Methanol Oxidation In Alkaline Media Research Articles

Methanol oxidation on Pd/Pt(poly) in alkaline solution

Bimetallic electrodes prepared by Pd nanoislands spontaneously deposited on polycrystalline platinum, Pt(poly), at submonolayer coverage were explored for methanol oxidation in alkaline media. Characterization of obtained Pd/Pt(poly) nanostructures was performed ex situ by AFM imaging, spectroscopic ellipsometry and by X-ray photoelectron spectroscopy. In situ characterization of the obtained electrodes and subsequent methanol oxidation measurements were performed by cyclic voltammetry in 0.1 M KOH. Platinum surface with 35% Pd coverage exhibited the highest catalytic activity for methanol oxidation in alkaline media, exceeding those of bare Pt and Pd. Both synergistic and electronic effects are responsible for such enhanced catalysis. The origin of the synergistic effect and possible reaction pathways for methanol oxidation were discussed taking into account the activity of obtained bimetallic electrodes for the oxidation of CO and formaldehyde, as the most probable reaction intermediates.

Facile synthesis of Pt–Pd bimetallic nanoparticles by plasma discharge in liquid and their electrocatalytic activity toward methanol oxidation in alkaline media

The Pt–Pd bimetallic nanoparticles for direct methanol fuel cell applications were successfully prepared by plasma discharge in aqueous solution. The obtained nanoparticles were characterized by energy dispersive X-ray spectroscopy, X-ray diffraction spectroscopy, and transmission electron microscopy. During plasma discharge, the nanoparticles were produced from the erosion of electrodes. It was noted that the erosion amount of anode electrodes was much greater than that of cathode electrodes so that the composition of Pt–Pd bimetallic nanoparticles could be changed with different power types and electrode configurations. Diffraction patterns fitted from Gaussian devolution indicated that the crystalline phase of Pt40Pd60 products was composed of pure Pt, pure Pd and Pt–Pd alloy phases. The morphology of synthesized nanoparticles showed that nanowires connected with quasi-spherical nanoparticles with 2–3nm in diameter were observed and large spherical particles with >50nm in diameter were also detected intermittently. The cyclic voltammetric measurement and continuous potential scan demonstrated that Pt40Pd60 had much higher catalytic activity and better resistance to CO poisoning than Pt94Pd6 and Pt1Pd99 for methanol oxidation. These results indicate that the Pt40Pd60 could be an excellent candidate for the direct methanol fuel cell applications.

Electrocatalysis of carbon black- or chitosan-functionalized activated carbon nanotubes-supported Pd with a small amount of La2O3 towards methanol oxidation in alkaline media

The Pd/C catalysts with and without a small amount of La2O3 were synthesized by a simple reduction reaction with sodium borohydride in aqueous solution. The structure and morphology of these catalysts were characterized by X-ray diffraction, energy dispersive X-ray spectroscopy and transmission electron microscopy. The electrocatalytic performance of these catalysts for methanol oxidation in alkaline media was investigated using cyclic voltammetry, chronoamperometry and CO stripping experiments. The results show that the Pd–La2O3/C catalyst has a higher catalytic activity than the Pd/C catalyst, but the effect of La2O3 cannot be explained by a bi-functional mechanism. X-Ray photoelectron spectroscopy analyses suggest that the higher content of metallic Pd caused by the addition of La2O3 contributes to the better catalytic activity of Pd–La2O3/C. Based on the good electrocatalytic performance of Pd–La2O3/C, the Pd–La2O3 catalyst supported on chitosan (CS)-functionalized activated carbon nanotubes was prepared, and it exhibited a better catalytic activity. The improvement is attributed to the good dispersion status of metal particles and the further increase of metallic Pd due to the presence of CS.

Carbon nanofibers doped by NixCo1−x alloy nanoparticles as effective and stable non precious electrocatalyst for methanol oxidation in alkaline media

Bimetallic alloys have superior physiochemical characteristics compared to the individual metals. In this study, NixCo1−x (x=0.0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0) alloy nanoparticles incorporated in carbon nanofibers are investigated as electrocatalysts for methanol oxidation in the alkaline media. Preparation of the introduced nanofibers is achieved by calcination of electrospun nanofibers composed of nickel acetate, cobalt acetate and poly(vinyl alcohol) in argon atmosphere. The catalytic activity of cobalt enhances the carbonization of the utilized polymer which results in producing nickel/cobalt alloys nanoparticles embedded in carbon nanofibers. Due to the synergistic influence of the introduced alloy, both of the current density and onset potential were distinctly affected by the nanoparticles composition; Ni0.5Co0.5 alloy nanoparticles-doped carbon nanofibers reveal current density and onset potential of 240mA/cm2 and 110mV [vs. Ag/AgCl], respectively. Interestingly it was proofed that, compared to nanoparticles, the nanofibrous morphology has a distinct positive influence on the electrocatalytic activity due to the effect of the one dimensional structure which facilitates the electrons transfer and consequently decreases the IR drop. The introduced nanofibers showed good stability because of the alloy structure. Overall, this study opens new avenue for the transition metals alloys and the nanofibrous morphology to be invoked to produce novel and effective class of non-precious electrocatalysts.

Nickel oxide/nitrogen doped carbon nanofibers catalyst for methanol oxidation in alkaline media

Uniform and highly doped nitrogen carbon nanofibers (N-CNFs) have been produced by electrospinning of solution mixture that contains polyacrylonitrile, polyaniline and graphene and followed by annealing at 1200°C. The NiO catalyst was loaded onto N-CNFs by chemical precipitation of Ni(OH)2 and treating at 400°C. The physicochemical characterizations show that the N-CNFs have an average diameter of 250nm with nitrogen-doping level of 17wt. % and BET surface area of 440m2g−1. The NiO catalyst with particle size of 7.0 to 8.0nm was uniformly loaded over the surface of the carbon nanofibers. The electrocatalytic activity of NiO/N-CNFs hybrid for methanol oxidation reaction in basic medium has been investigated by cyclic voltammetry and chronoamperometry techniques. The results show that the NiO/N-CNFs catalyst has superior specific and mass activities for methanol oxidation over the other nickel based catalysts. In addition negative shift in the methanol oxidation potential was observed which relies on the loading amount of NiO/N-CNFs catalyst. The highly doped nitrogen carbon nanofibers electrode based on polyacrylonitrile, polyaniline and graphene composite could be considered as a promising candidate to act as a catalyst support material.

Mesoporous Ti(0.5)Cr(0.5)N supported PdAg nanoalloy as highly active and stable catalysts for the electro-oxidation of formic acid and methanol.

We report a robust noncarbon Ti0.5Cr0.5N support synthesized by an efficient solid-solid phase separation method. This ternary nitride exhibits highly porous, sintered, and random network structure with a crystallite size of 20-40 nm, resulting in a high specific surface area. It is not only kinetically stable in both acid and alkaline media, but also electrochemically stable in the potential range of fuel cell operation. Two typical anode reactions, formic acid oxidation in acid media and methanol oxidation in alkaline media, are employed to investigate the possibility of Ti0.5Cr0.5N as an alternative to carbon. Bimetallic PdAg nanoparticles (∼4 nm) act as anode catalysts for the two anode reactions. PdAg/Ti0.5Cr0.5N exhibits much higher mass activity and durability for the two reactions than PdAg/C and Pd/C catalyst, suggesting that mesoporous Ti0.5Cr0.5N is a very promising support in both acid and alkaline media.

Green synthesis of core–shell gold–palladium@palladium nanocrystals dispersed on graphene with enhanced catalytic activity toward oxygen reduction and methanol oxidation in alkaline media

Well-defined core–shell gold–palladium@palladium nanocrystals (AuPd@Pd) are facilely prepared by a simple and green wet-chemical method at 25 °C. A Good's buffer, 2-[4-(2-hydroxyethyl)-1-piperazinyl] ethanesulfonic acid (HEPES), is used as a reducing agent and a shape-directing agent, while there is no template, seed, organic solvent, or surfactant involved. The AuPd@Pd nanocrystals are uniformly dispersed on graphene nanosheets by ultrasonication, resulting in the formation of graphene supported AuPd@Pd (G-AuPd@Pd). The as-prepared nanocomposites exhibit the improved catalytic activity, good tolerance, and better stability for oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) in alkaline media, compared with the G-Pd and commercial Pd black catalysts. The as-developed method may provide a promising pathway for large-scale fabrication of AuPd-based catalysts.

Electrocatalysis of carbon black- or poly(diallyldimethylammonium chloride)-functionalized activated carbon nanotubes-supported Pd–Tb towards methanol oxidation in alkaline media

The Pd–Tb/C catalysts with different Pd/Tb ratios were synthesized by a simple simultaneous reduction reaction with sodium borohydride in aqueous solution. The structure and morphology of those catalysts had been characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The electrocatalytic performance of those catalysts for methanol oxidation in alkaline media was investigated using cyclic voltammetry (CV), linear sweep voltammetry (LSV) and CO stripping experiments. It is found that the 20%Pd–1%Tb/C catalyst has a higher catalytic activity than the 20%Pd/C catalyst, but the effect of Tb cannot be explained by a bi-functional mechanism. According to the X-Ray photoelectron spectroscopy (XPS) analyses, it is suggested that the higher content of metallic Pd caused by the addition of Tb contributes to the better catalytic activity of 20%Pd–1%Tb/C. Based on the good electrocatalytic performance of 20%Pd–1%Tb/C, the 20%Pd–1%Tb catalyst supported on poly(diallyldimethylammonium chloride) (PDDA)-functionalized activated carbon nanotubes was prepared, and it exhibits a better catalytic activity. The improvement mainly results from the further increase of metallic Pd due to the presence of PDDA.

Highly active Pt-on-Au catalysts for methanol oxidation in alkaline media involving a synergistic interaction between Pt and Au

Several Pt-on-Au/SnO2-CNTs catalysts with different Pt loadings are synthesized through site-selective electrodeposition for catalytic methanol oxidation reaction (MOR) in alkaline media. The catalysts are tested to exhibit extremely high Pt mass activity towards MOR, and the catalytic mechanism is proposed based on the synergetic effect between Pt and Au, in which the Pt entities provide Pt-OH for oxidation of alkoxide (CH3O−) while the Au surfaces provide adsorption sites for alkoxide. It is expected that this mechanism could be extended to developing high performance non-Pt catalysts for MOR in alkaline media.

Electrocatalytic performance of Pd–Ni nanowire arrays electrode for methanol electrooxidation in alkaline media

A successful approach to prepare the Pd–Ni nanowire arrays electrode without carbon supports was reported. The morphology and crystallinity of nanowire were characterized by transmission electron microscopy, selected-area electron diffraction (SAED), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses, respectively. The results show that the diameters of the nanowire are in the range of 65–75 nm, and the polycrystalline binary solid solution alloy is formed in the Pd–Ni nanowire. Cyclic voltammograms, chronoamperograms, and electrochemical impedance spectroscopy demonstrate that the Pd–Ni nanowire arrays electrodes show excellent electrocatalytic performance for methanol oxidation in alkaline media. The catalytic activity of Pd–Ni nanowire arrays electrode is ~1.39 times higher than that of the Pd nanowire arrays electrode and ~2.28 times higher than that of the commercial Pd/C catalyst. This is mostly owing to the transfer of electron density from Ni to Pd. These results indicate that Pd–Ni nanowire arrays electrode is very promising in an alkaline direct methanol fuel cell.

Reduction free room temperature synthesis of a durable and efficient Pd/ordered mesoporous carbon composite electrocatalyst for alkaline direct alcohols fuel cell

The development of easy and environmentally benign synthesis methods of efficient electrocatalysts for use in energy conversion applications motivates researchers all over the world. Here we report a novel and versatile method to synthesize well-dispersed palladium-functionalized ordered mesoporous carbons (Pd–OMCs) at room temperature without any reducing agent by one-pot mixing of tri(dibenzylideneacetone)palladium(0) (Pd2DBA3) and OMCs together in a common N,N-dimethylformamide (DMF) solution. The formation of Pd nanoparticles and their crystallization on the OMC is catalyzed by protons in the solution and can thus be controlled by the solution pH. The complete process and the as-prepared nanocomposite was characterized by UV-spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectrum (XPS), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The electrocatalytic property of the decorated material was examined with cyclic voltammetry (CV). The Pd–OMC composite shows up to two times higher electrocatalytic ability with a significantly better durability towards ethanol and methanol oxidation in alkaline media compared to commercial high surface area conductive carbon black Vulcan XC-72 decorated with equivalent Pd nanoparticles. Our described method provides new insight for the development of highly efficient carbon based nanocatalysts by simple and environmentally sound methods.

Electrochemical Synthesis of Monodisperse Nickel with Predominant {111} Orientation and High Electro-Oxidation Activity for Methanol

Controllable crystal facet of Ni nanoparticles modified glass carbon electrodes (Ni/GC) were successfully in situ prepared by different applied potential ranges of cyclic voltammetry and were employed as catalyst for methanol oxidation in alkaline media. By altering the scanning potential ranges, different crystal facets and size of Ni nanoparticles can be obtained and the crystal facets of such Ni nanoparticles had a direct influence on their catalytic activity. The Ni/GC prepared at a range of scanning potential from −2.0 to −2.2 V vs. Ag/AgCl presented the highest catalytic activity for methanol oxidation with a current density of 8.47 mA/cm2. The much improved catalytic activity may be attributed to the applied reduction potentials which effect on the rate of nucleation and growth of nickel nanoparticles, making the Ni nanoparticles along {111} direction growth to expose more active sites.

Star-shaped Pd@Pt core–shell catalysts supported on reduced graphene oxide with superior electrocatalytic performance

A surfactantless, one-pot reduction approach for Pd@Pt core–shell nano-stars on reduced graphene oxide with enhanced catalytic activity and stability for methanol oxidation in alkaline media.

Simple synthesis of hollow Pt–Pd nanospheres supported on reduced graphene oxide for enhanced methanol electrooxidation

Shape-controlled synthesis of bimetallic catalysts attracts increasing attention, because their catalytic performance is closely correlated with the size, shape and crystal structure. In this report, a rapid and simple route is developed for large-scale synthesis of Pt–Pd hollow nanospheres (Pt–Pd HNSs) supported on reduced graphene oxide nanosheets (RGOs) under mild conditions, while no surfactant, seed, or template is involved. The as-prepared nanocomposites display the improved electrocatalytic activity and better stability for methanol oxidation in alkaline media, compared with commercial Pt black and Pd black catalysts. This work may open a new route for construction of Pt-based bimetallic catalysts in fuel cells.

Electrocatalytic activity of nanostructured Ni and Pd–Ni on Vulcan XC-72R carbon black for methanol oxidation in alkaline medium

Ni and Pd–Ni nanoparticles were chemically deposited on Vulcan XC-72R carbon black by impregnation method using NaBH4 as a reducing agent. The prepared electrocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX). The electrocatalytic activity of Ni/C and Pd–Ni/C electrocatalysts towards methanol oxidation in 0.5 M KOH solution was examined using cyclic voltammetry and chronoamperometry. Two methanol oxidation peaks were observed on the Pd–Ni/C at 0 and +860 mV. Their current density values are higher than those at Pd/C and Ni/C electrocatalysts by 1.92 and 1.68 times, respectively. The catalytic rate constant of methanol oxidation reaction at Ni/C and Pd–Ni/C electrocatalysts in (0.2 M MeOH + 0.5 M KOH) solution was estimated using double-step chronoamperometry as 5.64 × 103 and 6.25 × 103 cm3 mol−1 s−1, respectively. Pd–Ni/C is more stable than Pd/C and Ni/C electrocatalysts. Therefore, Pd–Ni/C is a suitable as a less expensive electrocatalyst for methanol oxidation in alkaline medium.

Ionic Liquid-Assisted Synthesis of Au–Pt Bimetallic Particles for Enhanced Methanol Electrooxidation

A facile ionic liquid-assisted route is proposed for the successful synthesis of Au–Pt bimetallic particles with a core–shell structure at room temperature. The synthesized bimetallic particles exhibit flowerlike morphologies with a tunable composition (Au and Pt) by controlling the molar ratios between metal precursors. Specifically, the synthesized Au–Pt particles exhibit efficient electrocatalytic activities toward methanol oxidation in alkaline media, which indicates their useful application in direct methanol fuel cells.

Microwave heated synthesis of carbon supported Pd, Ni and Pd–Ni nanoparticles for methanol oxidation in KOH solution

Pd, Ni and Pd–Ni nanoparticles uniformly dispersed on Vulcan XC-72R carbon black are prepared by microwave-irradiation using NaBH4 as a reducing agent. Pd/C, Ni/C and Pd–Ni/C electrocatalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX). Pd–Ni alloy was formed with an average particle size of 3nm. Kinetic parameters such as the electron transfer coefficient value (α) and electron transfer rate constant of Ni/C and Pd–Ni/C electrocatalysts in 0.5M KOH solution were calculated. The prepared electrocatalysts were examined for methanol oxidation in alkaline medium. The long-term stability of electrocatalysts in (0.6M MeOH+0.5M KOH) solution was studied using repeated cyclic voltammetry and chronoamperometry. Two methanol oxidation peaks were observed at Pd–Ni/C at 0 and +913mV. Their current density values are higher than those at Pd/C and Ni/C electrocatalysts by 3.84 and 1.43 times, respectively. The catalytic rate constant at Ni/C and Pd–Ni/C was estimated using double-step chronoamperometry as 1.80×103 and 5.88×103cm3mol−1s−1, respectively. Pd–Ni/C showed better stability performance when compared to Pd/C and Ni/C electrocatalysts.

Carbon Aerogels Supported Pt Nanoparticles as Electrocatalysts for Methanol Oxidation in Alkaline Media

AbstractCarbon aerogels (CAs) were prepared by sol‐gel polycondensation of resorcinol and formaldehyde with BET surface area of 616 m2 g−1 and the average pore size of 9.8 nm. The prepared CAs were used as supports for Pt nanoparticles for methanol oxidation in alkaline media. In comparison with Pt supported on commercial Vulcan XC‐72R carbon (Pt/C) electrocatalysts, Pt supported on CAs (Pt/CAs) electrocatalysts exhibited higher peak current density and more negative onset potential toward methanol oxidation. The effects of different parameters such as NaOH concentration, methanol concentration, and scan rate on the methanol oxidation reaction were investigated in detail. The results showed that the Pt/CAs electrocatalysts had promising application for methanol oxidation in alkaline media.

Enhanced photo-electrocatalytic performance of Pt/RGO/TiO2 on carbon fiber towards methanol oxidation in alkaline media

In the present work, a novel electrode composed of TiO2, reduced graphene oxide (RGO) and Pt nanoparticles on carbon fiber (CF), denoted as Pt/RGO/TiO2/CF, has been fabricated successfully and employed as a photo-electrocatalyst for methanol oxidation in alkaline media. The spherical TiO2 nanoparticles are loaded on CF surface by an in situ method and wrapped by the gauze-like RGO. Meanwhile, the RGO effectively extends the absorption edge to visible light region based on the UV–vis diffuse reflectance absorption spectra (DRS) and promotes the good dispersion of Pt nanoparticles electro-deposited on the surface of RGO-wrapped TiO2. The as-prepared Pt/RGO/TiO2/CF electrode shows enhanced electrocatalytic activity and stability compared with Pt/TiO2/CF and Pt/CF electrodes both with and without light irradiation. The RGO plays an important role for the enhancement of electrocatalytic and photo-electrocatalytic performance. Moreover, Pt/RGO/TiO2/CF presents a higher photo-electrocatalytic activity for methanol oxidation with light irradiation than that without light irradiation due to the synergistic effect among them.

Catalytic Activity of Porous Pd-Ni Thin Foam towards Electrooxidation of Methanol

Porous Pd-Ni thin foam was fabricated by a rapid one-step electrodeposition process within hydrogen bubble dynamic template and characterized by SEM, EDS, and cyclic voltammetry. Morphology and composition of the foam can be modified significantly by applying different deposition conditions, such as concentration ratio of Pd (II) ions to Ni (II) ions in electrolytic solution and deposition time. Electrocatalytic activities of the foam towards methanol oxidation in alkaline media were investigated, which depend mainly on Pd components and its morphology. Low nickel content can assist Pd further enhance the electrocatalytic performance, particularly the tolerance to intermediates of methanol oxidation, while high nickel content brings adverse effect. The high catalytic activity and the low cost of the Pd-Ni foams enable them to be promising electrocatalysts for the oxidation of methanol in alkaline media.