Marian Chatenet

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.

First Insight into Fluorinated Pt/Carbon Aerogels as More Corrosion-Resistant Electrocatalysts for Proton Exchange Membrane Fuel Cell Cathodes

This study evaluates the fluorination of a carbon aerogel and gives first insights into its durability when used as platinum electrocatalyst substrate for proton exchange membrane fuel cell (PEMFC) cathodes. Fluorine has been introduced before or after platinum deposition. The different electrocatalysts are physico-chemically and electrochemically characterized, and the results discussed by comparison with commercial Pt/XC72 from E-Tek. The results demonstrate that the level of fluorination of the carbon aerogel can be controlled. The fluorination modifies the texture of the carbons by increasing the pore size and decreasing the specific surface area, but the textures remain appropriate for PEMFC applications. Two fluorination sites are observed, leading to both high covalent C-F bonds and weakened ones, the quantity of which depends on whether the treatment is done before or after platinum deposition. The order of the different treatments is very important. Indeed, the presence of platinum contributes to the fluorination mechanism, but leads to amorphous platinum, which is demonstrated rather inactive towards the oxygen reduction reaction. On the contrary, a better durability was demonstrated for the fluorinated and then platinized catalyst compared both to the same but not fluorinated catalyst and to the reference commercial material (based on the loss of the electrochemical real surface area after accelerated stress tests).

Insertion/Disinsertion of Hydrogen in Tailored Pd Layers Deposited on Pt(111) Surface in Alkaline and Acidic Medium

AbstractPd1ML/Pt(111) and Pd16ML/Pt(111) electrodes were prepared and studied by cyclic voltammetry in both acidic and alkaline electrolytes. Regardless of the electrolyte pH, hydrogen insertion/disinsertion was observed for the Pd16ML/Pt(111) electrode and absent for the Pd1ML/Pt(111) electrode. In the former case (Pd16ML/Pt(111) electrode), hydrogen insertion/disinsertion proceed at different kinetics in acidic and alkaline media, the kinetics being slower in alkaline versus acidic medium. On the contrary, similar rates of insertion/disinsertion of hydrogen were measured at the two pH values (H/Pdxa0≈xa00.45), demonstrating that the thermodynamics of hydrogen insertion is not depending on the electrolyte pH.n Graphical Abstract