Electrocatalytic Activity of Different Phases of Molybdenum Carbide/Carbon and Platinum-Molybdenum Carbide/Carbon Composites toward the Oxygen Reduction Reaction (original) (raw)
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Evidence of High Electrocatalytic Activity of Molybdenum Carbide Supported Platinum Nanorafts
Journal of The Electrochemical Society, 2015
A remarkable new supported metal catalyst structure on Mo 2 C substrates, 'rafts' of platinum consisting of less than 6 atoms, was synthesized and found to be catalytically active electrocatalyst for oxygen reduction. A novel catalytic synthesis method: Reduction-Expansion-Synthesis of Catalysts (RES-C), from rapid heating of dry mixture of solid precursors of molybdenum, platinum and urea in an inert gas environment, led to the creation of unique platinum Nanorafts on Mo 2 C. The Pt Nanorafts offer a complete utilization of the Pt atoms for electrocatalysis with no "hidden" atoms. This structure is strongly affected by its interaction with the substrate as was observed by XPS. In this work, we show for the first time, evidence of electrocatalytic activity with such small clusters of non-crystalline Pt atoms as catalysts for oxygen reduction. Electrochemical half-cell characterization shows that this structure permit more efficient utilization of platinum, with mass activity conservatively measured to be 50% that of platinum particles generated using traditional approaches. Moreover, as cathode fuel cell catalysts, these novel material may dramatically enhance stability, relative to the commercial Pt/carbon catalysts.
Journal of Solid State Electrochemistry, 2013
Micro-and mesoporous carbide-derived carbons synthesized from molybdenum and tungsten carbides were used as porous supports for a platinum catalyst. Synthesized materials were compared with commercial Vulcan XC72R conducting furnace black. The scanning electron microscopy, X-ray diffraction, Raman spectroscopy, high-resolution transmission electron microscopy, and low-temperature N 2 adsorption methods were applied to characterize the structure of catalysts prepared. The kinetics of oxygen electroreduction in 0.5 M H 2 SO 4 solution was studied using cyclic voltammetry and rotating disk electrode methods. The synthesized carbidederived carbons exhibited high specific surface area and narrow pore size distribution. The platinum catalyst was deposited onto the surface of a carbon support in the form of nanoparticles or agglomerates of nanoparticles. Comparison of carbide-derived carbons and Vulcan XC72R as a support showed that the catalysts prepared using carbide-derived carbons are more active towards oxygen electroreduction. It was shown that the structure of the carbon support has a great influence on the activity of the catalyst towards oxygen electroreduction.
Carbon-Supported Mo2C for Oxygen Reduction Reaction Electrocatalysis
Nanomaterials
Molybdenum carbide (Mo2C)-based electrocatalysts were prepared using two different carbon supports, commercial carbon nanotubes (CNTs) and synthesised carbon xerogel (CXG), to be studied from the point of view of both capacitive and electrocatalytic properties. Cation type (K+ or Na+) in the alkaline electrolyte solution did not affect the rate of formation of the electrical double layer at a low scan rate of 10 mV s−1. Conversely, the different mobility of these cations through the electrolyte was found to be crucial for the rate of double-layer formation at higher scan rates. Molybdenum carbide supported on carbon xerogel (Mo2C/CXG) showed ca. 3 times higher double-layer capacity amounting to 75 mF cm−2 compared to molybdenum carbide supported on carbon nanotubes (Mo2C/CNT) with a value of 23 mF cm−2 due to having more than double the surface area size. The electrocatalytic properties of carbon-supported molybdenum carbides for the oxygen reduction reaction in alkaline media were ...
International Journal of Hydrogen Energy, 2009
Oxygen reduction reaction (ORR) Polyaniline Polypyrrole Poly(3-methylthiophene) a b s t r a c t Platinum-free electrocatalysts based on electroconductive polymer, modified with cobalt, were prepared and characterized for the oxygen reduction reaction (ORR). The carbonsupported materials were: carbon/polyaniline/cobalt, carbon/polypyrrole/cobalt and carbon/poly(3-methylthiophene)/cobalt. Also the corresponding cobalt-free precursors were studied. EDAX studies show that in cobalt-modified catalysts, significant percentages of cobalt, between 5 and 7% in weight, are present. FTIR, TGA, and EDAX studies confirmed that the addition of cobalt modifies the chemical structure of C-Pani, C-Ppy, and C-P3MT materials. Cyclic voltammetry shows reduction peaks corresponding to the ORR for all materials and kinetic parameters were calculated based on lineal voltammetry using RDE at different rotating speeds. It was found that C-P3MT-Co has highest exchange current densities, followed by C-Ppy and C-Ppy-Co. All samples have Tafel slopes between À110 and À120 V/dec, indicating that the first electron transfer is the decisive step in the global ORR. Potentiostatic tests showed an adequate stability of cobalt-modified samples in acid medium at ORR potentials. Based on the potential range at which ORR occurs, the exchange current density and stability tests, it is concluded that the best material for potential application as fuel cell cathode catalyst is C-Ppy-Co.
ChemElectroChem, 2018
Replacing Pt‐based catalysts with noble‐metal free catalysts for the oxygen reduction reaction (ORR) is one of the most important topics currently in electrocatalysis. Iron‐ and nitrogen‐doped carbon materials have shown great promise in this area. In this work, we demonstrate the remarkable electrocatalytic activity towards the ORR of carbide‐derived carbon (CDC) and multi‐walled carbon nanotube (MWCNT) composite catalysts. The CDC material is synthesized from titanium carbide and doped using 1,10‐phenanthroline and iron (II) acetate. The material is then mixed with MWCNTs and further modified with dicyandiamide (DCDA) and additional iron by using a multi‐step pyrolysis procedure. The morphology, structure, porosity, and elemental composition are then comprehensively studied with scanning electron microscopy, X‐ray photoelectron spectroscopy, N2 physisorption, and inductively coupled plasma mass spectroscopy. The electrocatalytic activity of the catalysts for the ORR is studied usi...
Investigation of the oxygen reduction reaction on Pt–WC/C electrocatalysts in alkaline media
Electrochimica Acta, 2013
The activity of Pt catalysts dispersed on tungsten carbide (WC) prepared with a high surface area carbon with two different WC/C ratios is investigated for the oxygen reduction reaction (ORR) in alkaline electrolyte. The electrochemical methods employed are cyclic voltammetry (CV) and steady-state polarization carried out on an ultrathin catalyst layer deposited on the disk of a rotating ring-disk electrode. The PtWC-based catalysts show higher activity for the ORR compared to Pt/C, also involving a transfer of 4 electrons per oxygen molecule. CV and X-ray absorption near edge structure spectroscopy (XANES) results for the PtWC-based materials indicate weaker Pt-OH x interaction in these materials, resulting in a lower Pt-oxide coverage and explaining the increased rate of the ORR, as compared to Pt/C
Structure and Activity of Carbon-Supported Pt−Co Electrocatalysts for Oxygen Reduction
The Journal of Physical Chemistry B, 2004
Carbon-supported Pt-Co electrocatalysts in the Pt:Co atomic ratio 85:15, mainly for application in polymer electrolyte fuel cells, have been prepared by different methods. The materials were tested in single cells with respect to the oxygen reduction reaction and their performances were compared. Of the several methods considered, the preparation of the electrocatalyst via the deposition and reduction of a Co precursor on previously formed carbon-supported platinum gave the best results. By increasing the Co content, a decrease of metal particle size and an improvement in the activity for the ORR of these catalysts was observed. For the electrocatalysts with a Pt:Co atomic ratio of 75:25, a good stability upon cycling was also found.
Electrochimica Acta, 2014
Oxygen electroreduction reaction (ORR) on pristine porous carbide derived carbons (CDCs) and on CDC supports modified with Pt-nanoclusters has been studied in 0.5 M H 2 SO 4 solution using cyclic voltammetry, rotating disk electrode and electrochemical impedance spectroscopy methods. The CDCs were prepared from Mo 2 C (noted as C(Mo 2 C)) at different fixed chlorination temperatures from 600 • C to 1000 • C. The CDCs have tuneable specific surface area, micro-and mesoporosity, good electrical conductivity and corrosion stability at positive electrode potentials. Pt-nanoclusters were deposited onto/into C(Mo 2 C) powders using sodium borohydride reduction method. The X-ray diffraction and high-resolution transmission electron microscopy were applied for the structural and chemical characterization, and the nitrogen sorption method was used for the porosity analysis of the electrode materials studied. The cathodic current densities depend strongly on the synthesis temperature of C(Mo 2 C), indicating that, in addition to the specific surface area and porosity, the crystallinity (density of defects in amorphous areas) has noticeable influence on the ORR rate. Impedance data demonstrated nearly capacitive behaviour in the low AC frequency region, explained by quick cathodic ORR followed by slow adsorption step of the intermediates and reaction products at/inside microporous-mesoporous C(Mo 2 C) and Pt-C(Mo 2 C) electrodes.
Scientific reports, 2015
A novel and facile two-step strategy has been designed to prepare high performance bi-transition-metals (Fe- and Mo-) carbide supported on nitrogen-doped graphene (FeMo-NG) as electrocatalysts for oxygen reduction reactions (ORR). The as-synthesized FeMo carbide -NG catalysts exhibit excellent electrocatalytic activities for ORR in alkaline solution, with high onset potential (-0.09 V vs. saturated KCl Ag/AgCl), nearly four electron transfer number (nearly 4) and high kinetic-limiting current density (up to 3.5 mA cm(-2) at -0.8 V vs. Ag/AgCl). Furthermore, FeMo carbide -NG composites show good cycle stability and much better toxicity tolerance durability than the commercial Pt/C catalyst, paving their application in high-performance fuel cell and lithium-air batteries.