Solvent effects on Pt-Ru/C catalyst for methanol electro-oxidation

Alloying degree, particle size and the level of dispersion are the key structural parameters of Pt-Ru/C catalyst in fuel cells. Solvent(s) used in the preparation process can affect the particle size and alloying degree of the object substance, which lead to a great positive impact on its properties. In this work, three types of solvents and their mixtures were used in preparation of the Pt-Ru/C catalysts by chemical reduction of metal precursors with sodium borohydride at room temperature. The structure of the catalysts was characterized by X-ray diffraction (XRD) and Transmission electron microscopy (TEM). The catalytic activity and stability for methanol electro-oxidation were studied by Cyclic Voltammetry (CV) and Chronoamperometry (CA). Pt-Ru/C catalyst prepared in H₂O or binary solvents of H₂O and isopropanol had large particle size and low alloying degree leading to low catalytic activity and less stability in methanol electro-oxidation. When tetrahydrofuran was added to the above solvent systems, Pt-Ru/C catalyst prepared had smaller particle size and higher alloying degree which resulted in better catalytic activity, lower onset and peak potentials, compared with the above catalysts. Moreover, the catalyst prepared in ternary solvents of isopropanol, water and tetrahydrofuran had the smallest particle size, and the high alloying degree and the dispersion kept unchanged. Therefore, this kind of catalyst showed the highest catalytic activity and good stability for methanol electro-oxidation.     

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.     

用于直接甲醇燃料电池的高活性PtCo-CNT@TiO_2复合纳米阳极催化剂

采用溶胶凝胶法制备CNT@TiO_2载体,利用电沉积法制备用于直接甲醇燃料电池的PtCo-CNT@TiO_2阳极催化剂。采用透射电子显微镜(TEM)、X射线衍射(XRD)和电化学工作站对其进行表征。结果表明,PtCo-CNT@TiO_2复合纳米材料有明显的结晶,且金属粒子围绕在TiO_2包覆的碳纳米管的周围,用于直接甲醇燃料电池阳极催化剂具有较高的活性与稳定性。该PtCo-CNT@TiO_2催化剂的电化学比表面积为164 m~2/g,65℃时甲醇的氧化峰电流达到45 mA/cm~2,计时电流曲线表明300 s后PtCo-CNT@TiO_2的氧化电流趋于24 mA/cm~2,在碱性条件下甲醇的氧化峰电流为39.7 mA/cm~2。     

Polyoxometalate-modified carbon nanotubes: new catalyst support for methanol electro-oxidation

A new catalyst support, polyoxometalate-modified carbon nanotubes, is presented in this paper through the chemisorption between polyoxometalate and carbon. Pt and Pt-Ru nanoparticles were electrochemically deposited on polyoxometalate-modified carbon nanotubes electrodes, and their electrocatalytic properties for methanol electro-oxidation are investigated in detail. Due to the unique electrical properties of carbon nanotubes and the excellent redox properties and the high protonic conductivity of polyoxometalate, for the similar deposition charge of Pt and Pt-Ru catalysts, 1.4 times larger exchange current density, 1.5 times higher specific activity, and better cycle stabilities can be obtained at polyoxometalate-modified carbon nanotube electrodes as compared to the electrodes without polyoxometalate modification. These results show that polyoxometalate-modified carbon nanotubes as a new catalyst support have good potential application in direct methanol fuel cells.     

A high dispersed Pt0.35Pd0.35Co0.30/C as superior catalyst for methanol and formic acid electro-oxidation

Pt：Pd：Co ternary alloy nanoparticles were synthesized by sodium borohydride reduction under nitrogen, and were supported on carbon black as catalysts for methanol and formic acid electro-oxidation. Compared with Pt0.65C00.35/C, Pt/C, Pd0.65C00.35/C, and Pd/C catalyst, Pt0.35Pd0.35Co0.30/C exhibited relatively high durability and strong poisoning resistance, and the Pt-mass activity was 3.6 times higher than that of Pt/C in methanol oxidation reaction. Meanwhile, the Pt0.35Pd0.35Co0.30/C exhibited excellent activity with higher current density and higher CO tolerance than that of Pt0.6sCo0.35/C, Pt/C, Pd0.65C00.35/ C, and Pd/C in formic acid electro-oxidation.     

Ru effect on the catalytic performance of Pd@Ru/C catalysts for methanol electro-oxidation

Pd@Ru bimetallic nanoparticles deposited on carbon black electro-catalysts have been fabricated by microwave-assisted polyol reduction method and investigated for methanol electro-oxidation(MEO). The structure and electro-catalytic properties of the as-prepared catalysts were characterized by XRD, SEM, TEM and cyclic voltammetry(CV) techniques. The results showed that the introduction of Ru element(2-10 wt%) into Pd 20 wt%/C(hereafter, denoted as Pd/C) produced a series of core-shell structured binary catalysts. Pd@Ru 5 wt%/C(hereafter, denoted as Pd@Ru5/C) catalyst displayed the highest catalytic activity towards MEO. And the mass activity of Pd@Ru5/C electrode catalyst at E =-0.038 V(vs. Hg/HgO) was 1.42 times higher than that of Pd/C electrode catalyst. In addition, the relationship between the catalytic stability for MEO on Pd@Ru/C catalysts and the value of Jbp/Jfp(the ratio of MEO peak current density in the negative scan and positive scan) were also investigated. The result demonstrated that Pd@Ru5/C offering the smallest value of Jbp/Jfpdisplayed the best stable catalytic performance.     

Carbon nanotubes-Nafion composites as Pt-Ru catalyst support for methanol electro-oxidation in acid media

Carbon nanotubes-Nafion (CNTs-Nafion) composites were prepared by impregnated CNTs with Nafion in ethanol solution and characterized by FT-IR. Pt-Ru catalysts supported on CNTs-Nafion composites were synthesized by microwave-assisted polyol process. The physical and electrochemical properties of the catalysts were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), CO stripping voltammetry, cyclic voltammetry (CV) and chronoamperometry (CA). The results showed that the Nafion incorporation in CNTs-Nafion composites did not significantly alter the oxygen-containing groups on the CNTs surface. The Pt-Ru catalyst supported on CNTs-Nafion composites with 2 wt% Nafion showed good dispersion and the best CO oxidation and methanol electro-oxidation activities.     

Highly active Pd containing EMT zeolite catalyst for indirect oxidative carbonylation of methanol to dimethyl carbonate

Palladium containing EMT zeolite catalyst(Pd/EMT) was prepared and used for the indirect oxidative carbonylation of methanol to dimethyl carbonate(DMC).The EMT zeolite was employed as a new catalyst support and compared with the conventional Pd containing FAU zeolite catalyst(Pd/FAU).The Pd/EMT in contrast to the Pd/FAU catalyst exhibited high intrinsic activity with the turnover frequency of 0.25 s^-1 vs.0.11 s^-1.The Pd/EMT catalyst showed high CO conversion of 82% and DMC selectivity of 79%,that maintained for at least 130 h,while the activity of the Pd/FAU catalyst rapidly deteriorated within 12 h.The enhanced interactions between Pd and EMT zeolite inhibited the sintering of palladium clusters and maintained the Pd2+ active sites in the Pd/EMT catalyst.The stabilization of the mono-dispersed Pd clusters within the EMT zeolite is paramount to the excellent performance of the catalyst for the indirect oxidative carbonylation of methanol to DMC.     

Highly shape-selective Zn-P/HZSM-5 zeolite catalyst for methanol conversion to light aromatics

A highly shape-selective and relatively long-lifetime HZSM-5-based catalyst (Zn-2P/HZSM-5) was prepared by chemical modification with both ZnSiF₆·6H₂O and H₃PO₄ solution. The phosphoric acid modification could effectively modulate the Brønsted acid strength of the HZSM-5 catalyst, which promotes the oligomerization, alkylation, cyclization, and hydrogen transfer reactions. The introduction of Zn-Lewis acid sites significantly improved the dehydroaromatization of higher olefins. All of these were very beneficial for the generation of BTX (i.e. benzene, toluene, and xylene) hydrocarbons in aromatization of methanol. The coke amount and the average rate of coke formation decreased over the Zn-2P/HZSM-5 catalysts, which may largely be ascribed to its lower strong acid sites and lower outer surface acidity. The catalytic performance of methanol aromatization showed that the Zn-2P/HZSM-5 catalyst exhibited the highest BTX selectivity of about 46.76% and the longest catalytic lifetime of about 498 h at T = 400 °C, P = 0.1 MPa, and weight hourly space velocity = 0.7 h⁻¹.     

Highly active water-soluble olefin metathesis catalyst

A novel water-soluble ruthenium olefin metathesis catalyst supported by a poly(ethylene glycol) conjugated saturated 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene ligand is reported. The catalyst displays improved activity in ring-opening metathesis polymerization, ring-closing metathesis, and cross-metathesis reactions in aqueous media.     

NiO增强Pt/C催化剂催化氧化甲醇活性的研究

本文基于NiO作为Pt催化甲醇助催化剂的思路,通过Pt纳米颗粒担载在NiO修饰的碳材料载体上制备了Pt/NiO-C催化剂,系统地研究了不同的NiO/C热处理温度对Pt粒径的影响,并重点探讨了Pt对NiO的质量比对催化氧化甲醇的影响。X射线衍射分析结果显示NiO和Pt均为立方晶系,且NiO的加入有利于主催化剂Pt形成较小的粒径,且经400℃热处理NiO修饰的C材料作为载体有利于Pt的有效分散。所获得的Pt/NiO-C催化剂的电化学活性在甲醇酸性溶液中通过循环伏安法(CV)和计时电流法(CA)进行性能测试。CV测试结果显示以Pt/NiO重量比为4∶1的催化剂其电氧化甲醇活性最大,其峰值氧化电流密度达806 mA/mgPt,是Pt/C催化剂的1.64倍。CA测试结果显示Pt/NiO-C比Pt/C具有更好的抗CO中毒性能和稳定性。     

High-loading Pt nanoparticles on mesoporous carbon with large mesopores for highly active methanol electro-oxidation

High metal-loading Pt/C electrocatalysts are important for the fabrication of thin-layered membrane electrode assemblies (MEAs). However, the preparation of high-loading Pt catalysts with a narrow size distribution of nanoparticles remains a challenge. Herein, ordered mesoporous carbon (OMC) with large mesopores (~15 nm) and a high surface area (1316.0 m² g^?1) was fabricated using a SiO₂ nanosphere array as a template. This material was developed to support a high loading of Pt nanoparticles (60 wt%) and was then used as an electrocatalyst for the methanol oxidation reaction (MOR). The prepared Pt/OMC contains Pt nanoparticles with an average size of ~1.9 nm that are uniformly dispersed on the mesoporous walls of the OMC. The Pt/OMC catalyst exhibits smaller Pt nanoparticle size, greater Pt dispersion, larger specific electrochemically active surface area (ECSA), and higher electrocatalytic activity for the MOR than the carbon black (Vulcan XC-72R)-supported Pt and the commercial Pt/C catalysts.     

Highly graphitized carbon-wrapped PtFeCo alloy with enhanced durability and activity toward methanol electro-oxidation

Exploring efficient strategies to construct durable and active Pt-based electrocatalysts toward methanol oxidation reaction (MOR) remains great significance for the application of direct methanol fuel cells (DMFCs). Here, we report a facile pyrolysis procedure for fabricating carbon layer wrapped PtFeCo alloy nanoparticles supported on nitrogen-doped carbon nanotubes (NCNT). Physical characterizations demonstrate that the nitrogen-doped carbon support is highly graphitized and the PtFeCo particles are firmly wrapped by the graphitized carbon. Since the wrapping of highly graphitized carbon effectively prevents PtFeCo alloy from metal dissolution, the durability of the synthesized PtFeCo/Co–NCNT_a catalyst has been substantially improved, remaining about 76% of its initial mass activity after 1000 cycles of durability test in acid condition. In addition, due to the strain and ligand effects caused by alloying Pt with Fe and Co, the PtFeCo/Co–NCNT_a catalyst exhibits a greatly enhanced mass activity of 4.2-fold and a specific activity of 6.3-fold higher than those of commercial Pt/C-JM catalyst. Consequently, this work may provide an effective route for preparing durable and active Pt-based catalysts for methanol electro-oxidation.     

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.     

Highly efficient Fe/N/C catalyst using adenosine as C/N-source for APEFC

An environmentally friendly precursor, adenosine, has been used as a dual source of C and N to synthesize nitrogen-doped carbon catalyst with/without Fe. A hydrothermal carbonization method has been used and water is the carbonization media. The morphology of samples with/without Fe component has been compared by HRTEM, and the result shows that Fe can promote the graphitization of carbon. Further electro-chemical test shows that the oxygen reduction reaction(ORR) catalytic activity of Fe-containing sample(C–Fe N) is much higher than that of the Fe-free sample(C–N). Additionally, the intermediates of C–Fe N formed during each synthetic procedure have been thoroughly characterized by multiple methods,and the function of each procedure has been discussed. The C–Fe N sample exhibits high electro-catalytic stability and superior electro-catalytic activity toward ORR in alkaline media, with its half-wave potential 20 mV lower than that of commercial Pt/C(40 wt%). It is further incorporated into alkaline polymer electrolyte fuel cell(APEFC) as the cathode material and led to a power density of 100 m W/cm~2.     

PdCo/RGO催化剂对甲酸的氧化电催化性能

采用硼氢化钾还原法制备了石墨烯负载PdCo催化剂(PdCo/RGO),对催化剂进行了结构形貌表征并考察了其对甲酸氧化的催化性能.表征结果表明催化剂形成了立方面心结构的PdCo合金纳米颗粒.与Pd/RGO催化剂相比,PdCo/RGO催化剂上Pd颗粒团聚现象明显改善,平均粒径大大减小且分散性更好.电化学性能测试结果表明,相比于Pd/RGO催化剂,不同比例的PdCo/RGO催化剂具有不同的甲酸氧化电催化活性和稳定性;其中2Pd1Co/RGO性能最佳,最大甲酸氧化峰电位负向移动约60mV,电流密度增大到2.2倍.PdCo/RGO催化剂催化性能优异,显示了很好的甲酸阳极催化剂应用前景.     

Highly active silica-supported rhodium chloride catalyst for ethylene dimerization

Ethylene dimerization was carried out with rhodium chloride supported on silica gel. This heterogenized catalyst is remarkably more active for ethylene dimerization than homogeneous rhodium chloride by the factor of 10⁴- fold per unit g atom of rhodium. The catalytic activity is remarkably enhanced in the presence of hydrogen chloride, as was found with homogeneous rhodium complex catalyst. The active rhodium species, which is different from free rhodium chloride is highly dispersed on silica gel, as in molecular form not in clusters. It is considered that the hydroxyl group of silica gel contributes to the formation of the active rhodium species and that the enhancement of the catalytic activity is due to the ligand effect of ⩾ SiO on Rh.     

Highly active copper-based catalyst for atom transfer radical polymerization

Atom transfer radical polymerization (ATRP) generally requires a catalyst/initiator molar ratio of 0.1 to 1 and catalyst/monomer molar ratio of 0.001 to 0.01 (i.e., catalyst concentration: 1000-10,000 ppm versus monomer). Herein, we report a new copper-based complex CuBr/N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) as a versatile and highly active catalyst for acrylic, methacrylic, and styrenic monomers. The catalyst mediated ATRP at a catalyst/initiator molar ratio of 0.005 and produced polymers with well-controlled molecular weights and low polydispersities. ATRP occurred even at a catalyst/initiator molar ratio as low as 0.001 with copper concentration in the produced polymers as low as 6-8 ppm (catalyst/monomer molar ratio = 10(-5)). The catalyst structures were studied by X-ray diffraction and NMR spectroscopy. The activator CuIBr/TPEN existed in solution as binuclear and mononuclear complexes in equilibrium but as a binuclear complex in its single crystals. The deactivator CuIIBr2/TPEN complex was mononuclear. High stability and appropriate KATRP (ATRP equilibrium constant) were found crucial for the catalyst working under high dilution or in coordinating solvents/monomers. This provides guidance for further design of highly active ATRP catalysts.     

Highly active ruthenium-based catalyst for metathesis of cyano-contained olefins

Ruthenium benzylidene complex (H₂IMes)(2-CH₃-C₅H₄N)(Cl)₂RuCHPh [H₂IMes = 1,3-bis(2,6-dimethylphenyl)-4,5-dihydroimidazol-2-ylidene] (4), which introduced ortho substituted pyridine as dissociating ligand to weaken Ru-N bond and accelerate initiation through steric hindrance, was prepared by the reaction of (H₂IMes)(PPh₃)(Cl)₂RuCHPh (1) with 2-methylpyridine and proved to exhibit enhanced catalytic activity for cyano-contained olefin metathesis.     

High loading Pt nanoparticles on ordered mesoporous carbon sphere arrays for highly active methanol electro-oxidation

Three-dimensionally (3D) ordered mesoporous carbon sphere arrays (OMCS) are explored to support high loading (60 wt%) Pt nanoparticles as electrocatalysts for the methanol oxidation reaction (MOR). The OMCS has a unique hierarchical nanostructure with ordered large mesopores and macropores that can facilitate high dispersion of the Pt nanoparticles and fast mass transport during the reactions. The prepared Pt/OMCS exhibits uniformly dispersed Pt nanoparticles with an average size of 2.0 nm on the mesoporous walls of the carbon spheres. The Pt/OMCS catalyst shows significantly enhanced specific electrochemically active surface area (ECSA) (73.5 m² g^-1) and electrocatalytic activity (0.69 mA cm^-2) for the MOR compared with the commercial 60 wt% Pt/C catalyst.