Etude du mécanisme de la réaction d'oxydation de l'éthanol sur électrocatalyseurs à base de Pt, Rh, SnO2 sur support carboné en milieu acide

The study of the ethanol oxidation reaction (EOR) mechanism was performed on carbon supported bi- and tri-metallic Pt-, Rh-, SnO2-based electrocatalysts via electrochemical coupled techniques (DEMS, in situ FTIR). Two of the most important issues related to the EOR have been broached: the dehydrogenation of the ethanol molecule and its C-C bond breaking.The investigation of some experimental parameters, such as the thickness of the electrocatalyst layer, enabled demonstrating the better complete ethanol electrooxidation into CO2 for large electrocatalysts layers, combined to the enhanced poisoning effect inside the catalyst layer by very strong adsorbates.The performances of each electrocatalyst were compared and evidenced an improved selectivity of the EOR on Pt-Rh-SnO2/C, as well as the generation of higher currents at low potential at room temperature. The tendency was amplified at elevated temperatures (T = 60 °C).L'étude du mécanisme de la réaction d'oxydation de l'éthanol (EOR) a été réalisée sur des électrocatalyseurs bi- et tri-métalliques à base de Pt, Rh et SnO2 sur support carboné à l'aide de méthodes électrochimiques couplées (DEMS, in situ FTIR). Deux importantes problématiques de l'EOR ont été abordées: la déshydrogénation de la molécule d'éthanol et la cassure de sa liaison C-C.L'investigation de certains paramètres expérimentaux, comme l'épaisseur de la couche d'électrocatalyseur, a permis de démontrer q'une couche active épaisse conduit à une meilleure électrooxydation plus complète de l'éthanol en CO2, mais également que l'empoisonnement de l'électrocatalyseur par de très forts adsorbats advient dans l'épaisseur de couche active.Les performances de chaque électrocatalyseur ont été comparées entre elles et ont mis en évidence une meilleure sélectivité de l'EOR sur Pt-Rh-SnO2/C, ainsi que l'engendrement de courants plus élevés à bas potentiel à température ambiante. La tendance est amplifiée à température plus élevée (T = 60 °C)

Towards 'Pt-free' Anion-Exchange Membrane Fuel Cells: Fe-Sn Carbon Nitride-Graphene 'Core-Shell' Electrocatalysts for the Oxygen Reduction Reaction

We report on the development of two new Pt-free electrocatalysts (ECs) for the oxygen reduction reaction (ORR) based on graphene nanoplatelets (GNPs). We designed the ECs with a core-shell morphology, where a GNP core support is covered by a carbon nitride (CN) shell. The proposed ECs present ORR active sites that are not associated to nanoparticles of metal/alloy/oxide, but are instead based on Fe and Sn sub-nanometric clusters bound in coordination nests formed by carbon and nitrogen ligands of the CN shell. The performance and reaction mechanism of the ECs in the ORR are evaluated in an alkaline medium by cyclic voltammetry with the thin-film rotating ring-disk approach and confirmed by measurements on gas-diffusion electrodes. The proposed GNP-supported ECs present an ORR overpotential of only ca. 70 mV higher with respect to a conventional Pt/C reference EC including a XC-72R carbon black support. These results make the reported ECs very promising for application in anion-exchange membrane fuel cells. Moreover, our methodology provides an example of a general synthesis protocol for the development of new Pt-free ECs for the ORR having ample room for further performance improvement beyond the state of the art

Mechanistic study of the ethanol oxidation reaction on carbon supported Pt-, Rh- and SnO2-based electrocatalysts in acidic medium

L'étude du mécanisme de la réaction d'oxydation de l'éthanol (EOR) a été réalisée sur des électrocatalyseurs bi- et tri-métalliques à base de Pt, Rh et SnO2 sur support carboné à l'aide de méthodes électrochimiques couplées (DEMS, in situ FTIR). Deux importantes problématiques de l'EOR ont été abordées: la déshydrogénation de la molécule d'éthanol et la cassure de sa liaison C-C.L'investigation de certains paramètres expérimentaux, comme l'épaisseur de la couche d'électrocatalyseur, a permis de démontrer q'une couche active épaisse conduit à une meilleure électrooxydation plus complète de l'éthanol en CO2, mais également que l'empoisonnement de l'électrocatalyseur par de très forts adsorbats advient dans l'épaisseur de couche active.Les performances de chaque électrocatalyseur ont été comparées entre elles et ont mis en évidence une meilleure sélectivité de l'EOR sur Pt-Rh-SnO2/C, ainsi que l'engendrement de courants plus élevés à bas potentiel à température ambiante. La tendance est amplifiée à température plus élevée (T = 60 °C).The study of the ethanol oxidation reaction (EOR) mechanism was performed on carbon supported bi- and tri-metallic Pt-, Rh-, SnO2-based electrocatalysts via electrochemical coupled techniques (DEMS, in situ FTIR). Two of the most important issues related to the EOR have been broached: the dehydrogenation of the ethanol molecule and its C-C bond breaking.The investigation of some experimental parameters, such as the thickness of the electrocatalyst layer, enabled demonstrating the better complete ethanol electrooxidation into CO2 for large electrocatalysts layers, combined to the enhanced poisoning effect inside the catalyst layer by very strong adsorbates.The performances of each electrocatalyst were compared and evidenced an improved selectivity of the EOR on Pt-Rh-SnO2/C, as well as the generation of higher currents at low potential at room temperature. The tendency was amplified at elevated temperatures (T = 60 °C)

Electrooxidation of Ethanol at Room Temperature on Carbon-Supported Pt and Rh-Containing Catalysts: A DEMS Study

The electrocatalytic activity of Pt/C and Pt-Rh/C electrocatalysts for the ethanol oxidation reaction (EOR) was investigated by potentiostatic and potentiodynamic techniques by differential electrochemistry mass spectrometry (DEMS) in a flow cell system. The 10 wt% electrocatalysts were synthesized by a modified polyol method and physically characterized by different techniques including X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). The chronoamperometry study shows that, although the ethanol oxidation starts at lower potential on Pt-Rh/C, the kinetics of the reaction is faster on Pt/C. Differential Electrochemical Mass Spectrometry (DBMS) allowed the detection of volatile intermediates/products of the EOR. At low potential, the ionic current corresponding to the signal m/z = 15 increases, conversely to the signal m/z = 44; this points out the production of adsorbed CRx species and thus possibly of adsorbed CO either during the negative scan or the previous positive scan of the cyclic voltammetry. The CO2 current efficiency (CCE) was also determined on both electrocatalysts after calibration of the m/z = 22 signal: the CCE value can reach up to 25% on Pt-Rh/C at room temperature, compared to ca. 5% on Pt/C

Influence of the Temperature for the Ethanol Oxidation Reaction (EOR) on Pt/C, Pt-Rh/C and Pt-Rh-SnO2/C

International audienc

\u201cCore-shell\u201d carbon nitride electrocatalysts for the oxygen reduction reaction (ORR) based on graphene and related materials for application in low-temperature fuel cells

Fuel cells (FCs) are a family of advanced energy conversion systems characterized by an outstanding energy conversion efficiency, up to two-three times as high as typical internal combustion engines (ICEs). Furthermore, FCs show a number of other attractive features including a simple engineering of the power plant and a high compatibility with the environment. In particular, FCs operating at a low temperature (T<200\ub0C) are typically characterized by a very high energy and power density. As a consequence, they are very promising candidates to provide power to a number of applications, ranging from portable electronic devices to light-duty vehicles. one important bottleneck in the operation of FCs functioning at a low temperature is the sluggishness of the ORR. Suitable ORR electrocatalysts (ECs) are needed to achieve a level of permormance compatible with applications. This contribution describes the preparation of innovative ORR ECs on the basis of the unique protocols developed in our laboratory. The proposed ECs are characterized by "core-shell" morphology. In detail, the "core" consists of sheets/nanoplatelets of graphene and related materials. The latter are covered by a carbon nitride "shell", which coordinates nanoparticles bearinf the ORR active sites through "nitrogen coordiantion nests". The chemical composition of the proposed "core-shell" ECs is determined by inductively-coupled plasma atomic emission spectroscopy (ICP-AES) and microanalysis. The structure of the materials is studied by powder X-ray diffraction (XRD); the morphology is inspected by high-resolution scanning electron microscopy (HR-SEM) and high-resolution transmission electron microscopy (HR-TEM). The electrochemical performance, reaction mechanism and selectivity of the ECs in the ORR is evaluated "ex situ" by cyclic voltammetry with the rotating ring-disk electrode (CV-TF-RRDE) method. Finally, the most promising ECs are used to fabricate membrane-electrode assemblies (MEAs), which are tested in single fuel cell in operating conditions

Graphene-Supported 'Core-Shell'\u9d Carbon Nitride Fe- and Sn-Based Electrocatalysts for the Oxygen Reduction Reaction (ORR)

One of the major obstacles for the development of feasible low-temperature fuel cells (e.g., proton-exchange membrane fuel cells, PEMFCs, and anion-exchange membrane fuel cells, AEMFCs) is the sluggishness of the oxygen reduction reaction (ORR) kinetics. As of today, carbon-supported Pt-based nanocrystals are the most efficient electrocatalysts (ECs) for the ORR. However, the low abundance of platinum and the insufficient durability of these ECs, which results from the degradation of the carbon support, constitute some of the major obstacles for large-scale commercialization of PEMFC and AEMFC technology. In this study, new "Pt-free" electrocatalysts are prepared and studied for the ORR process. These ECs consist of alloyed Fe-Sn nanoparticles embedded in a carbon nitride \u201cshell\u201d a few nanometers thick, supported on conducting micrometric graphene sheets that act as the \u201ccore\u201d. The electrocatalytic precursors are prepared by a sol-gel/gel-plastic process following a protocol previously developed in our laboratory; afterwards, they undergo suitable pyrolysis and activation processes. The proposed electrocatalysts, both pristine (e.g., FeSn0.5-CNl 900/Gr) and activated (e.g., FeSn0.5-CNl 900/Gra) are extensively characterized in order to gain a full understanding of their structural features, proprieties and electrocatalytic performance. The chemical composition is determined by inductively-coupled plasma atomic emission spectroscopy (ICP-AES). The structure is elucidated by powder X-Ray diffraction (XRD); the morphology is inspected by high-resolution scanning electron microscopy (HR-SEM) and high-resolution transmission electron microscopy (HR-TEM). Finally, \u201cex situ\u201d cyclic voltammetry with the rotating ring-disk electrode (CV-TF-RRDE) and \u201cin situ\u201d single fuel cell measurements are carried out to evaluate the electrocatalytic performance as well as to study the ORR mechanism. The preliminary CV-TF-RRDE investigations in an alkaline medium exhibit promising results. Indeed, the catalysts exhibit an overpotential ca. 70 mV higher with respect to a 20 wt.% Pt/C reference

Effect of Graphite and Copper Oxide on the Performance of High Potential Li[Fe1/3Ni1/3Co1/3]PO4 Olivine Cathodes for Lithium Batteries

This report describes the preparation, characterization, and coin cell prototype testing of new Li[Fe1/3Ni1/3Co1/3]PO4 high voltage olivine cathodes for lithium secondary batteries (LFNCPs) obtained by treating the precursors with Cu and Cu+C sources. The morphology, structure, interactions, and electrochemical properties of the obtained materials are extensively studied in order to elucidate the interplay in LFNCPs between graphite (C) and copper(II) carbonate (Cu) addition to the precursors and structural flexibility, relaxations, and electrochemical performance of obtained materials. In particular, the investigated LFNCPs cathodes are obtained by treating the reaction precursors with graphite nanoparticles and/or copper(II) carbonate. It is found that copper does not behave like a vicariant metal ion within the olivine structure of the cathodes, instead it forms segregated CuO nanoparticles which improve the charge-transfer kinetics during the charge/discharge processes of the cathode material. The graphite additive in precursors is found to decompose during the synthesis, resulting in an improved elasticity of the 3D structure of the olivine backbone. This increased structural flexibility facilitates the percolation of lithium ions along the 1D channels of the materials during the charge/discharge processes. Coin cell prototypes assembled with the proposed cathode materials show good specific capacities (>100 mAh g 121), good specific energies (455 mWh g 121), and a high working potential (>4.0 V)