Surface and electrochemical characterisation of a Pt-Cu/C nano-structured electrocatalyst, prepared by galvanic displacement (original) (raw)
Related papers
Catalysts, 2016
Pt(Cu)/C and Pt-Ru(Cu)/C electrocatalysts with core-shell structure supported on Vulcan Carbon XC72R have been synthesized by potentiostatic deposition of Cu nanoparticles on the support, galvanic exchange with Pt and spontaneous deposition of Ru species. The duration of the electrodeposition time of the different species has been modified and the obtained electrocatalysts have been characterized using electrochemical and structural techniques. The High Resolution Transmission Electron Microscopy (HRTEM), Fast Fourier Transform (FFT) and Energy Dispersive X-ray (EDX) microanalyses allowed the determining of the effects of the electrodeposition time on the nanoparticle size and composition. The best conditions identified from Cyclic Voltammetry (CV) corresponded to onset potentials for CO and methanol oxidation on Pt-Ru(Cu)/C of 0.41 and 0.32 V vs. the Reversible Hydrogen Electrode (RHE), respectively, which were smaller by about 0.05 V than those determined for Ru-decorated commercial Pt/C. The CO oxidation peak potentials were about 0.1 V smaller when compared to commercial Pt/C and Pt-Ru/C. The positive effect of Cu was related to its electronic effect on the Pt shells and also to the generation of new active sites for CO oxidation. The synthesis conditions to obtain the best performance for CO and methanol oxidation on the core-shell Pt-Ru(Cu)/C electrocatalysts were identified. When compared to previous results in literature for methanol, ethanol and formic acid oxidation on Pt(Cu)/C catalysts, the present results suggest an additional positive effect of the deposited Ru species due to the introduction of the bifunctional mechanism for CO oxidation.
The Journal of Physical Chemistry C, 2007
We establish relationships between the atomic structure, composition, electrocatalytic activity, and electrochemical corrosion stability of carbon-supported Pt-Co alloy nanoparticles in electrode catalyst layers. These Pt-Co catalysts have received much attention for use as cathode layers in polymer electrolyte membrane fuel cells (PEMFCs) because of their favorable oxygen-reduction-reaction (ORR) activity and suspected corrosion stability. We reported an enhancement of activity of low-temperature Pt 50 Co 50 of 3 times that of pure carbon supported Pt catalysts. The use of synchrotron X-ray diffraction has enabled structural characterization of the alloy nanoparticles both before and, importantly, after electrocatalysis under fuel cell like conditions. From this, a detailed picture of the relative activity and stability of Pt-Co alloy phases as a function of synthesis conditions has emerged. We have investigated the structure, composition, chemical ordering, and concentration of Pt-Co alloy phases in (i) a dry, freshly synthesized nanoparticle catalyst, (ii) the catalytic electrode layer in a proton-conducting polymer electrolyte before electrocatalytic activity, and (iii) the same electrode layer after electrocatalytic activity. We find that Pt 50 Co 50 catalysts annealed at 600°C consist of multiple phases: a chemically ordered face-centered tetragonal (fct) and two chemically disordered face-centered cubic (fcc) phases with differing stoichiometries. The Co-rich fcc phase suffers from corrosive Co loss during the preparation of conducting polymer electrode layers and, more significantly, during the ORR electrocatalysis. Most importantly, these fcc phases exhibit high catalytic activities for ORR (about 3× compared to a pure Pt electrocatalyst). Pt 50 Co 50 catalysts annealed at 950°C consist mainly of the fct Pt 50 Co 50 phase. This phase shows favorable stability to corrosion in the conducting polymer electrode and during electrocatalysis, as the relative intensities of fcc(111)/fct(101) peak ratio remained consistently around 0.5 before and after preparation of conducting polymer electrode layers and before and after electrochemical measurements; however, it exhibits a lower catalytic ORR activity compared to the low-temperature fcc alloy phases (about 2.5× compared to a pure Pt electrocatalyst). Our results demonstrate the complexity in these multiphase materials with respect to catalyst activity and degradation. By understanding of the relationships between crystallographic phase, chemical ordering, composition, and the resulting electrochemical activity and corrosion stability of fuel cell catalysts within polymer-electrolyte/catalyst composites, we can move toward the rational design of active and durable catalyst materials for PEMFC electrodes.
Journal of Materials Chemistry, 2007
Small platinum clusters have been prepared in zeolite hosts through ion exchange and controlled calcination/reduction processes. To enable electrochemical application, the pores of the Pt-zeolite were filled with electrically conductive carbon via infiltration with carbon precursors, polymerization, and pyrolysis. The zeolite host was then removed by acid washing, to leave a Pt/C electrocatalyst possessing quasi-zeolitic porosity and Pt clusters of well-controlled size. The electrocatalysts were characterized by TEM, XRD, EXAFS, nitrogen adsorption and electrochemical techniques. Depending on the synthesis conditions, average Pt cluster sizes in the Pt/C catalysts ranged from 1.3 to 2.0 nm. The presence of ordered porosity/structure in the catalysts was evident in TEM images as lattice fringes, and in XRD as a low-angle diffraction peak with d-spacing similar to the parent zeolite. The catalysts possess micro-and meso-porosity, with pore size distributions that depend upon synthesis variables. Electroactive surface areas as high as 112 m 2 g Pt 21 have been achieved in Pt/C electrocatalysts which show oxygen reduction performance comparable to standard industrial catalysts.
Carbon, 2006
Chemical modification of Carbon Vulcan XC-72R for fuel cell applications has been undertaken. Treated carbons were used as carriers for the deposition of Pt nanoparticles and used as electrocatalysts. The influence of the carbon treatment, as well as that of the Pt nanoparticles generation and their deposition route has been studied. The behaviour of the electrocatalysts in the CO and hydrogen oxidation reaction (HOR) has been studied. It was observed that carbon pre-treatment lead to difference behaviour in the CO oxidation reaction compared with the performance over non treated supports. In this way, CO oxidation was controlled by the nature of the support rather than by the nature of the Pt particles alone.
Materials Chemistry and Physics, 2011
Pt nanoparticles have been supported on different carbon materials for their use as electrocatalysts in polymeric electrolyte fuel cells. Carbon nanofibers (CNF) and ordered mesoporous carbon (CMK-3) have been studied as supports that could replace carbon black in the preparation of commercial electrocatalysts. The use of these non-conventional carbon materials allowed the determination of the influence of the support on the physicochemical properties of catalysts. Additionally, Pt catalyst supported on Vulcan XC-72R (commercial electrocatalyst support) has been prepared in order to establish a comparison. Catalysts were prepared by the incipient wetness impregnation method, and subsequently, they were reduced in a H 2 flow. Supports and catalysts were characterized by different analytical techniques in order to determine the effect of the support. Results proved that the support has a strong influence on the physicochemical properties of catalysts. These properties depended on the nature of the support and are associated with the metal-support interaction.
Chemistry of Materials, 2009
Supplemental information Characterization Nitrogen Porosimetry N 2 sorption analysis was performed on a Micromeritics Germini analyzer at-196 °C (77 K). The specific surface area was calculated using the BET method from the nitrogen adsorption data in the relative range (P/P 0) of 0.06-0.30. The samples were heated overnight at 100°C for degassing. The total pore volume was determined from the amount of N 2 uptake at P/P 0 = 0.95. The pore size distribution was derived from the adsorption branch of the isotherm based on the BJH model. Electron Microscopy Low-resolution images were visualized by TEM on a Phillips EM280 microscope with a 4.5 Å point-to-point resolution and operated at an 80 kV accelerating voltage. High resolution transmission electron microscopy (HRTEM) on the nanoparticles was performed using a JEOL 2010F TEM operating at 200 kV, and the carbon was imaged using a Hitachi HF-3300 at 300kV. Pictures were obtained at the optimum defocus condition. SEM-EDS was done to obtain average particle composition over a large area on a Hitachi S-4500 at 20 kV. X-ray photoelectron spectroscopy XPS was acquired using a Kratos AXIS Ultra DLD spectrometer equipped with a monochromatic Al X-ray source (Al Kα, 1.4866 keV) and operated with a 20 eV path energy for high resolution elemental scans and a160 eV for survey scans conducted at an angle of 45°. The sample was prepared by depositing the catalysts (1-2 mg) on the double sided copper tape and then placed into the vacuum chamber. Thermogravimetric analysis (TGA) TGA was conducted using a Perkin-Elmer TGA7 equipment under oxygen flow. Samples were heated to 750 °C at the rate of 25 °C/min. Samples were held at 50 °C for 10 min before increasing the temperature.
International Journal of Hydrogen Energy, 2014
Commercially available graphitized carbon nanofibers and multi-walled carbon nanotubes, two carbon materials with very different structure, have been functionalized in a nitric esulfuric acid mixture. Further on, the materials have been platinized by a microwave assisted polyol method. The relative degree of graphitization has been estimated by means of Raman spectroscopy and X-ray diffraction while the relative concentration of oxygen containing groups has been estimated by X-ray photoelectron spectroscopy, which resulted in a graphitic character trend: Pt/GNF > Pt/F-GNF \ Pt/MWCNT > Pt/F-MWCNT. Transmission electron microscopy showed that the Pt particle size is around 3 nm for all samples, which was similar to the crystallite size obtained by X-ray diffraction. The activity towards electrochemical reduction of oxygen has been quantified using the thin-film rotating disk electrode, which has shown that all the samples have a better activity than the commercially available electrocatalysts. The trend obtained for the graphitic character maintained for the electrochemical activity, while the reverse trend has been obtained for the accelerated ageing test. Long-term potential cycling has demonstrated that the functionalization improves the stability for multi-walled carbon nanotubes, at the cost of decreased activity.
Fabrication and Characterization of High-activity Pt/C Electrocatalysts for Oxygen Reduction
Bulletin of the Korean Chemical Society, 2010
A 20 wt % Pt/C is fabricated and characterized for use as the cathode catalyst in a polymer electrolyte membrane fuel cell (PEMFC). By using the polyol method, the fabrication process is optimized by modifying the carbon addition sequence and precursor mixing conditions. The crystallographic structure, particle size, dispersion, and activity toward oxygen reduction of the as-prepared catalysts are compared with those of commercial Pt/C catalysts. The most effective catalyst is obtained by ultrasonic treatment of ethylene glycol-carbon mixture and immediate mixing of this mixture with a Pt precursor at the beginning of the synthesis. The catalyst exhibits very uniform particle size distribution without agglomeration. The mass activities of the as-prepared catalyst are 13.4 mA/mgPt and 51.0 mA/mgPt at 0.9 V and 0.85 V, respectively, which are about 1.7 times higher than those of commercial catalysts.
Journal of Electroanalytical Chemistry, 1998
In situ X-ray absorption studies were done in 1 M HClO , with and without 0.3 M MeOH, on several well-defined carbon-supported Pt 4e lectrocatalysts with particle sizes in the range of 25 to 90 A. Data were obtained at several potentials in the range of 0.0 to 1.14 V vs. RHE. The results show that as the particle size is reduced below 50 A, the strength of adsorption of H, OH and C , moieties such as CO is 1 increased. The strong adsorption of OH explains the reduced specific activity for oxygen reduction on small particles. The reduced activity for methanol oxidation on the small particles is due to a combination of the increased strength of adsorption of both CO and OH. The strong adsorption of H at negative potentials on small Pt particles is sufficient to induce reconstruction and morphological changes in the Pt particles. Both XANES and EXAFS data on a 53 A particle at 0.84 V indicate that formation of PtOH is the rate determining step in the oxidation of methanol. All these affects are due to an increase in the number of Pt sites with low coordination on the small particles.