, while the improvement of Pt-Ni as anode for methanol oxidation is attributed to the presence of nonalloyed NiO species.

Pt-Co/C Electrocatalysts for Oxygen Reduction in H 2 / O 2 PEMFCs Synthesized by Borohydride Method

A Pt-Co/C electrocatalyst with Pt:Co atomic ratio 85:15, prepared by a low-temperature chemical reduction with sodium borohydride, was studied as possible cathode material for polymer electrolyte membrane fuel cells (PEMFCs). The physical characterization of this electrocatalyst was performed by energy-dispersive X-ray analysis, X-ray diffraction, and transmission electron microscopy. The performance of the material was evaluated by cyclic voltammetry and polarization experiments in a single PEMFC and compared with those of an unalloyed Pt/C catalyst prepared by the same method and a commercial Pt-Co/C catalyst. Both the Pt-Co/C catalysts were also submitted to a thermal treatment in a reducing atmosphere.

Correlação entre a atividade catalítica e o tamanho de partículas de Pt/C preparados por diferentes métodos

Pt/C electrocatalysts prepared by different methods were studied for the oxygen reduction reaction in H2/O2 fuel cells. This work analyses the physical and electrochemical characterization of Pt/C prepared by different methods by XRD, TEM, CV and CP. It was found that the electrochemical activity is correlated with the morphology and with the particle size of the catalysts.