纳米α-MnO2形貌调控方法初探

以KMnO4、十二烷基醇聚氧乙烯(3)醚(AEO-3)、聚乙二醇400(PEG400)为原料,采用常温液相还原反应法成功制备出球形和棒状纳米α-MnO2.分析了PEG400添加量对产物形貌、大小的影响,采用X射线衍射(XRD)、透射电镜(TEM)等测试手段对产物进行了袁征,结果表明,PEG400在α-MnO2形貌调控方面起着重要的作用.     

α-MnO2及掺杂Ti的研究

探讨了3×3隧道结构的a二氧化锰的合成以及掺杂Ti前后的电化学性能,结果表明掺杂后可充性明显改善,X衍射的结果表明经过有限的充放电过程,a二氧化锰的晶体结构基本得以保留.红外光谱的结果显示,掺杂的Ti不是简单的TiO2的形式.     

Urchin-like core-shell TiO2/α-MnO2 nanostructures as an active catalyst for rechargeable lithium-oxygen battery

A selection of appropriate electrocatalysts with a unique design is a promising solution to promote oxidation and reduction reactions in lithium-oxygen (Li-O₂) batteries. Here, an effective integrated design of urchin-like core-shell TiO₂/α-MnO₂ nanostructure is constructed to develop an efficient catalyst electrode for Li-O₂ batteries. For this purpose, TiO₂ nanoparticles are biosynthesized by an eco-friendly process using flower extract of Matricaria chamomilla as both reducing and stabilizing agents. Then, MnO₂ nanocrystals are grown on the surface of TiO₂ nanoparticles under different reaction times to observe their evolution in terms of morphology and crystalline structure of MnO₂. The electrochemical behavior of the as-prepared core-shell TiO₂/α-MnO₂ nanostructures is evaluated in Li-O₂ cells. The TiO₂/α-MnO₂ electrode is exhibited a lower overpotential and higher specific capacity than the bare TiO₂ electrode. This could have resulted from the bifunctional catalytic activity of TiO₂ and α-MnO₂ coupled with urchin-like MnO₂ nanostructures. Furthermore, the internal resistance of the cell is recorded using electrochemical impedance spectroscopy technique, and reactions of the Li⁺ and O₂ on the cathode surface are investigated by cyclic voltammetry.     

Mo掺杂α-MnO2电催化析氧反应的理论研究

析氧反应(Oxygen Evolution Reaction, OER)在解决能源短缺和环境问题中扮演了重要角色, 但需要巨大的过电位克服缓慢的动力学势垒, 因此开发高效电催化剂成为不可或缺的一步。本工作应用密度泛函理论研究了α-MnO₂(001)和Mo掺杂α-MnO₂(001)的电催化析氧反应性能, 根据反应路径计算了吉布斯自由能、态密度和差分电荷密度。研究结果表明Mo掺杂可以有效调节α-MnO₂(001)面的电子结构, 改善中间物和催化剂之间的脱吸附能力, 为OER提供更多的电子。吉布斯自由能结果表明Mo掺杂α-MnO₂(001)体系中*OOH生成O₂是发生OER的决速步骤, Mo掺杂降低了过电位, 产生的过电位为1.01 V, 表现出良好的析氧催化性能。     

α-MnO2@氮掺杂TiO2/碳纸多孔结构构筑高性能超级电容器

MnO2由于价格低廉、资源丰富、理论比电容高和环境友好等优点而成为理想的超级电容器电极材料.然而,如何通过成本低的合成方法获得高负载量和高性能的MnO2电极材料,仍是一项重大的挑战.因此,通过晶种辅助水热合成及氮化处理,在预处理碳纤维纸(CFP)表面生长了氮掺杂TiO2(N-TiO2)纳米棒阵列,然后再通过水热合成在N...     

Effect of Stoichiometry on Properties of Rare-Earth-Based Hydrogen Storage Alloy for Nickel-Metal Hydride Secondary Battery

Effect of stoichiometry on microstructures, electrochemical properties and PCT characteristics of the alloys MI(Ni0.71Co0.15-Al0.06Mn0.08)x (MI=Lanthanum-rich Michmetal, x=4.6~5.2) have been investigated. The lattice constants a, c, and cellvolumes of non-stoichiometric alloys are bigger than those of the stoichiometric alloy. With the increasing stoichiometry x,the value of a decreases, and the value of c and cell volume increases except for those of the stoichiometric alloy; the plateaupressure of PCT curve, discharge capacity and cycling stability all increase. The alloy with x=5.2 shows the highest dischargecapacity and the best cycling stability among the studied alloys.     

Large Magnetocaloric Effect at the Saturation Field of an S=1/2 Antiferromagnetic Heisenberg Chain

We report low-temperature magnetization measurements on a copper-containing coordination polymer [Cu(μ-C₂O₄)(4-aminopyridine)₂(H₂O)] _n . According to these measurements and previous results (Prokofiev et al. in Cryst. Res. Technol. 42, 394, 2007), the material is a very good realization of an S=1/2 antiferromagnetic Heisenberg chain with a small saturation field B _s =4.2 T, which marks the endpoint of a quantum-critical line in the B–T plane. Measurements of the magnetocaloric effect at low temperatures T=0.47 K across the saturation field yields a very large magnetothermal response with a characteristic sign change close to the quantum-critical point. The data are in good agreement with the quantum-critical behavior calculated on the basis of exact diagonalization and quantum Monte Carlo simulations.     

Boron Nanosheet?Supported Rh Catalysts for Hydrogen Evolution: A New Territory for the Strong Metal?Support Interaction Effect

High-efficiency electrochemical hydrogen evolution reaction (HER) offers a promising strategy to address energy and environmental crisis. Platinum is the most e...     

Resonance Effect on the Tunneling Reaction: H+H2→H2+H in Solid Hydrogen

The tunneling abstraction reaction: H+H₂H₂+H in -irradiated solid hydrogen has been studied using electron spin resonance (ESR) and electron-nuclear double resonance (ENDOR) spectroscopy and gas-chromatography. The rate constant for the tunneling reaction in solid hydrogen was found to decrease with the increase in the concentration of ortho-H₂ molecules in solid hydrogen. We concluded that the decrease in the rate constant is due to the energy level mismatching between reactant species of H+H₂ trapped and product species of H₂+H trapped in the reverse induced by inhomogeneous intermolecular interactions between ortho-H² molecules in solid hydrogen. This result indicates that resonance effects play an important role in tunneling reactions in solids.     

Substitution Effect of Pr for Ca in Bi2Sr2CaCu2O8+δ System

The Bi₂Sr₂CaCu₂O₈₊ system samples doped with Pr on Ca sites were synthesized. Resistivity temperature dependence, X-ray powder diffraction, and photoemission experiments have been performed. Both X-ray diffraction and photoemission measurements show that Pr ion enters the lattice with a valence higher than 3⁺, which supports the hole-filling mechanism of the suppression of superconductivity.     

Scaling Laws for the Magnetocaloric Effect in Calcium Deficiency Manganites La0.8Ca0.2−x □ x MnO3 with a Second-Order Magnetic Phase Transition

The magnetic entropy change (ΔS _M ) of polycrystalline samples La_0.8Ca_0.2?x □ _x MnO₃ (x=0.00; x=0.10 and x=0.20) with a second-order phase transition has been investigated. The field dependence of the magnetic entropy change expressed as ΔS _M ∝H ⁿ follows the phenomenological curves and at the temperature of the peak corresponds to a large field independent exponent of n=0.581; 0.642 and 0.671 for x=0.00; x=0.10 and x=0.20 samples, respectively. Then, we have constructed the phenomenological universal curve by normalizing the magnetic entropy change curves with respect to their maximum values, $\Delta S_{M_{\mathrm{max}}}$ , and rescaling the temperature axis. These universal curves collapse onto a single curve for any applied magnetic field for all samples. Moreover, we note that the universal curve for x=0.10 and x=0.20 samples collapses with a small deviation compared with x=0.00 sample. This is consistent with our previous work where we demonstrated that the magnetic phase transition relative to the samples x=0.00 belongs to the 3D-Ising universal class and to the 3D-Heisinberg class for x=0.10 and x=0.20 samples. This universal curve can be used to predict the response of materials in different conditions not available in the laboratory by extrapolations in field or temperature.     

Discriminatory Gate-Opening Effect in a Flexible Metal–Organic Framework for Inverse CO2/C2H2 Separation

Considering the significant application of acetylene (C₂H₂) in the manufacturing and petrochemical industries, the selective capture of impurity carbon dioxide (CO₂) is a crucial task and an enduring challenge. Here, a flexible metal–organic framework (Zn-DPNA) accompanied by a conformation change of the Me₂NH₂⁺ ions in the framework is reported. The solvate-free framework provides a stepped adsorption isotherm and large hysteresis for C₂H₂, but type-I adsorption for CO₂. Owing to their uptakes difference before gate-opening pressure, Zn-DPNA demonstrated favorable inverse CO₂/C₂H₂ separation. According to molecular simulation, the higher adsorption enthalpy of CO₂ (43.1 kJ mol⁻¹) is due to strong electrostatic interactions with Me₂NH₂⁺ ions, which lock the hydrogen-bond network and narrow pores. Furthermore, the density contours and electrostatic potential verifies the middle of the cage in the large pore favors C₂H₂ and repels CO₂, leading to the expansion of the narrow pore and further diffusion of C₂H₂. These results provide a new strategy that optimizes the desired dynamic behavior for one-step purification of C₂H₂.     

Substitution Effect of Sn for Cu in the Bi2Sr2CaCu2−xSnxO8+δ System

The Bi₂Sr₂CaCu₂O_8+δ system samples doped with Sn on Cu sites were synthesized. Resistivity temperature dependence, X-ray powder diffraction and photoemission experiments have been performed. Suppression of superconductivity in the Sn-doped Bi₂Sr₂CaCu₂O_8+δ system has been observed. X-ray photoemission measurements show that Sn ion enters the lattice. Our results reveal that Sn ions are mostly in bivalent states.     

A Metal–Organic Frameworks Derived 1T-MoS2 with Expanded Layer Spacing for Enhanced Electrocatalytic Hydrogen Evolution

Metal phase molybdenum disulfide (1T-MoS₂) is considered a promising electrocatalyst for hydrogen evolution reaction (HER) due to its activated basal and superior electrical conductivity. Here, a one-step solvothermal route is developed to prepare 1T-MoS₂ with expanded layer spacing through the derivatization of a Mo-based organic framework (Mo-MOFs). Benefiting from N,N-dimethylformamide oxide as external stress, the interplanar spacing of (002) of the MoS₂ catalyst is extended to 10.87 Å, which represents the largest one for the 1T-MoS₂ catalyst prepared by the bottom-up approach. Theoretical calculations reveal that the expanded crystal planes alter the electronic structure of 1T-MoS₂, lower the adsorption–desorption potentials of protons, and thus, trigger efficient catalytic activity for HER. The optimal 1T-MoS₂ catalyst exhibits an overpotential of 98 mV at 10 mA cm⁻² for HER, corresponding to a Tafel slope of 52 mV dec⁻¹. This Mo-MOFs-derived strategy provides a potential way to design high-performance catalysts by adjusting the layer spacing of 2D materials.     

High catalytic activity for formaldehyde oxidation of an interconnected network structure composed of δ-MnO2 nanosheets and γ-MnOOH nanowires

Among the transition metal oxide catalysts, manganese oxides have great potential for formaldehyde (HCHO) oxidation at ambient temperature because of their high activity, nontoxicity, low cost, and polybasic morphologies. In this work, a MnO₂-based catalyst (M-MnO₂) with an interconnected network structure was successfully synthesized by a one-step hydrothermal method. The M-MnO₂ catalyst was composed of the main catalytic agent, δ-MnO₂ nanosheets, dispersed in a nonactive framework material of γ-MnOOH nanowires. The catalytic activity of M-MnO₂ for HCHO oxidation at room temperature was much higher than that of the pure δ-MnO₂ nanosheets. This is attributed to the special interconnected network structure. The special interconnected network structure has high dispersion and specific surface area, which can provide more surface active oxygen species and higher surface hydroxyl groups to realize rapid decomposition of HCHO.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-020-00321-2