Elena Pastor | Universidad de La Laguna (original) (raw)
Papers by Elena Pastor
The use of high surface monolithic carbon as support for catalysts offers important advantage, su... more The use of high surface monolithic carbon as support for catalysts offers important advantage, such as elimination of the ohmic drop originated in the interparticle contact and improved mass transport by ad-hoc pore design. Moreover, the approach discussed here has the advantage that it allows the synthesis of materials having a multimodal porous size distribution, with each pore size contributing to the desired properties. On the other hand, the monolithic nature of the porous support also imposes new challenges for metal loading. In this work, the use of Hierarchical Porous Carbon (HPC) as support for PtPd nanoparticles was explored. Three hierarchical porous carbon samples (denoted as HPC-300, HPC-400 and HPC-500) with main pore size around 300, 400 and 500 nm respectively, are used as porous support. PtPd nanoparticles were loaded by impregnation and subsequent chemical reduction with NaBH 4 . The resulting material was characterized by EDX, XRD and conventional electrochemical techniques. The catalytic activity toward formic acid and methanol electrooxidation was evaluated by electrochemical methods, and the results compared with commercial carbon supported PtPd. The Hierarchical Porous Carbon support discussed here seems to be promising for use in DFAFC anodes.
International Journal of Hydrogen Energy
The present study is focused on the influence of Pt loading on the reactivity of catalysts prepar... more The present study is focused on the influence of Pt loading on the reactivity of catalysts prepared supporting the metal on novel core–shell molybdenum substrates. The electrocatalytic activity and stability of nine Pt/X@MoO3/C catalysts (where X denotes the nature of Mo-phases in the core of the core–shell Mo-particle: Mo2C, MoO2 and/or Mo0) with three Pt loading (5, 20 and 30 wt% Pt) were tested for carbon monoxide and methanol electro–oxidation reactions.For both reactions, Pt loading appears to be a key factor, obtaining the best performance for those catalysts with higher Pt content. Furthermore, it is observed that the nature of X@MoO3/C samples plays an important role as promoter for CO and methanol oxidation. MoO3-shell catalyzes and homogenizes the potentiodynamic responses, while the reduced Mo-phase in the core produces an electronic effect which determines the catalytic activity and stability during the electro-oxidation processes investigated.
The review article discusses the current status and recent findings of our investigations on the ... more The review article discusses the current status and recent findings of our investigations on the synthesis and characterization of carbon-supported PtRuMo electrocatalysts for direct alcohol fuel cells. In particular, the effect of the carbon support and the composition on the structure, stability and the activity of the PtRuMo nanoparticles for the electrooxidation of CO, methanol and ethanol have been studied. Different physicochemical techniques have been employed for the analysis of the catalysts structures: X-ray analytical methods (XRD, XPS, TXRF), thermogravimetry (TGA) and transmission electron microscopy (TEM), as well as a number of electrochemical techniques like CO adsorption studies, current-time curves and cyclic voltammetry measurements. Furthermore, spectroscopic methods adapted to the electrochemical systems for in situ studies, such as Fourier transform infrared spectroscopy (FTIRS) and differential electrochemical mass spectrometry (DEMS), have been used to evaluate the oxidation process of CO, methanol and ethanol over the carbon-supported PtRuMo electrocatalysts.
Applied Catalysis B Environmental
Pt–Ru catalysts supported on carbon nanofibers were synthesized by different synthesis methods: r... more Pt–Ru catalysts supported on carbon nanofibers were synthesized by different synthesis methods: reduction with sodium borohydride, methanol and formate ions (denoted as BM, MeOH and SFM, respectively). The catalyst synthesized by the SFM route was heat-treated (denoted as SFM TT) in order to enhance its catalytic activity, generating in this way a new catalyst. Physical characterization was performed by means of energy-dispersive X-ray (EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Results showed that Pt–Ru/CNF catalysts with similar metal content (20 wt%) and atomic ratio (Pt:Ru 1:1) can be obtained by all methodologies. In order to determine the CO tolerance and the electroactive areas of the materials, adsorbed CO stripping experiments were performed. CO stripping curves were modified with the addition of Ru that shifts the onset and peak electrooxidation potentials to more negative values compared with those obt...
Journal of Solid State Electrochemistry
The electrochemical behavior of acetaldehyde on palladium and platinum electrodes in acidic media... more The electrochemical behavior of acetaldehyde on palladium and platinum electrodes in acidic media was comparatively studied by means of differential electrochemical mass spectrometry (DEMS) and in situ Fourier transform infrared spectroscopy (FTIRS) combined with cyclic voltammetry. It was observed that acetaldehyde decomposition depends on the catalyst material, applied potential, and reactant concentration. Additionally, it was detected that acetaldehyde adsorbs and dissociates at potentials lower than 0.60 V vs RHE, producing methane and adsorbed CO on Pd; while C-2-species, CHx and COad are formed on Pt. Besides carbon dioxide, acetic acid and adsorbed acetate were observed at E > 0.6 V, and their contribution increased with acetaldehyde concentration. Differences between Pt and Pd in potential dependence of the products and intermediates were established. Calibration of the mass spectrometer, together with the use of labeled acetaldehyde and IR spectra, allows establishment ...
Electrochimica Acta
Spectroelectrochemical methods, in-situ Fourier Transform Infrared (FTIR) and Differential Electr... more Spectroelectrochemical methods, in-situ Fourier Transform Infrared (FTIR) and Differential Electrochemical Mass Spectroscopy (DEMS), are used to study the formation of poly(N-methylaniline) (PNMANI) by anodic oxidation of N-methylaniline (NMANI). The methods are used to elucidate the structural changes during redox switching of PNMANI and the nature of the degradation products of PNMANI produced during electrochemical oxidation. The results are discussed in comparison with those previously reported for aniline. The early stages of NMANI oxidation leads to the formation of dimers by head-to-tail coupling (product = N,N'-dimethyl-4-aminodiphenylamine, DMADA) and tail-to-tail coupling (product = N,N'-dimethylbenzidine, DMBz). It seems that, when N-methylaniline is oxidized, it is formed more tail-to-tail dimer than in the case of aniline, due to steric and electronic effects of the N-substituent methyl groups. The head-to-tail dimer (DAMADA) is irreversibly adsorbed on the elec...
Applied Catalysis B Environmental
Pd nanoparticles have been supported onto different novel carbon materials to be 14 used in the e... more Pd nanoparticles have been supported onto different novel carbon materials to be 14 used in the electroreduction of CO 2 to high-added value products. Carbon nanocoils 15 (CNCs), carbon nanofibers (CNFs) and ordered mesoporous carbon materials (OMCs) 16 have been studied as support of the catalysts. In addition, Pd catalyst supported onto 17
Chemical Communications
The faradaic efficiency of CO2 electroreduction is significantly affected by the thickness of Pd ... more The faradaic efficiency of CO2 electroreduction is significantly affected by the thickness of Pd nanoshells on Au cores. The ratio of hydrogen evolution to CO2 reduction was determined by differential electrochemical mass spectrometry. Decreasing the Pd shell thickness from 10 to 1 nm leads to a twofold increase in faradaic efficiency.
The Journal of Physical Chemistry, 1996
ABSTRACT Electrochemical oxidation/reduction reactions of ethanol in 1 M HClO4 were studied on po... more ABSTRACT Electrochemical oxidation/reduction reactions of ethanol in 1 M HClO4 were studied on porous Pt, Pt0.92Ru0.08, Pt0.85Ru0.15, and Ru under potentiodynamic conditions. The electrodes with defined bulk and surface compositions were made by electrodeposition on porous Au substrates. Cyclic voltammetry in combination with on-line mass spectrometry (DEMS) was employed to correlate faradaic currents with ion currents associated to reaction products. The formation of both CO2 and ethanal was unequivocally identified during ethanol oxidation on PtRu and Pt by using d3-ethanol. On pure Ru neither faradaic currents were observed nor oxidation/reduction products could be detected by mass spectrometry. The reduction of ethanol on Pt and PtRu to methane and ethane was found in the potential range of hydrogen adsorption. The yields of oxidation and reduction products and the corresponding onset potentials for their formation are greatly influenced by the Ru content. Alloys with high Ru content exhibit a lower reaction rate for ethanol electrooxidation. On the other hand, the selectivity for ethanal production is significantly enhanced for PtRu as compared to pure Pt.
Journal of Power Sources, 2015
h i g h l i g h t s g r a p h i c a l a b s t r a c t Mesoporous Pt material (MPPt) was successfu... more h i g h l i g h t s g r a p h i c a l a b s t r a c t Mesoporous Pt material (MPPt) was successfully modified by Sn adatoms (MPPt/Sn). The CO tolerance was evaluated at MPPt, MPPt/Sn and commercial Pt 3 Sn/C catalysts. The catalytic activity toward methanol oxidation for all electrodes was evaluated. CO and methanol oxidation reactions were studied at 25 and 60 C by DEMS. Energy conversion efficiency from methanol to CO 2 for all catalysts was calculated.
Electrocatalysis, 2011
Pt nanoparticles with bi-dimensional geometry and circular shape have been synthesized and studie... more Pt nanoparticles with bi-dimensional geometry and circular shape have been synthesized and studied by in situ Fourier transform infrared spectroscopy, scanning tunneling microscopy, CO stripping voltammetry, cyclic voltammetry, and methanol oxidation in acidic and alkaline media. The experimental results suggest that Pt nanodiscs present a bi-dimensional (111) order domain on the surface and a high density of step edge sites mainly with and (100) orientations. A clear correlation between the atomic surface arrangement and the catalytic activity towards the CO and methanol oxidation, as well as the voltammetric profiles in the electrolyte, was observed. Additionally, infrared spectra proved the high density of low-coordinated Pt atoms present in the nanoparticle and that CO adsorbed in linear configuration is the main adsorbate. The electrochemical study was compared with that of spherical Pt particles supported on carbon (Pt/C 20 wt.%, Etek).
The Journal of Physical Chemistry C, 2013
ABSTRACT PtRu catalysts were prepared using a highly mesoporous carbon xerogel submitted to diffe... more ABSTRACT PtRu catalysts were prepared using a highly mesoporous carbon xerogel submitted to different oxygen functionalization treatments: diluted and concentrated nitric acid as well as gas-phase 5% O2–N2 oxidation. Catalysts with 20 wt % loading and equimolar Pt:Ru metallic phase were prepared using an impregnation procedure involving chemical reduction with formic acid. The so-obtained carbon materials, as well as the different catalysts synthesized, were characterized by means of N2 physisorption, temperature-programmed desorption (TPD), X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Cyclic voltammetry and chronoamperometry were performed to study their activity toward carbon monoxide and methanol oxidation. Functionalization of the carbon support was found to play a definitive role in the interaction between carbon material and the active phase, determining metallic dispersion, alloying degree, and reduction extent. The activity of the catalysts in methanol electro-oxidation was directly related to the metal oxidation state and alloying degree.
Sensor Letters, 2008
ABSTRACT Platinum nanoparticles supported on functionalized carbon nanofibers (CNFs) have been pr... more ABSTRACT Platinum nanoparticles supported on functionalized carbon nanofibers (CNFs) have been prepared as electrocatalyst for Proton Exchange Membrane Fuel Cells. CNFs, obtained by catalytic decomposition of methane over a high-nickeled catalyst, were pre-oxidised to create oxygen surface groups under treatments of different severity with liquid oxidising agents. Pt was then deposited by ion exchange of Pt(NH3)4Cl2 in neutral and basic media, and reduced under a hydrogen flow at 350 °C. It was observed that deposited platinum increases with both the quantity of oxygen groups and pH of the precursor solution. The maximum Pt loading was 2.2 wt%, deposited on CNFs treated with a mixture of nitric and sulphuric acid for 0.5 h at boiling temperature. Platinum particles, characterized by transmission electron microscopy, X-ray diffraction and CO chemisorption, were well dispersed and their average size was smaller than 3 nm in most of the samples. Finally, electrochemical studies showed that these catalysts, even with a low Pt loading on the carbon nanofibers, present high electrocatalytic activity towards methanol oxidation.
Langmuir, 2000
ABSTRACT Acetaldehyde oxidation at Pt(111) and Pt(100) follows at least two parallel reaction pat... more ABSTRACT Acetaldehyde oxidation at Pt(111) and Pt(100) follows at least two parallel reaction pathways leading to CO2 and acetic acid as soluble products. The former is produced via strongly adsorbed intermediates. Besides adsorbed CO, also species containing two C atoms, possibly η1-acetaldehyde and η1-acetyl, are formed. These species are strongly bonded to the surface. None of these adsorbates are the intermediate leading to the formation of acetic acid.
Langmuir, 2002
ABSTRACT The electrochemical behavior of ethanol and acetaldehyde was studied at rhodium electrod... more ABSTRACT The electrochemical behavior of ethanol and acetaldehyde was studied at rhodium electrodes in acid solutions using electrochemical mass spectrometry (DEMS). Acetaldehyde and CO2 were detected from bulk ethanol, whereas only CO2 was recorded from acetaldehyde. The production of acetic acid could not be confirmed with this method. The formation of methane was established from both molecules, which suggests that the fragmentation of the C−C chain occurs during the electroreduction and/or adsorption processes. Adsorbed species were isolated by applying a flow cell procedure. The residues produce CO2 and methane during oxidation and reduction reactions, respectively, the amount of these compounds depending on the adsorption potential. By use of isotopic labeled 12CH313CH2OH and 12CH313CHO, the contribution of each C atom in the adsorbate was distinguished. It was established that the CH3 group oxidizes at potentials within the O adsorption potential region of rhodium during the positive-going sweep and also at E < 0.60 V during the reverse scan. The CH2OH or CHO groups yield CO2 in the same potential region as COad. The influence of the anion on these reactions was established using sulfuric and perchloric acids as base electrolytes, being noticeable for ethanol adsorption. Compared to Pt, Rh electrodes exhibit an enhanced activity for deprotonation and C−C cleavage reactions.
Journal of Power Sources, 2013
Carbon nanocoils (CNCs) were proposed as electrocatalysts support. Electrocatalyst' performance s... more Carbon nanocoils (CNCs) were proposed as electrocatalysts support. Electrocatalyst' performance strongly depended on the synthesis method. CNCs-supported showed better electrochemical behaviour than E-TEK electrocatalysts. By using CNCs as support the reaction route of intermediates is favoured. Intermediates oxidation is facilitated by the use of CNCs as support.
Journal of Natural History, 2008
... biological diversity in the Mediterranean]. Paper presented at: UNEP(OCA)/MED IG 10/4;. 2 Dec... more ... biological diversity in the Mediterranean]. Paper presented at: UNEP(OCA)/MED IG 10/4;. 2 December 1996 , Monaco. View all references) due to over exploitation, as it is now captured very rarely. Information available on the ...
Journal of The Electrochemical Society, 2001
ABSTRACT Electrochemical and nonelectrochemical reactions of the H2O2/CO system on a Pt electrode... more ABSTRACT Electrochemical and nonelectrochemical reactions of the H2O2/CO system on a Pt electrode were studied in 2 M H2SO4 with cyclic voltammetry and on-line mass spectrometry. It was found that a complete CO monolayer is chemically stable in the presence of dissolved H2O2. However, H2O2 oxidizes adsorbed CO to CO2 at lower potentials than those required for electrochemical CO adsorbate oxidation when the Pt electrode is partially covered by CO. Furthermore, it was observed that a complete CO monolayer on Pt inhibits the electrochemical reduction of H2O2 to H2O in CO-containing electrolyte.
Journal of Electroanalytical Chemistry, 1999
ABSTRACT The electrochemical behavior of propargyl alcohol (PA) on palladium electrodes in 0.1 M ... more ABSTRACT The electrochemical behavior of propargyl alcohol (PA) on palladium electrodes in 0.1 M HClO4 was studied by differential electrochemical mass spectrometry (DEMS). Experiments with the alcohol present in the bulk of the solution have shown that the sole oxidation product is CO2. During potential cycling in the hydrogen adsorption/absorption region, C3- (propylene and propane) and C2- (ethane and traces of ethene/ethyne) hydrocarbons, as well as allyl alcohol, were produced. On the other hand, PA forms strongly bonded species on palladium which can be studied using a flow cell procedure. The maximum adsorption of PA was observed in the potential range 0.25–0.65 V. As for bulk studies, only CO2 was detected during the oxidation of the residues. However, some differences should be mentioned in respect of the reduction reactions: only propane, propylene and allyl alcohol were observed from the adlayer. According to these results, and taking into account the values of the charges involved in the adsorption (Qt) and oxidation (Qox) processes, different structures were proposed for the adsorbed species. From these structures, the formation of the reduction products was justified. Results were compared with previously reported data for platinum and gold in acid media.
Journal of Electroanalytical Chemistry, 1999
The oxidative ethanol adsorption and electrochemical surface reactions of adsorbed intermediates ... more The oxidative ethanol adsorption and electrochemical surface reactions of adsorbed intermediates were studied on electrodeposited Pt, Ru, Pt 0.92 Ru 0.08 and Pt 0.85 Ru 0.15 in 1 M HClO 4 . A flow cell procedure was performed in order to separate surface reactions of intermediates formed in the oxidative ethanol adsorption from those reactions for ethanol in the bulk electrolyte solution. Oxidation and reduction reactions of adsorbed species were studied by potential-controlled electrodesorption spectrometry. No adsorbate formation was observed on a pure Ru electrode. In all cases, CO 2 was the sole product formed in the oxidative electrodesorption of the adsorbates. Using 12 CH 3 12 CH 2 OH and 12 CH 3 13 CH 2 OH, the oxidation reaction pathways of each C-atom to CO 2 were followed. On the other hand, methane and ethane were detected during the reductive electrodesorption of adlayer species. The onset potential for these reduction products shifts to more negative potentials as the Ru content of the alloy increases. The methane to ethane yield ratio decreases in the sequence Pt \ Pt 0.92 Ru 0.08 \ Pt 0.85 Ru 0.15 . A critical interpretation of the experimental data leads to a tentative yield of different adsorbed species as function of the Ru surface concentration.
The use of high surface monolithic carbon as support for catalysts offers important advantage, su... more The use of high surface monolithic carbon as support for catalysts offers important advantage, such as elimination of the ohmic drop originated in the interparticle contact and improved mass transport by ad-hoc pore design. Moreover, the approach discussed here has the advantage that it allows the synthesis of materials having a multimodal porous size distribution, with each pore size contributing to the desired properties. On the other hand, the monolithic nature of the porous support also imposes new challenges for metal loading. In this work, the use of Hierarchical Porous Carbon (HPC) as support for PtPd nanoparticles was explored. Three hierarchical porous carbon samples (denoted as HPC-300, HPC-400 and HPC-500) with main pore size around 300, 400 and 500 nm respectively, are used as porous support. PtPd nanoparticles were loaded by impregnation and subsequent chemical reduction with NaBH 4 . The resulting material was characterized by EDX, XRD and conventional electrochemical techniques. The catalytic activity toward formic acid and methanol electrooxidation was evaluated by electrochemical methods, and the results compared with commercial carbon supported PtPd. The Hierarchical Porous Carbon support discussed here seems to be promising for use in DFAFC anodes.
International Journal of Hydrogen Energy
The present study is focused on the influence of Pt loading on the reactivity of catalysts prepar... more The present study is focused on the influence of Pt loading on the reactivity of catalysts prepared supporting the metal on novel core–shell molybdenum substrates. The electrocatalytic activity and stability of nine Pt/X@MoO3/C catalysts (where X denotes the nature of Mo-phases in the core of the core–shell Mo-particle: Mo2C, MoO2 and/or Mo0) with three Pt loading (5, 20 and 30 wt% Pt) were tested for carbon monoxide and methanol electro–oxidation reactions.For both reactions, Pt loading appears to be a key factor, obtaining the best performance for those catalysts with higher Pt content. Furthermore, it is observed that the nature of X@MoO3/C samples plays an important role as promoter for CO and methanol oxidation. MoO3-shell catalyzes and homogenizes the potentiodynamic responses, while the reduced Mo-phase in the core produces an electronic effect which determines the catalytic activity and stability during the electro-oxidation processes investigated.
The review article discusses the current status and recent findings of our investigations on the ... more The review article discusses the current status and recent findings of our investigations on the synthesis and characterization of carbon-supported PtRuMo electrocatalysts for direct alcohol fuel cells. In particular, the effect of the carbon support and the composition on the structure, stability and the activity of the PtRuMo nanoparticles for the electrooxidation of CO, methanol and ethanol have been studied. Different physicochemical techniques have been employed for the analysis of the catalysts structures: X-ray analytical methods (XRD, XPS, TXRF), thermogravimetry (TGA) and transmission electron microscopy (TEM), as well as a number of electrochemical techniques like CO adsorption studies, current-time curves and cyclic voltammetry measurements. Furthermore, spectroscopic methods adapted to the electrochemical systems for in situ studies, such as Fourier transform infrared spectroscopy (FTIRS) and differential electrochemical mass spectrometry (DEMS), have been used to evaluate the oxidation process of CO, methanol and ethanol over the carbon-supported PtRuMo electrocatalysts.
Applied Catalysis B Environmental
Pt–Ru catalysts supported on carbon nanofibers were synthesized by different synthesis methods: r... more Pt–Ru catalysts supported on carbon nanofibers were synthesized by different synthesis methods: reduction with sodium borohydride, methanol and formate ions (denoted as BM, MeOH and SFM, respectively). The catalyst synthesized by the SFM route was heat-treated (denoted as SFM TT) in order to enhance its catalytic activity, generating in this way a new catalyst. Physical characterization was performed by means of energy-dispersive X-ray (EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Results showed that Pt–Ru/CNF catalysts with similar metal content (20 wt%) and atomic ratio (Pt:Ru 1:1) can be obtained by all methodologies. In order to determine the CO tolerance and the electroactive areas of the materials, adsorbed CO stripping experiments were performed. CO stripping curves were modified with the addition of Ru that shifts the onset and peak electrooxidation potentials to more negative values compared with those obt...
Journal of Solid State Electrochemistry
The electrochemical behavior of acetaldehyde on palladium and platinum electrodes in acidic media... more The electrochemical behavior of acetaldehyde on palladium and platinum electrodes in acidic media was comparatively studied by means of differential electrochemical mass spectrometry (DEMS) and in situ Fourier transform infrared spectroscopy (FTIRS) combined with cyclic voltammetry. It was observed that acetaldehyde decomposition depends on the catalyst material, applied potential, and reactant concentration. Additionally, it was detected that acetaldehyde adsorbs and dissociates at potentials lower than 0.60 V vs RHE, producing methane and adsorbed CO on Pd; while C-2-species, CHx and COad are formed on Pt. Besides carbon dioxide, acetic acid and adsorbed acetate were observed at E > 0.6 V, and their contribution increased with acetaldehyde concentration. Differences between Pt and Pd in potential dependence of the products and intermediates were established. Calibration of the mass spectrometer, together with the use of labeled acetaldehyde and IR spectra, allows establishment ...
Electrochimica Acta
Spectroelectrochemical methods, in-situ Fourier Transform Infrared (FTIR) and Differential Electr... more Spectroelectrochemical methods, in-situ Fourier Transform Infrared (FTIR) and Differential Electrochemical Mass Spectroscopy (DEMS), are used to study the formation of poly(N-methylaniline) (PNMANI) by anodic oxidation of N-methylaniline (NMANI). The methods are used to elucidate the structural changes during redox switching of PNMANI and the nature of the degradation products of PNMANI produced during electrochemical oxidation. The results are discussed in comparison with those previously reported for aniline. The early stages of NMANI oxidation leads to the formation of dimers by head-to-tail coupling (product = N,N'-dimethyl-4-aminodiphenylamine, DMADA) and tail-to-tail coupling (product = N,N'-dimethylbenzidine, DMBz). It seems that, when N-methylaniline is oxidized, it is formed more tail-to-tail dimer than in the case of aniline, due to steric and electronic effects of the N-substituent methyl groups. The head-to-tail dimer (DAMADA) is irreversibly adsorbed on the elec...
Applied Catalysis B Environmental
Pd nanoparticles have been supported onto different novel carbon materials to be 14 used in the e... more Pd nanoparticles have been supported onto different novel carbon materials to be 14 used in the electroreduction of CO 2 to high-added value products. Carbon nanocoils 15 (CNCs), carbon nanofibers (CNFs) and ordered mesoporous carbon materials (OMCs) 16 have been studied as support of the catalysts. In addition, Pd catalyst supported onto 17
Chemical Communications
The faradaic efficiency of CO2 electroreduction is significantly affected by the thickness of Pd ... more The faradaic efficiency of CO2 electroreduction is significantly affected by the thickness of Pd nanoshells on Au cores. The ratio of hydrogen evolution to CO2 reduction was determined by differential electrochemical mass spectrometry. Decreasing the Pd shell thickness from 10 to 1 nm leads to a twofold increase in faradaic efficiency.
The Journal of Physical Chemistry, 1996
ABSTRACT Electrochemical oxidation/reduction reactions of ethanol in 1 M HClO4 were studied on po... more ABSTRACT Electrochemical oxidation/reduction reactions of ethanol in 1 M HClO4 were studied on porous Pt, Pt0.92Ru0.08, Pt0.85Ru0.15, and Ru under potentiodynamic conditions. The electrodes with defined bulk and surface compositions were made by electrodeposition on porous Au substrates. Cyclic voltammetry in combination with on-line mass spectrometry (DEMS) was employed to correlate faradaic currents with ion currents associated to reaction products. The formation of both CO2 and ethanal was unequivocally identified during ethanol oxidation on PtRu and Pt by using d3-ethanol. On pure Ru neither faradaic currents were observed nor oxidation/reduction products could be detected by mass spectrometry. The reduction of ethanol on Pt and PtRu to methane and ethane was found in the potential range of hydrogen adsorption. The yields of oxidation and reduction products and the corresponding onset potentials for their formation are greatly influenced by the Ru content. Alloys with high Ru content exhibit a lower reaction rate for ethanol electrooxidation. On the other hand, the selectivity for ethanal production is significantly enhanced for PtRu as compared to pure Pt.
Journal of Power Sources, 2015
h i g h l i g h t s g r a p h i c a l a b s t r a c t Mesoporous Pt material (MPPt) was successfu... more h i g h l i g h t s g r a p h i c a l a b s t r a c t Mesoporous Pt material (MPPt) was successfully modified by Sn adatoms (MPPt/Sn). The CO tolerance was evaluated at MPPt, MPPt/Sn and commercial Pt 3 Sn/C catalysts. The catalytic activity toward methanol oxidation for all electrodes was evaluated. CO and methanol oxidation reactions were studied at 25 and 60 C by DEMS. Energy conversion efficiency from methanol to CO 2 for all catalysts was calculated.
Electrocatalysis, 2011
Pt nanoparticles with bi-dimensional geometry and circular shape have been synthesized and studie... more Pt nanoparticles with bi-dimensional geometry and circular shape have been synthesized and studied by in situ Fourier transform infrared spectroscopy, scanning tunneling microscopy, CO stripping voltammetry, cyclic voltammetry, and methanol oxidation in acidic and alkaline media. The experimental results suggest that Pt nanodiscs present a bi-dimensional (111) order domain on the surface and a high density of step edge sites mainly with and (100) orientations. A clear correlation between the atomic surface arrangement and the catalytic activity towards the CO and methanol oxidation, as well as the voltammetric profiles in the electrolyte, was observed. Additionally, infrared spectra proved the high density of low-coordinated Pt atoms present in the nanoparticle and that CO adsorbed in linear configuration is the main adsorbate. The electrochemical study was compared with that of spherical Pt particles supported on carbon (Pt/C 20 wt.%, Etek).
The Journal of Physical Chemistry C, 2013
ABSTRACT PtRu catalysts were prepared using a highly mesoporous carbon xerogel submitted to diffe... more ABSTRACT PtRu catalysts were prepared using a highly mesoporous carbon xerogel submitted to different oxygen functionalization treatments: diluted and concentrated nitric acid as well as gas-phase 5% O2–N2 oxidation. Catalysts with 20 wt % loading and equimolar Pt:Ru metallic phase were prepared using an impregnation procedure involving chemical reduction with formic acid. The so-obtained carbon materials, as well as the different catalysts synthesized, were characterized by means of N2 physisorption, temperature-programmed desorption (TPD), X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Cyclic voltammetry and chronoamperometry were performed to study their activity toward carbon monoxide and methanol oxidation. Functionalization of the carbon support was found to play a definitive role in the interaction between carbon material and the active phase, determining metallic dispersion, alloying degree, and reduction extent. The activity of the catalysts in methanol electro-oxidation was directly related to the metal oxidation state and alloying degree.
Sensor Letters, 2008
ABSTRACT Platinum nanoparticles supported on functionalized carbon nanofibers (CNFs) have been pr... more ABSTRACT Platinum nanoparticles supported on functionalized carbon nanofibers (CNFs) have been prepared as electrocatalyst for Proton Exchange Membrane Fuel Cells. CNFs, obtained by catalytic decomposition of methane over a high-nickeled catalyst, were pre-oxidised to create oxygen surface groups under treatments of different severity with liquid oxidising agents. Pt was then deposited by ion exchange of Pt(NH3)4Cl2 in neutral and basic media, and reduced under a hydrogen flow at 350 °C. It was observed that deposited platinum increases with both the quantity of oxygen groups and pH of the precursor solution. The maximum Pt loading was 2.2 wt%, deposited on CNFs treated with a mixture of nitric and sulphuric acid for 0.5 h at boiling temperature. Platinum particles, characterized by transmission electron microscopy, X-ray diffraction and CO chemisorption, were well dispersed and their average size was smaller than 3 nm in most of the samples. Finally, electrochemical studies showed that these catalysts, even with a low Pt loading on the carbon nanofibers, present high electrocatalytic activity towards methanol oxidation.
Langmuir, 2000
ABSTRACT Acetaldehyde oxidation at Pt(111) and Pt(100) follows at least two parallel reaction pat... more ABSTRACT Acetaldehyde oxidation at Pt(111) and Pt(100) follows at least two parallel reaction pathways leading to CO2 and acetic acid as soluble products. The former is produced via strongly adsorbed intermediates. Besides adsorbed CO, also species containing two C atoms, possibly η1-acetaldehyde and η1-acetyl, are formed. These species are strongly bonded to the surface. None of these adsorbates are the intermediate leading to the formation of acetic acid.
Langmuir, 2002
ABSTRACT The electrochemical behavior of ethanol and acetaldehyde was studied at rhodium electrod... more ABSTRACT The electrochemical behavior of ethanol and acetaldehyde was studied at rhodium electrodes in acid solutions using electrochemical mass spectrometry (DEMS). Acetaldehyde and CO2 were detected from bulk ethanol, whereas only CO2 was recorded from acetaldehyde. The production of acetic acid could not be confirmed with this method. The formation of methane was established from both molecules, which suggests that the fragmentation of the C−C chain occurs during the electroreduction and/or adsorption processes. Adsorbed species were isolated by applying a flow cell procedure. The residues produce CO2 and methane during oxidation and reduction reactions, respectively, the amount of these compounds depending on the adsorption potential. By use of isotopic labeled 12CH313CH2OH and 12CH313CHO, the contribution of each C atom in the adsorbate was distinguished. It was established that the CH3 group oxidizes at potentials within the O adsorption potential region of rhodium during the positive-going sweep and also at E < 0.60 V during the reverse scan. The CH2OH or CHO groups yield CO2 in the same potential region as COad. The influence of the anion on these reactions was established using sulfuric and perchloric acids as base electrolytes, being noticeable for ethanol adsorption. Compared to Pt, Rh electrodes exhibit an enhanced activity for deprotonation and C−C cleavage reactions.
Journal of Power Sources, 2013
Carbon nanocoils (CNCs) were proposed as electrocatalysts support. Electrocatalyst' performance s... more Carbon nanocoils (CNCs) were proposed as electrocatalysts support. Electrocatalyst' performance strongly depended on the synthesis method. CNCs-supported showed better electrochemical behaviour than E-TEK electrocatalysts. By using CNCs as support the reaction route of intermediates is favoured. Intermediates oxidation is facilitated by the use of CNCs as support.
Journal of Natural History, 2008
... biological diversity in the Mediterranean]. Paper presented at: UNEP(OCA)/MED IG 10/4;. 2 Dec... more ... biological diversity in the Mediterranean]. Paper presented at: UNEP(OCA)/MED IG 10/4;. 2 December 1996 , Monaco. View all references) due to over exploitation, as it is now captured very rarely. Information available on the ...
Journal of The Electrochemical Society, 2001
ABSTRACT Electrochemical and nonelectrochemical reactions of the H2O2/CO system on a Pt electrode... more ABSTRACT Electrochemical and nonelectrochemical reactions of the H2O2/CO system on a Pt electrode were studied in 2 M H2SO4 with cyclic voltammetry and on-line mass spectrometry. It was found that a complete CO monolayer is chemically stable in the presence of dissolved H2O2. However, H2O2 oxidizes adsorbed CO to CO2 at lower potentials than those required for electrochemical CO adsorbate oxidation when the Pt electrode is partially covered by CO. Furthermore, it was observed that a complete CO monolayer on Pt inhibits the electrochemical reduction of H2O2 to H2O in CO-containing electrolyte.
Journal of Electroanalytical Chemistry, 1999
ABSTRACT The electrochemical behavior of propargyl alcohol (PA) on palladium electrodes in 0.1 M ... more ABSTRACT The electrochemical behavior of propargyl alcohol (PA) on palladium electrodes in 0.1 M HClO4 was studied by differential electrochemical mass spectrometry (DEMS). Experiments with the alcohol present in the bulk of the solution have shown that the sole oxidation product is CO2. During potential cycling in the hydrogen adsorption/absorption region, C3- (propylene and propane) and C2- (ethane and traces of ethene/ethyne) hydrocarbons, as well as allyl alcohol, were produced. On the other hand, PA forms strongly bonded species on palladium which can be studied using a flow cell procedure. The maximum adsorption of PA was observed in the potential range 0.25–0.65 V. As for bulk studies, only CO2 was detected during the oxidation of the residues. However, some differences should be mentioned in respect of the reduction reactions: only propane, propylene and allyl alcohol were observed from the adlayer. According to these results, and taking into account the values of the charges involved in the adsorption (Qt) and oxidation (Qox) processes, different structures were proposed for the adsorbed species. From these structures, the formation of the reduction products was justified. Results were compared with previously reported data for platinum and gold in acid media.
Journal of Electroanalytical Chemistry, 1999
The oxidative ethanol adsorption and electrochemical surface reactions of adsorbed intermediates ... more The oxidative ethanol adsorption and electrochemical surface reactions of adsorbed intermediates were studied on electrodeposited Pt, Ru, Pt 0.92 Ru 0.08 and Pt 0.85 Ru 0.15 in 1 M HClO 4 . A flow cell procedure was performed in order to separate surface reactions of intermediates formed in the oxidative ethanol adsorption from those reactions for ethanol in the bulk electrolyte solution. Oxidation and reduction reactions of adsorbed species were studied by potential-controlled electrodesorption spectrometry. No adsorbate formation was observed on a pure Ru electrode. In all cases, CO 2 was the sole product formed in the oxidative electrodesorption of the adsorbates. Using 12 CH 3 12 CH 2 OH and 12 CH 3 13 CH 2 OH, the oxidation reaction pathways of each C-atom to CO 2 were followed. On the other hand, methane and ethane were detected during the reductive electrodesorption of adlayer species. The onset potential for these reduction products shifts to more negative potentials as the Ru content of the alloy increases. The methane to ethane yield ratio decreases in the sequence Pt \ Pt 0.92 Ru 0.08 \ Pt 0.85 Ru 0.15 . A critical interpretation of the experimental data leads to a tentative yield of different adsorbed species as function of the Ru surface concentration.