Papers by Patrick Bertrand
Analytical Chemistry, 2007
Journal of Physical Chemistry B, Jul 27, 2002
Three catalysts for the electroreduction of oxygen have been prepared by pyrolyzing between 400 a... more Three catalysts for the electroreduction of oxygen have been prepared by pyrolyzing between 400 and 1000°C two iron precursors (Fe acetate or Fe porphyrin) adsorbed on a synthetic carbon made from the pyrolysis of PTCDA (perylene tetracarboxylic dianhydride) in a H 2 /NH 3 /Ar atmosphere. One Fe loading (0.2 wt %) has been used for the catalyst made from the salt precursor. Two Fe loadings (0.2 and 2.0 wt %) have been used for the catalyst made from the porphyrin precursor. These three catalysts have been analyzed by ToF SIMS and RDE (or GDE) in order to find correlations between ions detected by ToF SIMS and the catalytic activity. These correlations provide information about the number and the structure of the catalytic sites, which are active in these materials. By following the variation of FeN x C y + ions, it is found that (i) two different catalytic sites exist simultaneously in all catalysts made with the Fe salt or the Fe porphyrin; (ii) one site, named FeN 4 /C, is at the origin of three families of FeN x C y + ions: FeN 4 C y + , FeN 3 C y + , and FeN 1 C y +. The most representative ion of that site is FeN 4 C 8 +. The other site, labeled FeN 2 /C, is at the origin of the family of FeN 2 C y + ions. The most representative ion of that site is FeN 2 C 4 + ; (iii) the abundance of FeN 2 /C goes through a maximum for catalysts pyrolyzed between 700 and 900°C. When Fe acetate is the Fe precursor, FeN 2 /C may represent up to 80% of the catalytic sites, while this falls to a maximum of about 50% when Fe porphyrin is the precursor; (iv) FeN 2 /C is more electrocatalytically active than FeN 4 /C; (v) at high porphyrin loading (2.0 wt % Fe), the catalytic sites bound to the carbon support are covered with a porous layer of pyrolyzed Fe porphyrin.
Surface and Interface Analysis, Jun 5, 2012
ABSTRACT Molecular semiconductor devices, such as light-emitting diodes and photovoltaic cells, h... more ABSTRACT Molecular semiconductor devices, such as light-emitting diodes and photovoltaic cells, have recently received considerable attention because of their compatibility with flexible substrates and large-area applications. Because of the importance of the interfacial properties for the performance of the devices, these organic (multi)layers constitute an important field of application for molecular depth profiling by SIMS. In this contribution, we investigate the use of C60n+ and Ar1000–2000+ cluster projectiles at different energies (ranging from 2.5 to 20 keV) as sputter ions for the organic depth profiling of fullerene-based films and heterojunctions. The bilayers consist of C60 fullerenes on tin phthalocyanine (SnPc), deposited on silicon substrates. Our preliminary results showed that C60 films could not be successfully profiled using C60n+ ions in regular analysis conditions (room temperature). In contrast, with Ar clusters, the depth profiling is successful (except for 20 keV Ar1000) and the sputtered volume shows a linear relationship with the Ar cluster energy. Surprisingly, for a given total energy of the projectiles, Ar2000 sputters approximately two times more than Ar1000. The observations are tentatively explained as being the result of a balance between the sputtering and the cross-linking efficiency for the different bombardment conditions, larger clusters being expected to naturally induce less cross-linking than smaller clusters with the same total energy. Copyright © 2012 John Wiley &amp; Sons, Ltd.
Revista Mexicana De Fisica, Feb 1, 2006
The development of a sprayed ZnO thin film-based NO 2 sensor is reported. The effect of In-doping... more The development of a sprayed ZnO thin film-based NO 2 sensor is reported. The effect of In-doping on the sensor performance is studied. With the addition of 3 wt % of indium nitrate to the spraying solution, a good sensor response to 5 ppm of NO 2 at 275 • C and an important decrease in the device electrical resistance is obtained. The dependence of the electrical resistance on temperature in several gas atmospheres is also considered. A possible sensitization mechanism is discussed.
The Journal of Physical Chemistry, Nov 1, 1995
Chloroaluminum phthalocyanine (ClAlPc) thin films, vacuum sublimed on Sn02-covered glass substrat... more Chloroaluminum phthalocyanine (ClAlPc) thin films, vacuum sublimed on Sn02-covered glass substrates, were exposed to KC1 solutions of various pH values (from 2.0 to 8.0) in the fluid cell of an atomic force microscope (AFM). The evolution of the surface morphology of the film was followed in situ. Complementary experiments on the film morphology were also performed by scanning electron microscopy. The chemical evolution of the film surface was obtained by time-of-flight secondary ion mass spectrometry. On the one hand, when ClAlPc is immersed in KCl solutions at pH = 2.0 or 3.0, a slow dissolution of the outermost surface of the film occurs. This is followed by the hydrolysis of ClAlPc in solution to form first the hydroxyaluminum phthalocyanine (HOAlPc) and then the p-oxo-dimer, PcAlOAlPc. The latter recrystallizes as long needles on top of the initial film, thereby changing drastically its surface morphology. On the other hand, when ClAlPc is immersed in KC1 solutions at pH = 5.7 or 8.0, the hydrolysis of ClAlPc occurs at the surface of the film without noticeable morphological modifications. A subsequent immersion of the film in KC1 at pH = 2.0 may have the same effect on the film morphology as the one previously described for pH = 2.0 or 3.0, as long as mechanical energy is provided to the film, either by ultrasound or by the cantilever tip of the AFM. When the latter is involved, the source of mechanical energy is localized in space and patterning of the surface morphology becomes possible.
Applied Surface Science, Jul 1, 2006
Pristine and Au-covered molecular films have been analyzed by ToF-SIMS (TRIFT TM), using 15 keV G... more Pristine and Au-covered molecular films have been analyzed by ToF-SIMS (TRIFT TM), using 15 keV Ga + (FEI) and 15 keV C 60 + (Ionoptika) primary ion sources. The use of C 60 + leads to an enormous yield enhancement for gold clusters, especially when the amount of gold is low (2 nmol/ cm 2), i.e. a situation of relatively small nanoparticles well separated in space. It also allows us to extend significantly the traditional mass range of static SIMS. Under 15 keV C 60 + ion bombardment, a series of clusters up to a mass of about 20,000 Da (Au 100 À : 19,700 Da) is detected. This large yield increase is attributed to the hydrocarbon matrix (low-atomic mass), because the yield increase observed for thick metallic films (Ag, Au) is much lower. The additional yield enhancement factors provided by the Au metallization procedure for organic ions (MetA-SIMS) have been measured under C 60 + bombardment. They reach a factor of 2 for the molecular ion and almost an order of magnitude for Irganox fragments such as C
Langmuir, Aug 30, 2001
We show in this paper that it is possible to locally detect additives on the surface of polypropy... more We show in this paper that it is possible to locally detect additives on the surface of polypropylene with chemically modified atomic force microscopy (AFM) tips. Gold-coated AFM tips modified with methyl and hydroxyl terminated self-assembled alkanethiol monolayers were used to measure adhesion forces on a process-stabilizing agent (Irgafos 168), an antioxidant (Irganox 1010), and UV-light stabilizers (Tinuvin 770, Dastib 845, Chimassorb 944, and Hostavin N30). Pull-off force measurements carried out on these pure additive films have shown that it is possible to discriminate between antioxidants and UV-light stabilizers. We have evidenced a characteristic fingerprint for each additive, according to the functionality of the tip used and the medium wherein the force measurements are realized (water or nitrogen atmosphere). Similarly we have measured pull-off forces on a melt-pressed polypropylene sample stabilized with Irgafos 168, Irganox 1010, and Tinuvin 770. These adhesion force measurements show that the extreme surface of the polymer is mainly made of a layer of Tinuvin 770. These results have been compared to those obtained from time-of-flight secondary ion mass spectrometry measurements.
Journal of Power Sources, Jul 1, 1996
Belgique stract ron phthalocyanine (FePc) and tetracarboxylic iron phthalocyanine (FePcTc) have b... more Belgique stract ron phthalocyanine (FePc) and tetracarboxylic iron phthalocyanine (FePcTc) have been adsorbed on carbon black (C). The resulting >clC and FePcTc/C have been heat-treated in Ar at various temperatures ranging from 100 to 1100 °C to obtain catalysts for the ctroreduction of oxygen. The electrochemical properties of these materials have been measured by rotating disk electrode and in polymer :lrolyte fuel cells. These properlies have been correlated with the bulk and surface characterizations of the catalysts. The most active alyst is unpymlyzed FePcTc/C but it is also the least stable one. The only catalysts which are active and stable are those obtained at htgh olysis temperatures (> 900 °C). At those temperatures there is no Fe-N bond anymore, and Fe is mainly observed as a metal surrounded a g raphitic envelope. After I 0 h in a fuel cell at 50 °C, 0.5 V versus reversible hydrogen electrode (R HE), FePcTc/C and FePc/C pyrolyzed 1000 °C yielded currents 37 and 40% that of a commercial Pt catalyst containing the same metal loading (2 wt .%). re.~peet ively.
Electrochimica Acta, 1997
The role of nitrogen and iron in the generation of catalysts for oxygen reduction in acidic media... more The role of nitrogen and iron in the generation of catalysts for oxygen reduction in acidic media has been investigated by using two independent organic precursors. The Fe and N precursors were polyvinylferrocene adsorbed on carbon black and acetonitrile vapor, respectively. These precursors were pyrolyzed at 1000 C. A catalyst is obtained only if Fe and N are present together in the reactor during pyrolysis. Inactive Fe clusters surrounded by a protective graphitic envelope are produced when adsorbed polyvinylferrocene is pyrolyzed alone at 1OOO'C. The latter material may, however, be activated by a second pyrolysis in acetonitrile vapor. The characterization of the catalyst indicates that the iron is oxidized (Fe" and Fe"'), but no strong Fe-N, bonds were unequivocally detected by ToF SIMS. Lifetime testing of the catalyst in a polymer electrolyte fuel cell demonstrated stable currents for at least 300 h. The current density measured with a catalyst containing 1 wt% Fe was about l/3 of that measured with a commercial Pt-based catalyst containing 2 wt% metal loading. #
Journal of Physical Chemistry B, Oct 27, 2000
ABSTRACT
Journal of Applied Physics, Feb 1, 1993
The close-spaced vapor transport (CSVT) technique is used to grow GaAs epitaxial layers from vari... more The close-spaced vapor transport (CSVT) technique is used to grow GaAs epitaxial layers from various n- or p-type doped GaAs sources. The transport agent is H2O with PH2O = 4.58 Torr. n-type layers can be grown with Te- or Ge-doped GaAs sources. The transport coefficients of both dopants (ratio of the electrically active dopant concentration in the layer to the electrically active dopant concentration in the source) is 100% for Te or Ge, in the substrate temperature range comprised between 750 and 850 °C. p-type layers are obtained with Zn-doped GaAs sources. The transport coefficient of Zn is about 1% and is also independent of the substrate temperature. The transport coefficients and their independence on temperature are in agreement with a mass-transport controlled model based on the hypothesis that the transport reactions of GaAs and the doping impurities are in equilibrium at the source and substrate temperatures. Si-doped GaAs cannot be used as a source to obtain conductive n-type layers. When undoped semi-insulating (SI)-GaAs wafers are used as sources in CSVT, n-type layers are obtained. They are characterized by ND−NA=9×1015–3×1016 cm−3 and μ300K=3000–4000 cm2 V−1 s−1, independent of the temperature, in the temperature range investigated. Glow discharge mass spectroscopy analyses performed on a source and on a layer indicate that C, O, Si, and S are the major residual impurities in the GaAs layer. All these impurities have their origin in the technique (reactor, transport agent). Ge is also present in the layers, as indicated by photoluminescence. It is a minor impurity. Its origin is probably the SI-GaAs source.
Electrochimica Acta, 1998
Different quantities of iron tetraphenylporphyrin (FeTPP) have been adsorbed onto carbon black (X... more Different quantities of iron tetraphenylporphyrin (FeTPP) have been adsorbed onto carbon black (XC) and pyrolyzed at 1000°C to produce catalysts containing iron loadings of 2, 4 and 6 wt%. The relative catalytic activities for oxygen reduction in polymer electrolyte fuel cells and in rotating disk electrode cells was: 4 > 2 > 6 wt% Fe. All these catalysts demonstrated stable behavior in a fuel cell element at 0.5 V vs RHE and at 50°C until the 10th h of operation when slow decaying of the catalytic activity began. Reloading of the catalysts containing 2 and 4 wt% Fe with further quantities of FeTPP followed by pyrolysis at 1000°C to increase the iron content to 4 and 8 wt% Fe, respectively, produced catalysts having smaller catalytic activities than the starting products. Efforts to remove iron-based material [cc-Fe, Fe(C) and various carbides] from the catalysts by acid digestion (HCl, pH = 0.5, T = 2O"C, t = 6 weeks) only succeeded in removing a small part (< 25%) of the bulk iron content from the catalyst. Most of the iron remained encapsulated in an acid resistant graphite-like protective coating. The catalytic activities of the acid washed catalysts are superior to those of the starting products, but showed the same decaying catalytic activity after spending 10 h in a fuel cell environment as did the nonacid washed catalysts. The role of the acid digestion as an important step in removing material which would otherwise block the access of the oxygen molecules to the active site of the FeTPP/XC materials is hypothesized. The material obtained following adsorption of hydrogen tetraphenylporphyrin onto the carbon black support and pyrolysis at 1000°C showed negligible catalytic activity. Exposure to an aqueous solution of FeS04 caused the adsorption of iron ions onto the nitrogen containing surface of the product, but did not improve the catalytic activity towards oxygen reduction. Improved catalytic activity is only observed after pyrolizing the C-N-Fe material at 1000°C. The occurrence of catalytic activity requires, therefore, a carbon black support, a source of iron and nitrogen as well as thermal treatment at elevated temperature.
The Journal of Physical Chemistry C, 2011
The high cost of proton-exchange-membrane fuel cells would be considerably reduced if platinumbas... more The high cost of proton-exchange-membrane fuel cells would be considerably reduced if platinumbased catalysts were replaced by iron-based substitutes, which have recently demonstrated comparable activity for oxygen reduction, but whose cause of activity decay in acidic medium has been elusive. Here, we reveal that the activity of Fe/N/C-catalysts prepared through a pyrolysis in NH 3 is mostly imparted by acid-resistant FeN 4-sites whose turnover frequency for the O 2 reduction can be regulated by fine chemical changes of the catalyst surface. We show that surface N-groups protonate at pH 1 and subsequently bind anions. This results in decreased activity for the O 2 reduction. The anions can be removed chemically or thermally, which restores the activity of acid-resistant FeN 4-sites. These results are interpreted as an increased turnover frequency of FeN 4-sites when specific surface N-groups protonate. These unprecedented findings provide new perspective for stabilizing the most active Fe/N/C-catalysts known to date.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1998
In a round robin experiment a set of ®ve polycrystalline, metallic samples is studied by low-ener... more In a round robin experiment a set of ®ve polycrystalline, metallic samples is studied by low-energy ion scattering (LEIS) in ®ve dierent laboratories. The energy range is 0.6±3.5 keV and He and Ne ions are used. Even though different experimental setups are used the evaluated elemental sensitivity factors agree within AE20%. Reproducibility within single laboratories is better than 10%. In an additional study carried out in three laboratories the surface composition of an alloy, Cu 55 Pd 45 , was determined, using in situ calibration standards. These surface composition measurements agreed within AE3 at% demonstrating that quantitative composition determination is possible using this procedure.
Electrochimica Acta, Jun 1, 1996
Iron and cobalt tetraphenylporphyrins (FeTPP and CoTPP, respectively) have been adsorbed on carbo... more Iron and cobalt tetraphenylporphyrins (FeTPP and CoTPP, respectively) have been adsorbed on carbon black (C). The resulting FeTPP/C and CoTPP/C were heat-treated in Ar at various temperatures ranging from 100–1100 °C in order to produce catalysts for the electroreduction of oxygen in polymer electrolyte fuel cells. The catalysts have been characterized by XRD, XPS, ToF-SIMS, and bulk analyses. Their electrocatalytic properties have been evaluated by rotating disk electrode (rde) and gas diffusion electrode (gde) measurements. The highest rde activities at 0.70 V vs nhe were recorded for CoTPP/C and FeTPP/C heat-treated in the 500–700 °C range. In that temperature range, the increased catalytic activity originates from the well dispersed N4-metal moiety or from fragments of the original molecule still containing the metal bound to nitrogen. Short term stability tests on the initially most active catalysts revealed the instability of these catalysts in comparison to those obtained at higher pyrolysis temperatures (900–1000 °C). At these pyrolysis temperatures the active site of the catalysts is inorganic in nature. The presence of iron and cobalt in their metallic states in these catalysts has been confirmed using XRD. TEM of the catalysts pyrolyzed at these higher temperatures revealed that most of the iron and cobalt are encapsulated in a graphite-like coating. The better stability of these catalysts in the acidic environment of a working fuel cell may be ascribed to the presence of this protective coating. The activity of FeTPP/C pyrolyzed at 1000 °C was observed to increase with time in a manner similar to that of platinum-based catalysts. The activity of the former catalyst was determined to be approximately one half that of a commercial platinum catalyst containing the same amount of metal (2 wt%).
Journal of Physical Chemistry C, Apr 1, 2007
ABSTRACT
Electrochimica Acta, May 1, 1998
ÐFe-based catalysts for the reduction of oxygen in polymer electrolyte fuel cells (PEFCs) have be... more ÐFe-based catalysts for the reduction of oxygen in polymer electrolyte fuel cells (PEFCs) have been prepared from a precursor containing 10 wt% Fe as Fe(OH) 2 adsorbed on carbon black (Fe(OH) 2 /C). Activation of the precursor was performed in two steps: (i) H 2 reduction at 6008C; (ii) pyrolysis in acetonitrile (AN) vapor at various temperatures (400, 600, 800, 10008C). The electrocatalytic properties of all catalysts were tested in rotating disk electrode (RDE) experiments and in single H 2 /O 2 gas diusion electrode (GDE) assemblies. Catalysts for O 2 reduction were obtained for Fe(OH) 2 /C pyrolyzed at 6008C and higher. Stable currents in the fuel cell assembly were observed for the catalysts prepared at 8008C and higher. Leaching the excess iron from the catalysts by exposure to an H 2 SO 4 solution increased their catalytic activities. Exposure of the acid leached catalyst prepared at 10008C to Cl 2 at 6508C removed additional quantities of excess iron and increased the catalyst activity even further. The catalyst obtained after these treatments retained an iron content of 3.3 wt%. The survival of the catalytic activity in that material even after the Cl 2 treatment suggests that either Fe is present in the active site in a high oxidation state unleachable under the form of FeCl 3 , or that Fe is not a constituent of the active site. In this case, its role would be limited to catalyzing the formation of the carbon and nitrogen based active site. The XRD, XPS, ToF-SIMS and TEM analyses performed on the catalysts prepared during this study were inconclusive in resolving this issue as they all were dominated by the presence of inactive iron particles and AN pyrolysis products.
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Papers by Patrick Bertrand