Methanol Electrooxidation In Alkaline Media Research Articles

High Electrocatalytic Performance of CuCoNi@CNTs Modified Glassy Carbon Electrode towards Methanol Oxidation in Alkaline Medium

A novel non-precious multiwalled carbon nanotubes (CNTs)—supported metal oxide electrocatalyst was developed for methanol electrooxidation in alkaline medium. The catalyst was fabricated by simultaneous electrodeposition of copper-cobalt-nickel ternary nanostructures (CuCoNi) on a glassy carbon electrode (GCE) modified with CNTs. The proposed electrode was characterized using X-ray diffraction (XRD), energy dispersive X-ray (EDX), and scanning electron microscopy (SEM). The electrochemical behavior and the electrocatalytic performance of the suggested electrode towards the oxidation of methanol were evaluated by cyclic voltammetry (CV), linear sweep voltammetry (LSV), and chronoamperometry (CA) in alkaline medium. Several parameters were investigated, e.g., deposition time, potential scan rate, etc. Compared to Cu, Co, or Ni mono electrocatalysts, the electrode based on ternary-metals exhibited superior electrocatalytic activity and stability towards methanol electrooxidation. For instance, CuCoNi@CNTs/GCE has shown at least 2.5 times electrocatalytic activity and stability compared to the mono eletrocatalysts. Moreover, the present study found that the optimized loading level is 1500 s of simultaneous electrodeposition. At this loading level, it was found that the relation between the Ip/ν1/2 function and scan rate gives the characteristic features of a catalytic process. The enhanced activity and stability of CuCoNi@CNTs/GCE was attributed to (i) a synergism between three metal oxides coexisting in the same structure; (ii) the presence of CNTs as a support for the metal oxides, that offers high surface area for the deposited tertiary alloy and suppresses the aggregation and sintering of the metals oxide with time; as well as (iii) the increase of the conductivity of the deposited semiconducting metal oxides.

Enhanced Electrooxidation of Methanol via Ion Implantation of Co Nanoparticles onto 3D Ni Foam Templates

In this study, cobalt-nanoparticles (CoNPs) are directly synthesized on Ni foam by ion implantation to catalyze methanol electro-oxidation in alkaline medium, which is simple, cheap, environmentally friendly and easy to mass production. Several techniques, including scanning electron microscopy (SEM), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDS) have been employed to characterize the physicochemical properties of the as-prepared electrode. The electro-catalytic performances are investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA). The CoNPs/NF electrode shows prominent electro-catalytic activity toward the electro-oxidation of methanol because of the well preserved 3D mesoporous structure of Ni foam, which can provide adequate open spaces and shorter ion diffusion paths to increase the electrode/electrolyte contact interface and active sites for reaction.

Facile synthesis of Pd-decorated Pt/Ru networks with highly improved activity for methanol electrooxidation in alkaline media

Electrocatalytic activity toward methanol oxidation is greatly enhanced after partial replacement of Ru with Pd in Pt/Ru/Pd networks.

Nanoribbon-structured CdWO4–ZnO for multiple applications

A new cadmium tungstate–zinc oxide (CdWO4–ZnO) nanocomposite, prepared by a simple hydrothermal method, was characterised by X-ray powder diffraction, high-resolution transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy, elemental colour mapping, atomic force microscopy, photoluminescence spectroscopy, X-ray photoelectron spectroscopy and Brunauer–Emmett–Teller (BET) surface area measurements. FE-SEM and TEM images show the heterostructure of cadmium tungstate–zinc oxide with nanoribbons and nanoparticles. The BET surface area of cadmium tungstate–zinc oxide is 2·1 times that of zinc oxide. This heterostructured material shows an enhanced photocatalytic activity on the degradation of rhodamine B and reactive orange 4 under ultraviolet A light irradiation. Cadmium tungstate–zinc oxide exhibits higher electrocatalytic activity than zinc oxide and cadmium tungstate for methanol electrooxidation in alkaline medium. This coupled oxide shows increased hydrophobicity, compared to cadmium tungstate or zinc oxide. A significant antibacterial activity against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli was shown by this catalyst. The results offer new insights into the performance of a coupled semiconductor oxide with multiple applications in photocatalytic, electrocatalytic, self-cleaning and antibacterial activities.

Well-dispersed palladium nanoparticles on three-dimensional hollow N-doped graphene frameworks for enhancement of methanol electro-oxidation

In this work, palladium (Pd) nanoparticles/three-dimensional hollow N-doped graphene frameworks (HNGF) hybrid catalysts were fabricated by using amine-functionalized poly (glycidyl methacrylate) microspheres-templated HNGF as supporting materials for Pd nanoparticles (NPs). The results demonstrate that the Pd NPs with average sizes of ~5.5nm can be well dispersed on the surfaces of HNGF with internal circular holes of ~400nm. The Pd/HNGF catalysts exhibit high electrocatalytic activity and durability toward methanol electro-oxidation in alkaline medium, compared to Pd/graphene and Pd/carbon.

Methanol Oxidation on Ru- or Ni-Modified Pd-Electrocatalysts in Alkaline Media: A Comparative Differential Electrochemical Mass Spectrometry Study

The electrochemical oxidation of methanol on electrocatalysts is intensively investigated since direct methanol fuel cells (DMFCs) were proposed as a promising alternative as power source for mobile and back-up power applications. In DMFCs, methanol is oxidized at the anode and oxygen is reduced at the cathode to convert the chemical energy of the fuels to electric power. In recent years, the electrochemical oxidation of methanol in alkaline environment is rising in interest, because other electrocatalysts than the expensive platinum are feasible as anode and cathode catalysts in alkaline DMFCs. While multiple catalysts are feasible on the cathodic site, Palladium was proven to be a suitable substitute for Pt as anode catalyst for the electrochemical oxidation of alcohols in alkaline media [1], but needs further improvement to compete with Pt especially regarding methanol oxidation reaction. The catalytic activity of Pd catalysts was improved by alloying or mixing other metals (or metal oxides) to Pd [2,3] or by controlling the size and shape of Pd particles [4]. Besides high catalytic activity, the complete oxidation of methanol to CO2is of enormous interest, because the complete oxidation results in the highest possible faradaic efficiency with six electrons transferred per methanol molecule. In contrast, two or four electrons are transferred to the anode per methanol molecule, if methanol is not completely oxidized. Differential electrochemical mass spectrometry (DEMS) is used by different research groups to quantify a catalyst’s ability to completely oxidize methanol. While the methanol electrooxidation on Pt-based catalysts was investigated intensively via DEMS in acidic media, DEMS studies on Pd-based catalysts for methanol electrooxidation in alkaline media are rare. In former studies, we reported on PdXNi/C and PdXRu/C catalysts for methanol electrooxidation in alkaline media synthesized by wet-chemical reduction with sodium borohydride [2,3]. It was possible to show that these oxophilic metals have a positive effect on the catalytic activity towards methanol oxidation of Pd-based catalysts. Taking these studies into account, we herein investigated the influence of these metals on Pd-based electrocatalysts regarding methanol oxidation reaction via DEMS. Besides analyzing the product distribution from methanol bulk oxidation on PdXNi/C or PdXRu/C, the main interest of this work is to investigate how the addition of the metals to Pd influences the methanol oxidation mechanism and catalyst poisoning. Hence, standard electrochemical tests like cyclic voltammetry, chronoamperometry, COadsstripping or methanol adsorbate stripping were conducted in the DEMS flow cell. Figure 1 shows cyclic voltammograms and corresponding MS signals for produced CO2 (m/z = 44) and methyl formate (m/z = 60) for Pd/C, Pd5Ni/C and Pd3Ru/C during methanol electrooxidation. While both modified catalysts show higher current densities and lower onset potentials than Pd/C for the electrooxidation of methanol, the product distribution differs strongly depending on the added metal. For Ni-modified catalyst the formation of CO2 is significantly lower than for Pd/C. While the addition of Ni to Pd leads to a negative effect on the ability to completely oxidize methanol, Pd3Ru/C is able to oxidize methanol more efficiently to CO2 than Pd/C. For Pd3Ru/C, the CO2 formation is shifted to lower potentials while methyl formate is produced at higher potentials. This hints to a more selective production of CO2 at low potentials on Pd3Ru/C than on Pd/C or Pd5Ni/C. Besides DEMS experiments, measurements were carried out in dependence of methanol concentration or oxidation temperature using a 3-electrode setup with stationary electrolyte to determine the rate determining step and the activation energy of methanol electrooxidation on Pd/C and the modified catalysts. Fig. 1 – Methanol bulk oxidation on Pd/C, Pd5Ni/C and Pd3Ru/C investigated via cyclic voltammetry in a DEMS flow cell at 20 mV s-1 from 0.1 to 1.2 V (vs. RHE) with 0.1 M CH3OH + 0.5 M KOH solution as electrolyte. Corresponding mass spectrometry signals for CO2 (m/z 44) and HCOOCH3(m/z 60) are displayed to evaluate the product distribution during methanol oxidation reaction.

A Polymer Surfactant Assisted Method for the Synthesis of Clusters of Mn3O4 Nanoparticles on Few-Layer Exfoliated Graphene Platelet Surface and Its Application As Lithium-Ion Battery Anode

Composites synthesized through the deposition of Mn3O4 on graphene, carbon nanotube and other carbon based materials have attracted much attention recently as potential electrode materials for different electrochemical applications such as pseudocapacitor; Lithium-ion battery; and catalysis. The primary reason Mn3O4 is grown on these substrates in spite of having high charge storage capacity as pseudocapacitor or Lithium-ion battery electrodes on its own is to enhance its electrical conductivity and/or to impart flexibility to the electrode, which is difficult for a fully metallic electrode. Higher electrical conductivity prolongs the cycle life of an electrode. In addition, the substrate contributes capacity and thus, enhances the overall energy density of an electrode. Mn3O4 acts as a spacer and keeps graphene nanosheets separated when used as the substrate for capacitor electrode fabrication. This helps retain the high surface area of graphene nanosheets in the electrode which contributes additional capacitance. Mn3O4 supported on graphene and other carbon substrates have recently been investigated as catalyst for methanol electro-oxidation in alkaline media; CO oxidation; and Oxygen reduction reaction (ORR). High surface area substrate uniformly distributes metal particles and prevents their agglomeration and dissolution during catalytic process. In addition, high electrical conductivity of graphene and carbon substrates enhances the electronic conductivity of Mn3O4 which is of importance for superior catalytic activity. Composite of Mn3O4 combined with carbon based substrate has also found non-electrochemical application such as the removal of Pb and Cu ions from aqueous solution because of their adsorptive behaviour. A myriad of procedures have been adopted for the synthesis of Mn3O4 on graphene or other carbonaceous substrates. All of these methods involve one or more of the following factors that complicate the process, such as: long synthesis time; high synthesis temperature; use of hazardous/toxic chemicals; multistep process and the requirement for sophisticated device or highly controlled environment. In fact, the complicacies associated with the synthesis of Mn3O4 have already been acknowledged and investigations have been directed at finding relatively simpler route such as the use of microwave technique. In this research, we report the synthesis of clusters of nearly octahedral shaped Mn3O4 nanoparticles on few-layer exfoliated graphene platelet (15µm diameter, thickness 6-8 nanometer, 120-150 m2/g surface area) surface through a simple, wet-chemical, polyethyleneimine (PEI) mediated route. Few-layer exfoliated graphene platelets are ultrathin particles of graphite that can also be thought of as short stacks of graphene sheets prepared through proprietary manufacturing processes. Several grades and sizes with thicknesses ranging from 1-20 nanometers and width ranging from 1-50µm are manufactured by XG Sciences, Lansing, MI, USA. Unique manufacturing processes for these platelet materials are non-oxidizing; thus, yielding a pristine graphitic surface of sp2 carbon molecules. This makes these platelet particles especially suitable for applications requiring high electrical and thermal conductivities. The surface areas of the resulting platelets predominantly consist of the open surface areas of the graphene basal planes. The components involved in this synthesis method are manganese salts (KMnO4 and MnSO4.H2O); water; PEI; and few-layer exfoliated graphene platelet as the substrate. The synthesis is carried out at a temperature of 80°C only and in open air. Highly crystallized Mn3O4 particles, as observed by X-Ray Diffraction (XRD), can be synthesized on few-layer exfoliated graphene platelet surface. It has also been observed that PEI acts as a reducing agent and as a capping agent on a continuous network of ribbon-like Birnessite-MnO2 (IV) to produce a nearly octahedral shaped nanoparticles of Mn3O4 (II, III). It has already been mentioned that composites of Mn3O4 on graphene or other carbonaceous substrates find a myriad of applications. Thus, our research findings to synthesize few-layer exfoliated graphene platelet-Mn3O4 composite through a simple method should be of interest to a broad group of researchers. In this research, we have investigated the performance of this composite system as a Lithium-ion battery anode only. Our preliminary investigations reveal that the Mn3O4 composite synthesized through this method has just as much potential as the ones prepared through other alternative methods.

Ni3B–Ni nanocomposites for improved electrocatalytic activity in methanol oxidation reaction

The Ni–B-modified carbon paste electrodes were synthesized by the electroless deposition, followed by thermal treatment. Scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were performed to gather information about the morphology, crystallinity, and binding energy. The fabricated Ni–B/C electrodes are applied to methanol electrooxidation in alkaline media. The results show that Ni–B/C catalyst with a comparable amount of microcrystalline Ni and Ni3B, 59 and 41 wt%, displayed a significantly enhanced electrocatalytic activity, which is approximately three times the activity of the unheated Ni–B/C catalyst. The synergetic mechanism of methanol oxidation was proposed that involves one Ni3B site favor the adsorption and activation of the methanol molecule and one Ni site for oxidative mediation of methanol. In addition, the kinetic parameters of the reaction were calculated using linear sweep voltammetry. The illustration of the speculated methanol oxidation mechanism.

Methanol Oxidation in Alkaline Medium Using PtIn/C Electrocatalysts

Pt/C and PtIn/C with atomic ratios of 90:10, 70:30, and 50:50 were investigated for methanol electro-oxidation in alkaline media by using cyclic voltammetry (CV), chronoamperometry (CA), and direct methanol alkaline fuel cell (DMAFC). All electrocatalysts were synthesized using sodium borohydride method with 20 wt% of metals loading on carbon. X-ray diffraction (XRD) analysis revealed that bimetallic PtIn had faced centered cubic structure and, also, confirmed alloy formation for PtIn/C nanoparticles. Transmission electron micrographs showed metal nanoparticles with average particle size between 3.0 and 5.0 nm; however, the particle size increases when the In content was increased in PtIn/C. In the CV experiments, the onset potential of methanol electro-oxidation shifted to lower values as the indium content increased. Chronoamperometry experiments and direct methanol alkaline fuel cell suggested PtIn/C (70:30) as the most promising material for methanol electro-oxidation: this result could be explained by the presence of Pt and In in close contact (electronic effect) as the occurrence of oxy-hydroxy interactions.

Ni@Pt nanodisks with low Pt content supported on reduced graphene oxide for methanol electrooxidation in alkaline media

Ni@Pt/RGO nanodisks were synthesized and the electrooxidation of CO and methanol studied. The morphology, structure and composition of the Ni nanodisks were characterized by atomic force microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. Electrochemical characterization was performed by cyclic voltammetry and chronoamperometry. Results showed that Pt galvanostatically replaced Ni atoms maintaining the original (111) and (200) crystalline domains. XPS analysis indicates that negative charge transfer from Ni to Pt in the nanodisks and the presence of Ni-oxides/hydroxides species on the surface are key factors for the high electrochemical activity. The catalysts with low Pt content displayed higher CO tolerance and activity towards methanol electrooxidation. The synergy of the bifunctional effect and the NiPt electronic interaction makes Ni@Pt/RGO nanodisks good candidates for the methanol oxidation reaction in alkaline media, and consequently, in direct methanol alkaline membrane fuel cells.

Electrocatalytic performance of Ni-Ti-O nanotube arrays/NiTi alloy electrode annealed under H2 atmosphere for electro-oxidation of methanol

In the present study, Ni-Ti-O nanotube arrays (Ni-Ti-O NTs) were fabricated by anodizing NiTi alloy in a mixed solution consisted of ethylene glycol and glycerol. Then the Ni-Ti-O NTs were suffered annealing treatment under hydrogen atmosphere, leading to the significant improved electrocatalytic performance. The morphologies, the phases and the surface electronic states of Ni-Ti-O NTs samples before and after annealing were characterized by SEM, XRD and XPS, respectively. And their electrocatalytic properties for methanol oxidation were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in the alkaline media. Results show that electrocatalytic activity of the Ni-Ti-O NTs samples annealed under H2 exhibits a significant improvement because of the increases of the conductivity and the active sites provided by reduction of Ni3+. The Ni-Ti-O NTs samples with lower crystallinity annealed at 500 °C for 2 h have better electrocatalytic performance for methanol electro-oxidation in alkaline medium. The peak current density increases after a consecutive sweep for 1000 times and varies indistinctively after placing in the air for 30 days, indicating the excellent long-term electrocatalytic stability. The in situ formation of Ni-base material catalyst in Ni-Ti-O nanotube benefits improvement of the catalytic properties during long-term operation. The Ni-Ti-O NTs/Ni-Ti alloy is a desirable substitute of catalysts support material or it is also a promising electrocatalytic electrode for direct methanol fuel cells.

Cobalt/Chromium Nanoparticles-Incorporated Carbon Nanofibers as Effective Nonprecious Catalyst for Methanol Electrooxidation in Alkaline Medium

Cobalt-Chrome nanoparticles-incorporated carbon nanofibers (CNFs) are proposed as an effective nonprecious electrocatalyst for methanol oxidation in the alkaline media. The introduced nanofibers were prepared by simple technique, electrospinning. Carbonization of as-spun mat composed of chromium acetate, cobalt acetate and poly(vinyl alcohol) (PVA) at high temperature (900[Formula: see text]C) leads to production of the introduced nanofibers. The physicochemical characteristics were investigated by X-ray diffractometer (XRD), scanning electron microscope (SEM), field emission scanning electron microscope (FESEM), transmission electron microscope (TEM) equipped with EDX and TEM mapping. The exploited analyses confirmed that the final product is in the form of CNFs decorated by Co/Cr nanoparticles. Based on the results obtained from the cyclic voltammetry (CV) measurements, the proposed Co/Cr-incorporated CNFs possess high electrocatalytic activity toward methanol electrooxidation as a clear peak of methanol oxidation appeared with corresponding current density of 56[Formula: see text]mA/cm2. Moreover, the current density increased by increasing methanol concentration up to 4.0[Formula: see text]M. Overall, the proposed nanofibers open new avenue for platinum-free and stable nanostructural catalysts for fuel cell technology.

Synthesis of Clustered Mn3O4 Nanoparticles through a Polymer Surfactant Mediated Route on Few-Layer Exfoliated Graphene Platelet Surface and Its Application for Electrochemical Energy Storage: Lithium-Ion Battery Anode

Composites synthesized through the deposition of Mn3O4 on graphene, carbon nanotube and other carbon based materials have attracted much attention recently as potential electrode materials for different electrochemical applications such as pseudocapacitor; Lithium-ion battery; and catalysis. The primary reason Mn3O4 is grown on these substrates in spite of having high charge storage capacity as pseudocapacitor or Lithium-ion battery electrodes on its own is to enhance its electrical conductivity and/or to impart flexibility to the electrode, which is difficult for a fully metallic electrode. Higher electrical conductivity prolongs the cycle life of an electrode. In addition, the substrate contributes capacity and thus, enhances the overall energy density of an electrode. Mn3O4 acts as a spacer and keeps graphene nanosheets separated when used as the substrate for capacitor electrode fabrication. This helps retain the high surface area of graphene nanosheets in the electrode which contributes additional capacitance. Mn3O4 supported on graphene and other carbon substrates have recently been investigated as catalyst for methanol electro-oxidation in alkaline media; CO oxidation; and Oxygen reduction reaction (ORR). High surface area substrate uniformly distributes metal particles and prevents their agglomeration and dissolution during catalytic process. In addition, high electrical conductivity of graphene and carbon substrates enhances the electronic conductivity of Mn3O4 which is of importance for superior catalytic activity. Composite of Mn3O4 combined with carbon based substrate has also found non-electrochemical application such as the removal of Pb and Cu ions from aqueous solution because of their adsorptive behaviour. A myriad of procedures have been adopted for the synthesis of Mn3O4 on graphene or other carbonaceous substrates. All of these methods involve one or more of the following factors that complicate the process, such as: long synthesis time; high synthesis temperature; use of hazardous/toxic chemicals; multistep process and the requirement for sophisticated device or highly controlled environment. In fact, the complicacies associated with the synthesis of Mn3O4 have already been acknowledged and investigations have been directed at finding relatively simpler route such as the use of microwave technique. In this research, we report the synthesis of clusters of nearly octahedral shaped Mn3O4 nanoparticles on few-layer exfoliated graphene platelet (15µm diameter, thickness 6-8 nanometer, 120-150 m2/g surface area) surface through a simple, wet-chemical, polyethyleneimine (PEI) mediated route. Few-layer exfoliated graphene platelets are ultrathin particles of graphite that can also be thought of as short stacks of graphene sheets prepared through proprietary manufacturing processes. Several grades and sizes with thicknesses ranging from 1-20 nanometers and width ranging from 1-50µm are manufactured by XG Sciences, Lansing, MI, USA. Unique manufacturing processes for these platelet materials are non-oxidizing; thus, yielding a pristine graphitic surface of sp2 carbon molecules. This makes these platelet particles especially suitable for applications requiring high electrical and thermal conductivities. The surface areas of the resulting platelets predominantly consist of the open surface areas of the graphene basal planes. The components involved in this synthesis method are manganese salts (KMnO4 and MnSO4.H2O); water; PEI; and few-layer exfoliated graphene platelet as the substrate. The synthesis is carried out at a temperature of 80°C only and in open air. Highly crystallized Mn3O4 particles, as observed by X-Ray Diffraction (XRD), can be synthesized on few-layer exfoliated graphene platelet surface. It has also been observed that PEI acts as a reducing agent and as a capping agent on a continuous network of ribbon-like Birnessite-MnO2 (IV) to produce a nearly octahedral shaped nanoparticles of Mn3O4 (II, III). It has already been mentioned that composites of Mn3O4 on graphene or other carbonaceous substrates find a myriad of applications. Thus, our research findings to synthesize few-layer exfoliated graphene platelet-Mn3O4 composite through a simple method should be of interest to a broad group of researchers. In this research, we have investigated the performance of this composite system as a Lithium-ion battery anode only. Our preliminary investigations reveal that the Mn3O4 composite synthesized through this method has just as much potential as the ones prepared through other alternative methods.

Investigation of ruthenium promoted palladium catalysts for methanol electrooxidation in alkaline media

In this study, the investigation of binary palladium based electrocatalysts for methanol oxidation in alkaline media is reported. For this purpose, electrocatalysts with a loading of 20wt% metal on VulcanXC72-R were synthesized via wet chemical reduction with various compositions of palladium and ruthenium. Physical characterization via transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and inductively coupled plasma optical emission spectroscopy (ICP-OES) was done and verified the synthesis of nanoparticles on carbon support. Electrochemical evaluation of the catalytic behavior of Pd/C, Ru/C and PdXRu/C (X = 1, 3, 5) via cyclic voltammetry and chronoamperometry was conducted in a 3-electrode setup. These measurements suggested that Pd3Ru/C is a promising material for methanol oxidation reaction in alkaline media with an onset potential of 0.465 VRHE and a peak current density of over 1 A mg−1Pd. To further investigate the oxidation of methanol on Pd/C and Ru promoted catalysts, differential electrochemical mass spectrometry (DEMS) measurements were done. From these results a higher CO2 current efficiency (CCE) of 86% for Pd3Ru/C compared to 65% for Pd/C was found. Moreover, fuel cell tests verified the results and showed that Pd3Ru/C has the better performance.

Highly efficient anode catalyst with a Ni@PdPt core–shell nanostructure for methanol electrooxidation in alkaline media

To enhance the electrocatalytic activity of anode catalysts used in alkaline-media direct methanol fuel cells (DMFCs), a Ni@PdPt electrocatalyst was successfully prepared using a three-phase-transfer method. The Ni@PdPt electrocatalyst was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM) techniques. The experimental results indicate that the average particle size of the core–shell-structured Ni@PdPt electrocatalyst is approximately 5.6 nm. The Ni@PdPt electrocatalyst exhibits a catalytic activity 3.36 times greater than that of PdPt alloys for methanol oxidation in alkaline media. The developed Ni@PdPt electrocatalyst offers a promising alternative as a highly electrocatalytically active anode catalyst for alkaline DMFCs.

Highly active carbon supported palladium-rhodium PdXRh/C catalysts for methanol electrooxidation in alkaline media and their performance in anion exchange direct methanol fuel cells (AEM-DMFCs)

In this study carbon supported PdXRh electrocatalysts synthesized by wet chemical reduction process were tested for the potential use in anion-exchange membrane direct methanol fuel cells (AEM-DMFC) and compared to Pd/C and commercially available Pt/C. A metal loading of 20wt% on carbon was confirmed by thermogravimetric analysis (TGA) and catalyst compositions of PdRh3/C, PdRh/C and Pd3Rh/C were found via inductively coupled plasma optical emission spectroscopy (ICP-OES). Transmission electron microscopy (TEM) and x-ray diffraction (XRD) studies showed that the average particle and crystallite sizes of the PdXRh/C catalysts are in the range of 3.1 to 4.3nm. It was also found that these catalysts are not alloyed. Cyclic voltammetry (CV) data reveals a 85–140mV lower CH3OH oxidation onset potential and higher mass current densities for PdXRh/C catalysts compared with Pd/C. Steady-state measurements via chronoamperometry (CA) showed a good stability against poisoning during methanol oxidation and higher mass activities for PdRh/C and Pd3Rh/C compared to Pt/C. By using differential electrochemical mass spectrometry (DEMS) it was successfully shown that adding Rh to Pd results in an enhanced CO2 current efficiency (CCE) compared to Pd/C or Pt/C. AEM-DMFCs free from platinum were fabricated and single cell tests at 60°C showed a significant increase of power density at 0.5V cell potential from 4.8mWcm−2 for Pd/C to 16.5mWcm−2 for PdRh/C with the anode and cathode fed with 1M methanol+2M KOH and synthetic air, respectively. Peak power density of 104.9mWcm−2 was reached for PdRh/C anode catalyst at 80°C using higher KOH and methanol concentrations in anodic fuel and oxygen as cathodic oxidizer.

Electrocatalytic activity of porous nanostructured Fe/Pt-Fe electrode for methanol electrooxidation in alkaline media

An electrochemical approach to fabricate a nanostructured Fe/Pt-Fe catalyst through electrodeposition followed by galvanic replacement is presented. An Fe/Pt-Fe nanostructured electrode was prepared by deposition of Fe-Zn onto a Fe electrode surface, followed by replacement of the Zn by Pt at open-circuit potential in a Pt-containing alkaline solution. Scanning electron microscopy and energy-dispersive X-ray techniques reveal that the Fe/Pt-Fe electrode is porous and contains Pt. The electrocatalytic activity of the Fe/Pt-Fe electrode for oxidation of methanol was examined by cyclic voltammetry and chronoamperometry. The electrooxidation current on the Fe/Pt-Fe catalyst is much higher than that on flat Pt and smooth Fe catalysts. The onset potential and peak potential on the Fe/Pt-Fe catalyst are more negative than those on flat Pt and smooth Fe electrodes for methanol electrooxidation. All results show that this nanostructured Fe/Pt-Fe electrode is very attractive for integrated fuel cell applications in alkaline media.

Pdni-Based Catalysts for Anion-Exchange Membrane Direct Methanol Fuel Cell (AEM-DMFC)

New processes like oxidative bi-reforming of methane (e.g. from natural gas) developed by Olah et al. allows to produce methanol in an overall economic and energetically efficient process.[1,2] Compared to methane, methanol is a useful intermediate material in many chemical manufacturing processes as well as a safe-to-handle liquid fuel for transportation and mobile applications. Direct Methanol Fuel Cells (DMFCs) have attracted enormous attention as potential power sources for electronic devices and back-up power solution due to higher energy density than gaseous fuels such as hydrogen. However, problems like slow electro-kinetics of alcohol oxidation, costs of membranes and catalysts and alcohol crossover are hindering their commercialization.[3] Recent studies have shown that the electrocatalytic activity for alcohol oxidation in alkaline media is much higher than that in acidic media. The oxidation of methanol (MeOH) in alkaline media has shown higher current densities and smaller overpotentials compared to those in acidic media.[4] Besides this the catalyst materials used for alcohol oxidation reaction (AOR) and oxygen reduction in Anion-Exchange Membrane Direct Methanol Fuel Cells (AEM-DMFCs) are cheaper and more efficient than Pt.[5] Pd has proved to be a good electrocatalyst for AOR in alkaline medium, showing higher activity and better steady-state currents than Pt.[6] To improve the activity and stability towards alcohol oxidation, Pd-based catalysts including Pd-oxide composite, Pd-based binary and Pd-based ternary catalysts have been investigated by several research groups. In a former study we reported the high activity of carbon supported binary PdNi/C anode catalysts for AEM DMFCs.[7] Inspired by these findings we investigated on ternary PdNiSn/C and PdNiRu/C anode catalysts for AEM-DMFCs. Table 1 summarizes the electrocatalysts synthesized in this study. Table 1: Summary of synthesized electrocatalysts. Loading on carbon and composition of the catalysts were measured by thermogravimetric analysis coupled with inductively coupled plasma optical emission spectroscopy. Catalyst Ratio Pd:Metal Catalyst Composition Pd:Ni:Metal Loading [wt%] Pd/C 21.0 Pd3Ni1/C 3:1 3:0.95 19.6 Pd5Ni1/C 5:1 5:0.97 20.0 Pd3Ni0.5Ru0.5/C 3:1 3:0.43:0.49 19.7 Pd5Ni0.5Ru0.5/C 5:1 5:0.46:0.49 20.6 Pd3Ni0.5Sn0.5/C 3:1 3:0.44:0.51 19.4 Pd5Ni0.5Sn0.5/C 5:1 5:0.47:0.55 20.7 Electrochemical evaluation of the methanol electrooxidation in alkaline media was done via cyclic voltammetry (CV) and chronoamperometry (CA) in a standard 3-electrode set-up with mercury/mercury oxide reference electrode (MMO). In Figure 1A&B, it is observed that the tested materials present a lower onset potential and higher current densities for the AOR compared to Pt/C, Pd/C and PdNi/C. This is an evidence that the electrocatalysts presented here have an improved catalytic activity than the one reported before. Membrane electrode assemblies (MEAs) with the electrocatalysts were fabricated using a Tokuyama A201 as membrane and SGL 10AA and Freudenberg H2315 as anodic and cathodic diffusion layer, respectively. Figure 1C shows the Tafel plots derived from single cell performance tests. A significant increase of power densities for ternary catalysts compared to Pd/C or PdNi/C catalysts at fuel cell working potentials was observed. For a cell potential of 0.5V the performance magnifies from 4.8mW cm-2 for Pd/C to 23.2mW cm-2 for Pd3Ni0.5Ru0.5/C. These results are in accordance with the ones illustrated in Figure 1A&B. Further work will include tests on an AEM-DMFC short stack based on Pd3Ni0.5Ru0.5/C anode catalyst. Fig. 1 - Cyclic voltammetry (A) and chronoamperometry (B) curves of Pt/C, Pd/C, Pd3Ni/C and Pd3Ni0.5M0.5/C (M=Ru, Sn) catalysts for methanol electrooxidation in 0.5M KOH + 0.5M MeOH at room temperature; Tafel plots (C) from single cell performance tests of MEAs with Pd/C, Pd3Ni/C and Pd3Ni0.5M0.5/C (M=Ru, Sn) anode catalysts and Acta S.p.A. HYPERMEC™ 4020 cathode catalyst measured with 1M MeOH + 2M KOH and synthetic air as fuels at 60°C.

Cobalt-incorporated, nitrogen-doped carbon nanofibers as effective non-precious catalyst for methanol electrooxidation in alkaline medium

Among the nanosupports, carbon nanofibers distinctly enhance the performance of the functional electrocatalysts because the adsorption capacity and low resistance electron transfer due to the large axial ratio. Moreover, nitrogen doping shows positive influence toward electrooxidation ability. In this study, Co-incorporated and nitrogen-doped carbon nanofibers are introduced as effective non-precious electrocatalyst for methanol oxidation in the alkaline medium. The introduced NFs have been prepared using facile, simple, high yield, low cost, and effective technique; electrospinning. Typically, calcination of cobalt acetate/urea/poly(vinyl alcohol) electrospun mats at 850°C in argon atmosphere leads to produce the introduced nanofibers. The structure, composition and morphology were characterized by FT-IR, XRD, EDX, FE-SEM and TEM techniques. The electrocatalytic activity of the introduced nanofibers toward methanol oxidation was evaluated by cyclic voltammetry (CV). Study the influence of the nitrogen content could be investigated by adjusting the urea content in the original electrospun nanofiber mats. The results indicated that the activity of the catalyst increases with increasing urea content in the electrospun solution up to 4%. A maximum current density was 100.84mAcm−2 for Co/N(4%)-CNFs that was higher than the undoped ones (63.56mAcm−2). Moreover, good chemical stability was observed due to covering the metals NPs by carbon shells. Overall, nitrogen doping enhances electrocatalytic activity of Co/CNFs toward methanol oxidation in alkaline media.

Carbon supported trimetallic nickel–palladium–gold hollow nanoparticles with superior catalytic activity for methanol electrooxidation

In this paper, Ni nanoparticles (NPs) are prepared in an aqueous solution by using sodium borohydride as reducing agent. With Ni NPs as the sacrificial template, hollow NiPdAu NPs are successfully prepared via partly galvanic displacement reaction between suitable metal precursors and Ni NPs. The as-synthesized hollow NiPdAu NPs can well dispersed on the carbon substrate. Transmission electron microscopy, X-ray diffraction and inductively coupled plasma mass spectrometry are taken to analyze the morphology, structure and composition of the as-synthesized catalysts. The prepared catalysts show superior catalytic activity and stability for methanol electrooxidation in alkaline media compared with commercial Pd/C and Pt/C. Catalysts prepared in this work show great potential to be anode catalysts in direct methanol fuel cells.