Low Pt content Pt–Ru–Ir–Sn quaternary catalysts for anodic methanol oxidation in DMFC

In this communication we report our research work on low Pt content Pt–Ru–Ir–Sn quaternary catalysts for use in DMFC anodes. The carbon-supported quaternary metal alloy catalyst was synthesized according to the solution reduction method and was deposited onto a carbon fiber paper or a carbon aerogel nanofoam to form the anode for direct methanol fuel cells. The Pt loading of the electrode is 0.1 mg/cm². The testing results from a three-electrode electrochemical cell show that the simultaneous use of higher Ir (25–35 wt.%) and Sn (10 wt.%) content gives satisfactory stability and higher activity for methanol oxidation than the commercially available E-TEK anode (80%[0.5Pt 0.5Ru]/C on carbon cloth). Energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), scanning electron microscope (SEM), and Bruner–Emmett–Teller method (BET) measurements were carried out to characterize the composition, structure, morphology, and surface area of the developed catalysts.     

High loading of Pt–Ru nanocatalysts by pentagon defects introduced in a bamboo-shaped carbon nanotube support for high performance anode of direct methanol fuel cells

Bamboo-shaped carbon nanotubes (BCNTs), with a large amount of pentagon defects introduced in the walls, were explored as the support of high loaded Pt–Ru catalysts for the anode of direct methanol fuel cells (DMFCs) in comparison with conventional carbon nanotubes (CNTs) and Vulcan XC carbon black. By ethylene glycol reduction, Pt–Ru catalysts with a high loading (60 wt%) and uniform particle size of 2–3 nm were uniformly deposited on BCNTs; while 60 wt% Pt–Ru catalysts on CNTs resulted in significant agglomeration. The Pt–Ru/BCNT catalyst showed the highest activity on methanol oxidation in cyclic voltammetry and highest performance as the anode in a DMFC single cell. Such an enhancement was largely ascribed to an enhanced interaction of the introduced pentagon defects with Pt–Ru, which could promote a high loading and well dispersion of Pt–Ru catalysts and the charge transfer from Pt–Ru to the tubes.     

CO tolerant Pt/WC methanol electro-oxidation catalyst

Platinum supported on WC (Pt/WC) catalyst (20 wt.% Pt) was synthesized as a new methanol electro-oxidation catalyst. Particle size of 7.5 nm was obtained from X-ray diffraction results and a uniform distribution of particles was observed by transmission electron microscopy. In cyclic voltammetry (CV) measurement, the reduction peak potential of PtO increased from 0.72 V in commercial Pt/C to 0.76 V in Pt/WC. By combining the CV and CO stripping results, spill-over of H⁺ from Pt to WC was observed. Electrochemically active surface area calculated from the desorption area of H⁺ were 11.2 and 5.74 m²/g catalyst for Pt/WC and Pt/C, while those obtained from the desorption area of CO were 4.42 and 6.40 m²/g catalyst, respectively. CO electro-oxidation peak potential greatly decreased from 0.80 V in Pt/C to 0.68 V in Pt/WC. The reaction of WC with water to produce WC–OH could lower to CO electro-oxidation peak potential. Specific activity for methanol electro-oxidation increased from 144 mA/m² in Pt/C to 188 mA/m² in Pt/WC.     

Pt and Pt–Ru nanoparticles decorated polypyrrole/multiwalled carbon nanotubes and their catalytic activity towards methanol oxidation

Conducting polymer composite films comprised of polypyrrole (PPy) and multiwalled carbon nanotubes (MWCNTs) [PPy–CNT] were synthesized by in situ polymerization of pyrrole on carbon nanotubes in 0.1 M HCl containing (NH₄)S₂O₈ as oxidizing agent over a temperature range of 0–5 °C. Pt nanoparticles are deposited on PPy–CNT composite films by chemical reduction of H₂PtCl₆ using HCHO as reducing agent at pH = 11 [Pt/PPy–CNT]. The presence of MWCNTs leads to higher activity, which might be due to the increase of electrochemically accessible surface areas, electronic conductivity and easier charge-transfer at polymer/electrolyte interfaces allowing higher dispersion and utilization of the deposited Pt nanoparticles. A comparative investigation was carried out using Pt–Ru nanoparticles decorated PPy–CNT composites. Cyclic voltammetry demonstrated that the synthesized Pt–Ru/PPy–CNT catalysts exhibited higher catalytic activity for methanol oxidation than Pt/PPy–CNT catalyst. Such kinds of Pt and Pt–Ru particles deposited on PPy–CNT composite polymer films exhibit excellent catalytic activity and stability towards methanol oxidation, which indicates that the composite films is more promising support material for fuel cell applications.     

Fabrication and catalytic properties of Pt and Ru decorated TiO2⧹CNTs catalyst for methanol electrooxidation

Highly ordered anodic titania nanotube arrays provide a large surface area for electrodepositing nickel nanoparticles which are used as the catalyst for carbon nanotube growth. Pt and Ru nanoparticles, approximately 3 nm in diameter, are uniformly electrodeposited on the as synthesized titania-supported carbon nanotubes (CNTs), constructing a novel catalyst for electrocatalytic oxidation of methanol. An enhanced and stable catalytic activity is obtained due to the uniformly dispersed Pt and Ru nanoparticles, and the large CNT network facilitating the electron transfer between the adsorbed methanol molecules and the catalyst substrate. An oxidation peak current density of 55 mA/cm² is achieved at a low Pt load of 0.126 mg/cm² with a Pt/Ru mole ratio of 1:1.     

A novel MEA architecture for improving the performance of a DMFC

Direct methanol fuel cell (DMFC) consisting of a double-catalytic layered membrane electrode assembly (MEA) provide higher performance than that with the traditional MEA. This novel structured MEA includes a hydrophilic inner catalyst layer and a traditional electrode with an outer catalyst layer, which was made using both catalyst coated membrane (CCM) and gas diffusion electrode (GDE) methods. The inner catalyst was PtRu black on anode and Pt black on cathode. The outer catalyst was carbon supported Pt–Ru/Pt on anode and cathode, respectively. Thus in the double-catalytic layered electrodes three gradients were formed: catalyst concentration gradient, hydrophilicity gradient and porosity gradient, resulting in good mass transfer, proton and electron conducting and low methanol crossover. The peak density of DMFC with such MEA was 19 mW cm⁻², operated at 2 M CH₃OH, 2 atm oxygen at room temperature, which was much higher than DMFC with traditional MEA.     

Effect of Ru addition on the structural characteristics and the electrochemical activity for ethanol oxidation of carbon supported Pt–Sn alloy catalysts

Binary Pt–Sn/C (1:1) and ternary Pt–Sn–Ru/C (1:1:0.3 and 1:1:1) catalysts were synthesized by reduction of precursors with formic acid, and their activity for ethanol oxidation was compared with that of commercial Pt/C and Pt–Ru/C catalysts. Linear sweep voltammetry measurements at 40 and 90 °C showed that for potentials higher than 0.3 V vs. RHE, the Pt–Sn–Ru/C (1:1:0.3) catalyst presents the highest activity for ethanol electro-oxidation, while the electrochemical activity of the Pt–Sn–Ru/C (1:1:1) catalyst was lower than that of both the binary Pt–Sn/C and Pt–Ru/C catalysts. Tests in a single direct ethanol fuel cell confirmed the superior performance of the Pt–Sn–Ru/C (1:1:0.3) electrocatalyst. The positive effect of the Ru presence in the Pt–Sn–Ru/C (1:1:0.3) catalyst was ascribed to the interactions between Sn and Ru oxides.     

Investigation of the Pt–Ni–Pb/C ternary alloy catalysts for methanol electrooxidation

This research is aimed to increase the activity of anodic catalysts and thus to lower noble metal loading in anodes for methanol electrooxidation. The Pt–Ni–Pb/C catalysts with different molar compositions were prepared. Their performance were tested by using a glassy carbon disk electrode through cyclic voltammetric curves in a solution of 0.5 mol L⁻¹ CH₃OH and 0.5 mol L⁻¹ H₂SO₄. The performances of Pt–Ni–Pb/C catalyst with optimum composition (the molar ratio of Pt/Ni/Pb is 5:4:1) and Pt/C (E-Tek) were also compared. Their particle sizes and structures were determined by means of X-ray diffraction (XRD). The XRD results show, compared with that of Pt/C, the lattice parameter of Pt–Ni–Pb (5:4:1)/C catalyst decreases, its diffraction peaks are shifted slightly to a higher 2θ values. This indicates the formation of an alloy involving the incorporation of Ni and Pb atoms into the fcc structure of Pt. The electrochemical measurement shows the activity of Pt–Ni–Pb/C catalyst with an atomic ratio of 5:4:1 for methanol electrooxidation is the best among all different compositions. The activity of Pt–Ni–Pb (5:4:1)/C catalyst is much higher than that of Pt/C (E-Tek).     

Boron-doped diamond powder as catalyst support for fuel cell applications

The modification of boron-doped diamond powder with metallic oxides using the sol–gel method to prepare high area and very stable electrodes for the methanol oxidation reaction is reported here. The catalyst clusters thus prepared are irregularly distributed on the BDD powder surface having sizes varying between 500 nm and 5 μm and formed by the agglomeration of many nanoparticles. Electrochemical studies in acid media demonstrate that the deposited particles have a good electrical contact with the diamond powder surface and high purity. Moreover, the use of the sol–gel method on a BDD powder substrate leads to the formation of metallic and metallic oxides deposits of the desired composition. The electrocatalyst composite prepared in this manner (Pt–RuO_x/BDD powder) shows an excellent activity for methanol oxidation presenting an onset potential 20 mV lower than that observed on a Pt–Ru/C commercial catalyst, probably due to the ruthenium oxide contribution to the overall catalytic activity.     

Iodinated carbon materials for oxygen reduction reaction in proton exchange membrane fuel cell. Scalable synthesis and electrochemical performances

Doped graphene-based cathode catalysts are considered as promising competitors for ORR, but their power density has been low compared to Pt-based cathodes, mainly due to poor mass-transport properties. A new electrocatalyst for PEMFCs, an iodine doped grahene was prepared, characterized, and tested and the results are presented in this paper. We report a hybrid derived electrocatalyst with increased electrochemical active area and enhanced mass-transport properties. The electrochemical performances of several configurations were tested and compared with a typical Pt/C cathode configuration. As a standalone catalyst, the iodine doped graphene gives a performance with 60% lower than if it is placed between gas diffusion layer and catalyst layer. If it is included as microporous layer, the electrochemical performances of the fuel cell are with 15% bigger in terms of power density than the typical fuel cell with the same Pt/C loading, proving the beneficial effect of the iodine doped graphene for the fuel cell in the ohmic and mass transfer region. Moreover, the hybrid cathode manufactured by commercial Pt/C together with the material with best proprieties, is tested in a H₂-Air fuel cell and a power density of 0.55 W cm⁻² at 0.52 V was obtained, which is superior to that of a commercial Pt-based cathode tested under identical conditions (0.46 W cm⁻²).     

Aqueous treatment of single-walled carbon nanotubes for preparation of Pt–Fe core–shell alloy using galvanic exchange reaction: Selective catalytic activity towards oxygen reduction over methanol oxidation

We have demonstrated a new, cost effective synthesis of single-walled carbon nanotube supported Pt–Fe core–shell alloy catalyst (Pt–Fe/SWNT) for the direct methanol fuel cell using galvanic exchange reaction. The Pt–Fe/SWNTs have shown much larger Pt active surface area (150 m²/g-Pt) than the commercial catalyst (54 m²/g-Pt). Furthermore, four-fold enhancement of catalytic activity of the Pt–Fe/SWNTs for oxygen reduction reaction (ORR) has been observed. This catalyst has also demonstrated its tolerance to methanol in ORR.     

Impact of reforming catalyst on the anodic polarisation resistance in single-chamber SOFC fed by methane

This paper emphasises the electrochemical and catalytic properties of a Ni–10% GDC (10% gadolinium-doped ceria) cermet anode of a single-chamber solid oxide fuel cell (SC-SOFC). Innovative coupling of electrochemical impedance spectroscopy with gas chromatography measurements was carried out to characterise the anode material using an operando approach. The experiments were conducted in a symmetric anode/electrolyte/anode cell prepared by slurry coating resulting in 100 μm-thick anode layers. The electrochemical performance was assessed using a two-electrode arrangement between 400 °C and 650 °C, in a methane-rich atmosphere containing CH₄, O₂ and H₂O in a 14:2:6 volumetric ratio. The insertion of a Pt–CeO₂ based catalyst with high specific surface area inside the cermet layer was found to promote hydrogen production from the Water Gas Shift reaction and consequently to improve the electrochemical performances. Indeed, a promising polarisation resistance value of 12 Ω cm² was achieved at 600 °C with a catalytic loading of only 15 wt.%.     

Platinum nanocube catalysts for methanol and ethanol electrooxidation

We prepared Pt nanocube catalyst with about 3.6 nm in size by a polyol process in the presence of PVP as a stabilizer and Fe ion as a kinetic controller. The crystal structure of Pt nanocube with {1 0 0} faces was confirmed by field-emission transmission electron microscopy. In a cyclic voltammogram, we found that the Pt nanocube catalyst showed relatively high ratio of the forward anodic peak current to the reverse anodic peak current resulting in less accumulation of residues on the catalyst. The Pt nanocube catalyst with the edge of stepped {1 0 0} faces was preferable to breakage of CH₃OH and CH₃CH₂OH compared to polycrystalline Pt nanocatalyst. In an electrochemical measurement for methanol and ethanol electrooxidation, the Pt nanocube catalyst showed an excellent catalytic activity, i.e., lower onset potential and higher current density, compared to the polycrystalline Pt nanocatalyst.     

Fabrication of the catalytic electrodes for methanol oxidation on electrospinning-derived carbon fibrous mats

The carbon fibrous mats with high conductivity (50 S cm⁻¹) formed by carbon nanofibers with an average diameter of ∼150 nm have been fabricated by thermally treating the electrospun polyacrylonitrile fibers. The platinum clusters are electrodeposited on the carbon nanofibrous mats (CFMs) by multi-cycle CV method. In contrast to the catalytic peak current of methanol oxidation on commercial catalyst (185 mA mg⁻¹ Pt), the catalytic peak current on optimum Pt/CFM electrode reaches to ∼420 mA mg⁻¹ Pt despite of the large size (50–200 nm) of the Pt clusters, revealing that the special structure of carbon fibrous mats is favorable to improve the performance of catalyst.     

Pd/Pt core–shell nanowire arrays as highly effective electrocatalysts for methanol electrooxidation in direct methanol fuel cells

Highly ordered Pd/Pt–core–shell nanowire arrays (Pd/Pt NWAs) have been prepared by anodized aluminum oxide (AAO) template-electrodeposition and magnetron sputtering methods. Pd/Pt NWA electrode shows a very high electrochemical active surface area and high electrocatalytic activity for the methanol electrooxidation in acid medium for direct methanol fuel cells (DMFCs). The mass specific anodic peak current density is 756.7 mA mg⁻¹ Pt for the methanol oxidation on the Pd/Pt NWA electrode, an increase by a factor of four as compared to conventional E-TEK PtRu/C electrocatalysts. The mechanism of the significant enhancement of the Pd/Pt core/shell NWA nanostructure in the efficiency and electrocatalytic activity of Pt for the methanol electrooxidation in acid medium is discussed.     

Preparation process for improving cathode electrode structure in direct methanol fuel cell

The cathode electrode structure of the direct methanol fuel cell (DMFC) was improved by a novel catalyst ink preparation method. Regulation of the solvent polarity in the cathode catalyst ink caused increases in the electrochemical active surface (EAS) for the oxygen reduction reaction (ORR) as well as decreases in the methanol crossover effect. In a two-step preparation, agglomerates consisting of catalyst and Nafion ionomers were decreased in size, and polar groups in the ionomers formed organized networks in the cathode catalyst layer. Despite Pt catalysts in the cathode being only 0.5 mg cm^? 2, the maximum power density of the improved membrane electrode assembly (MEA) was 120 mW cm^? 2, at 3 M methanol, which was much larger than that of traditional MEA (67 mW cm^? 2).     

Platinum nanoparticles supported on nitrobenzene-functionalised graphene nanosheets as electrocatalysts for oxygen reduction reaction in alkaline media

A systematic study on the electrocatalytic properties of Pt nanoparticles supported on nitrobenzene-modified graphene (Pt-NB/G) as catalyst for oxygen reduction reaction (ORR) in alkaline solution was performed. Graphene nanosheets were spontaneously grafted with nitrophenyl groups using 4-nitrobenzenediazonium salt. The electrocatalytic activity towards the ORR and stability of the prepared catalysts in 0.1 M KOH solution have been studied and compared with that of the commercial Pt/C catalyst. The results obtained show that the NB-modified graphene nanosheets can be good Pt catalyst support with high stability and excellent electrocatalytic properties. The specific activity of Pt-NB/G for O₂ reduction was 0.184 mA cm⁻², which is very close to that obtained for commercial 20 wt% Pt/C catalyst (0.214 mA cm⁻²) at 0.9 V vs. RHE. The Pt-NB/G hybrid material promotes a four-electron reduction of oxygen and can be used as a promising cathode catalyst in alkaline fuel cells.     

Flexible free-standing graphene-silicon composite film for lithium-ion batteries

Flexible, free-standing, paper-like, graphene-silicon composite materials have been synthesized by a simple, one-step, in-situ filtration method. The Si nanoparticles are highly encapsulated in a graphene nanosheet matrix. The electrochemical results show that graphene-Si composite film has much higher discharge capacity beyond 100 cycles (708 mAh g^? 1) than that of the cell with pure graphene (304 mAh g^? 1). The graphene functions as a flexible mechanical support for strain release, offering an efficient electrically conducting channel, while the nanosized silicon provides the high capacity.     

A novel route for preparation of PtRuMe (Me = Fe,Co, Ni) and their catalytic performance for methanol electrooxidation

PtRuMe (Me = Fe, Co, Ni) catalysts dispersed on multi-wall carbon nanotubes (MWCNTs) were prepared by ultrasonic-assisted chemical reduction. X-ray diffraction (XRD) showed that Pt existed as face-centered cubic structure, while Ru and Me alloyed with Pt. The calculated particle sizes from XRD data are of 3.40, 3.40, 2.61 and 3.06 nm for PtRu, PtRuFe, PtRuCo and PtRuNi, respectively, and are consistent with TEM results. The electrochemical measurements showed that the addition of Me to PtRu enhances the electrocatalytic properties for methanol oxidation and PtRuNi has the best catalytic activity and stability.     

Preparation of a poly(methyl methacrylate)-reduced graphene oxide composite with enhanced properties by a solution blending method

Poly(methyl methacrylate) (PMMA)/graphene nanocomposites were prepared by a simple solution blending method. The glass transition temperature of the produced PMMA/graphene composite was increased by 37 °C with 1.0 wt.% RGO content, which is approximately 40% of improvement compared to that of pure PMMA. The thermal expansion coefficient (TEC) decreased by 68% with as low as 0.1 wt.% RGO loading. The electrical conductivity of the nanocomposites reached up to 0.037 S/m even with only 2.0 wt.% RGO, which increased by more than twelve orders of magnitude. The resulting nanocomposites showed that a stable colloidal suspension of graphene dispersion in organic solvent before blending with PMMA is necessary to fabricate the nanocomposites with enhanced properties.