Methanol Oxidation In Alkaline Solution Research Articles

(Digital Presentation) Facile Fabrication of Graphene Quantum Dot- Doped Polyaniline Embedded Cu Metal-Organic Frameworks Composite Electrode As Improved Anode Electrocatalyst for Methanol Oxidation

Nonrenewable energy sources accounted for roughly 80% of total energy consumption [1]. Solar energy, wind energy, geothermal energy, hydropower, and fuel cells (FCs) have all recently been described as renewable energy sources. In commercial uses, renewable energy has experienced meteorological and logistical obstacles. Because of advantages such as simple fabrication/operation conditions, eco-friendly, high energy conversion efficiency, and long-term durability, FCs technologies are considered one of the most important renewable energy sources for many applications such as portable devices, cars, and electricity plants [2–5]. Methanol can be utilized in direct methanol fuel cells (DMFC) to produce clean energy that can be used in smart electronic gadgets or small automobiles in this regard [6]. However, before DMFC can be used commercially, the slow oxidation kinetics and catalyst toxicity [7] must be resolved. Therefore, the development of direct methanol fuel cells (DMFCs) is one of the most promising technologies for the applications of these devices in stationary power supplies and electric vehicles [8]. Apart from the future of mobile devices such as mobile chargers, phones, computers, and many other applications, this energy is environmentally benign because no gases are emitted and the waste is simply clean water. The biggest issue that this technique may encounter is its high cost due to the usage of noble metal catalysts (platinum (Pt) and ruthenium (Ru)) [9]. Methanol is oxidized via a multi-electron process and several products and/or intermediates can be formed, depending on the electrolyte and the nature of the electrode. Electrode materials are important parameters in the electrochemical oxidation of methanol, where high efficient electrocatalysts are needed. Several metal oxides such as Fe2O3, CeO2, MoOx, Co3O4, NiO, and CuO has been used in various applications, such as catalysis, water splitting photocatalysis, solar cells and gas sensing, besides their uses to enhance the electrocatalytic activity for methanol oxidation [10-11].This paper describes the preparation of graphene quantum dot-doped polyaniline embedded copper metal-organic frameworks composite catalysts for investigating methanol oxidation in alkaline solutions. The electrode surface was characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and electrochemical impedance spectroscopy (EIS). After physicochemical characterizations of graphene quantum dot-doped polyaniline embedded copper metal-organic frameworks composite modified carbon ceramic electrode (Cu- MOF/GQDs-PAN/CCE), its electrocatalytic and stability characterizations toward methanol oxidation in alkaline media were investigated in detail by cyclic voltammetry and chronoamperometry. Results showed that, the electrocatalytic activity of the Cu- MOF/GQDs-PAN/CCE electrode is much higher than those of unmodified electrode under similar experimental conditions, showing the possibility of attaining good electrocatalytic anodes for fuel cells. Kinetic parameters such as the electron transfer coefficient (α) and the number of electrons involved in the rate determining step (nα) for the oxidation of methanol were determined utilizing cyclic voltammetry (CV). Keywords: Graphene quantum dot, Polyaniline, Metal-organic frameworks, electrocatalyst, MethanolReferences[1] S.K. Kamarudin, F. Ahmad, W.R.W. Daud, Overview on application of direct methanol fuel cell (DMFC) for portable electronic devices, Int. J. Hydrog. Energy 34 (2009) 6902–6916.[2] L. Carrette, K.A. Friedrich, U. Stimming, Fuel cells: principles, types, fuels and applications, ChemPhysChem 1 (2000) 162–193.[3] A.B. Stambouli, Fuel cells: The expectations for an environmental-friendly and sustainable source of energy, Renew. Sustain. Energy Rev. 15 (9) (2011) 4507– 4520.[4] P. Joghee, J.N. Malik, S. Pylypenko, R. O’Hayre, A review on direct methanol fuel cells – In the perspective of energy and sustainability, MRS Energy Sustain. 2 (2015), https://doi.org/10.1557/mre.2015.4.[5] D. Hassen, M.A. Shenashen, S.A. El-Safty, M.M. Selim, H. Isago, A. Elmarakbi, H. Yamaguchi, Nitrogen-doped carbon-embedded TiO2 nanofibers as promising oxygen reduction reaction electrocatalysts, J. Power Sources 330 (2016) 292– 303.[6] M. Mansor, S.N. Timmiati, K.L. Lim, W.Y. Wong, S.K. Kamarudin, N.H. Nazirah Kamarudin, Recent progress of anode catalysts and their support materials for methanol electrooxidation reaction, Int. J. Hydrogen Energy 44 (29) (2019) 14744–14769, https://doi.org/10.1016/j.ijhydene.2019.04.100.[7] Z. Mousavi, A. Benvidi, S. Jahanbani, M. Mazloum-Ardakani, R. Vafazadeh, H. R. Zare, Investigation of electrochemical oxidation of methanol at a carbon paste electrode modified with Ni(II)-BS complex and reduced graphene oxide nano sheets, Electroanalysis 28 (12) (2016) 2985–2992, https://doi.org/10.1002/ elan.201501183.[8] S. Wasmus, A. Küver, Methanol oxidation and direct methanol fuel cells: a selective review, J. Electroanal. Chem. 461 (1-2) (1999) 14–31.[9] M. Liu, R. Zhang, W. Chen, Graphene-Supported Nanoelectrocatalysts for Fuel Cells: Synthesis, Properties, and Applications, Chem. Rev. 114 (2014) 5117– 5160.[10] N. Spinner, W.E. Mustain, Electrochim. Acta 56 (2011) 5656.[11] M.S. Risbud, S. Baxter, M. Skyllas-Kazacos, Open Fuels Energy Sci. 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Foam Synthesis of Nickel/Nickel (II) Hydroxide Nanoflakes Using Double Templates of Surfactant Liquid Crystal and Hydrogen Bubbles: A High-Performance Catalyst for Methanol Electrooxidation in Alkaline Solution.

This work demonstrates the chemical synthesis of two-dimensional nanoflakes of mesoporous nickel/nickel (II) hydroxide (Ni/Ni(OH)2-NFs) using double templates of surfactant self-assembled thin-film and foam of hydrogen bubbles produced by sodium borohydride reducing agent. Physicochemical characterizations show the formation of amorphous mesoporous 2D nanoflakes with a Ni/Ni(OH)2 structure and a high specific surface area (165 m2/g). Electrochemical studies show that the electrocatalytic activity of Ni/Ni(OH)2 nanoflakes towards methanol oxidation in alkaline solution is significantly enhanced in comparison with that of parent bare-Ni(OH)2 deposited from surfactant-free solution. Cyclic voltammetry shows that the methanol oxidation mass activity of Ni/Ni(OH)2-NFs reaches 545 A/cm2 gcat at 0.6 V vs. Ag/AgCl, which is more than five times higher than that of bare-Ni(OH)2. Moreover, Ni/Ni(OH)2-NFs reveal less charge transfer resistance (10.4 Ω), stable oxidation current density (625 A/cm2 gcat at 0.7 V vs. Ag/AgCl), and resistance to the adsorption of reaction intermediates and products during three hours of constant-potential methanol oxidation electrolysis in alkaline solution. The high-performance electrocatalytic activity of Ni/Ni(OH)2 nanoflakes is mainly derived from efficient charge transfer due to the high specific surface area of the 2D mesoporous architecture of the nanoflakes, as well as the mass transport of methanol to Ni2+/Ni3+ active sites throughout the catalyst layer.

Electrodeposited palladium as efficient electrocatalyst for hydrazine and methanol electro-oxidation and detection

Electrodeposited palladium was used as an electrocatalyst for electrochemical oxidation of hydrazine and methanol and the development of a sensitive platform for their detection. The electrochemical behavior of the electrode was evaluated by cyclic voltammetry (CV) while electroanalytical properties were determined by means of differential pulse voltammetry (DPV). The electrodeposited Pd catalyst exhibited good electrocatalytic activity towards the oxidation of hydrazine in neutral solution and methanol oxidation in alkaline solution. Under optimized DPV conditions, the electrodeposited Pd electrode shows good sensing capability in hydrazine and methanol detection.

A Pd nanocatalyst supported on a polymer-modified hybrid carbon material for methanol oxidation

A hybrid carbon support is prepared by mixing graphene nanoplates (GNPs) with carbon nanotubes (CNTs) and modifying them with poly dimethyl diallyl ammonium chloride (PDDA). Pd nanoparticles are deposited onto the hybrid support by a microwave-assisted ethylene glycol reduction method. The obtained Pd/GNPs-PDDA-CNTs catalyst exhibits a high catalytic activity toward methanol oxidation in alkaline solution. Scanning electron microscope and transmission electron microscope images show that GNPs and CNTs contact intimately with each other and Pd nanoparticles are uniformly distributed over them. The linear sweeping voltammetry test indicates that Pd/GNPs-PDDA-CNTs has a low onset potential for methanol oxidation, which is attributed to the synergistic interaction between palladium and PDDA, as revealed by the X-ray photoelectron spectroscopy measurement. It is also observed that the poison resistance of the Pd nanocatalyst is improved to some extent due to the modification of the carbon support by the ionic polymer.

Eggshell-membrane-templated synthesis of C, S Doped Mesoporous NiO for methanol oxidation in alkaline solution

An interwoven hollow fiber structured mesoporous NiO catalyst doped with C, S was fabricated by the vacuum impregnation and thermal decomposition methods using eggshell membrane as template. The structure of the catalyst was characterized by X-ray diffraction, thermo-gravimetric analysis, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and specific surface area test. Under a high vacuum condition, the synthesized NiO material has a better interwoven fiber and mesoporous structure, which effectively increases the specific surface area of the material. C and S were doped into NiO via eggshell membrane pyrolysis, which then formed C–OH and SO42− species on the surface of the material. The electrocatalytic performance of the catalyst for the oxidation of methanol in alkaline solution was studied by cyclic voltammetry and chronoamperometry. The C, S doped mesoporous NiO material exhibits much higher catalytic efficiency and anti-poisoning ability than that of NiO nanoparticles due to the synergistic catalysis of NiO and doping C–OH and SO42− species.

Decoration of NiO hollow spheres composed of stacked nanosheets with CeO2 nanoparticles: Enhancement effect of CeO2 for electrocatalytic methanol oxidation

High-performance and low-cost electrocatalysts for electrochemical methanol oxidation reaction (MOR) are essential for the wide application of direct methanol fuel cells (DMFC). Herein, CeO2–NiO composites with CeO2 nanoparticles homogeneously supported on the surface of NiO hollow spheres composed of stacked nanosheets are synthesized via a facile two-step route and tested as noble-metal-free electrocatalysts towards methanol oxidation in alkaline solution. Optimal loading of CeO2 nanoparticles with a uniform size of ∼8 nm greatly enhances the electrocatalytic activity and stability comparing with pristine NiO hollow spheres for MOR. It is proposed that a synergistic effect resulting from the proper loading content and high dispersion of CeO2 nanoparticles on the surface of NiO nanosheets boosted the formation of active NiOOH species, which enhanced the electrocatalytic activity and stability of CeO2–NiO catslysts for MOR. CeO2 nanoparticles exhibit good promotion effect as co-catalyst in electrocatalysis, and CeO2–NiO nanocomposites show potential as inexpensive anode catalysts for DMFC applications.

Electrodeposited platinum on de-alloyed nanoporous gold with enhanced electro-catalytic performance

In this work, Pt nanoparticles were electrodeposited through cyclic voltammetry technique on three dimensional nanoporous gold prepared from Au-based metallic glass precursor by chemical de-alloying. The electro-catalytic properties of the as-prepared samples were tested through potential cycling towards methanol oxidation in alkaline solution. Current density plots vs scan numbers indicate that the electrodes are active for the electro-oxidation of methanol and the Pt nanoparticles electrodeposited on gold ligaments contribute to increasing catalytic properties. In particular, results indicate that nanoporous gold with 30 cycles of Pt electrodeposition exhibits competitive higher activity and longer durability towards methanol electro-oxidation.

Ni@Pd core-shell nanostructure supported on multi-walled carbon nanotubes as efficient anode nanocatalysts for direct methanol fuel cells with membrane electrode assembly prepared by catalyst coated membrane method

Multi-walled carbon nanotubes supported Ni@Pd core-shell nanoparticles (Ni@Pd/MWCNTs) are successfully synthesized by two-step reduction procedure. The Ni@Pd/MWCNTs electrocatalysts are characterized by using field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, high resolution transmission electron microscopy and X-ray photoelectron spectroscopy. According to characterization results, nanoparticles (5–10 nm) are spread on carbon support uniformly with high porosity. Moreover, the electrocatalytic performance of Ni@Pd/CNTs towards methanol electro-oxidation are evaluated using cyclic voltammetry, electrochemical impedance spectroscopy, chronoamperometry and chronopotentiometry methods in a conventional three-electrode cell. The results show that Ni@Pd/MWCNTs electrocatalysts have a good catalytic activity towards methanol oxidation in alkaline solutions. The performance of direct methanol fuel cell (DMFC) is evaluated in a single fuel cell set-up. The Membrane Electrode Assembly used in fuel cell set-up is prepared by catalyst-coated membrane technique. The catalyst loading is fixed at 0.5 mg Pt/C cm−2 for the cathode and 1.0 mg Ni@Pd/MWCNTs cm−2 for the anode. The used anolyte and catholyte are NaOH + CH3OH and H2SO4 + H2O2, respectively. The results exhibit that the maximum power density is about 67 mW cm−2 at 60 °C. The present paper clearly demonstrates the possibility of Ni@Pd/MWCNTs nanostructure as good performance and less expensive anode catalyst for DMFCs.

Synthesis, characterization, and electrocatalytic properties of La0.9Sr0.1Cr1−xCoxO3 perovskite oxides

Polycrystalline La0.9Sr0.1Cr1−xCoxO3 (0.0 ≤ x ≤ 0.4) solid solutions were synthesized by a sol-gel method using citric acid as chelating agent. Thermogravimetric and differential thermal analysis, Fourier-transform infrared spectroscopy, and X-ray diffraction (XRD) techniques are used to explore precursor decomposition and to establish adequate calcination temperature for the preparation of the polycrystalline. The samples obtained after calcination at 750 °C were characterized by several techniques. X-ray diffraction analyses reveal that that B-site doping of Co may lead to the transformation of its crystal structure from an orthorhombic to a rhombohedral phase, when Co content x ≥ 0.2. Scanning electron microscopy (SEM) shows that all samples have almost spherical nanoparticles with high crystallization. The increase in the fraction of the doped-Co leads to high agglomeration of particles while the porosity increases. Electrochemical measurements indicate that the catalytic activity toward methanol oxidation in alkaline solution is strongly influenced by cobalt doping. La0.9Sr0.1Cr0.6Co0.4O3-modified electrodes responded extremely well to methanol by giving high anodic current for methanol oxidation (over 46 mA cm−2 at 0.650 V vs Hg/HgO).

Enhanced electrocatalytic performance of mesoporous nickel-cobalt oxide electrode for methanol oxidation in alkaline solution

Nickel-cobalt oxides nanocomposites with different Ni/Co ratios are fabricated by micro-wave assisted synthesis. The texture, morphology, BET surface area and electrochemical performance are found strongly related to Ni and Co concentration. The results illustrate that a hierarchical porous assembly of nanoparticles of ∼10nm was obtained, and the ratio of Ni/Co in the nanocomposites was nearly identical to its precursors. The electro-oxidation behavior of meso-nickel-cobalt oxides outperform pure NiO and Co3O4 for methanol oxidation reaction (MOR). The Ni-Co-O nanocomposite displays a highly stable response during MOR and it considered to a favorable material to develop non-Pt based fuel cells.

Microwave assisted synthesis and characterization of Ni/NiO nanoparticles as electrocatalyst for methanol oxidation in alkaline solution

Nickel/Nickel oxide (Ni/NiO) nanoparticles catalyst is prepared by microwave-assisted liquid-phase deposition using ethylene glycol (EG) and water mixture under atmospheric conditions. The physicochemical characterizations of the catalyst carried out by surface area analyzer, x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), electron microscopes measurements suggest the formation of crystalline nanoparticles structure of NiO. The surface area of Ni/NiO prepared using EG/water mixture reaches 70 m2 g−1 which is 2-fold enhsancement in surface area in comparison with NiO prepared in pure EG and an order of magnitude higher than that of bulk nickel prepared in pure water. The methanol electro-oxidation activity of the Ni/NiO nanoparticles obtained in EG/water mixture displayed more than 4-fold increase in oxidation current at 1.7 V versus RHE in comparison with NiO nanoparticles obtained in EG and 20-fold increase compared to bulk nickel catalyst concord with the enhancement of electro-active surface area. The results show the Ni/NiO nanoparticles produced by microwave assisted synthesis has superior activity for methanol oxidation in alkaline solution over the other nickel based catalysts and has potential for mass production.

Thermal growth of NiO on interconnected Ni–P tube network for electrochemical oxidation of methanol in alkaline medium

A novel electrocatalyst for methanol oxidation reaction in alkaline medium is elaborately fabricated by a sponge-template method involving an electroless plating of amorphous Ni–P on sponge and the following annealing process at 500 °C in air. The electrocatalyst is characterized by NiO nanoparticle/nanoflake grown on the Ni–P alloy tube. The vital annealing process aims to remove templates, crystallize Ni–P, and generate NiO nanostructures on the outside surface of Ni–P tubes, thus leading to the final structure of NiO/Ni–P composites. The tubular Ni–P framework surface is decorated with microspherical NiO (EP-M) or nanoflake NiO (EP-F), which strongly depends on the electroless plating time. For comparison, porous NiO nanoflakes are also synthesized by chemical bath deposition. The EP-M containing ∼83.8 wt.% NiO and ∼16.2 wt.% Ni–P has the largest BET surface area of 210.03 m2 g−1 among the three samples. Moreover, the EP-M exhibits a high current density (∼467 A g−1) and long-term chronoamperometry stability (≥20,000 s) toward methanol oxidation in alkaline solution. The improved catalytic activity of the composite catalyst might be attributed to the strong electronic interaction between NiO and Ni–P as revealed by X-ray photoelectron spectroscopy.

Facile synthesis of PtPdPt nanocatalysts for methanol oxidation in alkaline solution

The platinum and palladium nanocomposites (PtPdPt) are successfully prepared by a facile process based on electrodeposition technique and studied as electrocatalysts for methanol oxidation in alkaline solution. The components and the morphological properties of the PtPdPt nanocomposites are investigated by means of scanning electron microscopy and X-ray diffraction techniques. Cyclic voltammogram (CV) analyses show that PtPdPt (706.1mAmg−1Pt) offers much higher specific surface area and electrocatalytic ability than Pt (388.1mAmg−1Pt) or PtPd (568.3mAmg−1Pt) does. And, the PtPdPt also exhibits excellent tolerance to intermediates poisoning (IF/IR=2.23).

Electrochemical properties, optical modeling and electrocatalytic activity of pulse-electropolymerized ternary nanocomposite of poly (methylene blue) in aqueous solution

This paper aims to investigate the relationship between surface morphology of poly (methylene blue) (PMB) films and pulse synthesis conditions. A simple and general strategy, namely in situ electropolymerization has been used for electrosynthesis of PMB on the Indium Tin Oxide (ITO) substrates by pulse galvanostatic method. The obtained surface analysis results revealed that the morphology and particle sizes of PMB strongly depended on the synthetic conditions. PMB nanoparticles with good electrochemical stability were obtained by optimization of synthetic conditions. Then, Ni (II) and Mn (II) ions were incorporated to electrode by immersion of the polymerically modified electrode in a stirred solution containing Ni and Mn ions to form Ni–Mn/PMB films. Furthermore, the experimental absorbance spectra of nanocomposite were compared with the results from the Maxwell-Garnett theory (MGT) and the value of energy, Eg, of composite obtained. Modified electrodes (Ni–Mn/poly methylene blue) were examined for their redox and electrocatalytic activities in the oxidation of methanol in alkaline solutions. The electrochemical results reveal that Ni–Mn/poly methylene blue modified electrode shows a significantly higher response for methanol oxidation in alkaline solution.

Application of nano-sized nanoporous zinc 2-methylimidazole metal-organic framework for electrocatalytic oxidation of methanol in alkaline solution

In this work, a novel non-platinum group metals (non-PGM) catalyst based on modified zinc 2-methylimidazole metal-organic framework (ZIF-8) is proposed and used for electrooxidation of methanol. Nano-sized particles of nonporous ZIF-8 are synthesized at room temperature using a simple template-free method. The synthesized ZIF-8 nanoparticles are characterized by X-ray diffraction, scanning electronic microscopy and nitrogen adsorption-desorption techniques. In order to decrease the overvoltage of methanol oxidation on carbon paste electrode (CPE), nickel species doped ZIF-8 modified carbon paste electrode (Ni/ZIF-8CPE) is fabricated as a modified electrode. Electrochemical techniques such as cyclic voltammetry and chronoamperometry are used to investigate the electrocatalytic activity of Ni/ZIF-8CPE toward methanol oxidation in alkaline solution. Cyclic voltammetry results show that oxidation current is considerably increased using Ni/ZIF-8CPE in comparison with unmodified CPE. Catalytic rate constant of methanol oxidation on Ni/ZIF-8CPE is obtained using chronoamperometric studies. Besides the good catalytic activity of the modified electrode toward methanol oxidation, it has other advantages such as simple preparation, ease of operation, good stability and low cost, which can be promising in the field of preparation of non-PGM electrocatalysts for application in fuel cells.

Methanol Oxidation on Pd-Ru/C Nanocatalysts: Role of Electronic Properties and FTIR Studies

In this work, methanol oxidation in alkaline solution was studied on carbon-supported Pd-Ru nanocatalysts of nominal Pd:Ru atomic composition 1:1. The synthesis of the catalysts involved the preparation of nanoparticles in colloidal state by a modified polyol method using two reducers. The nanoparticles were separated from the reaction medium and thoroughly cleaned by a sequence of centrifugation and redispersion steps. After that, the particles were supported on high surface area carbon powder (Vulcan XC-72, Cabot). The total metal load was 20 wt%. The carbon-supported catalyst obtained was repeatedly washed with dilute solution of KOH in ethanol, dilute solution of H2SO4, and hot water. After filtration, the catalyst was dried at 80o C. One sample of Pd/C prepared by the same method was used as reference material. Portions of the as-prepared Pd-Ru/C sample were thermally treated at 200 and 400oC during 4 hours in argon, aiming to verify if the degree of alloying could be increased. The catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Cyclic voltammetry (CV) in solutions devoid of alcohol was used to evaluate the general electrochemical behavior. The CV curves showed a quite thick double layer region indicating the presence of Ru species. The electrocatalytic activities towards methanol oxidation were studied by linear potential sweeps and chronoamperometry. Oxidation of adsorbed CO was also measured. The charges of CO stripping curves allowed determining the Pd electrochemically active areas that were used for calculating current densities. It was observed that the catalytic activity was slightly improved after heat treatment at 200oC, while the treatment at higher temperature had a detrimental effect. Measurements of X-ray absorption spectroscopy were carried out around the Pd L3 edge (3173 eV) in order to evaluate the relevance of electronic effects. Despite the fact that these experiments could only be made in high vacuum conditions, it was found that current densities of methanol oxidation measured at 0.5 V vs RHE can be correlated with the Pd 4d band vacancy. It was observed that the methanol oxidation current density increases as the Pd 4d band vacancy becomes larger, in a way similar to what was observed for methanol oxidation in acid solution on Pt-Ru catalysts [1,2]. In situ Fourier transform infrared spectroscopy (in situ FTIR) experiments were performed in order to determine the distribution of reaction products as a function of the applied potential. In a general manner, data showed the formation of formate and the presence of small amounts of adsorbed CO between 0.3 and 0.7 V. The formation of CO2was only observed above 0.7 V as result of the acidification of the thin layer of solution in contact with the catalyst that is caused by the production of protons during methanol oxidation. Acknowledgments Thanks are due to the Brazilian Agencies FAPESP (2014/12255-6; 2013/50206-4; 2013/01822-4) and CNPq (407143/2013-0) for financial support and fellowships. Thanks are also due to the Brazilian Synchrotron Light Laboratory (LNLS) for assisting XAS measurements.

Investigation of Co3O4 nanorods supported Pd anode catalyst for methanol oxidation in alkaline solution

A Co3O4 nanorod supported Pd electro-catalyst for the methanol electro-oxidation (MEO) has been fabricated by the combination of hydrothermal synthesis and microwave-assisted polyol reduction processes. The crystallographic property and microstructure have been characterized using XRD, SEM and TEM. The results demonstrate that Pd nanoparticles (PdNPs) with a narrow particle size distribution (3–5 nm) are uniformly deposited onto the surface of Co3O4 nanorods. Electrochemical measurements show that this catalyst having a larger electrochemically active surface area and a more negative onset-potential exhibits enhanced catalytic activity of 504 mA/mg Pd for MEO comparing with the Pd/C catalyst (448 mA/mg Pd). The dependency of logI against logv reveals that MEO on Pd-Co3O4 electrode is under a diffusion control. Electrochemical impedance spectroscopy (EIS) measurement agrees well with the CV results. The minimum charge transfer resistance of MEO on Pd-Co3O4 is observed at −0.05 V, which coincides with the potential of MEO peak.

Palladium nanoparticles assembled on multi-walled carbon nanotubes functionalised by methylene blue under ultraviolet light and electrocatalytic activity for methanol oxidation

In order to improve the utilisation and performance of anode catalysts in direct methanol fuel cells (DMFCs), functionalised multi-walled carbon nanotubes (MWCNTs) are used as a support for palladium (Pd) nanoparticles synthesised by photochemical reduction. MWCNTs are modified by methylene blue (MB) under ultraviolet light (fuv-MWCNTs), and then Pd nanoparticles are assembled on the fuv-MWCNTs to form composites (Pd/fuv-MWCNTs). The method is green, simple and does not destroy the pristine structure of the MWCNTs. The morphology and structure of prepared composites are characterised by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results show that Pd nanoparticles with face-centred cubic crystal structure are about 3.9 nm in size, and are uniformly dispersed on the surface of fuv-MWCNTs. X-ray photoelectron spectroscopy (XPS) reveals that N-containing and S-containing groups exist in fuv-MWCNTs. These groups might be active sites for assembly of Pd nanoparticles on the surface of fuv-MWCNTs, and can modify the electronic structure of Pd nanoparticles. Electrochemical experiments indicate that the prepared Pd/fuv-MWCNTs catalyst exhibits excellent catalytic performance. The catalytic activity of Pd/fuv-MWCNTs is 1.94 times higher than that of commercial Pd/C for methanol oxidation in alkaline solution. It indicates that UV irradiation can facilitate MB to functionalise MWCNTs, reinforce the modification of the electronic structure of Pd, and enhance the catalytic activity of Pd/fuv-MWCNTs.

Multi-laminated copper nanoparticles deposited on conductive substrates for electrocatalytic oxidation of methanol in alkaline electrolytes

A simple electrodeposition approach to grow multi-laminated copper particles on two conductive substrates is presented. Morphological and structural characterization was performed using SEM and XRD. The copper crystallites are preferentially oriented with {111} planes parallel to the substrate surfaces, providing an optimum interface for methanol oxidation. There are a large number of edges, corners, and atomic steps around individual multi-laminated nanostructured particles. The excellent electrocatalytic activity of the particles to methanol oxidation in alkaline solutions is demonstrated by cyclic voltammetry, electrochemical impedance spectroscopy and chronoamperometry. The presence of the conductive poly(2-amino-5-mercapto-1,3,4-thiadiazole) interlayer between the Cu particles and the carbon paste substrate results in larger specific surface areas of the particles and smaller charge-transfer resistances of methanol oxidation reaction in the lower potential range. Such an anisotropic laminated structure of non-noble metal nanomaterials deserves further investigation for finding a suitable alternative to noble metal-based anodic catalysts in fuel cells.

Synthesis of size-selected Pt nanoparticles supported on sulfonated graphene with polyvinyl alcohol for methanol oxidation in alkaline solutions

In this study, the size-selected platinum (Pt) nanoparticles are loaded on sulfonated graphene with polyvinyl alcohol (PVA) as the conductive polymer for fuel-cell applications. Methanol oxidation reactions and reliability of various catalysts based on carbon black, graphene, and sulfonated graphene catalyst supports are compared under alkaline conditions. When PVA is used as the conductive polymer in place of Nafion, both the electrochemical active surface area (ECSA) and the methanol oxidation property were superior, irrespective of the catalyst and support. On the other hand, the catalyst with Pt on sulfonated graphene (Pt/sG) outperforms those on other supports. For methanol oxidation, the catalyst decay occurs with a decay of only 9.06% for Pt/sG. It is suggested that the sulfonate functional group on graphene not only improves catalytic activity but can also enhance catalyst reliability.