Activity For Methanol Electrooxidation Research Articles

Core-shell structured tungsten–tungsten carbide as a Pt catalyst support and its activity for methanol electrooxidation

Tungsten carbide was synthesized by calcination of carbon cryogel containing tungsten in a form of metatungstate. Characterization by X-ray diffraction and transmission electron microscopy indicated core-shell structure of the particles with tungsten core and tungsten carbide shell, attached to graphitized carbon. Pt nanoparticles were deposited on this material and most of them were nucleated on tungsten carbide. Cyclic voltammetry of W-C support and Pt/W-C catalyst indicated hydrogen intercalation in surface hydrous tungsten oxide. Oxidation of COads on Pt/W-C commences earlier than on Pt/C for about 100 mV. The onset potentials of MOR on Pt/W-C and Pt/C are the same, but at more positive potentials Pt/W-C catalyst is more active. It was proposed that promotion of MOR is based on bifunctional mechanism that facilitates COads removal. Stability test was performed by potential cycling of Pt/W-C and Pt/C in the supporting electrolyte and in the presence of methanol. Pt surface area loss observed in the supporting electrolyte of both catalysts after 250 cycles was about 20%. Decrease in the activity for methanol oxidation was 30% for Pt/W-C, but even 48% for Pt/C. The difference was explained by the presence of hydrous tungsten oxide on Pt in Pt/W-C catalyst, which reduces accumulation of poisoning COads.

Anodization driven enhancement of catalytic activity of Pd towards electro-oxidation of methanol, ethanol and formic acid

The anodization of Pd in a 1.0M H2SO4 solution has been investigated, which enables spontaneous formation of Pd nanoparticles. Electrochemical measurements show that the anodized Pd exhibits significantly larger electrochemically active surface area (EASA) and excellent catalytic activity towards electro-oxidation of methanol, ethanol, and formic acid in comparison to the flat Pd. The electro-catalytic activity of the anodized Pd is ca. 260 and 210 times higher than that of the flat Pd for the oxidation of methanol and ethanol in the alkaline media, respectively. Moreover, the anodized Pd presents superior steady-state activity for the diffusion-controlled electro-oxidation of methanol, and the anodization greatly enhances the intrinsic catalytic activity of each Pd atom. The anodized Pd will be a promising candidate for anode catalysts of fuel cells.

Significantly enhanced electrocatalytic activity for methanol electro-oxidation on Ag oxide-promoted PtAg/C catalysts in alkaline electrolyte

Alloyed PtmAg nanostructures (m being the atomic Pt/Ag ratio, m=0.03–1.0) supported on carbon black were prepared and comprehensively characterized by ultraviolet–visible spectroscopy, X-ray diffraction, and transmission electron microscopy techniques. Cyclic voltammetry (CV) and chronoamperometry studies of methanol electro-oxidation reaction (MOR) in alkaline electrolyte indicated that the catalytic activity and CO tolerance of Pt were improved remarkably by the co-presence of Ag. A volcano relationship between the activity and m was found for the PtmAg/C catalysts, and both the highest mass-specific activity and the highest intrinsic activity of Pt were reached at m=0.5. Interestingly, we also found that the catalytic activity of the PtmAg/C catalysts strongly depended on the high-potential limit of CV. When the PtmAg/C catalysts were cycled up to 0.5V (vs. saturated calomel electrode), which induced a significant redox process of Ag, they showed ca. 50 times higher catalytic activity than those not subjected to the Ag redox process (up to 0.1V). Our study clearly demonstrated that the Ag oxide played a crucial role in promoting the catalytic role of Pt for MOR in alkaline electrolyte.

Gold nanoparticle-coated Ni/Al layered double hydroxides on glassy carbon electrode for enhanced methanol electro-oxidation

We report a facile electrochemical strategy for the synthesis of Ni/Al layered double hydroxides (LDHs) and gold nanoparticle (AuNPs)-coated glassy carbon electrode (GCE). The new electrode is named LDH/AuNPs/GCE. The new electrode is named LDH/AuNPs/GCE. The electrocatalytic activity of LDH/AuNPs toward methanol electro-oxidation was studied by cyclic voltammetry and chronoamperometry. Compared to the Ni/Al-LDH modified GCE without AuNPs film (LDH/GCE), the LDH/AuNPs/GCE exhibits remarkably higher catalytic activity for methanol electro-oxidation, e.g. the lower oxidation potential (0.57 V vs. SCE) and the higher current density (6-fold). The enhancement may be attributed to the higher electrocatalytic activity of Ni/Al-LDHs in the presence of AuNPs, the synergy effect between them, or both. The results presented here may be of broad interest not only for developing fuel cells but also for understanding of OH− electro-generated on noble metal surfaces.

Tetrahexahedral Pt Nanocrystal Catalysts Decorated with Ru Adatoms and Their Enhanced Activity in Methanol Electrooxidation

Tetrahexahedral Pt nanocrystals (THH Pt NCs) bound by well-defined high index crystal planes offer exceptional electrocatalytic activity, owing to a high density of low-coordination surface Pt sites. We report, herein, on methanol electrooxidation at THH Pt NC electrodes studied by a combination of electrochemical techniques and in situ FTIR spectroscopy. Pure THH Pt NC surfaces readily facilitate the dissociative chemisorption of methanol leading to poisoning by strongly adsorbed CO. Decoration of the stepped surfaces by Ru adatoms increases the tolerance to poisoning and thereby reduces the onset potential for methanol oxidation by over 100 mV. The Ru modified THH Pt NCs exhibit greatly superior catalytic currents and CO2 yields in the low potential range, when compared with a commercial PtRu alloy nanoparticle catalyst. These results are of fundamental importance in terms of model nanoparticle electrocatalytic systems of stepped surfaces and also have practical significance in the development of surface tailored, direct methanol fuel cell catalysts.

Porous Pt-Ni-P Composite Nanotube Arrays: Highly Electroactive and Durable Catalysts for Methanol Electrooxidation

Porous Pt-Ni-P composite nanotube arrays (NTAs) on a conductive substrate in good solid contact are successfully synthesized via template-assisted electrodeposition and show high electrochemical activity and long-term stability for methanol electrooxidation. Hollow nanotubular structures, porous nanostructures, and synergistic electronic effects of various elements contribute to the high electrocatalytic performance of porous Pt-Ni-P composite NTA electrocatalysts.

Graphene growth on nanodiamond as a support for a Pt electrocatalyst in methanol electro-oxidation

A core/shell structure nanodiamond/graphene (ND/G) was prepared by annealing ND in a vacuum at the temperatures of 1200 and 1500°C. ND/G with a controllable few-layer graphene covering on the ND surface was achieved. The prepared ND/G was used as a support for a platinum (Pt) electrocatalyst in direct methanol fuel cells. A higher dispersion of Pt nanoparticles was observed on ND/G compared to pristine NDs and the material showed better catalytic activity and greater stability for methanol electro-oxidation than Pt/ND.

An in situ attenuated total reflection-surface enhanced infrared absorption spectroscopic study of enhanced methanol electro-oxidation activity on carbon-supported Pt nanoparticles by poly(vinylpyrrolidone) of different molecular weights

The effect of the commonly used 55,000 Mw (PVP55) and a heavier chain of 360,000 Mw (PVP360) on commercial 40wt% Pt/C were probed using electrochemical methods and in situ SEIRAS experiments during the MOR and related gaseous CO oxidation. The polymer-modified samples exhibited an enhanced long-term CO tolerance with a small hindrance to the intrinsic activity of Pt/C. Increased water adsorption in the presence of polymer was observed to coincide with the oxidation of adsorbed CO and was related to the desorption of the surface-bound carbonyl of PVP via in situ SEIRAS. The notable differences between the adsorbate trends are indicative of adsorbed polymer interactions with the surface, but more interestingly is the strong dependence of the polymer molecular weight Mw that led to qualitatively different behavior. Understanding the effects of adsorbed PVP on electrocatalytic reactions is of fundamental and practical importance due to its widespread use in synthesized NPs targeted for fuel cell applications.

Low-temperature, seed-mediated synthesis of monodispersed hyperbranched PtRu nanoparticles and their electrocatalytic activity in methanol oxidation

We report a seed-mediated synthetic approach to produce hyperbranched PtRu alloy nanoparticles under mild conditions. As-synthesized PtRu particles have a high alloying degree, display high index facets, and show improved activity for electro-oxidation of methanol when compared to commercial PtRu black.

Relationships between structure and activity of carbon as a multifunctional support for electrocatalysts

We report on new insights into the relationships between structure and activity of glassy carbon (GC), as a model material for electrocatalyst support, during its anodization in acid solution. Our investigation strongly confirms the role of CFGs in promotion of Pt activity by the "spill-over" effect related to CO(ads) for methanol electrooxidation (MEO) on a carbon-supported Pt catalyst. Combined analysis of voltammetric and impedance behaviour as well as changes in GC surface morphology induced by intensification of anodizing conditions reveal an intrinsic influence of the carbon functionalization and the structure of a graphene oxide (GO) layer on the electrical and electrocatalytic properties of activated GC. Although GO continuously grows during anodization, it structurally changes from being a graphite inter-layer within graphite ribbons toward a continuous GO surface layer that deteriorates the native structure of GC. As a consequence of the increased distance between GO-spaced graphite layers, the GC conductivity decreases until the case of profound GO exfoliation under drastic anodizing conditions. This exposes the native, yet abundantly functionalized, GC texture. While GC capacitance continuously increases with intensification of anodizing conditions, the surface nano-roughness and GO resistance reach the highest values at modest anodizing conditions, and then decrease upon drastic anodization due to the onset of GO exfoliation. We found for the first time that the activity of a GC-supported Pt catalyst in MEO, as one of the promising half-reactions in polymer electrolyte fuel cells, strictly follows the changes in GC nano-roughness and GO-induced GC resistance. The highest GC/Pt MEO activity is reached when optimal distance between graphite layers and optimal degree of GC functionalization bring the highest amount of CFGs into intimate contact with the Pt surface. This confirms the promoting role of CFGs in MEO catalysis.

High Throughput Thin Film Pt-M Alloys for Fuel Electrooxidation: Low Concentrations of M (M = Sn, Ta, W, Mo, Ru, Fe, In, Pd, Hf, Zn, Zr, Nb, Sc, Ni, Ti, V, Cr, Rh)

Eighteen Pt-M binary (M = Sn, Ta, W, Mo, Ru, Fe, In, Pd, Hf, Zn, Zr, Nb, Sc, Ni, Ti, V, Cr, Rh) thin film composition spreads were deposited at low M concentrations using magnetron sputtering and screened for methanol and ethanol electrooxidation activity using a fluorescence assay. Characterization of these thin films was performed using high energy X-ray diffraction and X-ray fluorescence. The electrochemical fluorescence assay revealed highest activity in the films with M = Sn, Zn, In, Fe, and Ru. Pt-M (M = Sn, Zn, In) showed highest activity at concentrations below 5 atom-% with a high fraction of Pt fcc(111) texturing and Pt-Fe showing the best activity at 10 atom-% Fe. On the other hand, the best (most negative) fluorescence onset potential in the Pt-Ru system was observed at a concentration of 35 atom-% Ru with only slight texturing of the film. To explore the potential origins of the observed catalytic activity, preliminary calculations on the d-band center shift with alloying were performed for bulk concentrations of up to 30 atom-% for Fe and 16 atom-% for M = Sn, Zn.

A simple eco-friendly solution phase reduction method for the synthesis of polyhedra platinum nanoparticles with high catalytic activity for methanol electrooxidation

The conventional hydrogen gas reduction method for preparation of platinum nanoparticles is to bubble H2 gas into solution with a pre-existing platinum precursor. In this work, instead of bubbling hydrogen gas into Pt precursor solution, we reverse the addition sequence by quickly injecting the Pt precursor into a solution saturated with hydrogen gas. Colloidal Pt nanoparticles thus synthesized are polyhedra of different shapes. Carbon-supported Pt catalysts (Pt-1/C) are prepared by subsequently harvesting the Pt colloids and testing for the methanol oxidation reaction at room temperature. Transmission electron microscope (TEM) images are used to observe the Pt nanoparticle morphology and UV-vis spectra are used to monitor Pt precursor reduction with time. The Pt loadings are confirmed by thermogravimetric analysis. Interestingly, CO stripping cyclic voltammetry of Pt-1/C displayed double oxidation peaks with comparable intensities, one of which is 120 mV more negative than that of a typical CO oxidation peak on Pt. Besides the improved CO tolerance, Pt-1/C easily surpasses the mass activity of Pt/C from E-TEK by 55%. The method reported in this work presents a simple and eco-friendly route for producing carbon-supported platinum electrocatalysts with enhanced CO tolerance and mass activity.

Bifunctional anode catalysts for direct methanol fuel cells

Using the binding energy of OH* and CO* on close-packed surfaces as reactivity descriptors, we screen bulk and surface alloy catalysts for methanol electro-oxidation activity. Using these two descriptors, we illustrate that a good methanol electro-oxidation catalyst must have three key properties: (1) the ability to activate methanol, (2) the ability to activate water, and (3) the ability to react off surface intermediates (such as CO* and OH*). Based on this analysis, an alloy catalyst made up of Cu and Pt should have a synergistic effect facilitating the activity towards methanol electro-oxidation. Using these two reactivity descriptors, a surface PtCu3 alloy is proposed to have the best catalytic properties of the Pt–Cu model catalysts tested, similar to those of a Pt–Ru bulk alloy. To validate the model, experiments on a Pt(111) surface modified with different amounts of Cu adatoms are performed. Adding Cu to a Pt(111) surface increases the methanol oxidation current by more than a factor of three, supporting our theoretical predictions for improved electrocatalysts.

Influence of support’s oxygen functionalization on the activity of Pt/carbon xerogels catalysts for methanol electro-oxidation

Highly mesoporous carbon xerogels (CXs) were synthesized using two different resorcinol to catalyst, R/C, molar ratios and functionalized with different oxidation treatments. The synthesized carbon materials were used as supports for Pt particles, deposited by impregnation and reduction in formic acid. Both carbon supports and the catalysts prepared were characterized by means of N2 physisorption, scanning and transmission electron microscopy, temperature programmed desorption and X-ray diffraction. The electrochemical activity of the catalysts towards the oxidation of carbon monoxide and methanol was assayed by means of cyclic voltammetry and chronoamperometry. Textural characterization of the materials prepared evidenced more developed and mesopore-enriched porous structure for the carbon xerogel prepared using the highest R/C molar ratio. Enhanced textural properties of this material led to the preparation of highly active Pt-catalysts, which showed increased tolerance to CO and higher activity in methanol electro-oxidation, in comparison to Pt-E-TEK and the catalysts prepared in an analogous way using Vulcan XC-72R carbon black as support. Functionalization treatments resulted in enhanced dispersion, lower Pt crystal size and improved catalytic performance in the case of the catalysts prepared using the carbon xerogel possessing a less developed porous structure. Pt agglomeration was found to strongly determine the activity of the catalysts prepared. At high potentials, i.e. 1 V vs. RHE, the catalyst prepared using the carbon xerogel submitted to the most stringent oxidation treatment showed the highest specific peak activity towards methanol electro-oxidation, probably due to the positive influence of the presence of oxygen surface groups in Pt-carbon interaction, in spite of the higher agglomeration extent confirmed by TEM. On the other hand, at 0.60 V vs. RHE, highest activity towards methanol electro-oxidation was determined for the catalysts prepared using the non-functionalized carbon xerogel which can be explained in terms of enhanced reactant/product diffusion together with intrinsic higher catalytic activity due to lower Pt crystal size. In any case, the activity of this catalyst prepared using a carbon xerogel as support was found to be more than 2 times higher than the one determined for Pt/E-TEK, confirming the considerable improvement of the electrocatalytic system by means of optimization of the carbon support employed.

Fabrication and electrochemical property of hierarchically porous Au-Cu films

The paper presented an alloying/dealloying process for the fabrication of hierarchically porous alloy films (HPAFs). The fabrication process involved electrodeposition of copper on the substrate, annealing to produce new alloy phases, and selective dissolution of copper from the surface. Scanning electron microscopy (SEM) images suggested that the HPAFs were composed of large-sized ligament-channels structures (several micrometers) coupled with small-sized ligament-pores (tens nanometers) interpenetrating the big architectures. Energy dispersive X-ray analysis spectra (EDS) revealed the nonuniform distribution in chemical composition of the large-sized ligament-channel structures. Moreover, we demonstrated that the resulting materials showed catalytic activity for methanol electro-oxidation in alkali solution. We believe that the resulting HPAFs electrode is prospective in the fields of catalysis, sensors, and so on.

Enhanced activity of molybdovanadophosphoric acid modified Pt electrode for the electrooxidation of methanol

The Keggin-structure molybdovanadophosphoric acid (H 3+ x PMo 12− x V x O 40, x = 1, 2, 3, denoted as PMV) modified Pt electrode was studied by electrochemical measurements for methanol oxidation. It was discovered that both the catalytic activity and stability of the PMV modified Pt electrode were significantly enhanced. With the increase of the vanadium content in PMV, the catalytic activity and stability for methanol electrooxidation were also increased. The enhancements were attributed to the special properties of PMV, which increased the electron transfer coefficient of the rate-determining step. Therefore, the PMV has potential application as promoter for methanol electrooxidation in direct methanol fuel cell.

Microwave synthesis and characterization of Pt nanoparticles supported on undoped nanodiamond for methanol electrooxidation

Platinum nanoparticles supported on undoped nanodiamond (ND) with an average particle size of 50 nm were prepared using a microwave-heating polyol method. This method involves the addition of different amounts of chloroplatinic acid in the synthesis solution to obtain different Pt mass percentages. The Pt/ND catalysts were characterized by energy-dispersive spectroscopy, transmission electron microscopy, and X-ray diffraction. The small and uniform Pt nanoparticles were highly dispersed on ND supports. The mean size of the Pt particles was 4–5 nm. The effect of Pt loading on catalytic performance was investigated. Electrochemical measurements demonstrate that the Pt/ND catalysts prepared with proper Pt mass percentage exhibited a significantly high electrocatalytic activity for methanol electrooxidation.

Ultra-low-cost route to mesocellular siliceous foam from steel slag and mesocellular carbon foam as catalyst support in fuel cell

A large- and uniform-pore-sized mesocellular siliceous foam with a high surface area is successfully synthesized, using blast-furnace slag as an ultra-low-cost silica source, under neutral pH conditions. A high-purity silica source can be easily prepared from blast-furnace slag by extraction using an acid leaching process, followed by dissolution in NaOH solution. The mesocellular siliceous foam is synthesized by the interaction of these silicate precursors with P123 ((EO) 20(PO) 70(EO) 20) block copolymers in the presence of trimethylbenzene (TMB) used as a pore expander, followed by calcination at 550 °C in air. The resulting mesocellular siliceous foam denoted as MSU-F–SP has ∼30 nm sized large pores and high BET surface area of 554 m 2 g −1. The structure of MSU-F–SP is very similar to MSU-F silica synthesized from sodium silicate mixtures in the presence of P123 and TMB. Mesocellular carbon foam is easily synthesized through the direct carbonization of a tri-block copolymer in the as-synthesized mesostructured materials after acid-catalyzed polymerization using sulfuric acid. The sulfuric acid is used as a dehydration catalyst and the amount of sulfuric acid is controlled to optimize the pore structure. The mesocellular carbon foam synthesized using 0.16 mL of sulfuric acid per gram of composite material has the most uniform pore structures. A mesocellular carbon foam with high surface area and large mesopores allows good dispersion of Pt nanoparticles, leading to a higher methanol electro-oxidation activity in fuel cells compared to that of Pt nanoparticles on Vulcan XC-72.

Highly catalytic activity of Pt electrocatalyst supported on sulphated SnO 2/multi-walled carbon nanotube composites for methanol electro-oxidation

Highly catalytic active platinum nanoparticles supported on sulphated SnO 2/multi-walled carbon nanotube composites (Pt–S–SnO 2/MWCNT) are reported. As a novel catalyst support, S–SnO 2/MWCNT composites with both electron and proton conductivity can improve the catalytic activity and utilization of Pt catalyst in direct methanol fuel cell. X-ray diffraction and transmission electron microscopy show that the sulphated SnO 2 and Pt nanoparticle is coexist in the Pt–S–SnO 2/MWCNT composites and coated uniformly on the surface of the MWCNTs. Fourier transform infrared spectroscopy analysis proves that the MWCNT surfaces are modified with sulphated SnO 2 and a high concentration of SO x , and adsorbed OH species exist on the surface of the sulphated SnO 2. Electrochemical studies are carried out using cyclic voltammetry, chronoamperometry and CO stripping voltammetry. The results indicate that Pt–S–SnO 2/MWCNT catalysts have much higher catalytic activity and CO tolerance for methanol electrooxidation than Pt-SnO 2/MWCNTs, commercial Pt/C and PtRu/C.

Preparation of Pt Ag alloy nanoisland/graphene hybrid composites and its high stability and catalytic activity in methanol electro-oxidation

In this article, PtAg alloy nanoislands/graphene hybrid composites were prepared based on the self-organization of Au@PtAg nanorods on graphene sheets. Graphite oxides (GO) were prepared and separated to individual sheets using Hummer's method. Graphene nano-sheets were prepared by chemical reduction with hydrazine. The prepared PtAg alloy nanomaterial and the hybrid composites with graphene were characterized by SEM, TEM, and zeta potential measurements. It is confirmed that the prepared Au@PtAg alloy nanorods/graphene hybrid composites own good catalytic function for methanol electro-oxidation by cyclic voltammograms measurements, and exhibited higher catalytic activity and more stability than pure Au@Pt nanorods and Au@AgPt alloy nanorods. In conclusion, the prepared PtAg alloy nanoislands/graphene hybrid composites own high stability and catalytic activity in methanol electro-oxidation, so that it is one kind of high-performance catalyst, and has great potential in applications such as methanol fuel cells in near future.