Jinwen Qin

Graphene-wrapped WO3 nanoparticles with improved performances in electrical conductivity and gas sensing properties

WO3/graphene (GN) nanocomposites have been successfully synthesized using a facile three-step synthesis. First, an SrWO4/graphene oxide (GO) precursor was synthesized by homogeneous precipitation; second, the SrWO4/GO precursor was transformed into WO3/GO hybrids by acidification; and third, the WO3/GO hybrids were reduced to WO3/GNvia UV-assisted photoreduction in water instead of general alcoholic solvent at room temperature. The resulting WO3 nanoparticles anchored on graphene sheets as spacers to keep the neighboring sheets separated are approximately quadrangular with a side length of 50–200 nm. Compared with WO3/GO hybrids, WO3/GN nanocomposites show an enhanced electrical conductivity, which results in an improved gas sensing towards alcohol. This work provides a new insight into the fabrication of tungstate–graphene composites and facilitates their application in future.

In situ coupling of Co0.85Se and N-doped carbon via one-step selenization of metal–organic frameworks as a trifunctional catalyst for overall water splitting and Zn–air batteries

Developing efficient noble metal-free multifunctional electrocatalysts is highly effective to dramatically reduce the overall cost of electrochemical devices. In this work, we demonstrate for the first time a facile strategy for in situ coupling of ultrafine Co0.85Se nanocrystals and N-doped carbon (Co0.85Se@NC) by directly selenizing zeolitic imidazolate framework-67 (ZIF-67) polyhedra. Benefiting from the synergistic effect of the coupling between Co0.85Se and NC, the Co–N–C structure, and the porous conductive carbon network, Co0.85Se@NC affords excellent oxygen evolution reaction (OER) performance with a small overpotential, remarkable stability, and high faradaic efficiency. Furthermore, Co0.85Se@NC can also efficiently catalyze hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR), and we therefore investigated its applications as a trifunctional electrocatalyst for overall water splitting and Zn–air batteries. When used as both the anode and cathode for overall water splitting, a low cell voltage of 1.76 V is sufficient to reach the current density of 10 mA cm−2; the obtained Zn–air batteries exhibit a very low discharge–charge voltage gap (0.80 V at 10 mA cm−2) and long cycle life (up to 180 cycles). These results not only demonstrate a facile strategy for the synthesis of affordable Co0.85Se@NC but also present its huge potential as a trifunctional electrocatalyst for clean energy systems.

VN hollow spheres assembled from porous nanosheets for high-performance lithium storage and the oxygen reduction reaction

The facile synthesis of well-defined hollow structures via a simple method remains a great challenge, especially for transition-metal nitrides (TMNs). Herein, we demonstrate a template-assisted strategy for the fabrication of VN hollow spheres (VN HSs) assembled from porous nanosheets. The resultant VN HSs have a hierarchical macroporous–mesoporous structure (the macropore size: 250 nm and the mesopore sizes: 5–30 nm), high surface area (66 m2 g−1), and uniform mesoporous shell with a thickness of 55 nm. The hierarchical porous structure is particularly beneficial for the mass transfer of reactant species. In view of these structural advantages, the VN HSs exhibit excellent lithium storage performance and high catalytic activity for the oxygen reduction reaction (ORR). Therefore, this work provides a promising approach for the design and synthesis of hierarchical porous nitrides with significantly enhanced performances in lithium-ion batteries and other electrochemical energy conversion and storage devices.

Germanium Quantum Dots Embedded in N‐Doping Graphene Matrix with Sponge‐Like Architecture for Enhanced Performance in Lithium‐Ion Batteries

Germanium quantum dots embedded in a nitrogen-doped graphene matrix with a sponge-like architecture (Ge/GN sponge) are prepared through a simple and scalable synthetic method, involving freeze drying to obtain the Ge(OH)4 /graphene oxide (GO) precursor and subsequent heat reduction treatment. Upon application as an anode for the lithium-ion battery (LIB), the Ge/GN sponge exhibits a high discharge capacity compared with previously reported N-doped graphene. The electrode with the as-synthesized Ge/GN sponge can deliver a capacity of 1258 mAh g(-1) even after 50 charge/discharge cycles. This improved electrochemical performance can be attributed to the pore memory effect and highly conductive N-doping GN matrix from the unique sponge-like structure.

Structure Interlacing and Pore Engineering of Zn2GeO4 Nanofibers for Achieving High Capacity and Rate Capability as an Anode Material of Lithium Ion Batteries.

An interlaced Zn2GeO4 nanofiber network with continuous and interpenetrated mesoporous structure was prepared using a facile electrospinning method followed by a thermal treatment. The mesoporous structure in Zn2GeO4 nanofibers is directly in situ constructed by the decomposition of polyvinylpyrolidone (PVP), while the interlaced nanofiber network is achieved by the mutual fusion of the junctions between nanofibers in higher calcination temperatures. When used as an anode material in lithium ion batteries (LIBs), it exhibits superior lithium storage performance in terms of specific capacity, cycling stability, and rate capability. The pore engineering and the interlaced network structure are believed to be responsible for the excellent lithium storage performance. The pore structure allows for easy diffusion of electrolyte, shortens the pathway of Li(+) transport, and alleviates large volume variation during repeated Li(+) extraction/insertion. Moreover, the interlaced network structure can provide continuous electron/ion pathways and effectively accommodate the strain induced by the volume change during the electrochemical reaction, thus maintaining structural stability and mechanical integrity of electrode materials during lithiation/delithiation process. This strategy in current work offers a new perspective in designing high-performance electrodes for LIBs.

A three-dimensional hierarchically porous Mo2C architecture: salt-template synthesis of a robust electrocatalyst and anode material towards the hydrogen evolution reaction and lithium storage

Constructing a three-dimensional (3D) hierarchically porous architecture to increase the active sites and decrease the relevant transfer resistance has been considered as an effective strategy to improve the performance of nanomaterials in electrochemical energy conversion and storage. In this work, we for the first time demonstrate a facile and scalable salt-template method to prepare novel hierarchically macro–meso–microporous molybdenum carbide (Mo2C) with a 3D architecture (3DHP-Mo2C). Remarkably, the well-defined and abundant hierarchical macro–meso–micropores of 3DHP-Mo2C can not only significantly enhance the mass transport and electron transfer, but also markedly increase the specific surface area to effectively expose the electrochemically accessible active sites. Besides, X-ray absorption near-edge structure (XANES) measurements reveal that the carbide matrix can modify the d-electron configuration of the Mo2C particles and impart a moderate Mo–H binding energy. When evaluated as an electrocatalyst for the hydrogen evolution reaction (HER), 3DHP-Mo2C exhibits excellent electrocatalytic performance in terms of small overpotential under both acidic and basic conditions, along with exceptional stability. Apart from its outstanding HER performance, 3DHP-Mo2C also shows a high specific capacity, superior cycling stability and good rate capability as an anode material for lithium ion batteries (LIBs). This synthesis strategy may pave the way to the fabrication of a large variety of promising noble metal-free hybrid materials with a 3D hierarchical pore structure for achieving high-performance applications in energy fields.

Thermally removable in-situ formed ZnO template for synthesis of hierarchically porous N-doped carbon nanofibers for enhanced electrocatalysis

Rational design and simple synthesis of one-dimensional nanofibers with high specific surface areas and hierarchically porous structures are still challenging. In the present work, a novel strategy utilizing a thermally removable template was developed to synthesize hierarchically porous N-doped carbon nanofibers (HP-NCNFs) through the use of simple electrospinning technology coupled with subsequent pyrolysis. During the pyrolysis process, ZnO nanoparticles can be formed in situ and act as a thermally removable template due to their decomposition and sublimation under high-temperature conditions. The resulting HP-NCNFs have lengths of up to hundreds of micrometers with an average diameter of 300 nm and possess a hierarchically porous structure throughout. Such unique structures endow HP-NCNFs with a high specific surface area of up to 829.5 m2·g–1, which is 2.6 times higher than that (323.2 m2·g–1) of conventional N-doped carbon nanofibers (NCNFs). Compared with conventional NCNFs, the HP-NCNF catalyst exhibited greatly enhanced catalytic performance and improved kinetics for the oxygen reduction reaction (ORR) in alkaline media. Moreover, the HP-NCNFs even showed better stability and stronger methanol crossover effect tolerance than the commercial Pt-C catalyst. The optimized ORR performance can be attributed to the synergetic contribution of continuous and three-dimensional (3D) cross-linked structures, graphene-like structure on the edge of the HP-NCNFs, high specific surface area, and a hierarchically porous structure.

Point Decoration of Silicon Nanowires: An Approach Toward Single-Molecule Electrical Detection†

Probing interactions of biological systems at the molecular level is of great importance to fundamental biology, diagnosis, and drug discovery. A rational bioassay design of lithographically integrating individual point scattering sites into electrical circuits is capable of realizing real-time, label-free biodetection of influenza H1N1 viruses with single-molecule sensitivity and high selectivity by using silicon nanowires as local reporters in combination with microfluidics. This nanocircuit-based architecture is complementary to more conventional optical techniques, but has the advantages of no bleaching problems and no fluorescent labeling. These advantages offer a promising platform for exploring dynamics of stochastic processes in biological systems and gaining information from genomics to proteomics to improve accurate molecular and even point-of-care clinical diagnosis.

One-pot synthesis of MoSe2 hetero-dimensional hybrid self-assembled by nanodots and nanosheets for electrocatalytic hydrogen evolution and photothermal therapy

We designed and prepared a hetero-dimensional hybrid (HDH) based on molybdenum selenide (MoSe2) nanodots (NDs) anchored in few-layer MoSe2 nanosheets (NSs) (MoSe2 HDH) via a one-pot hydrothermal process. The MoSe2 HDH exhibits excellent electrocatalytic activity toward hydrogen evolution reaction (HER). This is because, on the one hand, the edge-abundant features of MoSe2 NDs and the unique defect-rich structure at the interface of MoSe2 NSs/NDs could bring in more active sites for HER; on the other hand, the random stacking of the flake-like MoSe2 NSs on the surface of the supporting electrode may achieve efficient charge transport. Additionally, the MoSe2 HDH shows good water stability, desirable biocompatibility, and high near infrared (NIR) photothermal conversion efficiency. Therefore, the MoSe2 HDH is investigated as a nanomedicine in NIR photothermal therapy (PTT) for cancer. Specifically, the MoSe2 HDH can be applied as a dual-modal probe for computed tomography (CT) and photoacoustic tomography (PA) imaging owing to its strong X-ray attenuation ability and NIR absorption. Therefore, the MoSe2 HDH, combining PTT with CT/PA imaging into one system, holds great potential for imaging-guided cancer theranostics. This work may provide an ingenious strategy to prepare other hetero-dimensional layered transition metal dichalcogenides.

Rational Construction of Multivoids-Assembled Hybrid Nanospheres Based on VPO4 Encapsulated in Porous Carbon with Superior Lithium Storage Performance

The design of a new nanostructured anode material with high tap density while still keeping the common advantages of the hollow structure is a great challenge for future lithium-ion batteries (LIBs). Here, multivoids-assembled hierarchically meso-macroporous nanospheres based on VPO4 encapsulated in porous carbon (MVHP-VPO4@C NSs) were designed and fabricated. This unique structure can evidently decrease the excessive interior space in hollow spheres or multishelled hollow spheres to gain high volumetric energy density and at the same time can alleviate the large mechanical strain during the cycling process. As expected, MVHP-VPO4@C NSs show good lithium storage behavior with gravimetric discharge capacity of 628 mAh g-1 after 100 cycles at a current density of 100 mA g-1. Furthermore, the full cell (LiFePO4 cathode//MVHP-VPO4@C NSs anode) also exhibits outstanding lithium storage performance. The insight obtained from this structure may provide guidance for the design of other electrode materials experiencing large volume variation during the lithiation-delithiation process.