Facile synthesis of PdAu/C by cold plasma for efficient dehydrogenation of formic acid

Decomposition of formic acid biomass to generate hydrogen is vital for coping with fossil energy depletion, environmental pollution, and developing clean, efficient, safe, and sustainable modern energy system. In this study, a PdAu/C−C bimetallic catalyst was prepared by the co-impregnation method followed by an atmospheric pressure (AP) cold plasma treatment to synthesize PdAu/C−P catalysts. The resulting PdAu/C−P showed excellent catalytic activity for the formic acid dehydrogenation (FAD) reaction. The total volume of H₂ and CO₂ released from the FAD reaction was about 375 mL after 4 h at 50 °C, and the initial turnover frequency (TOF_initial) was 808.6 h⁻¹. We used X−ray diffractometry (XRD), temperature programmed reduction (TPR) and high-resolution transmission electron microscopy (HRTEM) to show that plasma can effectively promote the redispersion of Pd−Au particles on the surface of the support. The average particle size of PdAu/C−P (3.5 ± 1.5 nm) was less than PdAu/C−C (4.4 ± 1.9 nm) and uniformly distributed. X-ray photoelectron spectroscopy (XPS), TPR, and HRTEM showed that PdAu/C−P has a higher degree of alloying. In addition, the strong electric field in the plasma facilitated more metal sites located on the outer surface of the support in PdAu/C−P, and the atomic ratio of M/C (M = Pd and Au) (0.0134) was much larger than that of PdAu/C−C (0.0060). The apparent activation energy (E_a) of PdAu/C−P for the FAD reaction was only 27.25 kJ mol⁻¹, and it had much higher activity and stability than the commercial Pd/C (Sigma−Aldrich). The total volume of H₂ and CO₂ produced over the PdAu/C−P for three cycles was 1.33, 5.87, and 8.56 times that of commercial Pd/C. Overall, the cold plasma enhanced the degree of alloying, promoted the redispersion of agglomerated particles, and regulated the surface enrichment of the active metal components. This is of great significance for guiding the preparation of high−performance multi-metal catalysts by cold plasma.     

Porous nitrogen doped carbon foam with excellent resilience for self-supported oxygen reduction catalyst

Fabrication of graphitized carbon materials (e.g. carbon nanotubes and graphene) normally entails the assistance of transition metal catalyst. In this paper, a nitrogen doped carbon foam (NCF) with both graphitized and porous carbon structure was fabricated by direct pyrolysis of melamine foam (MF) without using any transition metal catalyst. The graphitized carbon structure was possibly attributed to the triazine moieties in the MF precursor. The introduction of oxygen groups in the oxidation step resulted in the formation of large amount of micro- and mesopores and therefore high specific surface area. The NCF exhibited a three-dimensional cellular network consisting of carbon microfiber with abundant micro- and mesopores and giving rise to a specific surface area over 980 m² g⁻¹. Due to such graphitized porous structure, the NCF was demonstrated to have superior resilience, excellent electrocatalytic activity and good durability for oxygen reduction.     

真空助力器壳体铆接螺栓分布压力的计算

分析计算真空助力器壳体铆接螺栓铆接所需的铆接力和铆接成型后铆钉对真空助力器壳体铆接孔圆柱面上的径向分布压力,对助力器壳体加工制造具有参考价值,在对真空助力器壳体进行有限元分析和计算时,解决了确定边界条件的问题。     

A review on spindle thermal error compensation in machine tools

Thermal error caused by the thermal deformation is one of the most significant factors influencing the accuracy of the machine tool. Among all the heat sources which lead to the thermal distortions, the spindle is the main one. This paper presents an overview of the research about the compensation of the spindle thermal error. Thermal error compensation is considered as a more convenient, effective and cost-efficient way to reduce the thermal error compared with other thermal error control and reduction methods. Based on the analytical calculation, numerical analysis and experimental tests of the spindle thermal error, the thermal error models are established and then applied for implementing the thermal error compensation. Different kinds of methods adopted in testing, modeling and compensating are listed and discussed. In addition, because the thermal key points are vital to the temperature testing, thermal error modeling, and even influence the effectiveness of compensation, various approaches of selecting thermal key points are introduced as well. This paper aims to give a basic introduction of the whole process of the spindle thermal error compensation and presents a summary of methods applied on different topics of it.     

Preparation and characterization of highly stable protic-ionic-liquid membranes

A highly durable proton exchange membranes (PEM)s based on covalently supported ionic liquid (IL) bearing sulfonic acid imidazolium groups were successfully fabricated. The membrane preparation involved radiation induced grafting of 1-vinyl imidazole (1-VIm) onto poly(ethylene-co-tetraflouroethene) (ETFE) film, followed by covalent immobilization of 3-sulfopropyl and subsequent treatment with trifluoromethanesulfonic acid. The ionic conductivity of the supported IL membranes was increased with the increase in the concentration of IL and reached a maximum value of 138 mS cm⁻¹ in a fully hydrated state with an ion exchange capacity of 4.82 mmol g⁻¹ that is higher than Nafion with a similar thickness. The membranes displayed excellent chemical and mechanical stability. In addition, the dimensional and thermal stability of supported IL-membranes were significantly higher than commercial Nafion membranes.     

Effect of carriers on deposition morphologies and catalytic performances of NiCo2O4

In this study, NiCo₂O₄ with different morphologies were fabricated using carriers by homogeneous coprecipitation combined with a sintering method. The phase and microstructure were characterized by XRD, SEM, EDS, TEM and BET, and the catalytic performances were investigated by NaBH₄ hydrolysis experiments. These studies revealed that the deposition morphology of NiCo₂O₄ can be adjusted by using different kinds of carrier templates, and the supported NiCo₂O₄ samples presented the pine-needle-like, network-like, ball-cactus-like and dandelion-like morphologies respectively. The optimal catalytic activity, durability and stability make the network-like NiCo₂O₄ an appropriate catalyst for hydrogen generation of NaBH₄ hydrolysis. It was found that the network-like NiCo₂O₄ is the most reusable and durable catalyst for ten consecutive cycles and 100% hydrogen generation conversion rate without obvious decrease among these morphologies.     

Amide-containing segmented copolymers

This review highlights the synthesis, physical properties, and emerging technologies of state-of-the-art segmented copolymers containing amide hydrogen bonding sites. Amide hydrogen bonding plays a crucial role in the physical properties associated with amide-containing segmented copolymers. Amide hard segments are accessible in many different forms from amorphous alkyl amides to crystalline aramids and greatly influence copolymer morphology and mechanical properties. Variations in copolymer structure allow for the fine tuning of physical properties and the ability to predict mechanical performance based upon structural modifications. This review includes various synthetic methods for producing well-defined amide-containing segmented copolymers as well as common applications. Also, the morphological and mechanical properties associated with modifications in copolymer structure are discussed.     

Investigation of the versatility of SPES membranes customized with sulfonated molybdenum disulfide nanosheets for DMFC applications

Sulfonated poly(ether sulfone) (SPES) based proton exchange membranes (PEMs) are fabricated using sulfonated molybdenum disulfide (S-MoS₂) nanosheets via facile solution casting method. SPES (DS = 30%) and S-MoS₂ are synthesized and sulfonation is evidently observed in FTIR and XRD analysis. The anchoring of sulfonic acid group on exfoliated molybdenum disulfide (E-MoS₂) and elemental composition of S-MoS₂ are confirmed by XPS spectrum. Physico-chemical characteristics such as ion-exchange capacity (IEC), water uptake, swelling ratio and oxidation stability are found to be increases after the addition of S-MoS₂ into SPES matrix. Increment in S-MoS₂ content in SPES matrix decreases the surface contact angle due to the increase in hydrophilicity. Further, the dispersing ability of S-MoS₂ in SPES matrix is evidently shown by an increase in surface roughness, tensile strength and thermal stability of the SPES/S-MoS₂ nanocomposite membranes. On the whole, SPES/S-MoS₂-1 membrane showed the highest proton conductivity of 5.98 × 10⁻³ Scm⁻¹, selectivity of 19.6 × 10⁴ Scm⁻³s, peak power density of 28.28 mWcm⁻² and lesser methanol permeability of 3.05 × 10⁻⁸ cm²s⁻¹. The strong interfacial interaction between SPES and S-MoS₂ in nanocomposite membranes create strong hydrogen bond network to facilitate the proton conduction pathway via both vehicle and Grotthuss type mechanisms. Overall results suggested that the SPES/S-MoS₂ nanocomposite membranes are superior and appropriate alternative for commercially high-cost Nafion® membranes for use in renewable direct methanol fuel cell (DMFC) devices.