Activity For CO Electro-oxidation Research Articles

Restructuring of 4H phase Au nanowires and its catalytic behavior toward CO electro-oxidation

Au nanowires in 4H crystalline phase (4H Au NWs) are synthesized by colloid solution methods. The crystalline phase and surface structure as well as its performance toward electrochemical oxidation of CO before and after removing adsorbed oleylamine molecules (OAs) introduced from its synthesis are evaluated by high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), underpotential deposition of Pb (Pb-upd) and cyclic voltammetry. Different methods, i.e. acetic acid cleaning, electrochemical oxidation cleaning, and diethylamine replacement, have been tried to remove the adsorbed OAs. For all methods, upon the removal of the adsorbed OAs, the morphology of 4H gold nanoparticles is found to gradually change from nanowires to large dumbbell-shaped nanoparticles, accompanying with a transition from the 4H phase to the face-centered cubic phase. On the other hand, the Pb-upd results show that the sample surfaces have almost the same facet composition before and after removal of the adsorbed OAs. After electrochemical cleaning with continuous potential scans up to 1.3 V, CO electro-oxidation activity of the 4H Au sample is significantly improved. The CO electro-oxidation activity is compared with results on the three basel Au single crystalline surfaces reported in the literature, possible origins for its enhancement are discussed.

Atomic scale insights on the electronic and geometric effects in the electro-oxidation of CO on PtxRu1-x/Ru(0001) surface alloys

The enhanced activity of various bimetallic catalysts/electrodes in electrocatalytic reactions is usually ascribed to a bifunctional mechanism. This seems to neglect other effects arising from electronic modifications and further geometric effects, which are known to strongly affect the interaction of these surfaces with adsorbed species. In this work we elucidate the role of electronic and geometric effects on the activity of structurally well-defined PtRu electrodes in the bulk CO oxidation reaction, using model electrodes prepared and structurally characterized on an atomic scale by scanning tunneling microscopy under ultrahigh vacuum (UHV) conditions. Samples include PtxRu1-x/Ru(0001) surface alloys with varying Pt content consisting of a Ru(0001) substrate and a PtxRu1-x alloy surface layer as well as a Ru(0001) electrode covered by a pseudomorphic Pt monolayer (x = 1), and Pt(111) for comparison. Comparing the structural/chemical properties and the relative abundance of specific PtnRum ensembles on the electrode surfaces with the respective bulk CO electro-oxidation activity enabled us to identify Pt1Ru3 ensembles as the most active ensembles under the present conditions. The importance of electronic and geometric ensemble effects are discussed. The results demonstrate that the reactivity of bimetallic surfaces is much more complex than described by the classical bifunctional mechanism, which is proposed as a general feature.

Reductive-heat-treated platinum tungsten oxide catalyst with improved CO oxidation activity and CO gas sensing property

Reductive-heat-treated platinum tungsten oxide presented excellent CO electro-oxidation activity and was applied in electrochemical CO gas sensing method.

In situ electrochemical surface-enhanced Raman spectroscopy study of CO electrooxidation on PtFe nanocatalysts

Combination of spectroscopic techniques with electrochemistry is a promising way to elucidate electrocatalytic mechanisms at a molecular level. Surface-enhanced Raman spectroscopy (SERS) is a non-destructive, ultrasensitive fingerprint technique that can detect metal–adsorbate and metal oxide vibrations. However, it is hard to study nanocatalysts because of the morphology limitation of SERS. In this paper, core-shell-satellite nanostructures have been fabricated by assembling PtFe nanocatalysts on shell-isolated nanoparticles (SHINs). CO electrooxidation on these nanostructures was studied by in situ electrochemical shell-isolated nanoparticle-enhanced Raman spectroscopy (EC-SHINERS). The in situ spectroscopic results correlate well with the results obtained using cyclic voltammetry, and show that PtFe bimetallic nanocatalysts have improved CO electrooxidation activity. The in situ SHINERS studies also show that this improvement is the result of weaker CO adsorption on PtFe compared to Pt, as revealed by the red shift of the Raman band of the PtC stretching vibration on PtFe. This work demonstrates that this method is a powerful tool for in situ investigation of the electrocatalytic processes occurring on nanocatalysts and provides a better understanding of the reaction mechanisms.

Synthesis and evaluation of CO electro-oxidation activity of carbon supported SnO2, CoO and Ni nano catalysts for a PEM fuel cell anode

Fuel contaminants especially CO which have poisoning effect on anodic catalysts, are the main barriers to commercialization of PEM fuel cell technology. Many efforts have been done to discount the CO poisoning effect on anodic catalysts. The non-noble metal elements capability for CO electro-oxidation per-se has not been fully evaluated. In this paper, properties of non-noble metal catalysts for CO electro-oxidation were studied. To do this, carbon supported nano-catalysts of SnO2, Ni and CoO were synthesized via the borohydride reduction method. Their electrochemical activity for CO electro-oxidation was evaluated in an in-house made half-cell using a new electrochemical test procedure based on recording CV current under continuous CO gas flow over the catalyst surface. Then, electrochemical tests on the synthesized catalysts and commercial Pt20/C were performed. The max current charge obtained from CO electro-oxidation with commercial Pt20/C was 13,200 μA per mg of metal at 0.74 V and for SnO2/C, CoO/C and Ni/C were 630, 450 and 140 μA per mg of metal, respectively. These amounts were obtained at 0.58, 0.43 and 0.26 V. Results proved the capability of CoO/C and SnO2/C to perform the CO electro-oxidation reaction at low potentials in a PEM fuel cell anode condition.

Pt catalysts on PANI coated WC/C nanocomposites for methanol electro-oxidation and oxygen electro-reduction in DMFC

In the present study a Pt/PANI/WC/C electrocatalyst was developed to increase the methanol electro-oxidation and oxygen electro-reduction activity and stability of commercial Pt/C electrocatalyst. WC/C was coated with protonated polyaniline (PANI) in situ during the polymerization of aniline. Fourier transform infrared (FTIR) results illustrate the presence of PANI in the composite. The conductivity of PANI coated – WC/C has been compared with the conductivity of the corresponding mixtures of WC/C and Vulcan XC-72. X-ray diffraction results showed that Pt particles were dispersed on the support with mean particle size of about 10.56nm. Transition electron microscopy images showed that the nanosized WC/C were successfully coated by PANI. Based on the electrochemical properties characterized by cyclic voltammetry, CO stripping and rotating disk electrode measurements it was found that the as prepared Pt/PANI/WC/C electrocatalyst exhibited a comparable activity for methanol oxidation reaction and oxygen reduction reaction with respect to the commercial one. A significant reduction in the potential of CO electro-oxidation peak from 0.75V for Pt/C to 0.52V for Pt/PANI/WC/C electrocatalyst indicates that an increase in the activity for CO electro-oxidation is achieved by replacing the carbon support by PANI coated WC/C. Chronoamerometry results also showed, in the presence of methanol the Pt/PANI/WC/C electrocatalyst still maintains a higher current density than Pt/WC/C and Pt/C.

RhPt/graphite catalysts for CO electrooxidation: Performance of mixed metal and alloyed surfaces

Cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS) have been used to characterise novel PtRh mixed metal and surface alloyed active phases supported on 5% Pt/graphite catalysts (5% Pt/G). The active phases could be prepared using forced deposition or a combination of forced deposition and thermal annealing in a flowing 5% hydrogen in argon gas mixture at 700 K. The protocols employed originate directly from previous single crystal studies of Rh on Pt{100} whereby Rh overlayers (either singly adsorbed or as a ‘sandwich structure’ of alternate Pt/Rh/Pt layers) could be transformed into surface PtRh alloys by careful thermal annealing. We demonstrate that this method is also successful for the preparation of active supported catalysts for CO electrooxidation whereby a peak potential as low as 0.60 V (Pd/H) for the CO oxidation is reported (0.12 V lower than that on 5% Pt/G). Moreover, the onset potential for CO stripping is lowered to 0.33 V (Pd/H). The presence of alloyed PtRh phases gives rise to a small but reproducible 0.1–0.2 eV shift to higher binding energy of the Pt 4f 7/2 XPS peak together with strongly modified Pt and Rh electrosorption features in the CV which correlate with changes in surface composition. Unusual kinetic behaviour in the CO stripping peaks from the PtRh catalyst as a function of CO coverage is ascribed to competition between electrochemical oxide on Rh and CO-induced blocking of electrochemical oxide formation sites at the highest CO coverage. For PtRh alloys, the onset of electrochemical oxide formation shifts to more positive potentials relative to Rh overlayers and so a different behaviour towards CO electrooxidation is observed. • Novel synthesis method for Rh adlayers and PtRh alloys on graphite supported Pt. • CV and XPS characterisation of PtRh alloys as a function of composition. • CO electrooxidation kinetics on Rh adlayer and RhPt alloys are different. • Marked CO electrooxidation activity for PtRh alloys compared to pure Pt.

Electrocatalytic activity of surface oxides on platinum nanofacets and surfaces

We investigated electrochemical behavior of surface oxides of platinum formed by annealing in air. We studied the catalytic activity for CO electrooxidation using electrochemical, X-ray, and DFT methods. We find that all oxidized platinum surfaces are highly active initially for CO electrooxidation reaction in so-called preignition region. While the high activity of the monolayer oxide formed on extended Pt surfaces decreases after the initial CO-oxidation cycle, bilayer oxide formed on nanoscaled facets sustain the high CO electrooxidation activity. DFT calculations show that OH binds, as strongly to bilayer surface oxides as to metallic surface while CO does not, suggesting the bifunctional property of the bilayer oxide surface.

일산화탄소 산화를 위한 PtRu/C 시리즈 촉매의 합성 및 특성 연구

The electrocatalytic oxidation of CO was studied using carbon-supported 20 wt% PtRu (PtRu/C) catalysts, which were prepared with different Pt : Ru atomic ratios from 7 : 3 to 3 : 7 using a colloidal method combined with a freeze-drying procedure. The bimetallic PtRu/C catalysts were characterized by various physicochemical analyses, including X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). CO stripping voltammetry measurements indicated that the addition of Ru with a Pt catalyst significantly improved the electrocatalytic activity for CO electrooxidation. Among the tested catalysts, the Pt5Ru5/C catalyst had the lowest onset potential (vs.Ag/AgCl) and the largest CO EAS. Structural modification via lattice parameter change and electronic modification in the unfilled d band states for Pt atoms may facilitate the electrooxidation of CO.

Facile synthesis of Pt nanocrystals/graphene composite with excellent methanol electro-oxidation performance

Platinum nanocrystals/graphene nanosheets (Pt-NCs/GNS) composite has been synthesized by a chemical reduction of PtCl62− with formic acid (HCOOH) at room temperature. TEM analyses indicate that most of the Pt-NCs with a length of 10nm and width of 5nm has uniformly growth along the graphene basal plane, making the effective contact of Pt and graphene, which would be favorable for enhancing the utility of Pt catalyst. Electrochemical tests show that the current density of the resulting Pt/GNS catalyst for methanol electro-oxidation is up to 412.6Ag−1 Pt, which is about 2.3 times as that of the commercial Pt/C(JM) catalyst. Moreover, the Pt/GNS catalyst exhibits better durability toward methanol electro-oxidation and outstanding CO electro-oxidation activity than the commercial Pt/C(JM) catalyst.

Platinum Activity for CO Electrooxidation: from Single Crystal Surfaces to Nanosurfaces and Real Fuel Cell Nanoparticles

The understanding of CO oxidation on platinum catalysts is a key point in several low-temperature fuel cell technologies: direct-alcohol fuel cells or proton-exchange membrane fuel cell fed with reformate hydrogen, for example. For this purpose, studies were carried out on different platinum surfaces, from single crystals surfaces with a well-defined orientation to platinum nanoparticle polyoriented surfaces. This article presents the CO electrooxidation on surfaces of Pt single crystals and Pt nanoparticles with different orientations and size ranges. The study of CO oxidation was completed with in situ reflectance spectroscopy coupled to electrochemical methods. The confrontation of CO oxidation behaviours observed on electrodes with oriented surfaces at macroscopic and nanoscopic size ranges allowed establishing a correlation between the surface structure and the CO oxidation voltammetric features.

Radiolytic Synthesis of Pt-Ru Catalysts Based on Functional Polymer-Grafted MWNT and Their Catalytic Efficiency for CO and MeOH

Pt-Ru catalysts based on functional polymer-grafted MWNT (Pt-Ru@FP-MWNT) were prepared by radiolytic deposition of Pt-Ru nanoparticles on functional polymer-grafted multiwalled carbon nanotube (FP-MWNT). Three different types of functional polymers, poly(acrylic acid) (PAAc), poly(methacrylic acid) (PMAc), and poly(vinylphenyl boronic acid) (PVPBAc), were grafted on the MWNT surface by radiation-induced graft polymerization (RIGP). Then, Pt-Ru nanoparticles were deposited onto the FP-MWNT supports by the reduction of metal ions usingγ-irradiation to obtain Pt-Ru@FP-MWNT catalysts. The Pt-Ru@FP-MWNT catalysts were then characterized by XRD, XPS, TEM ,and elemental analysis. The catalytic efficiency of Pt-Ru@FP-MWNT catalyst was examined for CO stripping and MeOH oxidation for use in a direct methanol fuel cell (DMFC). The Pt-Ru@PVPBAc-MWNT catalyst shows enhanced activity for electro-oxidation of CO and MeOH oxidation over that of the commercial E-TEK catalyst.

Investigation of Pt/WC/C catalyst for methanol electro-oxidation and oxygen electro-reduction

A Pt/WC/C catalyst is developed to increase the methanol electro-oxidation (MOR) and oxygen electro-reduction (ORR) activities of the Pt/C catalyst. Cyclic voltammetry and CO stripping results show that spill-over of H + occurs in Pt/WC/C, and this is confirmed by comparing the desorption area values for H + and CO. A significant reduction in the potential of the CO electro-oxidation peak from 0.81 V for Pt/C to 0.68 V for Pt/WC/C is observed in CO stripping test results. This indicates that an increase in the activity for CO electro-oxidation is achieved by replacing the carbon support with WC. Preferential deposition of Pt on WC rather than on the carbon support is investigated by complementary analysis of CO stripping, transmission electron microscopy and concentration mapping by energy dispersive spectroscopy. The Pt/WC/C catalyst exhibits a specific activity of 170 mA m −2 for MOR. This is 42% higher than that for the Pt/C catalyst, viz., 120 mA m −2. The Pt/WC/C catalyst also exhibits a much higher current density for ORR, i.e., 0.87 mA cm −2 compared with 0.36 mA cm −2 for Pt/C at 0.7 V. In the presence of methanol, the Pt/WC/C catalyst still maintains a higher current density than the Pt/C catalyst.

Radiolytic Deposition of Pt-Ru Catalysts on the Conductive Polymer Coated MWNT and their Catalytic Efficiency for CO and MeOH

Pt-Ru@CP-MWNT catalysts were prepared by radiolytic deposition of Pt-Ru nanoparticles on conduction polymer (CP) coated multi walled carbon nanotubes (MWNTs) surfce. Three different types of conducting polymers; polypyrrole(PPy), polyaniline(PANI), and polythiophene (PTh), were coated on the MWNTs surface by in situ polymerization. Then Pt-Ru nanoparticles were deposited onto CP-MWNTs composite by the reduction of metal ions using gamma-irradiation to obtain Pt-Ru@CP-MWNT catalysts. The size, morphology and composition of Pt-Ru@CP-MWNT catalysts were characterized by SEM, TEM and elemental analysis. The catalytic efficiency of Pt-Ru@CP-MWNT catalyst was examined for CO stripping. Pt-Ru@PPy-MWNT and Pt-Ru@PANI-MWNT electrodes show enhanced activity for electrooxidation of CO and methanol over Pt-Ru@PTh-MWNT catalyst.

CO Oxidation on Gold in Acidic Environments: Particle Size and Substrate Effects

The electrooxidation of carbon monoxide on titania- and carbon-supported gold nanoparticles of mean diameters <6.5 nm was studied in 0.5 M HClO4. The samples were prepared by physical vapor deposition, and the activity of the supported particles compared with the reaction at bulk, polycrystalline gold. Carbon-supported gold exhibited activity for CO oxidation only at potentials similar to that observed for bulk gold. Decreasing the particle size below ∼2.5 nm resulted in a sharp decay in catalytic activity. Titania-supported gold exhibited catalytic activity at overpotentials significantly below those of bulk gold, and the activity was strongly particle-size-dependent. A maximum in activity was observed at ∼3.0 nm, and a sharp reduction in activity is observed below ∼2.5 nm. The results highlight two important effects. Titania is responsible for a strong substrate-induced activity for CO electrooxidation on gold particles. In addition to the induced activity at low overpotentials, this titania-supported g...

Size effect of gold nanoparticles on the electrocatalytic oxidation of carbon monoxide in alkaline solution

This paper describes preliminary findings of Au nanoparticle on glassy carbon (GC) electrodes for electro-oxidation of carbon monoxide in basic conditions. Electrochemical cyclic voltammetric results showed that CO oxidation simultaneously occurred in the anodic and cathodic sweeps during one cycle, and CO electro-oxidation activity was remarkably different in the anode for the different sized Au nanoparticles. The ultrafine catalyst metal particles (2 and 6 nm Au) were more active compared to the larger ones (12, 24 and 41 nm Au). The dependence of the activity on the particle size can be explained in terms of their effect on the number of active sites and the different surface gold oxide species.

The Effect of the Particle Size on the Kinetics of CO Electrooxidation on High Surface Area Pt Catalysts

Using high-resolution transmission electron microscopy (TEM), infrared reflection-absorption spectroscopy (IRAS), and electrochemical (EC) measurements, platinum nanoparticles ranging in size from 1 to 30 nm are characterized and their catalytic activity for CO electrooxidation is evaluated. TEM analysis reveals that Pt crystallites are not perfect cubooctahedrons, and that large particles have "rougher" surfaces than small particles, which have some fairly smooth (111) facets. The importance of "defect" sites for the catalytic properties of nanoparticles is probed in IRAS experiments by monitoring how the vibrational frequencies of atop CO (nu(CO)) as well as the concomitant development of dissolved CO(2) are affected by the number of defects on the Pt nanoparticles. It is found that defects play a significant role in CO "clustering"on nanoparticles, causing CO to decrease/increase in local coverage, which yields to anomalous redshift/blueshift nu(CO) frequency deviations from the normal Stark-tuning behavior. The observed deviations are accompanied by CO(2) production, which increases by increasing the number of defects on the nanoparticles, that is, 1 < or = 2 < 5 << 30 nm. We suggest that the catalytic activity for CO adlayer oxidation is predominantly influenced by the ability of the surface to dissociate water and to form OH(ad) on defect sites rather than by CO energetics. These results are complemented by chronoamperometric and rotating disk electrode (RDE) data. In contrast to CO stripping experiments, we found that in the backsweep of CO bulk oxidation, the activity increases with decreasing particle size, that is, with increasing oxophilicity of the particles.