Novel synthesis of highly active Pt/C cathode electrocatalyst for direct methanol fuel cell

A 40 wt% Pt/C cathode electrocatalyst with controlled Pt particle size of approximately 2.9 nm showing better performance than commercial catalyst for direct methanol fuel cell was prepared by a polyol process with water but without using stabilizing agent.     

Highly stable PtRuTiOx/C anode electrocatalyst for direct methanol fuel cells

In the present investigation, PtRuTiO_x/C electrocatalyst was prepared by a modified polyol synthesis method and the as-prepared electrocatalyst was treated under the reductive atmosphere (30 vol% H₂ in Ar) at 500 °C for 2 h (denoted as PtRuTiO_x/C-500) to enhance the interaction between the metal particles and the support. For comparison, the commercial PtRu/C electrocatalyst was also treated by the same procedure as PtRuTiO_x/C (denoted as PtRu/C-500). Transmission electron microscopy results indicated that PtRuTiO_x/C electrocatalyst exhibited not only a uniform dispersion and narrow size distribution with a smaller particle size, but also excellent stability during the thermal treatment. In contrast, the commercial PtRu/C electrocatalyst is not stable during the thermal treatment and the metal particles greatly agglomerated. The results of CO-stripping voltammetry, single direct methanol fuel cell tests and life-time test jointly showed that PtRuTiO_x/C-500 had better durability than commercial PtRu/C while keeping a desirable activity toward methanol electro-oxidation, which may be attributed to the addition of titanium oxide that improved the interaction between noble metal particles and the support.     

Nanostructured PtRu/C as anode catalysts prepared in a pseudomicroemulsion with ionic surfactant for direct methanol fuel cell

Nanostructured PtRu/C catalysts have been prepared from a water-in-oil pseudomicroemulsion with the aqueous phase of a mixed concentrated solution of H(2)PtCl(6), RuCl(3), and carbon powder, oil phase of cyclohexane, ionic surfactant of sodium dodecylbenzene sulfonate (C(18)H(29)NaO(3)S), and cosurfactant n-butanol (C(4)H(10)O). Two different composing PtRu/C nanocatalysts (catalyst 1, Pt 20 wt %, Ru 15 wt %; catalyst 2, Pt 20 wt %, Ru 10 wt %) were synthesized. The catalysts were characterized by transmission electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy, and thermogravimetric analysis, and the particles were found to be nanosized (2-4 nm) and inherit the Pt face-centered cubic structure with Pt and Ru mainly in the zero valance oxidation state. The ruthenium oxide and hydrous ruthenium oxide (RuO(x)()H(y)()) were also found in these catalysts. The cyclic voltammograms (CVs) and chronoamperometries for methanol oxidation on these catalysts showed that catalyst 1 with a higher Ru content (15 wt %) has a higher and more durable electrocatalytic activity to methanol oxidation than catalyst 2 with low Ru content (10 wt %). The CV results for catalysts 1 and 2 strongly support the bifunctional mechanism of PtRu/C catalysts for methanol oxidation. The data from direct methanol single cells using these two PtRu/C as anode catalysts show the cell with catalyst 1 has higher open circuit voltage (OCV = 0.75 V) and maximal power density (78 mW/cm(2)) than that with catalyst 2 (OCV = 0.70 V, P(max) = 56 mW/cm(2)) at 80 degrees C.     

PtRu/carbon nanotube nanocomposite synthesized in supercritical fluid: a novel electrocatalyst for direct methanol fuel cells

Platinum/ruthenium nanoparticles were decorated on carbon nanotubes (CNT) in supercritical carbon dioxide, and the nanocomposites were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). TEM images show that the particles size is in the range of 5-10 nm, and XRD patterns show a face-centered cubic crystal structure. Methanol electrooxidation in 1 M sulfuric acid electrolyte containing 2 M methanol were studied onPtRu/CNT (Pt, 4.1 wt%; Ru, 2.3 wt%; molar ratio approximately Pt/Ru = 45:55) catalysts using cyclic voltammetry, linear sweep voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. All the electrochemical results show that PtRu/CNT catalysts exhibit high activity for methanol oxidation which resulted from the high surface area of carbon nanotubes and the nanostructure of platinum/ruthenium particles. Compared with Pt/CNT, the onset potential is much lower and the ratio of forward anodic peak current to reverse anodic peak current is much higher for methanol oxidation, which indicates the higher catalytic activity of PtRu/CNT. The presence of Ru with Pt accelerates the rate of methanol oxidation. The results demonstrated the feasibility of processing bimetallic catalysts in supercritical carbon dioxide for fuel cell applications.     

PtRu/Ti anodes with varying Pt ratio: Ru ratio prepared by electrodeposition for the direct methanol fuel cell

PtRu/Ti anodes with varying Pt ratio Ru ratio were prepared by electrodeposition of a thin PtRu catalyst layer onto Ti mesh for a direct methanol fuel cell (DMFC). The morphology and structure of the catalyst layers were analyzed by SEM, EDX and XRD. The catalyst coating layer shows an alloy character. The relative activities of the PtRu/Ti electrodes were assessed and compared in half cell and single DMFC experiments. The results show that these electrodes are very active for the methanol oxidation and that the optimum Ru surface coverage was ca. 9 at.% for DMFC operating at 20 degrees C and 11 at.% at 60 degrees C. The PtRu/Ti anode shows a performance comparable to that of the conventional carbon-based anode in a DMFC operating with 0.25 M or 0.5 M methanol solution and atmosphere oxygen gas at 90 degrees C.     

PtCeOx/C as a novel methanol-tolerant electrocatalyst of oxygen reduction for direct methanol fuel cells

A prominent methanol-tolerant characteristic of the PtCeO_x/C electrocatalyst was found during oxygen reduction reaction process. The carbon-supported platinum modified with cerium oxide (PtCeO_x/C) as cathode electrocatalyst for direct methanol fuel cells was prepared via a simple and effective route. The synthesized electrocatalysts were characterized by X-ray diffraction and transmission electron microscopy. It was found that the cerium oxide within PtCeO_x/C present in an amorphous form on the carbon support surface and the PtCeO_x/C possesses almost similar disordered morphological structure and slightly smaller particle size compared with the unmodified Pt/C catalyst.     

甲醇浓度对被动式自呼吸直接甲醇燃料电池性能的影响

依据单电池测试结果和甲醇传质理论考察了甲醇溶液的浓度对被动式自呼吸直接甲醇燃料电池（DMFC）性能的影响.研究结果表明,电池的法拉第效率和能量转化效率会随着浓度的增大而降低,采用4mol/L的甲醇溶液实现了最大的放电功率13.9mW/cm^2,并能在60mA下稳定放电长达20h.这取决于电池运行过程中电极内部的甲醇传质和甲醇透过的共同作用.     

High electrochemical activity of Pt/C cathode modified with NH4HCO3 for direct methanol fuel cell

The electrochemical activity of Pt/C cathode for direct methanol fuel cell was improved by introducing NH₄HCO₃ to the catalyst layer as the pore-forming agent during preparation process of catalyst-coated membrane. SEM analysis revealed that NH₄HCO₃ contributed to the formation of additional porosity and the dispersion of the catalyst particles. The modified catalyst layer promoted the electrochemical and mass transport processes. It was suggested that the optimal weight ratio of the catalyst to NH₄HCO₃ was 2:3. As a result, the single cell exhibited a 21% increment in the peak power density at 50 °C, with a highest electrochemical surface area of 446 cm² mg_Pt^–1. However, an extremely high content of NH₄HCO₃ yielded discontinuous pathways for the electron transfer in the catalyst layer.     

Synthesis of PtRu nanoparticles from the hydrosilylation reaction and application as catalyst for direct methanol fuel cell

Nanosized Pt, PtRu, and Ru particles were prepared by a novel process, the hydrosilylation reaction. The hydrosilylation reaction is an effective method of preparation not only for Pt particles but also for other metal colloids, such as Ru. Vulcan XC-72 was selected as catalyst support for Pt, PtRu, and Ru colloids, and TEM investigations showed nanoscale particles and narrow size distribution for both supported and unsupported metals. All Pt and Pt-rich catalysts showed the X-ray diffraction pattern of a face-centered cubic (fcc) crystal structure, whereas the Ru and Ru-rich alloys were more typical of a hexagonal close-packed (hcp) structure. As evidenced by XPS, most Pt and Ru atoms in the nanoparticles were zerovalent, except a trace of oxidation-state metals. The electrooxidation of liquid methanol on these catalysts was investigated at room temperature by cyclic voltammetry and chronoamperometry. The results concluded that some alloy catalysts showed higher catalytic activities and better CO tolerance than the Pt-only catalyst; Pt56Ru44/C have displayed the best electrocatalytic performance among all carbon-supported catalysts.     

Microwave synthesis of polymer-embedded Pt-Ru catalyst for direct methanol fuel cell

Platinum-ruthenium nanoparticles stabilized within a conductive polymer matrix are prepared using microwave heating. Polypyrrole di(2-ethylhexyl) sulfosuccinate, or PPyDEHS, has been chosen for its known electrical conductivity, thermal stability, and solubility in polar organic solvents. A scalable and quick two-step process is proposed to fabricate alloyed nanoparticles dispersed in PPyDEHS. First a mixture of PPyDEHS and metallic precursors is heated in a microwave under reflux conditions. Then the nanoparticles are extracted by centrifugation. Physical characterization by TEM shows that crystalline and monodisperse alloyed nanoparticles with an average size of 2.8 nm are obtained. Diffraction data show that crystallite size is around 2.0 nm. Methanol electro-oxidation data allow us to propose these novel materials as potential candidates for direct methanol fuel cells (DMFC) application. The observed decrease in sulfur content in the polymer upon incorporation of PtRu nanoparticles may have adversely affected the measured catalytic activity by decreasing the conductivity of PPyDEHS. Higher concentration of polymer leads to lower catalyst activity. Design and synthesis of novel conductive polymers is needed at this point to enhance the catalytic properties of these hybrid materials.     

Modification of multi-walled carbon nanotubes by microwave digestion method as electrocatalyst supports for direct methanol fuel cell applications

Multi-walled carbon nanotubes (MWCNTs) which were directly synthesized on carbon cloth were modified by a microwave digestion method in 5 M HNO₃ for supporting Pt nanoparticles. The characterizations of modified CNTs were carried out by TEM, XPS, FTIR and Raman spectroscopy. The HRTEM image shows the caps of MWCNTs are opened after modifying by microwave digestion method. The open-end and undamaged MWCNTs can provide a larger surface area for supporting more catalysts. Furthermore, the methanol electrocatalytic oxidation of microwave digestion treated Pt/MWCNTs electrode shows higher current density than pristine and nitric acid-treated MWCNTs from cyclic voltammograms. This can be an effective and undamaged method for modifying CNTs.     

Synthesis and characterization of Pd-La(OH)3/C electrocatalyst for direct ethanol fuel cell

The composite nanomaterial of Pd-La(OH)₃/C was successfully synthesized via intermittent microwave heating–glycol reduction method and characterized with X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. The TEM photograph shows that Pd-La(OH)₃ is well polymerized and dispersed on the carbon support. The performance of the prepared material for ethanol oxidation was evaluated by cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry (CA), and chronopotentiometry (CP) measurements in alkaline media. The results reveal that Pd-La(OH)₃/C has significantly higher activity and stability than that of Pd/C with the same Pd loading of 0.1 mg cm^?2. The stable potential reaches to ?0.38 V vs. Hg/HgO at 20 mA cm^?2 on the Pd-La(OH)₃/C electrode in CP curve. Single direct ethanol fuel cell (DEFC) was constructed using Pd-La(OH)₃/C electrode and MnO₂/C electrode as the ethanol anode and air cathode respectively, where the cell voltage can stay at 0.4 V under the current density of 20 mA cm^?2 by discharge test at room temperature.     

Microstructural and metal-support interactions of the Pt-CeO2/C catalysts for direct methanol fuel cell application

To understand the ceria promotion effect of Pt-CeO(2)/C catalysts on methanol oxidation, microstructural and metal-oxide interactions of Pt-CeO(2)/C catalysts with an atomic ratio of Pt/Ce between 0.14 and 1.4 were systematically examined using high-resolution transmission electron microscopy and electron energy loss spectroscopy (EELS). With an increasing Pt content in the catalysts, Pt particles gradually invaded into the ceria supports and decoration on Pt particles was observed. Simultaneously, the morphology of the supports was dramatically modified with nanocrystalline and amorphous ceria formed between and/or around the Pt particles. It reveals that the Pt-ceria interaction could take place in the catalysts and the influence of the interaction was enhanced with an increasing Pt/Ce ratio. The EELS study demonstrated that the strong Pt-ceria interaction was related to the redox reaction between Pt and ceria. Experimental results also suggested that the strong interaction between Pt and ceria could contribute to the promotion effect of ceria on the oxidation of methanol.     

采用简易方法合成直接乙醇固体氧化物燃料电池海胆状Pd催化层

在室温下,通过电位置换反应在固体氧化物燃料电池的Ni-YSZ(钇掺杂氧化锆)阳极表面制备海胆状Pd催化层。该催化层的结构和性能通过SEM、XRD和电化学等表征手段进行表征。结果表明,三维纳米花状Pd催化剂是由在Ni-YSZ阳极表面形成的多条纳米棒有序的组合而成。通过在Ni/YSZ阳极表面引入该催化层,相比与传统Ni-YSZ阳极,燃料电池的最高功率和稳定性都获得了很大的提升。该研究表明,电位置换反应是一种很高效的在传统Ni-YSZ阳极表面制备纳米抗积炭的功能层的方法。     

高分散PtRu/C催化剂的制备及对甲醇及吸附态CO的电催化氧化

采用化学还原浸渍法在两种不同条件下制备炭载PtRu催化剂,通过XRD和TEM技术对催化剂的晶体结构及微观形貌进行了分析,运用循环伏安法、线性扫描法来检测不同条件下制备的催化剂对甲醇及吸附态CO(COad)电催化氧化活性的影响.结果表明,不同条件下制备的催化剂Pt和Ru形成合金的程度不同,Pt-Ru合金原子的颗粒在载体炭上的粒径大小和分布不同,导致催化剂对甲醇及COad的电氧化催化活性不同.其中以甲醛为还原剂在乙二醇体系中制备的催化剂PtRu/C-2能形成较好的合金状态,粒径小,分布均匀,对甲醇及COad的氧化具有较高的电催化活性.     

Development of MEMS-based direct methanol fuel cell with high power density using nanoimprint technology

Performance of MEMS-based DMFC is low, because graphite-based porous electrodes show poor compatibility with MEMS technology. Nanoimprint technology was adopted in this paper to prepare fine pattern on proton exchange membrane (PEM) in MEMS-based DMFC as a promising alternative to the graphite-based porous electrodes. Micro-convex with the diameter of about 600 nm and the height of 50–70 nm was prepared on Nafion^® 117 membrane by the nanoimprint at 130 °C using silicon mold. Thick Pt film (20 nm) was deposited as catalyst directly on the nanoimprinted Nafion^® 117 membrane. Then the Pt-coated PEM was sandwiched with micro-channeled silicon plates to form a micro-DMFC. With passively feeding of 1 M methanol solution and air at room temperature, the as-prepared cell had the open circuit voltage (OCV) of 0.74 V and the maximum power density of 0.20 mW/cm². The measured OCV was higher than those (0.1–0.3 V) of the state-of-the-art MEMS-based DMFC with planar electrode and pure Pt catalyst.     

Preparation of MoO3/Pt electrodes by electrodeposition for a direct methanol fuel cell

MoO₃/Pt binary catalysts with various Mo/Pt ratios were prepared by an electrodeposition method for use as the anode in a direct methanol fuel cell. Pt was electrodeposited onto indium tin oxide (ITO) substrate, and then MoO₃ was electrodeposited from an Mo-peroxo electrolyte on the top of Pt with different deposition times. The crystallinity of synthesized films was analyzed by X-ray diffraction (XRD), and the oxidation state of both the platinum and molybdenum were determined by X-ray photoelectron spectroscopy (XPS) analyses. Scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM/EDS) was employed to investigate the surface morphology and composition. The catalytic activity and stability for methanol oxidation were measured using cyclic voltammetry and chronoamperometry in a mixture of 0.5 M H₂SO₄ and 0.5 M CH₃OH aqueous solution. Electrocatalytic activity for CO oxidation was also evaluated in a 0.5-M H₂SO₄ solution. The addition of a proper amount of MoO₃ was found to significantly improve both the catalytic activity and stability for methanol oxidation.     

A novel Pt/Au/C cathode catalyst for direct methanol fuel cells with simultaneous methanol tolerance and oxygen promotion

A novel Pt/Au/C catalyst was prepared by depositing the Pt and Au nanoparticles on the carbon support. The synthesized catalysts were characterized by energy-dispersive X-ray (EDX) and transmission electron microscopy (TEM), and electrochemically analyzed for activity towards oxygen-reduction reaction and methanol oxidation reaction. EDX and TEM results reveal that Pt nanoparticles supported on carbon supports were separated by Au nanoparticles. The electrochemical analysis indicate that the novel catalyst showed the enhanced methanol tolerance while maintaining a high catalytic activity for the oxygen-reduction reaction, which could be attributed to the less methanol adsorption on Pt/Au/C catalyst.     

Porous Ni@Pt core-shell nanotube array electrocatalyst with high activity and stability for methanol oxidation

Bimetallic core-shell nanostructures are emerging as more important materials than monometallic nanostructures, and have much more interesting potential applications in various fields, including catalysis and electronics. In this work, we demonstrate the facile synthesis of core-shell nanotube array catalysts consisting of Pt thin layers as the shells and Ni nanotubes as the cores. The porous Ni@Pt core-shell nanotube arrays were fabricated by ZnO nanorod-array template-assisted electrodeposition, and they represent a new class of nanostructures with a high electrochemically active surface area of 50.08 m(2) (g Pt)(-1), which is close to the value of 59.44 m(2) (g Pt)(-1) for commercial Pt/C catalysts. The porous Ni@Pt core-shell nanotube arrays also show markedly enhanced electrocatalytic activity and stability for methanol oxidation compared with the commercial Pt/C catalysts. The attractive performances exhibited by these prepared porous Ni@Pt core-shell nanotube arrays make them promising candidates as future high-performance catalysts for methanol electrooxidation. The facile method described herein is suitable for large-scale, low-cost production, and significantly lowers the Pt loading, and thus, the cost of the catalysts.     

Electrocatalytic performance of Pt/Ru/Sn/W fullerene electrode for methanol oxidation in direct methanol fuel cell

In this work,fullerene was modified by platinum,ruthenium,tin and tungsten nanoparticles.The material was characterized by XRD,ICP-OES and TEM micrograph.The average nanoparticle size on fullerene was 5-8 nm.The application of this material was investigated as a catalyst for methanol oxidation in direct methanol fuel cell.A glassy carbon electrode was modified by Pt/Ru/Sn/W fullerene and electrocatalytic activity of the electrode toward methanol oxidation in basic medium has been demonstrated and investigated using cyclic voltammetry.The catalyst showed good reactivity for methanol oxidation.