Electrocatalytic Activity For Methanol Oxidation Research Articles

Electrocatalytic Activity of Au Core Au-Pt Alloy Shell Nanoparticles Prepared on Ionic Liquid Surface Via Metal Sputtering Deposition

Pt-based bimetallic nanoparticles (NPs) have been considered to be promising materials as electrocatalysts for improving the performance of fuel cells such as a direct methanol fuel cell because of decreasing CO poisoning on Pt surface and enhancing reactivity of Pt via a ligand effect. The compositional control of electrocatalyst surface is of significant importance to effectively utilize noble metals and to improve the electrocatalytic activities, because electrochemical reactions only occurs on the surface of particle catalysts. In our previous study, we have reported a facile method to synthesize noble metal NPs by metal sputter deposition on room temperature ionic liquids (RTILs) under vacuum condition.(1) This RTIL/metal sputtering technique was also useful to prepare core-shell-structured particles of Au@In2O3 and Pt@In2O3, which were prepared by the successive sputter deposition of noble metals and Indium into RTILs. Recently we have reported that a monolayer of Au nanoparticles was formed on the RTIL surface with single step deposition process when Au sputter deposition was carried out onto the surface of RTILs containing hydroxyl-functionalized cations.(2)In this study, we report the synthesis of Au core-AuPt alloy shell NPs monolayer by the sequential sputter deposition of Au and Pt onto hydroxyl-functionalized RTILs. The surface coverage of Pt atoms on individual Au NPs could be controlled with variation of Pt sputtering time. Original Au NPs monolayer was prepared by the sputter deposition of Au on the surface of 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate (HyEMI-BF4) used as a RTIL with a discharge current of 10 mA under argon pressure of 20 Pa for 150 s. The subsequent sputter deposition of Pt was carried out on thus-obtained Au NPs monolayer. The sputtering condition used for Pt deposition was the same as that used for Au deposition except for sputtering time. The sputter deposition of Au changed the color of RTIL surface from colorless to reddish blue due to the Au film formation. By subsequent sputter deposition of Pt, the film on the solution surface tuned brownish. Extinction spectra of films showed an LSPR peak at 540 nm, the intensity of which was lessened with an increase in the Pt sputtering time and finally vanished after Pt sputter deposition for 80 min or more. This result suggested that the sputter deposition of Pt onto Au film caused surface modification of individual Au NPs. From TEM measurement, it was found that the films prepared by sputter deposition of Au and Pt were monolayers composed of spherical particles, the size of which increased with elapse of Pt sputtering time from 4.2 to 4.8 nm. Since pure Pt particles were not observed in the film, it was suggested that sputtered Pt species were simply deposited on individual Au particles floated on the RTIL surface without additional nucleation. The XPS measurement revealed that deposited Pt formed the surface layer composed of Au-Pt alloy on Au cores. The cyclic voltammograms of Au-Pt bimetallic NPs monolayers transferred on HOPG electrodes were measured in an N2-saturated 0.5 mol dm-3 H2SO4aqueous solution, in which a cathodic peak assigned to the reduction of Au oxide monolayer appeared at 1.2 V vs. RHE along with a pair of redox peaks attributable to the adsorption/desorption of hydrogen on Pt surface at ca. 0.02-0.04 V vs. RHE. The electrochemical surface areas (ECSA) of Au and Pt were obtained by measuring charges flowed in reduction of Au oxide monolayer and in hydrogen desorption on Pt surface, respectively. The fraction of Pt ECSA was higher than the Pt content in particles, regardless of Pt sputtering time, indicating that Pt atoms were predominantly deposited on the surface of Au particles. The methanol oxidation activity of the Au-Pt NPs monolayers was evaluated by a cyclic voltammetry in a 0.5 mol dm-3 KOH aqueous solution containing 0.5 mol dm-3methanol. The obtained voltammograms exhibited an anode peak at ca. 0.9 V vs. RHE, assignable to methanol oxidation (Fig. 1). The peak current intensity of methanol oxidation for Au-Pt bimetallic films was dependent on the Pt sputtering time but was larger than those of monometallic counterparts, indicating that the electrocatalytic activity for methanol oxidation was enhanced by the modification of Au NPs monolayer with AuPt alloy shell layer. The maximum intensity was obtained for the Au-Pt NPs film prepared with Pt sputtering time for 80 min. References T. Torimoto, et al., Appl. Phys. Lett., 89, 243117 (2006).T. Torimoto, et al., Phys. Chem. Chem. Phys., 17, 13150 (2015). Figure 1

Prussian Blue Nanocubes on Reduced Graphene Oxide As a Modified Platinum Electrode for Synergistic Methanol Oxidation

We report a facile synthetic strategy for the in-situ growth of high-quality Prussian blue nanocubes (PBNCs) at the amine functionalized silicate sol–gel matrix (TPDT)–RGO composite via the electrostatic interaction. Subsequently, Pt nanostructures are electrodeposited onto the preformed ITO/TPDT–RGO–PB electrode to prepare the RGO/PB/Pt catalyst. The significance of the present method is that the PBNCs could be in-situ grown by inter-connecting the RGO layers, led to 3D cage-like porous nanostructure. The modified electrodes are characterized by FESEM, EDAX, XRD, XPS and electrochemical techniques. The RGO/PB/Pt catalyst exhibits the synergistic electrocatalytic activity and high stability towards the methanol oxidation. The porous nature of the TPDT and PB, and unique electron transfer mediating behavior of PB integrated with RGO in the presence of Pt nanostructures facilitated synergistic electrocatalytic activity for methanol oxidation.

Ligand-Free Noble Metal Nanocluster Catalysts on Carbon Supports via "Soft" Nitriding.

We report a robust, universal "soft" nitriding method to grow in situ ligand-free ultrasmall noble metal nanocatalysts (UNMN; e.g., Au, Pd, and Pt) onto carbon. Using low-temperature urea pretreatment at 300 °C, soft nitriding enriches nitrogen-containing species on the surface of carbon supports and enhances the affinity of noble metal precursors onto these supports. We demonstrated sub-2-nm, ligand-free UNMNs grown in situ on seven different types of nitrided carbons with no organic ligands via chemical reduction or thermolysis. Ligand-free UNMNs supported on carbon showed superior electrocatalytic activity for methanol oxidation compared to counterparts with surface capping agents or larger nanocrystals on the same carbon supports. Our method is expected to provide guidelines for the preparation of ligand-free UNMNs on a variety of supports and, additionally, to broaden their applications in energy conversion and electrochemical catalysis.

Plasma synthesis of Pd/PdO supported on porous graphene as electrocatalyst for methanol oxidation

Pd/PdO nanoparticles supported on porous graphene (PG) are synthesized by a gas-liquid interfacial plasma method using Pd(NO3)2·2H2O as precursor. The Pd/PdO ratios can be controlled by changing the amount of Pd(NO3)2·2H2O. The synthesized Pd/PdO electrocatalysts exhibit a high electrocatalytic activity for methanol oxidation. The Pd/PdO nanoparticles attached on PG support shows better activity than that on oxidation carbon nanotubes support for methanol oxidation. In addition, our findings show that the PdO present in the Pd nanoparticles can enhance the electrocatalytic activity. It is worth to mention that the Pd/PdO nanoparticles supported on porous graphene catalysts show better electrochemical stability than that of commercial Pd/C catalyst.

In Situ Growth of Prussian Blue Nanostructures at Reduced Graphene Oxide as a Modified Platinum Electrode for Synergistic Methanol Oxidation.

Herein, we report a facile synthetic strategy for the in situ growth of Prussian blue nanostructures (PB NSs) at the amine-functionalized silicate sol-gel matrix (TPDT)-RGO composite via the electrostatic interaction. Subsequently, Pt nanostructures are electrodeposited onto the preformed ITO/TPDT-RGO-PB electrode to prepare the RGO/PB/Pt catalyst. The significance of the present method is that the PB NSs are in situ grown by interconnecting the RGO layers, leading to 3D cage-like porous nanostructure. The modified electrodes are characterized by FESEM, EDAX, XRD, XPS, and electrochemical techniques. The RGO/PB/Pt catalyst exhibits synergistic electrocatalytic activity and high stability toward methanol oxidation. The porous nature of the TPDT and PB and unique electron-transfer mediating behavior of PB integrated with RGO in the presence of Pt nanostructures facilitated synergistic electrocatalytic activity for methanol oxidation.

Facile Synthesis of Core/Shell-like NiCo2O4-Decorated MWCNTs and its Excellent Electrocatalytic Activity for Methanol Oxidation.

The design and development of an economic and highly active non-precious electrocatalyst for methanol electrooxidation is challenging due to expensiveness of the precursors as well as processes and non-ecofriendliness. In this study, a facile preparation of core-shell-like NiCo2O4 decorated MWCNTs based on a dry synthesis technique was proposed. The synthesized NiCo2O4/MWCNTs were characterized by infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and selected area energy dispersive spectrum. The bimetal oxide nanoparticles with an average size of 6 ± 2 nm were homogeneously distributed onto the surface of the MWCNTs to form a core-shell-like nanostructure. The NiCo2O4/MWCNTs exhibited excellent electrocatalytic activity for the oxidation of methanol in an alkaline solution. The NiCo2O4/MWCNTs exhibited remarkably higher current density of 327 mA/cm2 and a lower onset potential of 0.128 V in 1.0 M KOH with as high as 5.0 M methanol. The impressive electrocatalytic activity of the NiCo2O4/MWCNTs is promising for development of direct methanol fuel cell based on non-Pt catalysts.

Preparation and characterization of Pt–CeO2/C and Pt–TiO2/C electrocatalysts with improved electrocatalytic activity for methanol oxidation

Pt–TiO2/C and Pt–CeO2/C electrocatalysts were synthesized by solid state reaction of TiO2/C and CeO2/C powders using intermittent microwave heating, followed by chemical reduction of platinum ions using mixed reducing agents of ethylene glycol and sodium borohydride. The crystal structure, surface morphology and chemical composition of prepared electrocatalysts were investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDX). The phase angle values of different Pt diffraction planes in Pt–TiO2/C and Pt–CeO2/C were shifted in the positive direction relative to those in Pt/C. Pt particles with diameter values of 3.06 and 2.78nm were formed in Pt–TiO2/C and Pt–CeO2/C, respectively. The electrochemical performance of prepared electrocatalysts was examined using cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. Pt–CeO2/C showed an enhanced oxidation current density when compared to Pt/C. Long time oxidation test at Pt–TiO2/C and Pt–CeO2/C revealed their improved stability. Lower charge transfer resistance values were estimated at Pt–metal oxide/C electrocatalysts.

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.

Nitrogen-doped porous carbons supported Pt nanoparticles for methanol oxidation in alkaline medium

Honeycomb-like nitrogen-doped porous carbons (NPCs) have been prepared using ionic liquids 1-butyl-3-methylimidazolium dicyanamide (BMIMdca) as the carbon precursor, and silica spheres as the templates. The obtained NPCs were employed as supports of Pt nanoparticles for methanol oxidation in alkaline medium. The high surface area and the porous structure are beneficial to the uniform dispersion of Pt nanoparticles to increase their utilization. The electrocatalytic activity of methanol oxidation on Pt nanoparticles supported on NPCs (Pt/NPCs) is higher than that of Pt on commercial Vulcan XC-72R carbon (Pt/C). The results showed that NPCs are a potential candidate for application as electrocatalyst supports in alkaline direct methanol fuel cells.

Electrochemical Deposition of Pt–RuO x ⋅nH2O Composites on Conductive Diamond and Its Application to Methanol Oxidation in Acidic Media

Boron-doped diamond (BDD) films were used as substrates for the electrochemical deposition of a platinum–hydrous ruthenium oxide (Pt–RuO x ⋅nH2O) composite with promising electrocatalytic activity for methanol oxidation. The influence of the BDD surface termination was checked, and it was found that oxidized diamond (BDD-O) not only allows more efficient RuO x ⋅nH2O deposition but also enables a higher surface concentration of oxygenated carbon species. Scanning electron microscopy (SEM) and cyclic voltammetry experiments have shown that, with a BDD-O support, an increase of the oxide loading from ca. 3 to ca. 140 μg cm−2 results in an enhancement of approximately six times of the specific surface area of deposited Pt particles, with beneficial effects on the electrocatalytic activity for methanol oxidation. However, in terms of resistance to fouling, a lower amount of RuO x ⋅nH2O appeared to be more advantageous, probably due to the fact that, as evidenced by X-ray photoelectron spectroscopy (XPS), it allows higher surface concentration of oxidized species of both carbon and platinum. These species could act as oxygen donors and may facilitate further oxidation of carbon monoxide to CO2.

Electrocatalytic Study of Efficient Synthesized Graphene Nanosheets Incorporated with Pt Nanoparticles for Methanol Oxidation Reaction

AbstractGraphene nanosheets/Pt (GNS/Pt) nanocomposite was successfully fabricated via clean chemical reduction method. The nanocomposite was characterized by X‐ray diffraction, field emission scanning electron microscope and high resolution transmission electron microscope, which revealed that Pt nanoparticles were completely formed and homogenously distributed on the GNS. The electrochemical activities of the catalysts were investigated by cyclic voltammogram. The experimental results showed that GNS/Pt nanocomposites catalyst exhibited superior electrocatalytic activity for methanol oxidation. These results suggest that GNS/Pt nanocomposites would be a promising anode catalyst for DMFC.

Facile preparation of three-dimensional porous Pd–Au films and their electrocatalytic activity for methanol oxidation

Pd–Au porous foam films with three-dimensional hierarchical pores consisting of interconnected dendrite walls are obtained by using the hydrogen bubble dynamic template. The films are characterized by scanning electron microscope, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, as well as electrochemical techniques. The CV curves have confirmed that the Pd–Au catalysts have high catalytic activity toward methanol oxidation. The catalytic activities of these Pd–Au catalysts are strongly dependent on the atomic ratio of Pd/Au. Among all the Pd–Au catalysts, the Pd1Au1 catalyst is found to possess superior catalytic activity and stability toward methanol oxidation.

Preparation of Pt/poly(aniline-co-orthanilic acid) nanocomposites and their applications for electrocatalytic oxidation of methanol

Copolyanilines containing various molar feed ratios of aniline (Ani) and orthanilic acid (Oaa) units are chemically synthesized using ammonium persulfate as an oxidant. The structure and morphology of the poly(aniline-co-orthanilic acid)s are characterized using Fourier transform-infrared spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The XPS results show that a saturated doping state is achieved when the Ani/Oaa molar feed ratio is less than 20/1. The SEM images reveal that the copolyaniline films are composed of highly porous nanowires when the feed molar ratio of Ani/Oaa is more than 4/1. The poly(aniline-co-orthanilic acid)s are used as Pt catalyst supports. Transmission electron microscopy (TEM) results show that Pt particles disperse more uniformly onto the highly porous nanowires of P(Ani10-co-Oaa1) (feed molar ratio = 10:1) than onto other copolyanilines. The electrocatalytic behaviors of copolyaniline-Pt electrodes toward the oxidation of methanol are studied using cyclic voltammetry. Among the copolyaniline-Pt electrodes studied, the P(Ani10-co-Oaa1)-Pt electrode shows the highest electrocatalytic activity for methanol oxidation.

Direct synthesis of Fe-ZSM-5 zeolite and its prospects as efficient electrode material in methanol fuel cell

New method of direct synthesis of Fe-ZSM-5 zeolite using tetrapropyl ammonium bromide (TPABr) as the template is reported in this study. The synthesis was based on one step procedure and did not involve the usual ion-exchange step to effect incorporation of the metal ion. The zeolite sample was characterized by XRD, FT-IR, TGA, SEM with EDX, and BET adsorption techniques. The average diameter of the porous particle of zeolite was about 10µm and it was a spherical cluster of crystals of about 141nm long along one of its axis. Zeolite-modified glassy carbon electrode (GCE) was prepared by using the mixture of the synthesized zeolite and carbon black (Vulcan X-72) and casting it as a thin layer. With modified GCE as the working electrode, the oxidation of methanol in alkaline medium was studied by cyclic voltammetry. The response of the electrode for methanol oxidation in alkaline medium is promising and it highlights the candidature of the synthesized material for methanol fuel cell. The electrochemical behavior of Fe-ZSM-5 in acidic medium reveals the oxidation state of iron in the zeolite. Cationic iron in the zeolite framework imparts electrocatalytic activity for methanol oxidation.

Ni–P–SnO2/C composite: Synthesis, characterization and electrocatalytic activity for methanol oxidation in KOH solution

Ni–P–SnO2/C composite was prepared by electroless reduction of nickel ions on SnO2/C powder. The weight percentage of SnO2 in the prepared composite was varied as 2.5–20. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis were employed to investigate the morphology, particle size and chemical composition of Ni–P–SnO2/C composite. Nickel islands with an average diameter of 0.33 μm were formed in the composite containing 10 wt.% SnO2 [Ni–P–SnO2/C-10]. The electrochemical performance of Ni–P–SnO2/C composite in KOH solution was studied using cyclic voltammetry and electrochemical impedance spectroscopy (EIS). Its electron transfer coefficient and electron transfer rate constant values were determined as a function of SnO2 weight percentage. The impedance value was found to gradually decrease with increasing SnO2 content getting its lowest value in Ni–P–SnO2/C-10 composite. The effect of altering the sweeping potential and KOH concentration on NiOOH film thickness in Ni–P–SnO2/C composite was investigated. An enhanced electrocatalytic activity of the prepared composite towards methanol oxidation in KOH solution was shown. In presence of methanol, the diameter of semi-circle was greatly reduced to record a much lowered Rct value of 0.25 Ω cm2.

Facile electrochemical synthesis, using microemulsions with ionic liquid, of highly mesoporous CoPt nanorods with enhanced electrocatalytic performance for clean energy

We have established a facile and generalizable electrochemical synthesis of metallic mesoporous nanorods in the nanochannels of commercial polycarbonate membranes using microemulsions containing ionic liquids. Herein, we report the preparation of magnetic CoPt nanorods with various meso or nanopores distributions, depending on the microemulsion type (ionic liquid –in-water (IL/W), bicontinuous (β) or water-in-ionic liquid (W/IL)). The synthesized porous nanorods show a much enhanced electrocatalytic activity for methanol oxidation in comparison with compact Pt nanorods (up to 12 times) or Pt/C electrocatalyst (Pt nanoparticles or commercial black platinum). Therefore, the synthesized CoPt mesoporous nanorods could be excellent catalysts in direct methanol fuel cells (DMFC's), as they have high surface areas, large pore volumes and high corrosion stability, and they exhibit promising catalytic properties.

Stability and phase transfer of catalytically active platinum nanoparticle suspensions

In this work, we present a robust synthesis protocol for platinum nanoparticles that yields a monomodal dispersion of particles that are approximately 100 nm in diameter. We determine that these particles are actually agglomerates of much smaller particles, creating a “raspberry” morphology. We demonstrate that these agglomerates are stable at room temperature for at least 8 weeks by dynamic light scattering. Furthermore, we demonstrate consistent electrocatalytic activity for methanol oxidation. Finally, we quantitatively explore the relationship between dispersion solvent and particle agglomeration; specifically, particles are found to agglomerate abruptly as solvent polarity decreases.

Mesoporous zeolite LTA-encapsulated Ni(II)-Schiff base complex: an efficient heterogeneous catalyst for electrocatalytic oxidation of methanol in alkaline media

A series of Ni(II)-Schiff base complexes were encapsulated in mesoporous zeolite LTA (denoted as NiL/LTA with L = salen, salpn, salbn, salphen, and tBu4salen) and showed superior electrocatalytic activities for methanol oxidation in alkaline media. Different performances for methanol oxidation were due to the existence of different type of ligand that may originate from different steric and electronic effects exerted by the substituents present on the backbone of the salen ligands and/or by the different lengths of diamine bridge. The use of mesoporous zeolite LTA with nano-cages of 3 nm makes possible the interaction between the partially coordinated Ni(salen) in adjacent or appropriate sites in a nano-cage through the zeolite lattice oxygen, leading to the formation of new electrochemically accessible active sites and a great improvement in the electrocatalytic activities. A possible mechanism was proposed that electrocatalytic oxidation of methanol on NiL/LTA/GCEs was done by reaction with Ni(III)LO(OH) and also direct electro-oxidation reaction.

Carbon nanotubes supported cerium dioxide and platinum nanohybrids: Layer-by-layer synthesis and enhanced electrocatalytic activity for methanol oxidation

We successfully synthesize carbon nanotubes (CNTs) supported cerium dioxide and platinum (Pt/CeO2/CNTs) nanohybrids via layer-by-layer assembly. The composition, morphology and structure of the as-prepared Pt/CeO2/CNTs nanohybrids are characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectrometer (EDX), selected-area electron diffraction (SAED), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and inductively coupled plasma atomic emission spectrometry (ICP-AES). By comparison of the electrocatalytic properties of the Pt/CeO2/CNTs with the Pt/CNTs, we systematically investigate the promotion effect of CeO2 on the Pt/CeO2/CNTs catalysts towards methanol oxidation. It is found that the introduction of CeO2 not only enhances the electrocatalytic activity and stability of the Pt/CeO2/CNTs catalyst for methanol oxidation but also minimizes the CO poisoning, probably accounting for the good oxygen carrying capacity of CeO2 and its high stability in acidic solution.

Gold film supported nanostructured Cu/Pt catalyst with high electrochemical surface area and enhanced electrocatalytic activity for methanol oxidation

The rough Cu film was prepared by electrochemical reduction of copper ions at the surface of gold film electrode (GFE). Nanostructured Cu/Pt catalyst was prepared by partially galvanic replacement of Cu with platinum by simply immersion of Cu-coated gold film electrode in a K2PtCl6 aqueous solution. The structure and nature of the fabricated Cu and Cu/Pt species were characterized by scanning electron microscopy and energy dispersive X-ray spectrometry. Cu-/Pt-coated gold film electrode exhibits really high electrochemical active surface area and remarkable electrocatalytic activity toward methanol oxidation. The effect of electrodeposition potential on the stability of the catalyst during the formation of Cu layer was comparatively investigated by performing methanol oxidation using voltammetry methods.