N-doped hierarchically macro/mesoporous carbon with excellent electrocatalytic activity and durability for oxygen reduction reaction

A novel kind of N-doped hierarchically porous carbon materials (HPC-Ns) has been successfully synthesized with hierarchically macro/mesoporous silica as a hard template followed by a simple N-doping procedure using low-cost and nontoxic urea as the nitrogen source. The synthesized HPC-N samples demonstrated extensive three-dimensional (3D) connected macroporosity and partially ordered mesoporosity, extremely large specific surface area, favorable graphitization degree, and high relative content of pyridinic N, which is active to the oxygen reduction reaction (ORR). Due to the combined contributions of the above features, the metal-free HPC-Ns demonstrated excellent performance in ORR with a highly comparable limiting current density but much higher current output stability and resistance towards the fuel crossover effect compared to the commercial Pt/C, as well as the dominant 4 e⁻ reduction mechanism. Thus, it is believed that HPC-N has the potential to be used in polymer electrolyte membrane fuel cells.     

Growth of nano-textured graphene coatings across highly porous stainless steel supports towards corrosion resistant coatings

In this paper, we demonstrated for the first time the growth of 3D networks of graphene nano-flakes across porous stainless steel substrates of micron sized metal fibres, and its anti-corrosion properties. The controlled formation of graphene-grade coatings in the form of single sheets to complex and homogeneously distributed 2–4 μm long nano-pillars is demonstrated by Scanning Electron Microscopy. The morphology and stability of these structures are shown to be particularly related to the temperature and feed gas flow rate during the growth. The number of layers across the graphene materials was calculated from the Raman spectra and is shown to range between 3 and more than 15 depending on the growth conditions and to be particularly related to the time and flow rate of the experiment. The presence of the graphene was shown to massively enhance the specific surface area of the material and to contribute to the increased corrosion resistance and electrical conductivity of the material without compromising the properties or structure of the native stainless steel materials. This new approach opens up a new route to the facile fabrication of advanced surface coatings with potential applications in developing new thermal exchangers, separation and bio-compatible materials.     

Improved catalytic stability and anti-coking ability of Ni/La2O3–Al2O3 catalyst by doping alkaline earth metals for n-decane reforming

In this paper, a series of alkaline earth metals oxides doped Ni/La₂O₃–Al₂O₃ catalysts were synthesized by the coprecipitation method combined with two step impregnation methods. n-decane reforming was used to investigate these catalysts, in order to develop an excellent catalyst with better hydrogen selectivity, activity, stability, as well as lower carbon deposition. Deactivation by carbon deposition, the catalyst regenerability and stability tests were also used to weigh the selected catalyst. These catalysts are characterized by N₂ adsorption-desorption, XRD, NH₃-TPD, Raman, and TEM. The introduction of alkaline earth metals modifiers enhances the activity, stability and anti-coking ability, meanwhile the SrO modified Ni/La₂O₃–Al₂O₃ shows the best catalytic activity. Moreover, the hydrogen selectivity and conversion over regenerative Ni/La₂O₃–Al₂O₃/SrO catalysts were quite close to the results of fresh ones. The enhancements of M oxides doped catalysts (especially Sr) can be due to the improved textural properties, basicity, metal-support interaction and anti-coking ability. As a consequence, loading different metals in different ways helps to gradually improve the stability, activity and coking inhibition of catalysts is an effective approach to obtain a multi-function catalyst.     

Transition metal atom doped C2N as catalyst for the oxygen reduction reaction: A density functional theory study

The catalytic mechanism and activity of transition metal atom doped C₂N (M-C₂N, M = Fe, Co, Ni, and Cu) for the oxygen reduction reaction (ORR) are investigated in detail by density functional theory method. All the screened M-C₂N are thermodynamically stable based on the binding energy calculations. The adsorption energy results indicate that the adsorption strength of O₂ and ORR intermediates are decreased in the order of Fe-C₂N ˃ Co-C₂N ˃ Ni-C₂N ˃ Cu-C₂N, in which the adsorption energy values on Cu-C₂N are most close to those on the Pt(111). Based on the relative energy diagram of ORR, the energetically favorable pathway on Fe-C₂N and Co-C₂N is direct 4e⁻ mechanism, in which the O–O bond is directly dissociated after the second electron transfer. While for Ni-C₂N and Cu-C₂N, the most favorable pathway is indirect 4e⁻ mechanism, in which the H₂O₂ is formed as the intermediate product. For all studied M-C₂N, the Ni-C₂N and Cu-C₂N hold better catalytic activity, which could attribute to the contribution of metal atom and part of its activated nitrogen atoms.     

Effect of introducing a steam pipe to n-dodecane decomposition by in-liquid plasma for hydrogen production

A method has been developed to improve the hydrogen production efficiency (HPE) by in-liquid plasma n-dodecane decomposition. A thin steam pipe is placed over the plasma electrode to recover the thermal energy emitted from the plasma to its surroundings. The steam generated by this energy is supplied to the vaporized n-dodecane around the edge of the plasma to cause a steam reforming reaction (SRR). Water pyrolysis is suppressed by not supplying the steam directly to the plasma. A large amount of CO and a small amount of CO₂ were detected in the produced gas. This indicates that a strong SRR has occurred. The HPE obtained by this method is 0.28 Nm³/kWh, which is two times greater than those obtained by previous methods, and similar to or greater than the yield of water electrolysis. This result is a major advance in the field of plasma heavy hydrocarbon decomposition aimed at hydrogen production. HPE is expected to be further improved by simply increasing the input power, due to synergy between the heat recovery effect of the steam pipe and the bubble stabilization effect. This indicates that this method has a high potential.     

A review on anion exchange membranes for fuel cells: Anion-exchange polyelectrolytes and synthesis strategies

The energy distribution of the world is in a critical transition from traditional fossil fuel to new clean energy. Actually, the fuel cell is favored by researchers as an efficient and clean energy conversion equipment. The anion exchange membranes (AEMs) with excellent performance and long service life will become the development trend of alkaline fuel cells in the future. Compared with proton exchange membrane fuel cells (PEMFCs), its advantages of affordable price, work safety, and non-precious metal participation are widely favored by researchers. This paper reviews the performance of characteristics, synthesis methods, modification methods, and alkaline stability protection of anion-exchange polyelectrolytes (AEPs), and the current research and development status of AEPs used in AEMs are summarized. The evaluation and comparison of different types of AEPs and AEMs based on different AEPs are put forward. This review is expected to further deepen the understanding of AEPs in AEMFC.     

Density functional theory study of the copper phthalocyanine based metal−organic frameworks as the highly active electrocatalysts for the oxygen reduction

Recently, the copper phthalocyanine based 2D conjugated MOFs have been demonstrated that it can efficiently catalyze the oxygen reduction reaction (ORR) experimentally. Herein, the inherent properties and ORR mechanism of PcCu-O₈-M (M = Fe, Co, Ni, Cu) containing two potential active sites (M–O₄ and Cu–N₄ sites) are investigated by density functional theory methods. The binding energy of oxygen-containing intermediates on PcCu-O₈-M indicates that the binding strength of 1OOH, 1O, and 1OH at the M–O₄ site is more moderate than that at the Cu–N₄ site. For all studied sites, their potential-determining steps are the step of O₂ → 1OOH except for the Ni–O₄ site of PcCu-O₈-Ni (1OH → H₂O). Among all sites of PcCu-O₈-M, the Fe–O₄ and Co–O₄ sites have excellent ORR activity with the overpotentials of 0.46 and 0.49 V, respectively, and the Cu–N₄ site of PcCu-O₈-Co possesses the relatively high ORR activity with the overpotential of 0.79 V. It can be concluded that compared with the Cu–N₄ site, the M–O₄ site plays major role for each PcCu-O₈-M during the ORR process. Moreover, the charge analysis of PcCu-O₈-Co suggests that the ORR activities of the Co–O₄ and Cu–N₄ sites are mainly originated from metal atoms (Co atom and Cu atom) as well as the O and N atoms (O and N-1) coordinated with metal atoms. In addition, PcCu-O₈-Co has high poisoning-tolerance ability to NO, NH₃, CO, SO₂, and H₂S.     

Dynamic simulation of a cryogenic batch distillation process for hydrogen isotopes separation

The operational flexibility of cryogenic batch distillation may propel its application in the Isotope Separation System of the fusion reactor. The batch distillation, unlike continuous distillation, is not a steady-state process. In order to obtain improved separation efficiency, a reasonable dynamic model of batch distillation should be developed. In this paper, dynamic simulations of the batch distillation separation process of a hydrogen-deuterium mixture were performed utilizing Aspen Plus and Aspen Dynamics. The validity of the established simulation model was firstly verified by our experimental results. Following that, two dynamic control structures, i.e., composition control and temperature control, were added to improve the recovery efficiency of batch distillation light component products. In comparison with the distillation without dynamic control structure, the distillation with composition control and temperature control can improve the H₂ recovery ratio by 5.45% and 5.09%, respectively.     

短切玄武岩纤维增强环氧树脂复合涂层的制备及性能研究

目的 研究玄武岩纤维/树脂基体界面对涂层性能的影响,通过界面结构的调控提升复合涂层的综合性能。方法 采用酸刻蚀、活化和化学接枝等改性方法处理短切玄武岩纤维,制备短切玄武岩纤维增强环氧复合涂层。通过扫描电子显微镜、硬度测试、摩擦磨损测试、热重分析、电化学测试等方法研究短切玄武岩纤维不同表面改性方法(酸刻蚀、酸刻蚀+化学接枝、活化处理、活化+化学接枝)和添加量对涂层硬度、摩擦磨损性能及腐蚀防护性能的影响。结果 4种表面改性方法均对短切玄武岩纤维的表面活性有提升效果,改善了短切玄武岩纤维与环氧树脂的相容性。其中,活化+化学接枝协同改性的效果最为显著,经过该方法改性后,复合涂层的硬度、耐磨性、耐热性显著提高。与环氧涂层相比,复合涂层的摩擦因数降低了0.113,硬度提高了32.59%,相同温度(320℃)下的重量损失降低了5%。同时,复合涂层的耐蚀性也显著增强,浸泡133 d后的涂层阻抗值仍保持1×10⁸?·cm²以上。结论 表面改性使短切玄武岩纤维与环氧树脂之间相容性增强,进而形成了强有力的相互作用与结合,使得环氧涂层的硬度、耐磨性能、耐热性能和腐蚀...     

一种油田防垢剂的合成及评价实验研究

以过硫酸铵-亚硫酸氢钠为氧化还原引发体系、亚硫酸氢钠同时作链转移剂合成低相对分子量的聚丙烯酸钠,作为一种油田防垢剂。研究了单体、引发剂及链转移剂的用量、反应温度和时间等对产物相对分子质量的影响,并对不同相对分子量的产物进行了防垢性能的评价。结果表明反应温度为60℃、单体质量分数30%、引发剂用量0.6%、链转移剂用量5%、反应时间2 h时,可制得聚丙烯酸钠的粘均相对分子质量在2 000~3 000,作为油田防垢剂防垢效率高、效果好。