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.

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.

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.

Embedding ZnSe nanodots in nitrogen-doped hollow carbon architectures for superior lithium storage

Transition metal chalcogenides represent a class of the most promising alternative electrode materials for high-performance lithium-ion batteries （LIBs） owing to their high theoretical capacities. However, they suffer from large volume expansion, particle agglomeration, and low conductivity during charge/discharge processes, leading to unsatisfactory energy storage performance. In order to address these issues, we rationally designed three-dimensional （3D） hybrid composites consisting of ZnSe nanodots uniformly confined within a N-doped porous carbon network （ZnSe ND@N-PC） obtained via a convenient pyrolysis process. When used as anodes for LIBs, the composites exhibited outstanding electrochemical performance, with a high reversible capacity （1,134 mA.h.g-1 at a current density of 600 mA.g-1 after 500 cycles） and excellent rate capability （696 and 474 mA.h.g-1 at current densities of 6.4 and 12.8 A.g-1, respectively）. The significantly improved lithium storage performance can be attributed to the 3D architecture of the hybrid composites, which not only mitigated the internal mechanical stress induced by the volume change and formed a 3D conductive network during cycling, but also provided a large reactive area and reduced the lithium diffusion distance. The strategy reported here may open a new avenue for the design of other multi functional composites towards high-performance energy storage devices.