Self-Assembly 3D Porous Crumpled MXene Spheres as Efficient Gas and Pressure Sensing Material for Transient All-MXene Sensors

Environmentally friendly degradable sensors with both hazardous gases and pressure efficient sensing capabilities are highly desired for various promising applications,including environmental pollution monitoring/prevention,wisdom medical,wearable smart devices,and artificial intelligence.However,the transient gas and pressure sensors based on only identical sensing material that concurrently meets the above detection needs have not been reported.Here,we present transient all-MXene NO_(2) and pressure sensors employing three-dimensional porous crumpled MXene spheres prepared by ultrasonic spray pyrolysis technology as the sensing layer,accompanied with water-soluble polyvinyl alcohol substrates embedded with patterned MXene electrodes.The gas sensor achieves a ppb-level of highly selective NO_(2) sensing,with a response of up to 12.11%at 5 ppm NO_(2) and a detection range of 50 ppb-5 ppm,while the pressure sensor has an extremely wide linear pressure detection range of 0.14-22.22 kPa and fast response time of 34 ms.In parallel,all-MXene NO_(2) and pressure sensors can be rapidly degraded in medical H_(2)O_(2) within 6 h.This work provides a new avenue toward environmental monitoring,human physiological signal monitoring,and recyclable transient electronics.

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-yield production of porous carbon spheres derived from enzymatic hydrolysis lignin for zinc ion hybrid capacitors

The widespread implementation of supercapacitors is hindered by the limited energy density and the pricey porous carbon electrode materials.The cost of porous carbon is a significant factor in the overall cost of supercapacitors,therefore a high carbon yield could effectively mitigate the production cost of porous carbon.This study proposes a method to produce porous carbon spheres through a spray drying technique combined with a carbonization process,utilizing renewable enzymatic hydrolysis lignin as the carbon source and KOH as the activation agent.The purpose of this study is to examine the relationship between the quantity of activation agent and the development of morphology,pore structure,and specific surface area of the obtained porous carbon materials.We demonstrate that this approach significantly enhances the carbon yield of porous carbon,achieving a yield of 22%in contrast to the conventional carbonization-activation method(9%).The samples acquired through this method were found to contain a substantial amount of mesopores,with an average pore size of 1.59 to 1.85 nm and a mesopore ratio of 25.6%.Additionally,these samples showed high specific surface areas,ranging from 1051 to 1831 m2·g^(−1).Zinc ion hybrid capacitors with lignin-derived porous carbon cathode exhibited a high capacitance of 279 F·g^(−1) at 0.1 A·g^(−1) and an energy density of 99.1 Wh·kg^(−1) when the power density was 80 kW·kg^(−1).This research presents a novel approach for producing porous carbons with high yield through the utilization of a spray drying approach.

Steady rotation of a composite sphere in a concentric spherical cavity

The problem of steady rotation of a composite sphere located at the centre of a spherical container has been investigated. A composite particle referred to in this paper is a spherical solid core covered with a permeable spherical shell. The Brinkman＇s model for the flow inside the compos- ite sphere and the Stokes equation for the flow in the spheri- cal container were used to study the motion. The torque ex- perienced by the porous spherical particle in the presence of cavity is obtained. The wall correction factor is calculated. In the limiting cases, the analytical solution describing the torque for a porous sphere and for a solid sphere in an un- bounded medium are obtained from the present analysis.

Integrated interconnected porous and lamellar structures realized fast ion/electron conductivity in high-performance lithium-sulfur batteries

The practical application of high-energy-density lithium-sulfur(Li-S)batteries have been highly praised for energy storage devices,while are largely hindered by the“shuttling effect”.Herein,core-shell carbon spheres composed of interlinked porous core and lamellar shell were designed to restrain the polysulfide shuttling.The microporous structure with pore size of around 1 nm effectively trap lithium polysulfides.Furthermore,the interconnected porous core shortens the ion transfer distance and the lamellar carbon shell endows the carbon spheres with fast electron conduction,finally facilitating polysulfide conversion kinetics.Therefore,the Li-S batteries with the carbon spheres as the interlayer show high discharge specific capacity of 1002 m Ah/g at 2 C with 574 m Ah/g remaining after 600 cycles,and high areal capacity of 5.48 m Ah/cm^(2) with sulfur loading of 4.67 mg/cm^(2) at 0.1 C.The corresponding pouch cells also exhibit stable cycling stability with an initial discharge specific capacity of 1082 m Ah/g at 0.1 C.

Synthesis of porous carbon spheres derived from lignin through a facile method for high performance supercapacitors

Porous carbon spheres（PCS） derived from lignin have been prepared through a facile method and fabricated as electrodes for electric double-layer capacitors. Spherical shaped mixtures of lignosulfonate and crystalized KOH are formed by spray drying of a solution of lignosulfonate and KOH. Activation by KOH is performed at high temperatures along with lignosulfonate carbonization. With an appropriate pore structure, the obtained PCS have a specific surface area of 1372.87 m^2 g^-1 and show a capacitance of 340 F g^-1 in 3 M KOH at a current density of 0.5 A g^-1. Moreover, a symmetric supercapacitor fabricated using the PCS as electrodes show a maximum capacitance of 68.5 F g^-1, and an energy density of 9.7 W h kg^-1 at a power density of 250 W kg^-1. The capacity retention is more than 94.5% after 5000 galvanostatic chargedischarge cycles. The excellent characteristics seem to be ascribed to the pore structures of PCS that have a large specific surface area and a low electrical resistance.

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.

Porous carbon spheres anode with the stable output of low delithiation plateau and constant delithiation ratio for lithium ion hybrid capacitor

Porous carbon spheres derived from the facile hydrothermal treatment associated with the calcination process exhibit the good spherical morphology and unique porous structure.For the Li-based half-cell test,porous carbon spheres electrode not only exhibits larger reversible capacities and better compatibility as compared to the widely-used graphite,but also provides stable delithiation plateaus under different current density.Additionally,the delithiation ratio below 1 V almost accounts for a constant value(around 70%)with the increase of current density,evidencing that Li intercalation storage is the dominant model and Li insertion/extraction processes are propitious.The lithium ion hybrid capacitor configured with S-doped mesoporous graphene and porous carbon spheres as cathode and anode,delivers satisfied energy and power densities(up to 177 Wh kg^(−1) and 12,303 W kg^(−1),respectively)as well as long-term cyclability,which is superior to the corresponding S-doped mesoporous graphene//graphite and activated carbon//porous carbon spheres.In addition,the developed synthesis strategy is in favor of the realization of the scalable production of porous carbon spheres.

Sandwich-like chitosan porous carbon Spheres/MXene composite with high specific capacitance and rate performance for supercapacitors

The application of porous carbon microspheres derived from pure biomass in supercapacitors is restricted due to their limited reactive groups.MXene owns a combination of redox Faradic surface with good metallic conductivity and hydrophilicity,which assists to obtain high pseudocapaci-tance and energy density.Herein,Ti_(3)C_(2)T_(x)MXene was introduced to chitosan-based porous carbon microsphere(CPCM)to fabricated sandwich-like structure(CPCM/MXene)through electrostatic interaction.The Ti_(3)C_(2)T_(x)protected the spherical structure of CPCM.Meanwhile,CPCM hindered the reaggregation of Ti_(3)C_(2)T_(x)by inserting in the Ti_(3)C_(2)T_(x)layers,promoting the electrolyte migra-tion kinetics.The synergistic effect endowed CPCM/MXene high specific capacitance of 362 F/g at current density of 0.5 A/g and acceptable cycling stability with 93.87%capacitance retention at a high current density of 10 A/g after 10,000 cycles.Furthermore,CPCM/MXene displayed a high energy density of 27.8 W/(h•kg)at 500.0 W/kg of power density.These satisfactory perfor-mances prove that combining Ti_(3)C_(2)T_(x)MXene nanosheets with porous carbon microspheres is a considering method to construct a new generation electrode material of supercapacitor.

Preparation of porous polyimide microspheres by thermal degradation of block copolymers

A new preparation method has been developed for thermally stable porous polyimide microspheres. Porous polyimide microspheres were prepared using trib]ock copolymers that consisted of a thermally stable polyimide derived from pyromellitic dianhydride/4,4＇-oxydianiline as the continuous phase and a thermally labile polyether as the dispersed phase. Spheres of copolymers were generated in a nonaqueous emulsion and then gradually heated to complete the imidization to form a microphase-separated structure. Subsequently, thermal treatment at a slightly reduced pressure removed the labile blocks and produced pores. Under suitable decomposition conditions, the pore size of the porous polyimide was in the range of 200-400nm.

Preparation of porous silica spheres with self-dispersing properties

A sol-gel procedure in a water/oil emulsion was introduced for the synthesis of porous silica spheres. Tetraethoxysilane was used as the silica source. The specific surface area and total pore volume of the product reached 772.3 m2/g and 0.663 cm3/g, respectively. The electrolyte washing process conferred a surface charge to the product, which displayed self-dispersal properties in water. The porous spheres have potential applications in the fields of drug delivery, controlled release capsules, indoor air pollutant scavengers, and hydrogen storage agents. The oil phase, which accounts for over 8O% of the chemical cost of the procedure, could largely be recycled by filtering, standing, and layering. The whole procedure is suitable for application as an industrial process.

Sculpturing solid polymer spheres into internal gridded hollow carbon spheres under controlled pyrolysis micro-environment

Porous carbon spheres with an internal gridded hollow structure and microporous shell have always been attractive as carbon hosts for electrochemical energy storage. Such carbon hosts can limit active species loss and enhance electronic conductivity throughout the entire framework. Herein, a synthesis approach of internal gridded hollow carbon spheres is developed from solid polymer spheres rather than originally gridded polymer spheres under a controlled pyrolysis micro-environment. The crucial point of this approach is the fabrication of a silica fence around solid polymer spheres, under which the free escaping of the pyrolysis gas will be partly impeded, thus offering a reconstitution opportunity for an internal structure of solid polymer spheres. As a result, the interior of carbon spheres is sculptured into a gridded hollow structure with microporous skin. Furthermore, the size and density of carbon-bridge grids can be modulated by altering the crosslinking degree of polymer spheres and varying pyrolysis conditions. Such gridded hollow carbon spheres show good performance as sulfur hosts for Li-S battery.

Phenylenediamine-formaldehyde chemistry derived N-doped hollow carbon spheres for high-energy-density supercapacitors

Porous carbon spheres represent an ideal family of electrode materials forsupercapacitors because of the high surface area,ideal conductivity,negligible aggregation,and ability to achieve space efficient packing.However,the development of new synthetic methods towards porous carbon spheres still remains a great challenge.Herein,N-doped hollow carbon spheres with an ultrahigh surface area of2044 m^(2)/g have been designed based on the phenylenediamine-formaldehyde chemistry.When applied in symmetric supercapacitors with ionic electrolyte(EMIBF_4),the obtained N-doped hollow carbon spheres demonstrate a high capacitance of 234 F/g,affording an ultrahigh energy density of 114.8 Wh/kg.Excellent cycling stability has also been achieved.The impressive capacitive performances make the phenylenediamine-formaldehyde resin derived N-doped carbon a promising candidate electrode material for supercapacitors.

In-situ deposition of Pd/Pd_(4)S heterostructure on hollow carbon spheres as efficient electrocatalysts for rechargeable Li-O_(2)batteries

The sluggish kinetics of oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)have always restricted the development of lithium oxygen batteries(LOBs).Herein,hollow carbon spheres loaded with Pd/Pd_(4)S heterostructure(Pd/Pd_(4)S@HCS)were successfully prepared via the in-situ deposition to improve the electrocatalytic activities for both ORR and OER in LOBs.With the welldispersed Pd/Pd_(4)S nanoparticles,the hierarchical composite with large specific surface area offers favorable transport channels for ions,electron and oxygen.Especially,the Pd/Pd_(4)S nanoparticles could exhibit excellent electrochemical performance for ORR and OER due to their intrinsic catalytic property and interfacial effect from the heterostructure.Therefore,the LOBs with Pd/Pd_(4)S@HCS as cathode catalyst show improved specific capacities,good rate ability and stable cycling performance.

Diffusion-controlled synthesis of Cu-based catalysts for the Rochow reaction

The properties of materials are strongly dependent on their structures. The diffusion effect is a main kinetic factor that can be used to regulate the growth and structure of materials. In this work, we developed a systematic and feasible strategy to synthesize Cu2O solid spheres and hexahedrons by controlling the diffusion coefficients. These Cu2O products can be successively transformed into corresponding Cu hollow spheres and hexahedrons as well as CuO porous spheres and hexahedrons by controlling hydrogen diffusion in hydrazine hydrate solution and controlling oxygen diffusion in air, respectively. The formation of these transformations was also discussed in detail. Tested for Rochow reaction, the as-prepared Cu2O solid and CuO porous spheres exhibit higher dimethyldichlorosilane selectivity and Si conversion than Cu hollow spheres, which is attributed to the active sites for CH3Cl adsorption formed in CuxSi phase after the removal of oxygen atoms in Cn2O and CuO in the formation of dimethylchlorosilane. The present work not only develops a feasible method for preparing well shape-defined Cu2O solid spheres and hexahedrons but also clarifies the respective roles of Cu, Cu2O and CuO in dimethyldichlorosilane synthesis via Rochow reaction.