Atomically dispersed Mn-Nx catalysts derived from Mn-hexamine coordination frameworks for oxygen reduction reaction

Metal-organic frameworks recently have been burgeoning and used as precursors to obtain various metal-nitrogen-carbon catalysts for oxygen reduction reaction(ORR).Although rarely studied,Mn-N-C is a promising catalyst for ORR due to its weak Fenton reaction activity and strong graphitization catalysis.Here,we developed a facile strategy for anchoring the atomically dispersed nitrogen-coordinated single Mn sites on carbon nanosheets(MnNCS)from an Mn-hexamine coordination framework.The atomically dispersed Mn-N4 sites were dispersed on ultrathin carbon nanosheets with a hierarchically porous structure.The optimized MnNCS displayed an excellent ORR performance in half-cells(0.89 V vs.reversible hydrogen electrode(RHE)in base and 0.76 V vs.RHE in acid in half-wave potential)and Zn-air batteries(233 mW cm^(−2)in peak power density),along with significantly enhanced stability.Density functional theory calculations further corroborated that the Mn-N4-C1_(2)site has favorable adsorption of*OH as the rate-determining step.These findings demonstrate that the metal-hexamine coordination framework can be used as a model system for the rational design of highly active atomic metal catalysts for energy applications.

Cellulose nanofiber-derived carbon aerogel for advanced room-temperature sodium–sulfur batteries

Room-temperature sodium–sulfur(RT/Na–S)batteries are regarded as promising large-scale stationary energy storage systems owing to their high energy density and low cost as well as the earth-abundant reserves of sodium and sulfur.However,the diffusion of polysulfides and sluggish kinetics of conversion reactions are still major challenges for their application.Herein,we developed a powerful and functional separator to inhibit the shuttle effect by coating a lightweight three-dimensional cellulose nanofiber-derived carbon aerogel on a glass fiber separator(denoted NSCA@GF).The hierarchical porous structures,favorable electronic conductivity,and three-dimensional interconnected network of N,S-codoped carbon aerogel endow a multifunctional separator with strong polysulfide anchoring capability and fast reaction kinetics of polysulfide conversion,which can act as the barrier layer and an expanded current collector to increase sulfur utilization.Moreover,the hetero-doped N/S sites are believed to strengthen polysulfide anchoring capability via chemisorption and accelerate the redox kinetics of polysulfide conversion,which is confirmed from experimental and theoretical results.As a result,the assembled Na–S coin cells with the NSCA@GF separator showed a high reversible capacity(788.8 mAh g^(−1) at 0.1 C after 100 cycles)and superior cycling stability(only 0.059%capacity decay per cycle over 1000 cycles at 1 C),thereby demonstrating the significant potential for application in high-performance RT/Na–S batteries.

MicroRNA-188-5p targeting Forkhead Box L1 promotes colorectal cancer progression via activating Wnt/β-catenin signaling

Objective:MicroRNA-188-5p(miR-188)enhances oncologic progression in various human malignancies.This study aimed to explore its role in colorectal cancer(CRC).Materials and Methods:Human CRC tissues paired with normal tissues,and several CRC cell lines were utilized.Real-time quantitative PCR was applied to measure the expression of miR-188.Overexpression and knockdown were used to access the function of miR-188 and to investigate whether FOXL1/Wnt signaling mediates such function.The proliferation,migration and invasion of cancer cells were evaluated by CCK8,wound-healing and transwell assays,respectively.Whether FOXL1 acted as a direct target of miR-188 was verified by dual-luciferase reporter assays.Results:Levels of miR-188 were upregulated in CRC tissues than in paired-normal tissues,as well as in various CRC cell lines.High expression of miR-188 was strongly associated with advanced tumor stage,accompanied with significant tumor cell proliferation,invasion and migration.It was confirmed that FOXL1 played positive crosstalk between miR-188 regulation and downstream Wnt/β-catenin signaling activation.Conclusions:All findings indicate that miR-188 promotes CRC cell proliferation and invasion through targeting FOXL1/Wnt signaling and could be served as a potential therapeutic target for human CRC in the future.

Defect reduction to enhance the mechanical strength of nanocellulose carbon aerogel

Carbon aerogels prepared from renewable nano building blocks are rising-star materials and hold great promise in many fields.However,various defects formed during carbonization at high temperature disfavor the stress transfer and thus the fabrication of flexible carbon aerogel from renewable nano building blocks.Herein,a structural defect-reducing strategy is proposed by altering the pyrolysis route of cellulose nanofiber.Inorganic salt that inhibits the generation of tar volatilization during pyrolysis can prevent the formation of various structural defects.Microstructure with fewer defects can reduce stress concentration and remarkably enhance the compressibility of carbon aerogel,thus increasing the maximum stress retention of carbon aerogel.The carbon aerogel also has high stress sensor sensitivity and excellent temperature coefficient of resistance.The structural defect-reducing strategy will pave a new way to fabricate high-strength carbon materials for various fields.

Recent progress and future perspectives of flexible metal‐air batteries

With the rapid development of wearable and intelligent flexible electronic devices(FEDs),the demand for flexible energy storage/conversion devices(ESCDs)has also increased.Rechargeable flexible metal‐air batteries(MABs)are expected to be one of the most ideal ESCDs due to their high theoretical energy density,cost advantage,and strong deformation adaptability.With the improvement of the device design,material assemblies,and manufacturing technology,the research on the electrochemical performance of flexible MABs has made significant progress.However,achieving the high mechanical flexibility,high safety,and wearable comfortability required by FEDs while maintaining the high performance of flexible MABs are still a daunting challenge.In this review,flexible Zn‐air and Li‐air batteries are mainly exemplified to describe the most recent progress and challenges of flexible MABs.We start with an overview of the structure and configuration of the flexible MABs and discuss their impact on battery performance and function.Then it focuses on the research progress of flexible metal anodes,gel polymer electrolytes,and air cathodes.Finally,the main challenges and future research perspectives involving flexible MABs for FEDs are proposed.

Thermoelectric generator based on anisotropic wood aerogel for low-grade heat energy harvesting

Thermoelectric generators(TEGs)have received increasing attention due to their potential to harvest low-grade heat energy(<100℃ )and provide power for the Internet of Things(IoT)and wearable electronic devices.Herein,a wood-based ordered framework is used to fabricate carbon nanotube/poly(3,4-ethylenedioxythiophene)(CNT/PEDOT)wood aerogel for TEG.The prepared CNT/PEDOT wood aerogel with an anisotropic structure exhibits a low thermal conductivity of 0.17 W m^(−1)K^(−1)and is advantageous to develop a sufficient temperature gradient.Meanwhile,CNT/PEDOT composites effectively decouple the relationship between the Seebeck coefficient and electrical conductivity by energy filtering effect to enhance thermoelectric(TE)output properties.The vertical TEG assembled by the CNT/PEDOT wood aerogels reveals an output power of 1.5μW and a mass-specific power of 15.48μW g^(−1)at a temperature difference of 39.4 K.Moreover,the layered structure renders high compressibility and fatigue resistance.The anisotropic structure,high mechanical performance,and rapid thermoelectric response,enabling the TEG based on CNT/PEDOT wood aerogel offer opportunities for continuous power supply to low-power electronic devices.

Monocular vision for variable spray control system

The monocular vision-based system can obtain the leaf wall area characterizing the canopy parameter for online detection and real-time variable spraying,aiming to improve the accuracy of orchard spraying equipment and the utilization efficiency of pesticide.This study established a spraying system,in which canopy parameters were collected by monocular vision,and the spray volume decision coefficient was constructed by the leaf wall area and the L^(*)value in International Commission on Illumination Lab color space to control the duty cycle of each solenoid valve to achieve variable spraying.Four spray flow models were designed to determine the spray volume decision coefficient.The coefficients of determination of the spray volumes with the duty cycle range of 15%to 65%were all over 94 and the error of the leaf wall area values obtained using the improved super green algorithm(calculated as ExG=2.1G–1.1R–1.1B)was only 0.5%.The test showed that there is a negative relationship between canopy denseness and L^(*),and the value of L^(*)is smaller in the dense area compared with the sparse area;the actual flow generated by the system is similar to the theoretical flow when the duty cycle is 65%.The field validation tests showed that the variable spraying system could refine the droplet size and increase the droplet density to a certain extent with the same coverage rate,which had advantages over the continuous spraying.In terms of droplet deposition,DV0.1 and DV0.9 were reduced by 2μm and 18μm,respectively,and the increase of droplet density to 75 droplets/cm2.At the same time,the improvement of droplet distribution uniformity and droplet penetration by 16%and 3%,respectively.Compared with continuous spraying,variable spraying can achieve 55.64%savings.The study demonstrates the feasibility of monocular vision in guiding spraying operations and provides a reference for the use of monocular vision in plant protection operations.

Metal coordination assists fabrication of multifunctional aerogel

Interfacial design is one of the most promising ways in improving mechanical properties of nanocomposites.In this work,a multifunctional aerogel with excellent mechanical performances,sensing sensitivity,and fire retardancy is fabricated by taking advantage of metal coordination between biopolymer and Fe3+.Montmorillonite(MMT)nanosheets are added to induce a‘brick and mortar’structure.The coordination remarkably reduces structural defects,leading to well-formed lamellas that can effectively distribute stress under sever compression without plastic deformation.The structural merits impart the aerogel highly reversible compressibility even at 99%strain and superior durability.Besides,it demonstrates high sensing performance in wearable health monitoring devices,and shows fire resistance property that can maintain elasticity in a flame.The work offers a facile and effective method to create multifunctional aerogels from various polymers.