Bi/Bi_(3)Se_(4) nanoparticles embedded in hollow porous carbon nanorod:High rate capability material for potassium-ion batteries

Considering their superior theoretical capacity and low voltage plateau,bismuth(Bi)-based materials are being widely explored for application in potassium-ion batteries(PIBs).Unfortunately,pure Bi and Bibased compounds suffer from severe electrochemical polarization,agglomeration,and dramatic volume fluctuations.To develop an advanced bismuth-based anode material with high reactivity and durability,in this work,the pyrolysis of Bi-based metal-organic frameworks and in-situ selenization techniques have been successfully used to produce a Bi-based composite with high capacity and unique structure,in which Bi/Bi_(3)Se_(4)nanoparticles are encapsulated in carbon nanorods(Bi/Bi_(3)Se_(4)@CNR).Applied as the anode material of PIBs,the Bi/Bi_(3)Se_(4)@CNR displays fast potassium storage capability with 307.5 m A h g^(-1)at 20 A g^(-1)and durable cycle performance of 2000 cycles at 5 A g^(-1).Notably,the Bi/Bi_(3)Se_(4)@CNR also showed long cycle stability over 1600 cycles when working in a full cell system with potassium vanadate as the cathode material,which further demonstrates its promising potential in the field of PIBs.Additionally,the dual potassium storage mechanism of the Bi/Bi_(3)Se_(4)@CNR based on conversion and alloying reaction has also been revealed by in-situ X-ray diffraction.

Novel Bilayer-Shelled N,O-Doped Hollow Porous Carbon Microspheres as High Performance Anode for Potassium-Ion Hybrid Capacitors

With the advantages of high energy/power density,long cycling life and low cost,dual-carbon potassium ion hybrid capacitors(PIHCs)have great potential in the field of energy storage.Here,a novel bilayer-shelled N,O-doped hollow porous carbon microspheres(NOHPC)anode has been prepared by a self-template method,which is consisted of a dense thin shell and a hollow porous spherical core.Excitingly,the NOHPC anode possesses a high K-storage capacity of 325.9 mA h g^(−1)at 0.1 A g^(−1)and a capacity of 201.1 mAh g^(−1)at 5 A g^(−1)after 6000 cycles.In combination with ex situ characterizations and density functional theory calculations,the high reversible capacity has been demonstrated to be attributed to the co-doping of N/O heteroatoms and porous structure improved K+adsorption and intercalation capabilities,and the stable long-cycling performance originating from the bilayer-shelled hollow porous carbon sphere structure.Meanwhile,the hollow porous activated carbon microspheres(HPAC)cathode with a high specific surface area(1472.65 m^(2)g^(−1))deriving from etching NOHPC with KOH,contributing to a high electrochemical adsorption capacity of 71.2 mAh g^(−1)at 1 A g^(−1).Notably,the NOHPC//HPAC PIHC delivers a high energy density of 90.1 Wh kg^(−1)at a power density of 939.6 W kg^(−1)after 6000 consecutive charge-discharge cycles.

N-doped graphene quantum dot-decorated N-TiO2/P-doped porous hollow g-C_(3)N_(4) nanotube composite photocatalysts for antibiotic photodegradation and H2 production

Exclusive responsiveness to ultraviolet light (~3.2 eV) and high photogenerated charge recombination rate are the two primary drawbacks of pure TiO_(2). We combined N-doped graphene quantum dots (N-GQDs), morphology regulation, and heterojunction construction strategies to synthesize N-GQD/N-doped TiO_(2)/P-doped porous hollow g-C_(3)N_(4) nanotube (PCN) composite photocatalysts (denoted as G-TPCN). The optimal sample (G-TPCN doped with 0.1wt% N-GQD, denoted as 0.1% G-TPCN) exhibits significantly enhanced photoabsorption, which is attributed to the change in bandgap caused by elemental doping (P and N), the improved light-harvesting resulting from the tube structure, and the upconversion effect of N-GQDs. In addition, the internal charge separation and transfer capability of0.1% G-TPCN are dramatically boosted, and its carrier concentration is 3.7, 2.3, and 1.9 times that of N-TiO_(2), PCN, and N-TiO_(2)/PCN(TPCN-1), respectively. This phenomenon is attributed to the formation of Z-scheme heterojunction between N-TiO_(2) and PCNs, the excellent electron conduction ability of N-GQDs, and the short transfer distance caused by the porous nanotube structure. Compared with those of N-TiO_(2), PCNs, and TPCN-1, the H2 production activity of 0.1%G-TPCN under visible light is enhanced by 12.4, 2.3, and 1.4times, respectively, and its ciprofloxacin (CIP) degradation rate is increased by 7.9, 5.7, and 2.9 times, respectively. The optimized performance benefits from excellent photoresponsiveness and improved carrier separation and migration efficiencies. Finally, the photocatalytic mechanism of 0.1% G-TPCN and five possible degradation pathways of CIP are proposed. This study clarifies the mechanism of multiple modification strategies to synergistically improve the photocatalytic performance of 0.1% G-TPCN and provides a potential strategy for rationally designing novel photocatalysts for environmental remediation and solar energy conversion.

Defects enriched hollow porous Co-N-doped carbons embedded with ultrafine CoFe/Co nanoparticles as bifunctional oxygen electrocatalyst for rechargeable flexible solid zinc-air batteries

The construction and design of highly efficient and inexpensive bifunctional oxygen electrocatalysts substitute for noble-metal-based catalysts is highly desirable for the development of rechargeable Zn-air battery(ZAB).In this work,a bifunctional oxygen electrocatalysts of based on ultrafine CoFe alloy(4-5 nm)dispersed in defects enriched hollow porous Co-N-doped carbons,made by annealing SiO2 coated zeolitic imidazolate framework-67(ZIF-67)encapsulated Fe ions.The hollow porous structure not only exposed the active sites inside ZIF-67,but also provided efficient charge and mass transfer.The strong synergetic coupling among high-density CoFe alloys and Co-N_(x) sites in Co,N-doped carbon species ensures high oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)activity.First-principles simulations reveal that the synergistic promotion effect between CoFe alloy and Co-N site effectively reduced the formation energy of from O^(*)to OH^(*).The optimized CoFe-Co@PNC exhibits outstanding electrocatalytic stability and activity with the overpotential of only 320 mV for OER at 10 mA·cm^(−2) and the half-wave potential of 0.887 V for ORR,outperforming that of most recent reported bifunctional electrocatalysts.A rechargeable ZAB constructed with CoFe-Co@PNC as the air cathode displays long-term cyclability for over 200 h and high power density(152.8 mW·cm^(−2)).Flexible solid-state ZAB with our CoFe-Co@PNC as the air cathode possesses a high open circuit potential(OCP)up to 1.46 V as well as good bending flexibility.This universal structure design provides an attractive and instructive model for the application of nanomaterials derived from MOF in the field of sustainable flexible energy applications device.

Mechanism investigation of enhanced electrochemical H_(2)O_(2) production performance on oxygen-rich hollow porous carbon spheres

Electrochemical oxygen reduction is a promising approach for the sustainable decentralized production of H_(2)O_(2),but its viable commercialization is hindered by the insufficient development of efficient electrocatalysts.Here,we demonstrate a promising carbon-based catalyst,consisting of oxygen-rich hollow mesoporous carbon spheres(HMCSs),for selective oxygen reduction to H_(2)O_(2).The as-prepared HMCS exhibits high onset potential(0.82 V)and half-wave potential(0.76 V),delivering a significant positive shift compared with its oxygen-scarce counterparts and commercial Vulcan carbon.Moreover,excellent H2O2 selectivity(above 95%)and electrochemical stability(7%attenuation after 10 h operation)make this material a state-of-the-art catalyst for electrochemical H_(2)O_(2) production.The outstanding performance arises from a combination of several aspects,such as porous structure-facilitation of mass transport,large surface area,and proper distribution of oxygen-containing functional groups modification on the surface.Furthermore,the proposed oxygen reduction reaction(ORR)mechanism on HMCS surface reveals that-OH functional groups help promote the first electron transfer process while other oxygen modification facilitate the second electron transfer.

Hierarchical porous nitrogen,oxygen,and phosphorus ternary doped hollow biomass carbon spheres for high-speed and long-life potassium storage

Limited lithium resources have promoted the exploration of new battery technologies.Among them,potassium-ion batteries are considered as promising alternatives.At present,commercial graphite and other carbon-based materials have shown good prospects as anodes for potassium-ion batteries.However,the volume expansion and structural collapse caused by periodic K+insertion/extraction have severely restricted further development and application of potassium-ion batteries.A hollow biomass carbon ball(NOP-PB)ternarily doped with N,O,and P was synthesized and used as the negative electrode of a potassium-ion battery.X-ray photoelectron spectroscopy,Fourier‐transform infrared spectroscopy,and transmission electron microscopy confirmed that the hollow biomass carbon spheres were successfully doped with N,O,and P.Further analysis proved that N,O,and P ternary doping expands the interlayer distance of the graphite surface and introduces more defect sites.DFT calculations simultaneously proved that the K adsorption energy of the doped structure is greatly improved.The solid hollow hierarchical porous structure buffers the volume expansion of the potassium insertion process,maintains the original structure after a long cycle and promotes the transfer of potassium ions and electrons.Therefore,the NOP‐PB negative electrode shows extremely enhanced electrochemical performance,including high specific capacity,excellent long‐term stability,and good rate stability.

High-loading, ultrafine Ni nanoparticles dispersed on porous hollow carbon nanospheres for fast (de)hydrogenation kinetics of MgH_(2)

Magnesium hydride(MgH2) is one of the most promising hydrogen storage materials for practical application due to its favorable reversibility, low cost and environmental benign;however, it suffers from high dehydrogenation temperature and slow sorption kinetics.Exploring proper catalysts with high and sustainable activity is extremely desired for substantially improving the hydrogen storage properties of MgH2. In this work, a composite catalyst with high-loading of ultrafine Ni nanoparticles(NPs) uniformly dispersed on porous hollow carbon nanospheres is developed, which shows superior catalytic activity towards the de-/hydrogenation of MgH2. With an addition of 5wt% of the composite, which contains 90 wt% Ni NPs, the onset and peak dehydrogenation temperatures of MgH2are lowered to 190 and 242 ℃, respectively. 6.2 wt% H2is rapidly released within 30 min at 250 ℃. The amount of H2that the dehydrogenation product can absorb at a low temperature of 150 ℃ in only 250 s is very close to the initial dehydrogenation value. A dehydrogenation capacity of 6.4wt% remains after 50 cycles at a moderate cyclic regime, corresponding to a capacity retention of 94.1%. The Ni NPs are highly active,reacting with MgH2and forming nanosized Mg2Ni/Mg2NiH4. They act as catalysts during hydrogen sorption cycling, and maintain a high dispersibility with the help of the dispersive role of the carbon substrate, leading to sustainably catalytic activity. The present work provides new insight into designing stable and highly active catalysts for promoting the(de)hydrogenation kinetics of MgH2.

Direct transformation of ZIF-8 into hollow porous carbons and hollow carbon composites

Hollow porous carbons(HPCs)are a class of porous materials with advantages of high surface to volume ratio,large interior cavities,low density,and short diffusion length,which are promising in various applications.Direct carbonization of carbon precursors is the simplest and the most cost-effective method to prepare porous carbons,however,it often leads to non-hollow structures.Herein,we demonstrate the preparation of HPCs through a direct carbonization method with a two-step heating process of zeolitic imidazolate framework-8(ZIF-8)and tetrafluoroterephthalonitrile(TFTPN).During the carbonization,ZIF-8 nanoparticles first react with TFTPN at low temperature to create polymer coatings on the surface,which are then converted into HPCs at elevated temperature.The obtained HPCs show hierarchically porous structure with high specific surface areas and pore volumes.Additionally,this method has been adopted to fabricate Au@HPCs yolk–shell composites,exhibiting good catalytic performance in nitrobenzene reduction.The developed synthesis strategy can enrich the toolbox for the preparation of novel HPCs and their composites.

Chemical synthesis of magnetic nanocrystals:Recent progress

Colloidal chemical synthesis of various types of magnetic nanocrystals is discussed with regard to recent discoveries. We first outline the chemical preparation of single-component magnetic nanocrystals with controlled size, shape, and uniformity based on several solution-phase methods, especially thermal decomposition and/or reduction method. Then we discuss the synthetic strategies of multi-component nanocrystals incorporating at least one magnetic component by manipulating heterogeneous nucleation and growth process. Toward the end, approaches for preparing hollow/porous magnetic nanocrystals are highlighted. We believe that the summarized chemical synthesis will pave the way for the future development of extraordinary magnetic nanocrystals.

Hierarchical porous hollow graphitized carbon@MoS_(2)with wideband EM dissipation capability

Core-shell materials are promising broadband electromagnetic(EM)absorption materials since the highly component manipulation performance,interfacial effect etc.Herein,a well-defined core-shell shaped structure constructed by 2-dimensional Mo S_(2)nanosheets-coated porous hollow carbon has been successfully designed with controlled pore-sizes of the core,adjustable shell content,and structure.By effectively optimizing the parameters for these factors,the as-prepared hierarchical porous hollow C@Mo S_(2)sample enables an ultra-width EM absorption ability(covering 11.4-18.0 GHz)at a thickness of only 2.0 mm.The detailed contributions of each component and structure on the excellent EM absorption capability have been investigated.These encouraging results indicate that the development of core-shell composites with multiple controllable physical factors is of great significance for the future ultra-wideband electromagnetic absorbers.

微液滴限域合成和调控空心多孔Ir基电解水催化剂及其传质促进作用

Maximally exploiting the active sites of iridium catalysts is essential for building low-cost proton exchange membrane(PEM)electrolyzers for green H_(2)production.Herein,we report a novel microdrop-confined fusion/blasting(MCFB)strategy for fabricating porous hollow IrO_(1-x)microspheres(IrO_(1-x)-PHM)by introducing explosive gas mediators from a NaNO_(3)/glucose mixture.Moreover,the developed MCFB strategy is demonstrated to be general for synthesizing a series of Ir-based composites,including Ir-Cu,Ir-Ru,Ir-Pt,Ir-Rh,Ir-Pd,and Ir-Cu-Pd and other noble metals such as Rh,Ru,and Pt.The hollow structures can be regulated using different organics with NaNO_(3).The assembled PEM electrolyzer with IrO_(1-x)-PHM as the anode catalyst(0.5 mg/cm^(2))displays an impressive polarization voltage of 1.593and 1.726 V at current densities of 1 and 2 A/cm^(2),respectively,outperforming commercial IrO_(x)catalysts and most of the ever-reported iridium catalysts with such low catalyst loading.More importantly,the breakdown of the polarization loss indicates that the improved performance is due to the facilitated mass transport induced by the hollowness.This study offers a versatile platform for fabricating efficient Irbased catalysts for PEM electrolyzers and beyond.

Sb nanoparticles encapsulated in N-doped carbon nanotubes as freestanding anodes for high-performance lithium and potassium ion batteries

Sb-based materials with high specific capacity have targeted as an alternative anode material for alkali metal ion batteries.Herein,Sb nanoparticles embedded in hollow porous N-doped carbon nanotubes(Sb@N-C nanotubes)are used as freestanding anode for Li-ion batteries(LIBs)and K-ion batteries(PIBs).The Sb@N-C nanotubes demonstrate exceptional reversible capacity of643 mAh·g^(-1)at 0.1 A·g^(-1)with long cycle stability,as well as outstanding rate performance(219.6 mAh·g^(-1)at10 A·g^(-1))in LIBs.As the anode material of PIBs,they reveal impressive capacity of 325.4 mAh·g^(-1)at 0.1 A·g^(-1).The superior electrochemical properties mainly originate from the novel structure.To be specific,the obtained 3D connected network allows for quick ion and electron migration,and prevents the aggregation of Sb nanoparticles.The hollow porous nanotubes can not only accommodate the volume expansion of Sb nanoparticles during cycling,but also facilitate the infiltration of the electrolyte and reduce the ion diffusion length.This work provides a new insight for designing advanced Sb-based anodes for alkali metal ion batteries.

TiO_2-modified nano-egg-shell Pd catalyst for selective hydrogenation of acetylene

Pd-based egg-shell nano-catalysts were prepared using porous hollow silica nanoparticles （PHSNs） as support, and the as-prepared catalysts were modified with TiO2 to promote their selectivity for hydro-genation of acetylene. Pd nanoparticles were loaded evenly on PHSNs and TiO2 was loaded on the active Pd particles. The effects of reduction time and temperature and the amount of TiO2 added on catalytic per-formances were investigated by using a fixed-bed micro-reactor. It was found that the catalysts showed better performance when reduced at 300 ℃ than at 500℃, and if reduced for 1 h than 3 h. When the amount of Ti added was 6 times that of Pd, the catalyst showed the highest ethylene selectivity.