Yanfang Gao

Ordered Assembly of NiCo2O4 Multiple Hierarchical Structures for High-Performance Pseudocapacitors

The design and development of nanomaterials has become central to the advancement of pseudocapacitive performance. Many one-dimensional nanostructures (1D NSs), two-dimensional nanostructures (2D NSs), and three-dimensional hierarchical structures (3D HSs) composed of these building blocks have been synthesized as pseudocapacitive materials via different methods. However, due to the unclear assembly mechanism of these NSs, reports of HSs simultaneously assembled from two or more types of NSs are rare. In this article, NiCo2O4 multiple hierarchical structures (MHSs) composed of 1D nanowires and 2D nanosheets are simply grown on Ni foam using an ordered two-step hydrothermal synthesis followed by annealing processing. The low-dimensional nanowire is found to hold priority in the growth order, rather than the high-dimensional nanosheet, thus effectively promoting the integration of these different NSs in the assembly of the NiCo2O4 MHSs. With vast electroactive surface area and favorable mesoporous architecture, the NiCo2O4 MHSs exhibit a high specific capacitance of up to 2623.3 F g(-1), scaled to the active mass of the NiCo2O4 sample at a current density of 1 A g(-1). A nearly constant rate performance of 68% is achieved at a current density ranging from 1 to 40 A g(-1), and the sample retains approximately 94% of its maximum capacitance even after 3000 continuous charge-discharge cycles at a consistently high current density of 10 A g(-1).

Biomass-Swelling Assisted Synthesis of Hierarchical Porous Carbon Fibers for Supercapacitor Electrodes

The preparation of porous materials from renewable energy sources is attracting intensive attention due to in terms of the application/economic advantage, and pore structural design is core in the development of efficient supercapacitors or available porous media. In this work, we focused on the transformation of natural biomass, such as cotton, into more stable porous carbonaceous forms for energy storage in practical applications. Biomorphic cotton fibers are pretreated under the effect of NaOH/urea swelling on cellulose and are subsequently used as a biomass carbon source to mold the porous microtubule structure through a certain degree of calcining. As a merit of its favorable structural features, the hierarchical porous carbon fibers exhibit an enhanced electric double layer capacitance (221.7 F g-1 at 0.3 A g-1) and excellent cycling stability (only 4.6% loss was observed after 6000 cycles at 2 A g-1). A detailed investigation displays that biomass-swelling behavior plays a significant role, not only in improving the surface chemical characteristics of biomorphic cotton fibers but also in facilitating the formation of a hierarchical porous carbon fiber structure. In contrast to traditional methods, nickel foams have been used as the collector for supercapacitor that requiring no additional polymeric binders or carbon black as support or conductive materials. Because of the absence of additive materials, we can further enhance capacitance. This remarkable capacitive performance can be due to sufficient void space within the porous microstructure. By effectively increasing the contact area between the carbon surface and the electrolyte, which can reduce the ion diffusion pathway or buffer the volume change during cycling. This approach opens a novel route to produce the abundantly different morphology of porous biomass-based carbon materials and proposes a green alternative method to meet sustainable development needs.

Ni0.9Co1.92Se4 nanostructures: binder-free electrode of coral-like bimetallic selenide for supercapacitors

Coral-like Ni0.9Co1.92Se4 nanostructured materials have been prepared through a simple and controlled two-step solvothermal method, which present a handsome electrochemical performance. The specific capacitance reaches 1021.1 F g−1 under the current density of 2 mA cm−2 over a 0.5 V electrode potential window with an areal capacitance of 6.43 F cm−2. A superior rate capability of 77% is achieved with discharge rates increasing from 2 to 50 mA cm−2, as well as a good cycling stability of 88.39% after 5000 cycles. Furthermore, a good energy density of 26.29 W h kg−1 is achieved under the power density of 265 W kg−1 when assembled into a Ni0.9Co1.92Se4//AC asymmetric supercapacitor with the operating potential window extended to 1.5 V. The high performance can be attributed to the coral-like architectures with rich redox reactions, high conductivity and transport rate for both electrons and electrolyte ions. Our results suggest that the coral-like Ni0.9Co1.92Se4 nanostructured electrode materials may be a good choice for supercapacitors.

Electrocatalytic oxidation of formaldehyde on direct electrodeposited graphene–platinum nanoparticles composites electrode

The one-step electrochemical deposition of highly dispersed platinum nanoparticles on graphene to fabricate a new Pt/EG/GC modified electrode for formaldehyde determination in aqueous solution. Catalyst surface morphology was characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM), the composition analysis was carried out on energy-dispersive X-ray spectroscopy (EDS). The electrochemical performances of the electrode were investigated by cyclic voltammetry, and clear amperometric responses were obtained in the scan process. The correlation coefficient was 0.998 of the linear relation between current values and concentrations, the Pt/EG/GC electrode exhibited a low limit of detection (0.04 mM), high sensitivity (0.0162 mA mM−1) and long working life. These characteristics make the Pt/EG/GC electrode appropriate for the formaldehyde determination based on formaldehyde electric catalytic oxidation.

Enhancing visible light photocatalytic activity of BiOBr/rod-like BiPO4 through a heterojunction by a two-step method

Visible light driven BiOBr/rod-like BiPO4 composites with different BiOBr to BiPO4 molar ratios were fabricated via a facile deposition-precipitation method. X-ray powder diffraction, field emission scanning electron microscopy, transmission electron microscopy, UV-Vis diffuse reflectance spectroscopy and Brunauer–Emmett–Teller surface area were used to characterize the as-synthesized samples. Results showed that the BiOBr/rod-like BiPO4 composite with equal mole ratio exhibited the best photocatalytic performance for rhodamine B (RhB) degradation under visible light irradiation. The enhanced photocatalytic performance could be mainly attributed to the effective separation of the photogenerated electrons and holes at the heterojunction interface of p-BiOBr and n-BiPO4.

Microstructure and Ionic Conductivity of Sb-doped Li7La3Zr2O12 Ceramics: Microstructure and Ionic Conductivity of Sb-doped Li7La3Zr2O12 Ceramics

The garnet-related oxides Li7-xLa3Zr2-xSbxO12 (x = 0, 0.075) were prepared by solid-state reaction method. Crystal structure, microstructure, conductivity, and element distribution were characterized for the pure and Sb-doped Li7La3Zr2O12. Ionic conductivity of the Li7La3Zr2O12 is enhanced by Sb doping. An amorphous Li-La-Zr-Al-O thin film which is formed on the grain boundary of Sb-doped samples not only suppresses the abnormal grain growth but also eliminates the pores on the grain boundary. The ionic conductivity of Sb doped Li7-xLa3Zr2-xSbxO12 ceramic with x = 0.075 sintered at 1160°C reaches about 3.40×10 S/cm.采用传统固相反应法制备了锑掺杂的锆镧酸锂固体电解质陶瓷。对陶瓷的晶体结构、显微结构及元素分布、离子电导率进行了研究。结果表明: 少量锑掺杂可明显提高锆镧酸锂固体电解质陶瓷的离子电导率。1160℃烧结的锑掺杂固体电解质中, 晶粒表面形成无定型的薄膜。此薄膜抑制了晶粒生长, 消除了晶界上的气孔, 提高了陶瓷致密度, 提高了陶瓷的离子导电率。1160℃烧结得到的Li 6.925 La 3 Zr 1.925 Sb 0.075 O 12 陶瓷离子电导率高达3.40×10 -4 S/cm。采用传统固相反应法制备了锑掺杂的锆镧酸锂固体电解质陶瓷。对陶瓷的晶体结构、显微结构及元素分布、离子电导率进行了研究。结果表明: 少量锑掺杂可明显提高锆镧酸锂固体电解质陶瓷的离子电导率。1160℃烧结的锑掺杂固体电解质中, 晶粒表面形成无定型的薄膜。此薄膜抑制了晶粒生长, 消除了晶界上的气孔, 提高了陶瓷致密度, 提高了陶瓷的离子导电率。1160℃烧结得到的Li 6.925 La 3 Zr 1.925 Sb 0.075 O 12 陶瓷离子电导率高达3.40×10 -4 S/cm。

Enhancing photocatalytic activity by tuning the ratio of hexagonal and orthorhombic phase Nb2O5 hollow fibers

Cotton was used as template for the fabrication of a biomorphic Nb2O5 photocatalyst with hexagonal and orthorhombic structures. The as-prepared Nb2O5 was characterized through X-ray diffraction (XRD), scanning electron microscopy (SEM), specific surface area and UV-Vis diffused reflectance spectra measurements. The photocatalytic activity of the Nb2O5 fibers was evaluated through degradation of methylene blue (MB) in aqueous solution exposed to UV light. SEM results show that biomorphic Nb2O5 fibers are both hollow and have porous walls. The architectures allow a more accessible surface for the photocatalytic decomposition of dyes molecules. The photocatalytic activity of physically mixed fibers with 75% H-Nb2O5 and 25% O-Nb2O5 phases is superior to those of pure H- and O-Nb2O5 phases, and other samples with different H- and O-Nb2O5 ratios. Such superior photocatalytic activity is mainly due to an optimal balance between the adsorption of MB and the absorption of UV light. Moreover, the large size of the Nb2O5 hollow fibers allows them to be easily separated from the solution.

A NEW HOMOGENEOUS ELECTROCATALYST FOR ELECTROCHEMICAL CARBONYLATION OF METHANOL TO DIMETHYL CARBONATE

Electrosynthesis of dimethyl carbonate (DMC) from methanol and carbon monoxide using an Cu(phen)Cl2 catalyst was achieved at room temperature and atmospheric pressure. The catalytic activity of the ligand 1,10-phenanthroline (phen) and the catalytic system were analyzed. The IR characterization results for the complex catalyst showed that copper ions were coordinated by nitrogen atoms of phen. In addition, the effects of the influencing factors, such as reaction time (t), reaction temperature (T) and the surface area of the working electrode (SWE) were studied.

Biogenic synthesis of photocatalytically active ZnS/ESM composites

The ZnS/ESM composites have been successfully fabricated using ESM (eggshell membrane), sodium sulfide and zinc sulfate as the main raw materials through an environmental and economical liquid impregnation method. The obtained samples were characterized via X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, UV-vis diffuse reflectance spectra and Fourier-transform infrared spectra. The results demonstrated that the formed ZnS nanoparticles uniformly distributed on the surface of the egg membrane fibers, and the crystallinity and the amount of the ZnS loaded on the ESM fibers could be adjusted by changing the cycle indices of the impregnation. Furthermore, we tested the photocatalytic effects and analyzed the mechanism of the resulting ZnS/ESM composites as photocatalysts to degrade the harmful organic pollutant methyl orange under UV light irradiation. The results showed that the ESM support made it easy to recover the photocatalysts and enhanced the intensity of light absorption and the stability of the ZnS/ESM composites as photocatalysts. Based on the high photocatalytic activity and good stability, the ZnS/ESM composites with 4 cycle indices of the impregnation can be expected to be a practical photocatalyst.

Enhanced catalytic performance of a Pt-xCeO2/Graphene catalyst for DMFCs by adjusting the crystal-plane and shape of nanoscale ceria

Oxygen storage capacity is influenced by the morphology and crystal-plane(s) of CeO2, which can thus affect the ability of this material to oxidise carbon monoxide. To investigate the effect of different morphologies/crystal-planes of CeO2 on the electrocatalytic performance of DMFCs (Direct Methanol Fuel Cell), three different types of CeO2 nanocrystals with different crystal-planes were synthesised and later assembled into Pt–xCeO2/Graphene composites with graphene and Pt nanoparticles as the electrocatalyst for DMFCs. According to the HRTEM images, the original morphology and crystal-plane structures of CeO2 are essentially maintained in the three types of Pt–xCeO2/Graphene composite catalysts investigated in this work. The catalytic performance of the Pt–xCeO2/Graphene composites for methanol electrocatalytic oxidation was investigated by a series of electrochemical measurements. Compared with the other catalysts, Pt–rCeO2/Graphene demonstrates superior catalytic activity (onset potential: 0.15 V) and the strongest resistance to poisoning by carbonaceous species (If/Ib: 2.11). The results of H2-TPR shows that rCeO2 with the {110} facet has the best surface reducibility among the xCeO2 with different facets being investigated, which provides a rationale for the superior performance of the Pt–rCeO2/Graphene catalyst. This study indicates that metallic oxides with a suitable crystal plane and shape can effectively enhance the electrocatalytic performance of Pt-based catalysts for methanol electrooxidation.