Xiaodan Cui

Hierarchical Sandwich-Like Structure of Ultrafine N-Rich Porous Carbon Nanospheres Grown on Graphene Sheets as Superior Lithium-Ion Battery Anodes

A sandwich-like, graphene-based porous nitrogen-doped carbon (PNCs@Gr) has been prepared through facile pyrolysis of zeolitic imidazolate framework nanoparticles in situ grown on graphene oxide (GO) (ZIF-8@GO). Such sandwich-like nanostructure can be used as anode material in lithium ion batteries, exhibiting remarkable capacities, outstanding rate capability, and cycling performances that are some of the best results among carbonaceous electrode materials and exceed most metal oxide-based anode materials derived from metal orgainc frameworks (MOFs). Apart from a high initial capacity of 1378 mAh g(-1) at 100 mA g(-1), this PNCs@Gr electrode can be cycled at high specific currents of 500 and 1000 mA g(-1) with very stable reversible capacities of 1070 and 948 mAh g(-1) to 100 and 200 cycles, respectively. At a higher specific current of 5000 mA g(-1), the electrode still delivers a reversible capacity of over 530 mAh g(-1) after 400 cycles, showing a capacity retention of as high as 84.4%. Such an impressive electrochemical performance is ascribed to the ideal combination of hierarchically porous structure, a highly conductive graphene platform, and high-level nitrogen doping in the sandwich-like PNCs@Gr electrode obtained via in situ synthesis.

Recent Progress in Metal–Organic Frameworks and Their Derived Nanostructures for Energy and Environmental Applications

Metal-organic frameworks (MOFs), as a very promising category of porous materials, have attracted increasing interest from research communities due to their extremely high surface areas, diverse nanostructures, and unique properties. In recent years, there is a growing body of evidence to indicate that MOFs can function as ideal templates to prepare various nanostructured materials for energy and environmental cleaning applications. Recent progress in the design and synthesis of MOFs and MOF-derived nanomaterials for particular applications in lithium-ion batteries, sodium-ion batteries, supercapacitors, dye-sensitized solar cells, and heavy-metal-ion detection and removal is reviewed herein. In addition, the remaining major challenges in the above fields are discussed and some perspectives for future research efforts in the development of MOFs are also provided.

High-performance dye-sensitized solar cells based on Ag-doped SnS2 counter electrodes

Tin disulfide (SnS2) has been considered as a prospective counter electrode (CE) material for dye-sensitized solar cells due to its good electrocatalytic properties. However, its low electronic and ionic conductivities pose challenges for using it in high-performance dye-sensitized solar cells (DSSCs). Herein, doping is utilized to improve the properties of SnS2 for application as a DSSC counter electrode. Ag-doped SnS2 samples with various doping amounts are prepared via a facile one-step solvothermal route. It is found that the DSSC based on a 5% Ag-doped SnS2 CE demonstrates the best performance showing an impressive photovoltaic conversion efficiency (PCE) of 8.70% which exceeds the efficiency of a Pt-based DSSC (7.88%) by 10.41%, while the DSSC consisting of undoped SnS2 only exhibits a PCE of 6.47%. Such an enhanced efficiency of the DSSC is attributed to the effectively improved electrocatalytic activity and mixed conductivity resulting from the Ag dopant. Therefore, the Ag-doped SnS2 CE proves to be a promising alternative to the expensive Pt CE in DSSCs and may pave a new way for large-scale production of new-generation DSSCs.

Hierarchical Graphene-Encapsulated Hollow SnO2@SnS2 Nanostructures with Enhanced Lithium Storage Capability

Complex hierarchical structures have received tremendous attention due to their superior properties over their constitute components. In this study, hierarchical graphene-encapsulated hollow SnO2@SnS2 nanostructures are successfully prepared by in situ sulfuration on the backbones of hollow SnO2 spheres via a simple hydrothermal method followed by a solvothermal surface modification. The as-prepared hierarchical SnO2@SnS2@rGO nanocomposite can be used as anode material in lithium ion batteries, exhibiting excellent cyclability with a capacity of 583 mAh/g after 100 electrochemical cycles at a specific current of 200 mA/g. This material shows a very low capacity fading of only 0.273% per cycle from the second to the 100th cycle, lower than the capacity degradation of bare SnO2 hollow spheres (0.830%) and single SnS2 nanosheets (0.393%). Even after being cycled at a range of specific currents varied from 100 mA/g to 2000 mA/g, hierarchical SnO2@SnS2@rGO nanocomposites maintain a reversible capacity of 664 mAh/g, which is much higher than single SnS2 nanosheets (374 mAh/g) and bare SnO2 hollow spheres (177 mAh/g). Such significantly improved electrochemical performance can be attributed to the unique hierarchical hollow structure, which not only effectively alleviates the stress resulting from the lithiation/delithiation process and maintaining structural stability during cycling but also reduces aggregation and facilitates ion transport. This work thus demonstrates the great potential of hierarchical SnO2@SnS2@rGO nanocomposites for applications as a high-performance anode material in next-generation lithium ion battery technology.

Effect of dopant concentration on visible light driven photocatalytic activity of Sn1−xAgxS2

Tin(iv) sulfide (SnS2), as a mid-band-gap semiconductor shows good potential as an excellent photocatalyst due to its low cost, wide light spectrum response and environment-friendly nature. However, to meet the demands of large-scale water treatment, a SnS2 photocatalyst with a red-shifted band gap, increased surface area and accelerated molecule and ion diffusion is required. Doping is a facile method to manipulate the optical and chemical properties of semiconductor materials simultaneously. In this work, SnS2 photocatalysts with varied Ag doping content are synthesized through a facile one-step hydrothermal method. The product is characterized by XRD, SEM, TEM and UV-Vis spectrometry. The photocatalytic activity of the as-prepared Sn1-xAgxS2 is studied by the degradation of methylene blue (MB) dye under solar light irradiation. It is found that increasing the Ag dopant concentration can effectively increase the solar light adsorption efficiency of the photocatalyst and accelerate heterogeneous photocatalysis. The optimal concentration of Ag dopant is found to be 5% with the highest rate constant being 1.8251 hour-1. This study demonstrates that an optimal amount of Ag doping can effectively increase the photocatalytic performance of SnS2 and will promote the commercialization of such photocatalysts in the photocatalytic degradation of organic compounds.

Direct growth of an economic green energy storage material: a monocrystalline jarosite-KFe3(SO4)2(OH)6-nanoplates@rGO hybrid as a superior lithium-ion battery cathode

The exploration of new inexpensive rechargeable batteries with high energy-density electrodes is a key to integrate renewable sources such as solar and wind, and address sustainability issues. Herein, a facile and scalable method is developed to prepare a two-dimensional earth-abundant jarosite-KFe3(SO4)2(OH)6/rGO hybrid via a solution-phase oxidation process at elevated temperature. In this synthesis, single-layer graphene sheets serve as both structure-directing agents and growth platforms to directly grow monocrystalline KFe3(SO4)2(OH)6 nanoplates with unique hexagonal shapes, forming a KFe3(SO4)2(OH)6/rGO hybrid. As a cathode for lithium batteries, the hybrid structure exhibits a high reversible capacity of 120.5 mA h g−1 after 100 cycles at a specific current of 2C and thus retains 88% of the maximum capacity. The monocrystalline jarosite-KFe3(SO4)2(OH)6-nanoplates/rGO hybrid exhibits a discharge capacity of 143.6, 113.9, 98.2, 83.9 and 65.9 mA h g−1 at 1, 2, 5, 10, and 20C, respectively, and retains a specific capacity of 134.4 mA h g−1 when the specific current returns from 20C to 1C, displaying an excellent rate capability. At a high rate of 10C, the jarosite-KFe3(SO4)2(OH)6/rGO composites maintained 70.7 mA h g−1 after 300 cycles with a capacity retention of 78.2%, indicating remarkable cycling stability even at a high rate. Compared with KFe3(SO4)2(OH)6 particles, the KFe3(SO4)2(OH)6/rGO nanocomposites exhibit remarkably prolonged cycling life and improved rate capability. Therefore, the earth-abundant jarosite-KFe3(SO4)2(OH)6/rGO hybrid demonstrates great potential for application as a high-performance cathode material in new-generation lithium-ion rechargeable batteries.