COads Stripping Voltammetry Research Articles

Preparation of Pt electrocatalyst supported by novel, Ti(1\u2212x)MoxO2-C type of composites containing multi-layer graphene

Ball milling is a relative simple and promising technique for preparation of inorganic oxide–carbon type of composites. Novel TiO2-C and Ti0.8Mo2O2-C type of composites containing multi-layer graphene were prepared by ball milling of graphite in order to get electrocatalyst supports for polymer electrolyte membrane fuel cells. Starting rutile TiO2 was obtained from P25 by heat treatment. Carbon-free Ti0.8Mo2O2 mixed oxide, prepared using our previously developed multistep sol–gel method, does not meet the requirements for materials of electrocatalyst support, therefore parent composites with Ti0.8Mo2O2/C = 75/25, 90/10 and 95/5 mass ratio were prepared using Black Pearls 2000. XRD study of parent composites proved that the oxide part existed in rutile phase which is prerequisite of the incorporation of oxophilic metals providing CO tolerance for the electrocatalyst. Ball milling of TiO2 or parent composites with graphite resulted in catalyst supports with enhanced carbon content and with appropriate specific surface areas. XRD and Raman spectroscopic measurements indicated the changes of graphite during the ball milling procedure while the oxide part remained intact. TEM images proved that platinum existed in the form of highly dispersed nanoparticles on the surface of both the Mo-free and of Mo-containing electrocatalyst. Electrocatalytic performance of the catalysts loaded with 20 wt% Pt was studied by cyclic voltammetry, COads-stripping voltammetry done before and after the 500-cycle stability test, as well as by the long-term stability test involving 10,000 polarization cycles. Enhanced CO tolerance and slightly lower stability comparing to Pt/TiO2-C was demonstrated for Pt/Ti0.8Mo2O2-C catalysts.

Effect of the reductive treatment on the state and electrocatalytic behavior of Pt in catalysts supported on Ti0.8Mo0.2O2-C composite

Ti(1-x)MoxO2-carbon composites are promising new supports for Pt-based electrocatalysts in polymer electrolyte membrane fuel cells offering exciting catalytic properties and enhanced stability against electrocorrosion. Pt and the mixed oxide form a couple liable for strong metal-support interaction (SMSI) phenomenon, generally manifesting itself in decoration of the metal particles by ultrathin layers of the support material upon annealing under reductive conditions. The aim of this work is to evaluate the SMSI phenomenon as a potential strategy for tailoring the properties of the electrocatalyst. A 20 wt% Pt/50 wt% Ti0.8Mo0.2O2-50 wt% C electrocatalyst prepared on Black Pearls 2000 carbon functionalized with HNO3 and glucose was reduced at 250 °C in H2 in order to induce SMSI. The electrocatalytic properties and the stability of the reduced and the original catalysts were analyzed by cyclic voltammetry and COads stripping voltammetry. Structural investigations as well as X-ray photoelectron spectroscopy (XPS) measurements were performed in order to obtain information about the details of the interaction between the oxide and the Pt particles. The electrochemical experiments pointed out a small loss of the electrochemically active surface area of Pt in the reduced catalyst along with enhanced stability with respect to the original one, while structural studies suggested only a minimal decrease of the Pt dispersion. At the same time, hydrogen exposure experiments combined with XPS demonstrated the presence of Mo species directly adsorbed on the Pt surface. Thus, the properties of the reduced catalyst can be traced to decoration of the surface of Pt by Mo-containing species.

Stability issues of CO tolerant Pt-based electrocatalysts for polymer electrolyte membrane fuel cells: comparison of Pt/Ti0.8Mo0.2O2–C with PtRu/C

The stability and CO tolerance of a self-made 20 wt% Pt/Ti0.8Mo0.2O2–C mixed oxide–carbon composite supported electrocatalyst was compared to those of a commercial state-of-the-art PtRu/C electrocatalyst by means of cyclic voltammetry and COads stripping voltammetry measurements. On the Pt/Ti0.8Mo0.2O2–C catalyst the oxidation of CO takes place at exceptionally low potential values (ECO,onset = 50 mV); the onset potential is shifted to less positive potentials by 150 mV compared to the PtRu/C catalyst. A stability test involving 500 polarization cycles revealed that the PtRu/C catalyst suffered more significant degradation than the composite supported Pt catalyst. XPS measurements indicated that the degradation is connected to ruthenium dissolution. At the same time, better electrocatalytic stability and increased CO tolerance of the Pt/Ti0.8Mo0.2O2–C electrocatalyst compared to the PtRu/C catalyst was evidenced.

Superior electrocatalytic activity of Pt[sbnd]SrCoO3−δ nanoparticles supported on functionalized reduced graphene oxide-chitosan for ethanol oxidation

Here, SrCoO3−δ was synthesized through a sol gel method and characterized with X-ray powder diffraction and scanning electron microscopy techniques. Graphene oxide was synthesized by a modified Hummers' method, then functionalized with 1, 1′-dimethyl-4, 4′-bipyridinium dichloride (methyl viologen) accompanied by Chitosan to prepare novel MV-RGO-CH. This was used as a support for nanoparticles to get PtSrCoO3−δ/MV–RGO-CH nanocomposite. Transmission electron microscopy image was used to show the morphology and distribution of nanoparticles. The electrocatalytic activity of PtSrCoO3−δ/MV–RGO-CH nanocomposite for ethanol electrooxidation was investigated by cyclic voltammetry, chronoamperometry, COads stripping voltammetry and electrochemical impedance spectroscopy techniques. The effects of some experimental factors for ethanol oxidation on the prepared nanocomposite were investigated and the optimum conditions were suggested. PtSrCoO3−δ/MV–RGO-CH nanocomposite showed higher catalytic activities than Pt/MV–RGO-CH for ethanol electrooxidation indicating that PtSrCoO3−δ/MV–RGO-CH nanocomposite could be a promising catalyst for direct ethanol fuel cells applications.

Electrocatalytic activity of Pt nanoparticles supported on novel functionalized reduced graphene oxide-chitosan for methanol electrooxidation

Here, graphene oxide (GO) was synthesized by a modified Hummers’ method and was functionalized with 1,1′-dimethyl-4,4′-bipyridinium dichloride (MV) accompanied by chitosan (CH) to prepare a novel MV-RGO-CH support. Pt/MV-RGO-CH catalyst was prepared by immobilization of the Pt nanoparticles on MV-RGO-CH support. The microstructure and morphology of the prepared catalyst was characterized by transmission electron microscopy and X-ray powder diffraction analysis. The electrocatalytic activity of Pt/MV-RGO-CH catalyst was investigated for methanol electrooxidation through cyclic voltammetry (CV), COads stripping voltammetry, chronoamperometry, and electrochemical impedance spectroscopy (EIS) techniques. The effects of some experimental factors for methanol electrooxidation such as methanol concentration, scan rate and temperature were studied at the prepared catalyst. Durability of the catalyst was also investigated. Comparing the catalytic activity of the Pt/MV-RGO-CH nanocatalyst with Pt/CH and Pt/MV-RGO catalysts indicated that Pt/MV-RGO-CH has a very good catalytic activity for methanol electrooxidation.

Origin of Superior Activity of Ru@Pt Core-Shell Nanoparticles towards Hydrogen Oxidation in Alkaline Media

Platinum shows an exceptionally high activity for the hydrogen oxidation reaction (HOR) in acidic environment,[1] enabling ultra-low Pt-loadings on the anode side of proton exchange membrane fuel cells (PEMFCs).[2] Unlike in acid, this reaction is about two orders of magnitude slower on platinum and other platinum metals in alkaline electrolyte,[3]; [4] which has recently been suggested to be due to entropic effects.[5] Amongst other issues, the low HOR activity of Pt-based electrocatalysts in alkaline environment hinders the development of anion exchange membrane fuel cells (AEMFCs).[4] Bimetallic Pt-Ru catalysts were demonstrated to exhibit significantly higher HOR activities in acid[6]; [7] and base[8]–[10] compared to Pt catalysts. One hypothesis for the high HOR activity of Pt-Ru alloys in base is a bi-functional mechanism,[9]; [10] with hydrogen being adsorbed on Pt and hydroxide being supplied by more oxophilic Ru, whereby the presence of hydroxide in the vicinity of Pt-Hads would accelerate the rate of the hydrogen oxidation. The second hypothesis considers a modification of the electronic structure of platinum by ruthenium,[8] leading to a lower Pt-Hads binding energy and ultimately to a higher activity of platinum towards the oxidation of hydrogen. While the exposure of ruthenium on the surface of the catalyst is absolutely mandatory for a bi-functional mechanism, this is not the case for an activity enhancement due to a modification of the electronic structure of platinum. Based on this fundamental difference, we have attempted to identify the actual HOR mechanism on bimetallic Pt-Ru catalysts by evaluating Ru@Pt core-shell nanoparticles with various Pt-coverages and shell thicknesses. Pt-coverage and shell thickness were determined electrochemically via the Ru-oxide reduction peak and COads stripping voltammetry, a method established by El Sawy et al.[11] Considering a pure, bi-functional mechanism where hydroxide on Ru reacts with Hads on Pt, ruthenium is required to be on the surface of the catalytically active particle. Hence, we expect the highest activity at submonolayer Pt-coverage. For the bifunctional mechanism, covering the whole Ru-surface with Pt would result in a performance equal or similar to that of pure Pt (s. red line in Fig. 1). In contrast to that, for a purely electronic effect, Ru surface atoms would not be required for effective HOR catalysis and one would expect the best performing Ru@Pt catalysts to have a fully Pt-covered Ru surface or even multilayers of Pt; the optimum Pt-shell thickness would mainly depend on the range of the electronic effect (s. black line in Fig. 1). Based on this concept, we will present data to disentangle the mechanism of the hydrogen oxidation on bimetallic Pt-Ru catalysts. The activity of the developed catalysts will be compared to Pt catalysts prepared by the same method with a similar particle size as that of the Ru@Pt core-shell nanoparticles. Acknowledgment The authors of this work thank the microanalytical laboratory at TUM for quick and reliable elemental analysis. References 1 J. Durst; C. Simon; F. Hasche and H. A. Gasteiger, J. Electrochem. Soc., 1, F190-F203 (2015). 2 H. A. Gasteiger; J. E. Panels and S. G. Yan, J. Power Sources, 1-2, 162 (2004). 3 P. J. Rheinlander; J. Herranz; J. Durst and H. A. Gasteiger, J. Electrochem. Soc., 14, F1448–F1457 (2014). 4 W. Sheng; H. A. Gasteiger and Y. Shao-Horn, J. Electrochem. Soc., 11, B1529 (2010). 5 J. Rossmeisl; K. Chan; E. Skúlason; M. E. Björketun and V. Tripkovic, Catalysis Today, 36 (2016). 6 J. X. Wang; Y. Zhang; C. B. Capuano and K. E. Ayers, Scientific reports, 12220 (2015). 7 J. X. Wang; P. He; Y. Zhang and S. Ye, ECS Transactions, 3, 121 (2014). 8 K. Elbert; J. Hu; Z. Ma; Y. Zhang; G. Chen; W. An; P. Liu; H. S. Isaacs; R. R. Adzic and J. X. Wang, ACS Catal., 11, 6764 (2015). 9 S. St. John; R. W. Atkinson; R. R. Unocic; T. A. Zawodzinski and A. B. Papandrew, J. Phys. Chem. C, 24, 13481 (2015). 10 Y. Wang; G. Wang; G. Li; B. Huang; J. Pan; Q. Liu; J. Han; L. Xiao; J. Lu and L. Zhuang, Energy Environ. Sci., 1, 177 (2015). 11 El Sawy, Ehab N.; H. A. El-Sayed and V. I. Birss, Chem. Commun., 78, 11558 (2014). Figure 1

Origin of Superior Activity of Ru@Pt Core-Shell Nanoparticles towards Hydrogen Oxidation in Alkaline Media

There is an ongoing discussion about the nature of the high hydrogen oxidation reaction (HOR) activity of bimetallic Pt-Ru catalysts in alkaline media. We provide an insight on the HOR mechanism for this type of catalyst, excluding bifunctionality as the main driving force for the oxidation of hydrogen. In order to do so, we prepared and evaluated Ru@Pt core-shell nanoparticles with sub-, mono- and multilayered Pt-shells. Rotating disk electrode (RDE) studies in 0.1 M NaOH solution of all prepared catalysts, including Pt/C as a reference show that Ru particles fully encapsulated with a Pt-shell show significantly higher activity than Ru particles that are solely covered with Pt-submonolayers. Furthermore, we found a 4-fold enhancement of Ru@Pt vs. pure Pt with respect to the surface normalized HOR activity. The Ru@Pt catalysts were characterized by COads-stripping voltammetry, as well as cyclic voltammetry (CV) in order to identify the Pt-coverage and shell thickness.

Facile Synthesis of Pt-Cu (Ni, Co)/GNs-CD and Their Enhanced Electro-Catalytic Activity for Methanol Oxidation

In this paper, Pt-Cu (Ni, Co)/GNs-CD composites were prepared through aqueous solution synthesis method with NaBH4 as the reducing agent and β-Cyclodextrin (CD) functionalized graphene nanosheets (GNs-CD) as supporting materials. The introduction of the second metal (Cu, Ni, Co) makes bimetal alloy particles smaller in favor of high surface-to-volume ratios. Catalytic performances of as-prepared Pt-Cu (Ni, Co)/GNs-CD for methanol oxidation reaction (MOR) were investigated by cyclic voltammetry (CV), chronoamperometry, COads stripping voltammetry and electrochemical impedance spectrum (EIS). Compared with Pt/GNs-CD and commercial Pt/C, the Pt-Cu (Ni, Co)/GNs-CD composites exhibit an improved catalytic performance for MOR, suggesting that the introduction of non-precious metal is an effective strategy to improve Pt catalytic capacity. Especially, Pt-Cu/GNs-CD composite shows the best electro-catalytic performance among the as-tested three bimetal alloy catalysts. The superior catalytic activity of Pt-Cu/GNs-CD for MOR derives from the better modification of the electronic properties of Pt atoms and the stability of Pt-Cu alloy in acid media.

Enhanced electrocatalytic activity of Pt nanoparticles supported on functionalized graphene for methanol oxidation and oxygen reduction

Reduced graphene oxide (RGO) is modified with 1,1′-dimethyl-4,4′-bipyridinium dichloride (methyl viologen, i.e. MV) by a π–π interaction, and further used as support for immobilization of Pt nanoparticles to prepare a Pt/MV–RGO catalyst for direct methanol fuel cells. Transmission electron microscopy, X-ray powder diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy are used to characterize the morphology and microstructure of the prepared catalyst. Electrocatalytic performance of the as-prepared Pt/MV–RGO hybrid is investigated by cyclic voltammetry, linear scan voltammetry, COads stripping voltammetry and electrochemical impedance spectroscopy. The Pt/MV–RGO hybrid exhibits much higher catalytic activities than Pt/RGO toward both methanol oxidation and oxygen reduction, suggesting that Pt/MV–RGO hybrid could be a promising electrocatalyst for high-performance direct methanol fuel cells applications.

Pt supported on Nanostructured NCNTs/RGO Composite Electrodes for Methanol Electrooxidation

AbstractComposites consisting of N‐doped carbon nanotubes and reduced graphene oxide (NCNTs/RGO) are prepared directly on carbon cloth (CC) via H2‐assisted thermal reduction of graphene oxide (GO) followed by chemical vapor deposition of NCNTs to form NCNTs/RGO/CC. Pt nanoparticles are uniformly electrodeposited onto these nanostructured composite electrodes. The success of each preparation step is verified by Raman spectroscopy, X‐ray diffraction and scanning electron microscopy, respectively, indicating dense and homogeneous distribution of NCNTs and Pt. The resulting composite electrode exhibits enhanced mass specific activity for methanol oxidation in comparison to Pt‐NCNTs/CC (without RGO), as evaluated by cyclic voltammetry. The ratio of the forward to backward peak current values (if/ib) and the COad stripping voltammetry reveal high tolerance of Pt‐NCNTs/RGO/CC towards poisoning in comparison to Pt‐NCNTs/CC or literature reports, leading to an efficient methanol electrooxidation.

Insight into electrocatalytic stability of low loading Pt-Bi/GC and Pt/GC clusters in formic acid oxidation

Formic acid oxidation was examined on platinum-bismuth deposits on glassy carbon substrate prepared by two-step process, i.e., electrochemical deposition of Bi followed by electrochemical deposition of Pt as described in our previous article (J Electrochem Soc 161:H547–H554, 2014). Upon treatment of as-prepared clusters by slow anodic sweep, bimetallic structure consisting of Bi core occluded by Pt and Bi-oxide was obtained and exhibited significant activity and exceptional stability in HCOOH oxidation. In order to explain such electrocatalytic stability, in this work, the electrochemical properties of Pt@Bi/GC catalyst were investigated applying same protocols in supporting electrolyte with or without HCOOH and compared with Pt/GC. The protocols comprised potentiodynamic, quasi-steady-state, and chronoamperometric measurements combined with the surface characterization by COads stripping voltammetry. Application of potential cycling at Pt@Bi/GC electrode in supporting electrolyte containing HCOOH leads to minor change in surface morphology, mildly leaching of Bi from the electrode surface, and negligible decrease in activity. On the other hand, significant Bi dissolution and considerable decrease in activity are the effects of the same treatment without HCOOH. Contrary to Pt@Bi/GC, Pt/GC electrodes subjected to the same protocols exhibit completely opposite properties being more stabile during potential cycling without HCOOH than in the presence of this acid. Exceptional stability in formic acid oxidation of Pt@Bi/GC catalyst is thus most probably the result of the combination of predominant dehydrogenation path of the reaction, suppressed Bi leaching, and compensation of dissolved Bi from the core as its source due to which surface morphology endured minor changes.

One-step microwave synthesis of Pt (Pd)/Cu2O/GNs composites and their electro-photo-synergistic catalytic properties for methanol oxidation

A facile one-pot method was used to synthesize Pt/Cu2O/GNs and Pd/Cu2O/GNs composites. Pt or Pd nanoparticles are deposited onto graphene sheets (GNs) and Cu2O via synchronous reduction of K2PtCl4 (K2PdCl4), Cu(OH)2 and graphene oxide (GO) with glucose as a reducing agent under microwave irradiation. The formation of Cu2O promotes the nucleation of Pt(0) or Pd(0) particles and favors more complete reduction of PtCl42− or PdCl42−. Catalytic properties of as-prepared composites for methanol oxidation reaction (MOR) were evaluated by cyclic voltammetry (CV), chronoamperometry, COads stripping voltammetry and electrochemical impedance spectrum (EIS). Electrochemical experiments showed that Pt/Cu2O/GNs and Pd/Cu2O/GNs had much higher catalytic activity and stability for MOR and better resistance to CO poisoning compared with the commercially available Johnson Matthey 20% Pt/C catalyst (Pt/C-JM) and Sigma-Aldrich 20% Pd/C catalyst (Pd/C-SA). Especially under the UV irradiation, the total peak current density and catalytic stability of Pt/Cu2O/GNs and Pd/Cu2O/GNs drastically increase, which may result from the synergistic effect between the electro-catalytic and photo-catalytic properties. In brief, the cooperation among Pt (Pd), Cu2O and GNs promotes remarkably the catalytic performance for MOR on Pt/Cu2O/GNs and Pd/Cu2O/GNs either without light or with UV irradiation.

A green one-pot synthesis of Pt/TiO2/Graphene composites and its electro-photo-synergistic catalytic properties for methanol oxidation

A facile and green one-pot method was used to synthesize Pt/TiO2/Graphene composites with ethanol as a reducing agent under microwave irradiation. The as-prepared composites were characterized by SEM, TEM, EDX, XPS, XRD and Raman. Electrocatalytic performance of the Pt/TiO2/GNs composites was investigated by cyclic voltammetry (CV), chronoamperometric (CA), COad stripping voltammetry and electrochemical impedance spectrum (EIS). All experimental data have revealed that TiO2 (P25) not only enhanced the reduction ability of ethanol under microwave irradiation but also promoted Pt heterogeneous nucleation to form Pt nanoclusters which are around P25 and loaded on graphene nanosheets (GNs) surface. Electrochemical experiments showed that Pt/TiO2/GNs had much higher catalytic activity and stability toward methanol oxidation reaction (MOR) and better resistance to CO poisoning compared with Pt/GNs and the commercially available Johnson Matthey 20% Pt/C catalyst (Pt/C-JM). Especially under UV irradiation with 20min, Pt/TiO2/GNs composites showed an ultrahigh forward peak current density of 1354mAmg−1, nearly 2.5 times higher than that of Pt/C-JM, which indicated that the electrocatalytic and photocatalytic properties of Pt/TiO2/GNs had been integrated to boost the catalytic performance for MOR.

Shape-controlled synthesis of Pt nanoparticles via integration of graphene and β-cyclodextrin and using as a noval electrocatalyst for methanol oxidation

The integration of graphene nanosheets (GNs) and β-cyclodextrin (CD) may bring about large surface area and high conductivity of GNs and unique supramolecular recognition capability of CD together. In this paper, for the first time, GNs-CD was used as a supporting material to construct nanodendritic hydrangea-like Pt nanoparticles, which was implemented by a facile wet chemical procedure. β-CD on GNs surface was used to regulate the final morphology of Pt nanoparticles without additional capping agent and seeds, and GNs functioned as a matrix to obtain a relatively uniform distribution of Pt nano-clusters. Electrocatalytic performance of the as-prepared Pt/GNs-CD hybrid was investigated by cyclic voltammetry (CV), chronoamperometry, COad stripping voltammetry, and electrochemical impedance spectroscopy (EIS). The Pt/GNs-CD hybrid exhibited much higher catalytic activity and stability than Pt/GNs and Pt/Vulcan X72R towards methanol oxidation, suggesting that Pt/GNs-CD hybrid could be a promising electrocatalyst for high-performance direct methanol fuel cells (DMFCs) applications.

Effect of nitrogen-doped acetylene carbon black supported Pd nanocatalyst on formic acid electrooxidation

Nitrogen-doped acetylene carbon black (N-C) is prepared by annealing acetylene carbon black and melamine under the protection of N2 at different temperatures. The resultant N-C materials are used as the support of Pd catalyst (Pd/N-C) for formic acid electrooxidation (FAEO). The catalytic activity of the Pd/N-C catalyst towards FAEO is evaluated by cyclic voltammetry, COad stripping voltammetry and chronoamperometry. The results show that when the heat-treatment temperature of support is 900 °C, the corresponding catalyst, Pd/N-C-900, generate 2.84-fold and 0.96-fold higher activity than homemade and commercial Pd/C catalysts in 0.5 M H2SO4 and 0.5 M HCOOH solution. The COad stripping voltammetry results demonstrate that Pd/N-C-900 has much better resistance to CO poisoning. Moreover, the effect of formic acid concentration and the temperature on the Pd/N-C catalysts are also explored, which confirms the really enhanced performances for FAEO. It is founded that the doping of nitrogen results an increase in the performance for FAEO due to the improved Pd nanoparticles (Pd NPs) dispersion and the modified electronic effect. The results indicate that the Pd/N-C catalyst has great application prospect as a high-performance anode catalyst for direct formic acid fuel cells (DFAFCs).

Carbon riveted PtRu/C catalyst from glucose in-situ carbonization through hydrothermal method for direct methanol fuel cell

PtRu/C catalyst is synthesized by microwave-assisted polyol process. Then, the PtRu nanoparticles are riveted through glucose in-situ carbonization by hydrothermal method. X-ray diffraction, transmission electron microscopy, cyclic voltammograms, COad stripping voltammetry, electrochemical impedance spectroscopy and accelerated potential cycling tests have been carried out to characterize their properties. The experimental results indicate that the average sizes of PtRu nanoparticles grow up from 1.54 nm to 2.56 nm after hydrothermal method. The electrochemical active specific surface areas of as-prepared and carbon riveted PtRu/C are 73.0 m2 g−1 Pt and 89.6 m2 g−1 Pt, respectively. The durability of carbon riveted PtRu/C increases one time after APCT of 1000 cycles and its mass activity also enhances 6% in first cycles in comparison with that of as-prepared PtRu/C. An enhanced stability of carbon riveted PtRu/C is mainly attributed to the existence of carbon nanolayer on the surface of the support from glucose in-situ carbonization to inhibit the migration and coalescence of PtRu nanoparticles on the support during work. Besides, the increased ratio of Pt(0), Ru(0), and carbon groups with higher stability and the evidently decreased of PtO2 and RuOxHy on surface of carbon riveted PtRu/C is another important reason to enhance its durability.

High Activity and Stability of Pt2Bi Catalyst in Formic Acid Oxidation

Formic acid oxidation was studied on a new prepared Pt2Bi characterized by X-ray diffraction spectroscopy (phase composition), scanning tunneling microscopy (STM) (surface morphology), and COads stripping voltammetry (surface composition). Bulk composition of Pt2Bi revealed two phases—55% PtBi alloy and 45% Pt. Estimated contribution of pure Pt on the Pt2Bi surface (43.5%) determined by COads stripping voltammetry corresponds closely to bulk composition. Pt2Bi reveals high activity and stability in formic acid oxidation. High activity originates from the fact that formic acid oxidation proceeds completely through dehydrogenation path based on an ensemble effect. The high stability of Pt2Bi surface is induced by the suppression of Bi leaching as it was evidenced by insignificant changes of surface morphology and surface roughness shown by STM images before and after electrochemical treatment in formic acid containing solution. Pt2Bi is found to be powerful catalyst exhibiting up to two orders of magnitude larger current densities at 0.0 V and onset potential shifted for ∼0.2 V to more negative value relative to Pt under steady-state condition.

Effect of Temperature and Adsorption Potential on the Electro-oxidation of Adsorbed Carbon Monoxide on Carbon Supported PtRu

The effect of temperature and adsorption potential towards the electro-oxidation of pre-adsorbed carbon monoxide (COad) on carbon supported platinum-ruthenium alloy catalyst was studied by COad stripping voltammetry and chronoamperometry. The current transient during the CO adsorption process was analyzed at various adsorption potential to understand the catalytic reaction during the CO adsorption process. A clear correlation with the charge associated with CO oxidation during the CO adsorption process and potential was obtained. A linear decrease in the COad oxidation potential with a slope of −2.7 mV K−1 and an apparent activation energy of 126 kJ mol−1 was observed with increasing temperature when full CO coverage is achieved.

Characterization and electrocatalytic properties of PtRu/C catalysts prepared by impregnation-reduction method using Nd 2O 3 as dispersing reagent

A simple impregnation-reduction method introducing Nd 2O 3 as dispersing reagent has been used to synthesize PtRu/C catalysts with uniform Pt-Ru spherical nanoparticles. X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) analysis have been used to characterize the composition, particle size and crystallinity of the catalysts. Well-dispersed catalysts with average particle size about 2 nm are achieved. The electrochemically active surface area of the different PtRu/C catalysts is determined by the CO ad-stripping voltammetry experiment. The electrocatalytic activities of these catalysts towards methanol electrooxidation are investigated by cyclic voltammetry measurements and ac impedance spectroscopy. The in-house prepared PtRu/C catalyst (PtRu/C-03) in 0.5 M H 2SO 4 + 1.0 M CH 3OH at 30 °C display a higher catalytic activity and lower charge-transfer resistance ( R t) than that of the standard PtRu/C catalyst (PtRu/C-C). It is mainly due to enhanced electrochemically active specific surface, higher alloying extent of Ru and the abundant Pt 0 and Ru oxides on the surface of the PtRu/C catalyst.

Gold nanoparticles dispersed polyaniline grafted multiwall carbon nanotubes as newer electrocatalysts: Preparation and performances for methanol oxidation

Newer electrocatalysts were prepared by dispersing gold nanoparticles onto a polyaniline (PANI) grafted multiwall carbon nanotube (MWNT-g-PANI) matrix through a two-step electrochemical process. In the first step, PANI chains were grafted onto amine-functionalized MWNT (MWNT-NH 2) by electropolymerizing a mixture of aniline and MWNT-NH 2 (dispersed in cetyltrimethyl ammonium bromide) using cyclic voltammetry. In the second step, Au nanoparticles were dispersed into the film of MWNT-g-PANI by electrochemical reduction of HAuCl 4. MWNT-g-PANI-modified electrodes with varying amounts of Au nanoparticles were prepared. Films of MWNT-g-PANI-Au were analyzed by field emission transmission electron microscopy (FETEM). The FETEM images indicate that Au particles of 8–10 nm in size are uniformly distributed into MWNT-g-PANI. X-Ray diffraction patterns provide support for the existence of Au nanoparticles. The electrocatalytic properties of the MWNT-g-PANI-Au electrode toward oxidation of methanol and adsorbed carbon monoxide (CO ads) were investigated by chronoamperometry and CO ads stripping voltammetry and compared with the properties of MWNT-Au and pristine Au electrodes. MWNT-g-PANI-Au catalysts exhibit excellent electrocatalytic activity toward the oxidation of methanol and CO ads. Oxidation of methanol occurs at a much lower oxidation potential (780 mV) at the MWNT-g-PANI-Au electrode with high current densities compared with the MWNT-Au electrode (890 mV) and pristine Au electrode (930 mV), due to the dispersion of Au nanoparticles into the three-dimensional network of MWNT-g-PANI. Further, our results suggest that the MWNT-g-PANI-Au electrode has better oxidation kinetics for the oxidation of CO ads to CO 2 than the MWNT-Au and pristine Au electrodes. Our results indicate that the MWNT-g-PANI-Au catalyst can have potential applications in direct methanol fuel cells.