Hongbin Zhao

Evolution of ZnO microstructures from hexagonal disk to prismoid, prism and pyramid and their crystal facet-dependent gas sensing properties

Herein, the evolution of ZnO structures from hexagonal disk to prismoid, prism and pyramid was found via a facile two-step low temperature hydrothermal reaction, and the evolution was achieved by only adjusting the pH value of the reactive solution without the assistance of a template or a surfactant. The characterization results showed that the precursor (hexagonal Zn5(OH)8Cl2·2H2O disk) played a key role in the morphology evolution of ZnO during the early stage of the growth process and that the disks tended to stack together layer by layer in both directions (up and down) to form prismoid, prism and pyramid structures with the increase in pH value from 7 to 10. After calcination, the corresponding hexagonal ZnO microstructures were obtained. This structure evolution resulted in the weakening dominance of the (0001) plane in the total exposed crystal facets. Furthermore, despite the similar specific surface areas of the four hexagonal ZnO microstructures, the gas sensing properties of the sensors based on these microstructures deteriorated sequentially. At a working temperature of 330 °C, the ZnO disk with the most exposed (0001) plane showed the highest gas response toward ethanol, which was nearly 2, 3, and 6 times higher than those of the prismoid, prism and pyramid structures, respectively. This superior gas sensing performance strongly depends on the predominantly exposed polar facets (0001), which can provide more active sites for oxygen adsorption and subsequent reaction with the detected gas than other apolar facets. It demonstrates that the (0001) crystal facet plays a significant role in the gas sensing behavior of ZnO. This research will bring some inspiration to researchers for the fabrication of a high performance ZnO gas sensor as well as other metal oxides.

A MnO2/Graphene Oxide/Multi-Walled Carbon Nanotubes-Sulfur Composite with Dual-Efficient Polysulfide Adsorption for Improving Lithium-Sulfur Batteries

Lithium-sulfur batteries can potentially be used as a chemical power source because of their high energy density. However, the sulfur cathode has several shortcomings, including fast capacity attenuation, poor electrochemical activity, and low Coulombic efficiency. Herein, multi-walled carbon nanotubes (CNTs), graphene oxide (GO), and manganese dioxide are introduced to the sulfur cathode. A MnO2/GO/CNTs-S composite with a unique three-dimensional (3D) architecture was synthesized by a one-pot chemical method and heat treatment approach. In this structure, the innermost CNTs work as a conducting additive and backbone to form a conducting network. The MnO2/GO nanosheets anchored on the sidewalls of CNTs have a dual-efficient absorption capability for polysulfide intermediates as well as afford adequate space for sulfur loading. The outmost nanosized sulfur particles are well-distributed on the surface of the MnO2/GO nanosheets and provide a short transmission path for Li+ and the electrons. The sulfur content in the MnO2/GO/CNTs-S composite is as high as 80 wt %, and the as-designed MnO2/GO/CNTs-S cathode displays excellent comprehensive performance. The initial specific capacities are up to 1500, 1300, 1150, 1048, and 960 mAh g-1 at discharging rates of 0.05, 0.1, 0.2, 0.5, and 1 C, respectively. Moreover, the composite cathode shows a good cycle performance: the specific capacity remains at 963.5 mAh g-1 at 0.2 C after 100 cycles when the area density of sulfur is 2.8 mg cm-2.

Biological cell derived N-doped hollow porous carbon microspheres for lithium–sulfur batteries

Lithium–sulfur (Li–S) batteries are appealing for next generation efficient energy power systems due to their high energy density and low cost. Yeast cells, as a natural biotemplate, are self-duplicable, nitrogen-rich, inexpensive and regular in morphology. Yeast cells show promising applications in the synthesis of nitrogen-doped hollow porous carbon materials for energy storage and transition systems. In this work, we have developed a green and facile self-templating route through low-cost and renewable yeast cells with hollow structures to fabricate N-doped hollow porous carbon microspheres (NHPCMs) for encapsulating sulfur. The sulfur-loaded NHPCM (NHPCM@S) composite with 65 wt% sulfur is then used as the cathode material for Li–S batteries. These batteries exhibit a reversible specific capacity of 1202 mA h g−1 and a capacity retention of 725 mA h g−1 over 400 cycles at 0.1C with a capacity decay of 0.09% per cycle, as well as an enhanced rate performance of 587 mA h g−1 at 2C. In the NHPCM@S composite, the stable micro/mesoporous carbon shell acts as an efficient reservoir for soluble polysulfide, and the doped nitrogen in the carbon shell can offer exceptional electronic conductivity and strong adsorption for polysulfide species. This work demonstrates that an environmentally friendly, economical, sustainable, and self-templating route for N-doped hollow porous microspheres with natural and reproducible biological resources can lead to exciting developments in Li–S batteries and their practical applications in portable electronic devices, advanced electric vehicles, and energy storage systems.

IrNi nanoparticle-decorated flower-shaped NiCo 2 O 4 nanostructures: controllable synthesis and enhanced electrochemical activity for oxygen evolution reaction

In this work, we demonstrated the enhanced oxygen evolution reaction (OER) activity of flower-shaped cobalt-nickel oxide (NiCo2O4) decorated with iridium-nickel bimetal as an electrode material. The samples were prepared by carefully depositing pre-synthesized IrNi nanoparticles on the surfaces of the NiCo2O4 nano-flowers. Compared with bare NiCo2O4, IrNi, and IrNi/Co3O4, the IrNi/NiCo2O4 exhibited significantly enhanced electrocatalytic activity in the OER, including a lower overpotential of 210 mV and a higher current density at an overpotential of 540 mV. We found that the IrNi/NiCo2O4 showed more efficient electron transport behavior and reduced polarization because of its bimetal IrNi modification by analyzing its Tafel slope and turnover frequency. Furthermore, the electrocatalytic mechanism of IrNi/NiCo2O4 in the OER was studied, and it was found that the combined active sites of the composite effectively improved the rate determining step. The synergic effect of the bimetal and metal oxide plays an important role in this reaction, enhancing the transmission efficiency of electrons and providing more active sites for the OER. The results reveal that IrNi/NiCo2O4 is an excellent electrocatalyst for OER.摘要本文制备了一种双金属IrNi修饰的花状NiCo2O4复合材料, 并研究了其对于氧析出反应的电化学活性, 结果显示其电化学活性明显提升. NiCo2O4和IrNi分别通过水热法和热分解法制备, 再通过超声复合, 使得双金属附着在复合氧化物表面. 通过与纯NiCo2O4, IrNi以及IrNi/Co3O4相比较, 所制备的IrNi/NiCo2O4对于氧析出反应的性能最为优异. 在各个参数指标中, 拥有最低的过电势210 mV, 在540 mV的过电势下具有最高的电流密度. 电子转移数和塔菲尔斜率分析表明该复合材料由于修饰上了双金属材料, 极大地降低了极化, 具有更高效的电子转移速率. 此外本文还对电催化机理进行了研究, 发现复合材料结合反应位点有效改善了反应速率决定步骤. 其中, 协同效应起着至关重要的作用, 这一效应明显提高电子传输效率的同时提供了更多的活性位点. IrNi/NiCo2O4是一种出色的氧析出反应电催化剂.

Alleviating polarization by designing ultrasmall Li2S nanocrystals encapsulated in N-rich carbon as a cathode material for high-capacity, long-life Li–S batteries

Lithium sulfide (Li2S), which has a high theoretical specific capacity of 1166 mA h g−1, has potential application in cathode materials because of its high safety and compatibility with lithium-free anodes for Li–S batteries. However, its low electron conductivity and lithium transfer cause significant polarization in Li2S electrodes. Here, we demonstrate the use of ultrasmall Li2S nanocrystals encapsulated in N-rich carbon (NRC) as a cathode material for Li–S batteries. By evaporating a mixture of polyacrylonitrile (PAN) and Li2S in dimethylformamide (DMF) solution and then subjecting the mixture to carbonization, a nano-Li2S@NRC composite with ultrasmall Li2S well dispersed in its carbon matrix was successfully synthesized. The obviously lower potential barriers and excellent cycling performance of nano-Li2S@NRC electrodes confirm their improved polarization because of the size effect of Li2S nanocrystals and the good electron transfer between Li2S and N-doped carbon. The nano-Li2S@NRC cathode delivers a high initial specific capacity of 1046 mA h g−1 of Li2S (∼1503 mA h g−1 of S) at 0.25C and 958 mA h g−1 of Li2S (∼1376 mA h g−1 of S) at 0.5C with a favorable cycling performance with an ∼0.041% decay rate per cycle over 1000 cycles.

Effects of B-site Nb doping on the CO2 resistance and rate-controlling step of Ce0.8Gd0.2O2−δ–Pr0.6Sr0.4Co0.5Fe0.5O3−δ dual-phase membranes

Dense fluorite–perovskite-type dual-phase membranes of 60% Ce0.8Gd0.2O2−δ–40% Pr0.6Sr0.4Co0.5Fe0.4Nb0.1O3−δ (CG–PSCF0.4N0.1) were prepared successfully via ethylenediaminetetraacetic acid (EDTA)–citric acid method. Subsequently, the effects of B-site Nb doping on the CO2 resistance, oxygen permeability, and rate-controlling step of Ce0.8Gd0.2O2−δ–Pr0.6Sr0.4Co0.5Fe0.5O3−δ (CG–PSCF) were systematically investigated. The results of high-temperature in situ X-ray diffraction under pure CO2 atmosphere, X-ray photoelectron spectra, and oxygen permeation tests indicated that the thermal stability and CO2 resistance of CG–PSCF could be improved significantly via Nb doping. Furthermore, by measuring the distributions of permeation resistances at certain temperatures using the adopted permeation model, the rate-controlling step was determined, and the oxygen permeability degradation mechanism of CG–PSCF was attributed to the increased bulk diffusion resistance caused by phase transition of PSCF and formation of carbonate. All the results demonstrated that Nb doping has a positive effect on the oxygen permeation stability of CG–PSCF, and CG–PSCF0.4N0.1 dual-phase membranes have promising potential for oxy-fuel combustion.

Recent Progresses in Electrocatalysts for Water Electrolysis

The study of hydrogen evolution reaction and oxygen evolution reaction electrocatalysts for water electrolysis is a developing field in which noble metal-based materials are commonly used. However, the associated high cost and low abundance of noble metals limit their practical application. Non-noble metal catalysts, aside from being inexpensive, highly abundant and environmental friendly, can possess high electrical conductivity, good structural tunability and comparable electrocatalytic performances to state-of-the-art noble metals, particularly in alkaline media, making them desirable candidates to reduce or replace noble metals as promising electrocatalysts for water electrolysis. This article will review and provide an overview of the fundamental knowledge related to water electrolysis with a focus on the development and progress of non-noble metal-based electrocatalysts in alkaline, polymer exchange membrane and solid oxide electrolysis. A critical analysis of the various catalysts currently available is also provided with discussions on current challenges and future perspectives. In addition, to facilitate future research and development, several possible research directions to overcome these challenges are provided in this article.Graphical Abstract

High Efficiency Graphitized Carbon Coated Pt Composite for Hydrogen Electro-Oxidation and Hydrogen Storage

We reported a novel graphitized carbon coated Pt composite synthesized by one-pot TEOS polymerization-high temperature carbonation approach. Electrochemical measurements display that the obtained Pt/graphitized carbon (Pt@GC) shows high electrochemical activity toward hydrogen oxidation. Additionally, quartz crystal microbalance results for hydrogen adsorption indicate that Pt@GC has high performance of hydrogen storage. The synthesized Pt@GC composite shows significant potential applications in H2/O2 (air) fuel cell and hydrogen storage.

Recent progresses in advanced electrode materials, separators and electrolytes for lithium-ion batteries

Lithium-ion batteries (LIBs) possess several advantages over other types of viable practical batteries, including higher operating voltages, higher energy densities, longer cycle lives, lower rates of self-discharge and less environmental pollution. Therefore, LIBs have been widely and successfully applied in portable electronic devices and industrial fields. However, the rapidly increasing demands of new energy vehicles have also quickly increased the performance requirements of LIBs, including the need for higher power densities, greater capacity densities and better safety. As battery designs gradually standardize, improvements in LIB performances mainly depend on the technical progress in key electrode materials such as positive and negative electrode materials, separators and electrolytes. For LIB performances to meet the rising requirements, many studies on the structural characteristics and morphology modifications of electrode/separator/electrolyte materials with different synthesis methods have been conducted. In this review, recent progress of LIBs is reviewed with a focus on positive electrode materials, negative electrode materials, separators and electrolytes in terms of energy density, power density, life-cycle and safety. To accelerate the research and development and to overcome the challenges of LIB technology and application, several possible research directions are also discussed to further improve LIB performances.

Synthesis and Gas Sensing Properties of SnO2 Microplatelets

SnO2 microplatelets were fabricated by oxidizing SnO microplatelets which were synthesized via dissolution-recrystallization with aid of sonication. The microplatelets were both characterized by X-ray diffraction, thermogravimetric analyses and differential scanning calorimetry, and field-emission scanning electron microscopy. The as- synthesized SnO2 microplatelets are consist of round corner square platelets structures with side length of 8–13 μm and thickness of 2–4 μm. The sensing properties of the sensors fabricated from SnO2 microplatelets were investigated at 4.5 V working voltage. Our results show that the sensors exhibit the excellent gas-sensing properties toward H2S in terms of sensitivity and selectivity.