Carbonyl Chemical Route Research Articles

Platinum nanoparticles photo-deposited on SnO2-C composites: An active and durable electrocatalyst for the oxygen reduction reaction

Platinum nanoparticles (NPs) were photo-deposited on SnO2-C nanocomposites prepared by sol-gel method. Surface morphology of the prepared materials, examined by scanning electron microscopy (SEM) and transmission electron microscopy, confirmed selective deposition of Pt NPs on SnO2 nanoclusters formed on carbon surface. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) analysis, cyclic voltammetry (CV) and CO stripping experiments revealed modification of the electronic properties of the Pt NPs photo-deposited on the oxide-carbon composite in comparison to Pt/C prepared by the carbonyl chemical route. Rietveld refinement was employed to identify existing phases of catalysts and to determine the crystallite size. Micro-strain and intrinsic stacking fault increased and decreased, respectively, as a function of crystallite size. Pt loadings were determined by inductively coupled plasma mass spectrometry (ICP-MS). The oxygen reduction reaction (ORR) activity of the electrocatalysts was investigated in acid media using the rotating disk electrode (RDE) system. Accelerated durability test (ADT) results showed that photo-deposited Pt nanoparticles onto SnO2-C nanocomposite are more durable than those chemically deposited on carbon.

Synergistic effect of Yttrium and pyridine-functionalized carbon nanotube on platinum nanoparticles toward the oxygen reduction reaction in acid medium

Platinum, and platinum containing Yttrium (Y) species nanoparticles (NPs) supported by carbon black, Vulcan XC-72, oxidized multi-walled carbon nanotube, ox.MWCNT, pyridine functionalized multi-walled carbon nanotube, (ox.MWCNT)-Py, were prepared via carbonyl chemical route, followed by heat-treatment. X-ray diffraction (XRD) analyses showed, beside Pt fcc-phase, the presence of PtxY alloy in Pt-Y nanoobjects supported onto functionalized MWCNTs. X-ray photoelectron spectroscopy (XPS) revealed, essentially, that Pt surface was decorated by Y2O3; therefore, such nanoobjects were labeled Pt-Y. By analyzing the surface atomic ratio of Pt/N and Pt/Y in Pt-Y/(ox.MWCNT)-Py, it is suggested that Pt atoms interact with Y2O3, pyridine group, and Y nano-alloying Pt. The transmission electron microscopy (TEM) shows similar mean particle size values, in Pt-Y/Vulcan, Pt-Y/ox.MWCNT and Pt-Y/(ox.MWCNT)-Py, in opposition to Pt NPs supported onto Vulcan, ox.MWCNT and (ox.MWCNT). The surface electrochemistry demonstrated a unique behavior of Pt on Pt-Y/(ox.MWCNT)-Py with respect to other samples. The ORR kinetics of this catalyst was the highest among all the samples, revealing a synergistic effect of Y2O3, pyridine functionalization, and nano-alloyed Y alloyed on Pt toward ORR.

What Can We Learn in Electrocatalysis, from Nanoparticulated Precious and/or Non-Precious Catalytic Centers Interacting with Their Support?

This review is devoted to discussing the state of the art in the relevant aspects of the synthesis of novel precious and non-precious electrocatalysts. It covers the production of Pt- and Pd-based electrocatalysts synthesized by the carbonyl chemical route, the synthesis description for the preparation of the most catalytically active transition metal chalcogenides, then the employment of free-surfactants synthesis routes to produce non-precious electrocatalysts. A compilation of the best precious electrocatalysts to perform the hydrogen oxidation reaction (HOR) is described; a section is devoted to the synthesis and electrocatalytic evaluation of non-precious materials which can be used to perform the HOR in alkaline medium. Apropos the oxygen reduction reaction (ORR), the synthesis and modification of the supports is also discussed as well, aiming at describing the state of the art to improve kinetics of low temperature fuel cell reactions via the hybridization process of the catalytic center with a variety of carbon-based, and ceramic-carbon supports. Last, but not least, the review covers the experimental half-cells results in a micro-fuel cell platform obtained in our laboratory, and by other workers, analyzing the history of the first micro-fuel cell systems and their tailoring throughout the time bestowing to the design and operating conditions.

Influence of sp(3)-sp(2) Carbon Nanodomains on Metal/Support Interaction, Catalyst Durability, and Catalytic Activity for the Oxygen Reduction Reaction.

In this work, platinum nanoparticles were impregnated by two different techniques, namely the carbonyl chemical route and photodeposition, onto systematically surface-modified multiwalled carbon nanotubes. The different interactions between platinum nanoparticles with sp(2)-sp(3) carbon nanodomains were investigated. The oxidation of an adsorbed monolayer of carbon monoxide, used to probe electronic catalytic modification, suggests a selective nucleation of platinum nanoparticles onto sp(2) carbon nanodomains when photodeposition synthesis is carried out. XPS attests the catalytic center electronic modification obtained by photodeposition. DFT calculations were used to determine the interaction energy of a Pt cluster with sp(2) and sp(3) carbon surfaces as well as with oxidized ones. The interaction energy and electronic structure of the platinum cluster presents dramatic changes as a function of the support surface chemistry, which also modifies its catalytic properties evaluated by the interaction with CO. The interaction energy was calculated to be 8-fold higher on sp(3) and oxidized surfaces in comparison to sp(2) domains. Accelerated Stability Test (AST) was applied only on the electronic-modified materials to evaluate the active phase degradation and their activity toward oxygen reduction reaction (ORR). The stability of photodeposited materials is correlated with the surface chemical nature of supports indicating that platinum nanoparticles supported onto multiwalled carbon nanotubes with the highest sp(2) character show the higher stability and activity toward ORR.

On the Availability of Active Sites for the Hydrogen Peroxide and Oxygen Reduction Reactions on Highly Dispersed Platinum Nanoparticles

AbstractCarbon‐supported platinum nanoparticles (Pt/C) were synthesized by the carbonyl chemical route. The obtained Pt/C catalysts with different Pt mass loadings, varying from 5 to 50 wt %, showed constant morphology with particle sizes of about 2 nm and a dispersion of around 50 %. The electrochemical surface area, determined from CO stripping and hydrogen underpotential deposition, increased with the Pt mass loading, which confirmed that agglomeration was negligible. The oxygen reduction reaction (ORR) half‐wave potential was positively shifted with an increase in the Pt mass loading, and the ORR kinetic current was (40±10) μA cm−2Pt. The data collected on a rotating ring‐disk electrode for the ORR pathway revealed a two‐electron serial mechanism (hydrogen peroxide), instead of the four‐electron transfer (water). The determined turnover frequency factor indicated good selectivity of the Pt active sites for the ORR with 1 or 2 mm H2O2 in the electrolyte for samples with mass loadings ranging from 15 to 40 wt %. The ORR was markedly affected by the mass loading (5–10 wt % Pt/C) in the presence of 2 mm H2O2.

Carbon supported Pt-Y2O3 and Pt-Gd2O3 nanoparticles prepared via carbonyl chemical route towards oxygen reduction reaction: Kinetics and stability

The Pt-M2O3/C (M = Y and Gd) catalysts were synthesized via carbonyl chemical route, and heat-treated at 300 °C. Both catalysts are nanoparticulated with a face-centered cubic (fcc) structure with no secondary phase present as revealed by X-ray diffraction (XRD) patterns similar to Pt/C, generated in the same way. Data analyses of Pt-M2O3/C XRD patterns via the Williamson–Hall method were performed. The stacking fault, and micro-strain values increased with respect to Pt/C catalyst. The transmission electron microscopy (TEM) further revealed that nano-particles are homogeneously dispersed in both Pt/C and Pt-M2O3/C (M = Y and Gd). The mean particle size is close, ca. 3.4 nm for Pt/C, ca. 4.1 nm for Pt-Y2O3/C and ca. 3.6 nm for Pt-Gd2O3/C sample. Although the surface electrochemical studies (cyclic and CO-stripping voltammograms) showed similar Pt surface behavior, the kinetics of oxygen reduction reaction (ORR) on Pt-M2O3/C (M = Y and Gd) catalysts was higher than the homemade Pt/C and commercial Pt/C catalysts (20 wt. %, Johnson Matthey). After 6000 potential cycles (0.6–1.0 V vs. RHE) of accelerated stability test (AST), the remaining Pt active surface (based on hydrogen underpotential deposition region) and kinetic current density (at 0.9 V vs. RHE) in Pt-M2O3/C (M = Y and Gd) catalysts were higher than the reference Pt/C, and commercial Pt/C catalysts. These findings assess the positive effect of M2O3 (M = Y and Gd) in improving the activity and stability of Pt NPs towards ORR.

A highly efficient and stable oxygen reduction reaction on Pt/CeOx/C electrocatalyst obtained via a sacrificial precursor based on a metal-organic framework

Advanced Pt/CeOx/C nanocomposite, where C=porous carbon and multi-walled carbon nanotube (MWCNT), was synthesized using a precursor based on Ce-containing metal organic framework (MOF), via carbonyl chemical route, followed by heat-treatment at 900°C under argon atmosphere. Based on the analyses of powder X-ray diffraction (pXRD) data, and via the Williamson-Hall method, the lattice parameter, stacking fault and micro-strain values on Pt/CeOx/C was found to decrease, whereas the crystallite size increased with respect to the as-prepared sample. Combined with the results of transmission electron microscopy (TEM), these changes were related to the in-situ formation of intimately contacted Pt/CeOx nanoparticles (NPs), well-dispersed onto MWCNT support. However, both the pXRD and TEM results showed that the Pt NPs were agglomerated upon heating and finally detached from the support in the MOF-free samples. Thus, MOF could protect Pt nanoparticles (NPs) from agglomeration at high temperature. The X-ray photoelectron spectroscopy (XPS) showed that the Pt surface was less oxidized in Pt/CeOx/C nanocomposite in comparison to as-prepared and MOF-free samples. Moreover, only the Ce3+ was detected in the nanocomposite. These facts together with Raman spectroscopy and surface electrochemistry experiments assessed the stabilization of the electronic state of Pt° and Ce3+ via the interaction between Pt and CeOx. In addition, enhanced catalytic activity towards the oxygen reduction reaction (ORR) was observed in acid medium. The specific and mass activity at 0.9V/RHE on Pt/CeOx/C were ca. 1279μAcm−2Pt and 870mAmg−1Pt, respectively, ca. 10–11 fold higher than commercial Pt/C (Johnson Matthey, JM) in half-cell. Accelerating durability tests (ADT), after 16,000 potential cycles, demonstrated higher stability of Pt/CeOx/C in contrast to oxide-free and Pt/C (JM) catalyst. Compared with other homemade or commercial Pt/C (JM) cathodes, the innovative cathode catalyst showed enhanced cell performance in a H2/O2 micro-laminar flow fuel cell system.

Morphological impact onto organic fuel oxidation of nanostructured palladium synthesized via carbonyl chemical route

Nanostructured palladium (Pd) supported on carbon (Vulcan XC-72) substrate, prepared via carbonyl chemical route, showed Pd-mass depending morphology, reflected on the surface electrochemistry via cyclic, CO-stripping voltammograms, and performance in direct formic acid and direct methanol micro laminar flow fuel cell arrangement. Comparison was done with commercial Pd/C (30wt.%, ETEK) catalyst. The formic acid oxidation reaction (FAOR) studied in different acid media (0.1M HClO4, 0.5M H2SO4 and 0.5M H3PO4), indicated an enhanced FAOR activity on nanowire-like as compared to nanoparticles and nanorods as well as the commercial one in each electrolyte. Besides, the nanowire-like Pd/C catalyst also favored methanol (MOR) in 0.1M KOH. These facts confirm favorable morphological effect of nanowires for organic fuel oxidation in both acid and alkaline media.

Nanostructured palladium tailored via carbonyl chemical route towards oxygen reduction reaction

Carbon supported palladium nanostructures were synthesized via the carbonyl chemical route. Compared with nanostructured platinum, prepared via carbonyl chemical route, Pd nanomaterials showed mass-loading morphology, whereas particle size and morphology of Pt nanostructures was constant. The oxygen reduction reaction (ORR) on nanostructured Pd, with different morphology in both acid and alkaline medium was investigated. A relationship, based on X-ray diffraction structural analysis pattern, transmission electron microscope, with the Pd morphological effect on ORR activity was identified.

Materials for ORR Electrocatalysis: Catalytic Center and Substrate Effects

One of the most important challenges for polymer electrolyte membrane fuel cells (PEMFCs) in terms of facilitating its widespread commercial use is to improve the performance and durability of the electrocatalyst by developing novel catalysts (precious and non-precious catalytic centers) and support materials. One way to improve the oxygen reduction reaction (ORR) activity of Pt-based catalysts is to control Pt nanoparticles (Pt NPs) size, morphology and the dispersion onto substrates. Carbonyl chemical route for synthesizing Pt NPs facilitate a narrow particle size distributions (about 2-3 nm) [1], and homogeneous dispersion on different substrates [2,3]. A variety of carbon-based materials such as carbon nanotubes (CNT), graphite (HOPG), graphene, carbon nanohorns (CNH) and non-carbonaceous based materials, such as metal oxides (Titania, Yttria, Ceria, etc.,) [4,5] can be used as both catalyst and catalyst support materials. On the way to further explore the substrate effect on non-Pt electrocatalyst, CoSe2and CoO were supported on Carbon, CNH and nitrogen doped nanohorn (NCNH). The activity modulation in non-Pt catalysts was found to be strongly dependent on the morphology as well as the composition of substrate materials. The improved interaction of nitrogen species in NCNH and the metal centers modify the active reaction centers. This modified active reaction centers boost the catalytic activity with minimum overpotential for molecular oxygen reduction in alkaline medium (Figures 1a, b). Preliminary analysis indicates that this improved activity not only constrained in oxygen reduction but other catalytic reaction such as oxygen evolution reaction and hydrogen evolution reaction and further to an application on microfluidic fuel cells.AcknowledgementsAuthors acknowledge the partial support of the European Union’s Seventh Framework Programme (FP7/2007-2013) for the Fuel Cell and Hydrogen Joint Technology Initiative under grant agreement nr 303492 CathCat. SM U acknowledges the financial assistance through Raman-Charpak Fellowship, and JMMH acknowledges CONACyT fellowship. [1] N. Alonso-Vante, Fuel Cell, 2006, 6, 182-189.[2] J. Ma, A. S. Gago, W. Vogel, N. Alonso-Vante, Chemcatchem, 2013, 5, 701-705.[3] L. Timperman, Y.J. Feng, W. Vogel, N. Alonso-Vante, Electrochimica Acta, 2010, 55, 7558-7563.[4] Walter Vogel, Laure Timperman, Nicolas Alonso-Vante, Applied Catalysis A: General, 2010, 377, 167-173.[5] C.Liu , Y.Wei and K.Wang, Chem.Comm., 2010, 46, 2483-2485.

Induced electronic modification of Pt nanoparticles deposited onto graphitic domains of carbon materials by UV irradiation

Platinum nanoparticles deposited either by the photodeposition method or by the carbonyl chemical route are thought to be electronically modified onto carbon support. The deposition method is responsible for a controlled heterogeneous nucleation of platinum nanoparticles onto the substrate. By coupling results obtained from CO stripping experiments and X-ray photoelectron spectroscopy (XPS), there was a strong interaction between graphitic domains of carbonaceous supports and platinum nanoparticles. This phenomenon is at the origin of an increase of CO tolerance of the catalyst.

Performance Study of Platinum Nanoparticles Supported onto MWCNT in a Formic Acid Microfluidic Fuel Cell System

The Pt/MWCNT and Pt/C catalysts were synthesized using the carbonyl chemical route. The catalysts were physically and electrochemically characterized. An enhanced stability under potential cycling is obtained with Pt/MWCNT as compared to that of Pt/C. The evaluation of the electrochemical stability in a microfluidic fuel cell system was in good agreement with the results obtained in half-cell tests. Increasing the applied current from 10 to 40 mA, the Pt/MWCNT cathode potential in the fuel cell system depolarized 67% less than Pt/C. The performance of the fuel cell with Pt/MWCNT cathode was 2 times higher compared to Pt/C, under a constant current of 40 mA for 1000 s. The results from half-cell and fuel cell measurements showed that Pt/MWCNT is a more suitable cathode for microfluidic fuel cell than Pt/C due to the properties of the carbonaceous substrate. The Pt/MWCNT cathode was subsequently used in a formic acid microfluidic fuel cell to study several system parameters including formic acid concentration, cell orientation and bubble effect.

Synthesis, electrochemical characterization and molecular dynamics studies of surface segregation of platinum nano-alloy electrocatalysts

Alloy Pt-M (M = Co, Ni) nanocatalysts, supported on carbon Vulcan XC-72, were synthesized using the carbonyl chemical route. A high dispersion on such substrate was revealed by transmission electron microscopy (TEM). Alloy formation on the nanometre scale length was shown by high-resolution transmission microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDX) on a nanoparticle. The metal M in Pt-M nanoalloys segregates preferentially on the nanoparticles' surface, as determined by the hydrogen adsorption electrochemical reaction. An increased tolerance towards methanol of such nanoalloy materials was observed for the oxygen reduction reaction (ORR) in acid media. To better understand the structure and segregation phenomena of these nanoalloys, molecular dynamics (MD) with a self-optimized reactive force field was applied.

Substrate effect on oxygen reduction electrocatalysis

The oxygen reduction reaction (ORR) was investigated on carbon (XC-72) supported platinum nanoparticles, generated via the carbonyl chemical route and on oxide composites supported platinum generated via the UV-photo-deposition technique in sulfuric acid medium. The behavior of Pt/C was examined using a careful dosing of the catalyst loading spanning the range from 4.3 to 131 μg cm −2. The ORR electrochemical response of Pt/C (in line with recent literature data) is put into contrast with the Pt/oxide-composite systems. Our results point out that it is possible to use smaller amounts of catalyst for the ORR when platinum atoms interact with the oxide (anatase) surface of the substrate composite. Evidence of the incipient metal–substrate interaction is discussed in the light of the results of XRD experiments.

Electrochemical Behaviour of Platinum Nanoparticles Supported on Polypyrrole (PPy)/C Composite

We report on the synthesis of composites Polypyrrole/Carbon (PPy/C) to be used as matrix-support of platinum nanoparticles prepared by carbonyl chemical route. The composite materials with different PPy loading were characterized by physical chemical methods, such as elemental analysis, infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). The catalysts: 20 wt. % Pt/composites were used as substrates for the oxygen reduction reaction in acid medium. For the same catalyst loading (50 µg cm-2), it was observed that the nature of the composite strongly influences the electrochemical activity of nanoparticulated platinum.

Tailoring of metal cluster-like materials for the molecular oxygen reduction reaction

Abstract Research of nanometer scale range catalysts based on cluster-like mono-, bi-metallic, and chalcogenides for oxygen reduction reaction (ORR) as cathodes, a major challenge for polymer electrolyte membrane fuel cells (PEMFCs) nowadays, for facilitating efficient electron transfer using the carbonyl chemical route is reviewed. A strategy aimed at reducing the amount of expensive catalyst materials, giving the accessibility of non-noble materials and taking into account the activity and selectivity of cathodes for the ORR is devised as well.

Electrochemistry of platinum nanoparticles supported in polypyrrole (PPy)/C composite materials

Conducting polypyrrole (PPy)/C (Vulcan XC-72) composite materials were synthesized by chemical polymerization method. These materials were used as matrix to support platinum nanoparticles, which were produced by the carbonyl chemical route. For the same catalyst loading (50 μg cm−2), it was observed that the nature of the composite strongly influences the electrochemical activity of nanoparticulated platinum toward the oxygen reduction reaction in acid medium. The variation of the PPy/C ratio determines the so-called substrate effect for electrocatalysis.