Effects of the Electrodeposition Time in the Synthesis of Carbon-Supported Pt(Cu) and Pt-Ru(Cu) Core-Shell Electrocatalysts for Polymer Electrolye Fuel Cells (original) (raw)
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The synthesis of core-shell Pt(Cu) and Pt-Ru(Cu) electrocatalysts allows for a reduction in the amount of precious metal and, as was previously shown, a better CO oxidation performance can be achieved when compared to the nanoparticulated Pt and Pt-Ru ones. In this paper, the carbon black used as the support was previously submitted to electrochemical oxidation and characterized by XPS. The new catalysts thus prepared were characterized by HRTEM, FFT, EDX, and electrochemical techniques. Cu nanoparticles were generated by electrodeposition and were further transformed into Pt(Cu) and Pt-Ru(Cu) core-shell nanoparticles by successive galvanic exchange with Pt and spontaneous deposition of Ru species, the smallest ones being 3.3 nm in mean size. The onset potential for CO oxidation was as good as that obtained for the untreated carbon, with CO stripping peak potentials about 0.1 and 0.2 V more negative than those corresponding to Pt/C and Ru-decorated Pt/C, respectively. Carbon oxidation yielded an additional improvement in the catalyst performance, because the ECSA values for hydrogen adsorption/desorption were much higher than those obtained for the non-oxidized carbon. This suggested a higher accessibility of the Pt sites in spite of having the same nanoparticle structure and mean size.
Methanol electro-oxidation on Pt-Ru-P/C and Pt-Ru-P/MWCNT in acidic medium
Pt-Ru-P was prepared by the chemical reduction method using sodium hypophoshite as a reducing agent on Vulcan XC 72 and multi-walled carbon nano-tubes (MWCNTs). Sodium citrate was added as the stabilizer during electro-catalyst preparation. The electro-catalytic activity towards methanol oxidation in acidic medium was studied by cyclic voltammetry and linear sweep voltammetry. Pt-Ru-P/MWCNT showed excellent activity than Pt-Ru-P/C. This may be attributed to the effectiveness of the MWCNTs acting as good catalyst support material. The particle size of both electro-catalysts obtained with the transmission scanning electron microscopy (TEM) ranged between 2-4nm desirable for the direct methanol fuel cells.
The Journal of Physical Chemistry C, 2009
In this work, methanol oxidation was studied on carbon-supported Pt-Ru nanocatalysts, where the amounts of alloyed and oxide phases were modified by heat treatments in different atmospheres. Because particle growth was avoided using mild temperature conditions, the study reported here was conducted in the absence of particle size effects. All samples were characterized by X-ray diffraction and transmission electron microscopy. The general electrochemical behavior of the nanocatalysts was evaluated by cyclic voltammetry, and the electrocatalytic activity for the oxidation of methanol was studied in 0.5 mol L -1 methanol acid solutions by linear potential sweeps and chronoamperometry. The results obtained clearly evidence that the presence of oxide species is necessary to enhance the electrocatalytic activity for methanol oxidation. Oxidation of adsorbed CO was also measured. Both reactions, methanol and adsorbed CO oxidation, were found to be very sensitive to the surface changes produced by the heat treatments. Interestingly, the best catalyst for methanol oxidation was not found to be the most efficient for the oxidation of adsorbed CO. Electrocatalytic activities correlate well with oxidation states and electronic properties analyzed by X-ray photoelectron spectroscopy and in situ dispersive X-ray absorption spectroscopy.
Applied Catalysis B: Environmental, 2013
A bimetallic Pt-Cu carbon-supported catalyst (Pt(Cu)/C) has been prepared by a room temperature twostep procedure involving the chemical reduction of Cu ions by sodium borohydride in the presence of Vulcan XC72R carbon powder, followed by the partial galvanic replacement of Cu particle layers by Pt, upon immersion in a chloroplatinate solution. The characterization of the Pt(Cu)/C catalyst by XRD has proven the formation of a Pt-Cu alloy while cyclic voltammetry in deaerated acid revealed similar characteristics to those of pure Pt. These two findings point to the existence of Pt-rich outer layers and a Pt-Cu core. The electrocatalytic activity of the bimetallic Pt(Cu)/C catalyst towards methanol oxidation is comparable to or better than that of a commercial 20% Pt Vulcan XC72R catalyst (when assessed by voltammetric or prolonged chronoamperometric experiments respectively). This is attributed to the effect of Cu on CO poison adsorption and removal from Pt. Moreover, related to the same effect but also to the reduced Pt loading of the mixed Pt-Cu particles, the specific mass activity of the prepared catalyst is superior to that of the commercial catalyst. (S. Sotiropoulos). et al. applied the technique to the partial replacement of Ti surface layers or Cu and Pb polylayers by Pt, resulting in the latter case in Pt shell-Cu (or Pb) core particles, denoted as Pt(Cu) or Pt(Pb). Sotiropoulos and co-workers expanded the method to the replacement of Pb, Cu, Fe, Co, Ni polylayers by Pt and Au .
Electrochimica Acta, 2006
The methods developed and described in paper-part I are employed to prepare nanometer size Pt-Ru particles on a Vulcan ® XC72R substrate with controlled metal loading. Transmission Electron Microscopy (TEM) confirmed uniform particles size (average diameter 2 nm) and homogeneous dispersion of the particles over the substrate. Energy Dispersive X-ray absorption (EDX) analysis confirmed the compositional homogeneity. The catalytic activity of these supported nanoparticles with regard to methanol electrooxidation is investigated using cyclic voltammetry (CV), chronoamperometry (CA) and CO-stripping voltammetry techniques at temperatures between 25 and 60 • C. Such investigation concerns supported catalysts prepared with ca. 10 and 18 wt.% overall metal loading (Pt + Ru) onto the Vulcan ® XC72R substrate. Comparative testing of our catalysts and a commercial Pt-Ru/Vulcan reveals markedly superior activity for our catalysts. In fact, we observe for the latter a five-fold increase of the oxidation current as compared to a commercial Pt-Ru/Vulcan with equal metal loading. One of the reasons for the greater activity is found to be the very high dispersion of the metals over the substrate, i.e. the large surface area of the active phase. Other reasons are plausibly ascribable to the varied Pt/Ru composition and/or reduced presence of contaminants at the catalyst surface. (V. Tricoli). with respect to state of the art nanocatalysts based on binary Pt-Ru alloy.
Applied Catalysis B Environmental
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 Electroanalytical Chemistry, 2011
Carbon-supported Pt, Pt-Ru, Pt 3 -Sn electrocatalysts have been synthesized by a modified polyol method. Energy dispersive spectroscopic (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopic (XPS) analyses reveal that the as-prepared samples are composed of mainly Pt and RuO 2 or SnO 2 and the formation of alloys is found only after heat-treatment at 200°C in a flowing 10% H 2 -90% Ar atmosphere. The activity and durability for the methanol electro-oxidation reaction (MOR) have been evaluated by accelerated durability test (ADT) carried out by scanning the electrode potential for extended number of cycles in the potential ranges of 0.02-0.6, 0.02-0.8, and 0.02-1.2 V vs. NHE. Regardless of heat-treatment, the initial activity for MOR decreases in the order Pt-Ru/C > Pt 3 -Sn/C > Pt/C and the durability decreases in the order Pt/C > Pt 3 -Sn/C > Pt-Ru/C. During the ADT of the as-prepared Pt-Ru/C and Pt 3 -Sn/C, no detectable amount of dissolved Sn ions was found in the electrolyte solution, while almost 40% of Ru could be found in the electrolyte solution after ADT between 0.02 and 1.2 V vs. NHE. With MOR activity comparable to and durability better than that of Pt-Ru, the Pt-Sn based catalysts offer the potential to be employed as anode catalysts in direct methanol fuel cells.
Journal of Physical Chemistry C, 2012
The modification of carbon-supported Pt nanoparticles, high performance (HP) 20% Pt on Vulcan XC-72 carbon black (Pt/C electrocatalyst), by spontaneous deposition of Ru species is examined employing electrochemical and structural techniques. Thin-layer electrodes were prepared by applying aqueous catalyst inks of Pt/C on glassy carbon (GC) disks. Ru deposition was carried out by immersion of the prepared electrode in deaerated RuCl 3 / HClO 4 solutions. The subsequent cyclic voltammetry experiments of the modified electrocatalysts (Ru(Pt)/C) were performed in 0.5 M H 2 SO 4 to determine the Ru coverage and the electroactive surface. CO stripping voltammetry showed the promotional effect of Ru(Pt)/C for the CO oxidation compared to Pt/C. The structural characterization of the modified electrocatalysts was performed by transmission electron microscopy (TEM), energy dispersive X-ray (EDX) analyses, fast Fourier transform (FFT), selected-area electron diffraction (SAED), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). TEM observations revealed no appreciable signals of Ru agglomerates, and EDX confirmed the regular incorporation of Ru species to the nanoparticles. XRD analyses showed the characteristic profile of the Pt face-centered cubic (FCC) structure and the absence of crystalline Ru or Ru oxides. The application of the Williamson−Hall models indicated that Ru incorporation did not significantly affect the internal strain of the Pt nanoparticles, the increase of the crystallite size being attributed to an epitaxial growth of the Ru deposit. XPS measurements reported the presence of nonreducible RuO 2 and hydrous RuO 2 (RuO x H y) as the main Ru species in Ru(Pt)/C, the hydrous species justifying the promotional effect for the CO oxidation.
Chemistry - A European Journal, 2012
this composition effect plays a significant role in determining the degree of alloying or the atomic distribution between two different metals, thereby resulting in a significant influence on the activity, [9, 10] stability, [10] and selectivity of the NPs. [11] With the availability of modern techniques such as transmission electron microscopy (TEM) or scanning electron microscopy (SEM) coupled with energy-dispersive X-ray analysis (EDX), it is possible to obtain reasonably good estimates of the composition of the alloy in the bi-A C H T U N G T R E N N U N G metallic NPs. X-ray absorption spectroscopy (XAS) [12] is a powerful technique for investigating the internal structure of the bulk and surface regions of the NPs. The two techniques in combination provide mechanistic insight at the atomic level into the bulk surface chemistry of the NPs and the factors that enhance their catalytic properties. Among the different bimetallic systems, the carbon-supported Pt À Ru (Pt À Ru/C) bimetallic system has been receiving renewed interest from both scientific and industrial communities on account of its suitability as a catalyst for methanol oxidation in direct methanol fuel cells (DMFCs). [13] Although these bimetallic PtÀRu/C NPs are of significance, understanding the rationale underpinning their design is an ongoing challenge. Generally, the main problems in the preparation of these bimetallic Pt À Ru/C NPs are the poor content of Ru metals in the alloy and the increase in the size of the particle with respect to pure Pt. [13]