Amanda C. Garcia

Straightforward Synthesis of Carbon-Supported Ag Nanoparticles and Their Application for the Oxygen Reduction Reaction

In this paper we report a simple and environmentally friendly synthesis of silver nanoparticles (AgNps) and their activities towards the oxygen reduction reaction (ORR). Ultraviolet spectroscopy (UV–vis) and transmission electron microscopy confirmed the formation of poly(vinyl pyrrolidone)-protected colloidal AgNps through direct reduction of Ag+ by glycerol in alkaline medium at room temperature. For the ORR tests, the AgNps were directly produced onto carbon to yield the Ag/C catalyst. Levich plots revealed the process to occur via 2.7 electrons, suggesting that the carbon support contributes to the ORR. We discuss here possibilities of improving the catalytic properties of the Ag/C for ORR by optimizing the parameters of the synthesis.

Evaluation of Several Carbon-Supported Nanostructured Ni-Doped Manganese Oxide Materials for the Electrochemical Reduction of Oxygen

Physical and electrochemical properties of nanostructured Ni-doped manganese oxides MnOx catalysts supported on different carbon powder substrates were investigated so as to characterize any carbon substrate effect toward the oxygen reduction reaction ORR kinetics in alkaline medium. These NiMnOx/C materials were characterized using physicochemical analyses. Small insertion of Ni atoms in the MnOx lattice was observed, which consists of a true doping of the manganese oxide phase. The corresponding NiMnOx phase is present in the form of needles or agglomerates, with crystallite sizes in the order of 1.5–6.7 nm from x-ray diffraction analyses. Layered manganite MnOOH phase has been detected for the Monarch1000-supported NiMnOx material, while different species of MnOx phases are present at the E350G and MM225 carbons. Electrochemical studies in thin porous coating active layers in the rotating ring-disk electrode setup revealed that the MnOx catalysts present better ORR kinetics and electrochemical stability upon Ni doping. The ORR follows the so-called peroxide mechanism on MnOx/C catalysts, with the occurrence of minority HO2 � disproportionation reaction. The HO2 � disproportionation reaction progressively increases with the Ni content in NiMnOx materials. The catalysts supported on the MM225 and E350G carbons promote faster disproportionation reaction, thus leading to an overall four-electron ORR pathway.

NiMnOx/C: A Non-noble Ethanol-Tolerant Catalyst for Oxygen Reduction in Alkaline Exchange Membrane DEFC

A non-noble oxygen reduction catalyst based on nickel−manganese oxide supported on high-surface area carbon has been synthesized by a mild hydrothermal treatment, resulting in nanocrystalline needles. Cyclic voltammetry showed the electrochemical redox characteristics of this material, evidencing the appearance of peaks associated to consecutive reversible transitions involving Mn(IV)/Mn(III) and Mn(III)/Mn(II). The catalyst displayed a high activity for the oxygen reduction, despite that the complete reduction was not achieved, consuming less than three electrons of the four available in the oxygen molecule. More importantly, this activity did not decay under the presence of ethanol, revealing the high ethanol tolerance of this material. Finally, single-cell results have demonstrated the suitability of this material as cathode catalysts for alkaline DEFC: The open circuit voltage and the maximum power densities are close to those obtained by a standard Pt/C catalyst.