Nano-Au-decorated hierarchical porous cobalt sulfide derived from ZIF-67 toward optimized oxygen evolution catalysis:Important roles of microstructures and electronic modulation

Enhancing both the number of active sites available and the intrinsic activity of Co-based electrocatalysts simultaneously is a desirable goal.Herein,a ZIF-67-derived hierarchical porous cobalt sulfide decorated by Au nanoparticles(NPs)(denoted as HP-Au@CoxSy@ZIF-67)hybrid is synthesized by low-temperature sulfuration treatment.The well-defined macroporous-mesoporous-microporous structure is obtained based on the combination of polystyrene spheres,as-formed CoxSy nanosheets,and ZIF-67 frameworks.This novel three-dimensional hierarchical structure significantly enlarges the three-phase interfaces,accelerating the mass transfer and exposing the active centers for oxygen evolution reaction.The electronic structure of Co is modulated by Au through charge transfer,and a series of experiments,together with theoretical analysis,is performed to ascertain the electronic modulation of Co by Au.Meanwhile,HP-Au@CoxSy@ZIF-67 catalysts with different amounts of Au were synthesized,wherein Au and NaBH4 reductant result in an interesting“competition effect”to regulate the relative ratio of Co^(2+)/Co^(3+),and moderate Au assists the electrochemical performance to reach the highest value.Consequently,the optimized HP-Au@CoxSy@ZIF-67 exhibits a low overpotential of 340 mV at 10 mA cm^(-2)and a Tafel slope of 42 mV dec-1 for OER in 0.1 M aqueous KOH,enabling efficient water splitting and Zn-air battery performance.The work here highlights the pivotal roles of both microstructural and electronic modulation in enhancing electrocatalytic activity and presents a feasible strategy for designing and optimizing advanced electrocatalysts.

Novel method for identifying the stages of discharge underwater based on impedance change characteristic

It is difficult to determine the discharge stages in a fixed time of repetitive discharge underwater due to the arc formation process being susceptible to external environmental influences. This paper proposes a novel underwater discharge stage identification method based on the Strong Tracking Filter(STF) and impedance change characteristics. The time-varying equivalent circuit model of the discharge underwater is established based on the plasma theory analysis of the impedance change characteristics and mechanism of the discharge process. The STF is used to reduce the randomness of the impedance of repeated discharges underwater, and then the universal identification resistance data is obtained. Based on the resistance variation characteristics of the discriminating resistance of the pre-breakdown, main, and oscillatory discharge stages, the threshold values for determining the discharge stage are obtained. These include the threshold values for the resistance variation rate(K) and the moment(t).Experimental and error analysis results demonstrate the efficacy of this innovative method in discharge stage determination, with a maximum mean square deviation of Scrless than 1.761.

Electronic and thermal properties of Ag-doped single crystal zinc oxide via laser-induced technique

The doping of ZnO has attracted lots of attention because it is an important way to tune the properties of ZnO.Postdoping after growth is one of the efficient strategies.Here,we report a unique approach to successfully dope the single crystalline ZnO with Ag by the laser-induced method,which can effectively further post-treat grown samples.Magnetron sputtering was used to coat the Ag film with a thickness of about 50 nm on the single crystalline ZnO.Neodymium-doped yttrium aluminum garnet(Nd:YAG)laser was chosen to irradiate the Ag-capped ZnO samples,followed by annealing at700℃for two hours to form ZnO:Ag.The three-dimensional(3D)information of the elemental distribution of Ag in ZnO was obtained through time-of-flight secondary ion mass spectrometry(TOF-SIMS).TOF-SIMS and core-level x-ray photoelectron spectroscopy(XPS)demonstrated that the Ag impurities could be effectively doped into single crystalline ZnO samples as deep as several hundred nanometers.Obvious broadening of core level XPS profiles of Ag from the surface to depths of hundred nms was observed,indicating the variance of chemical state changes in laser-induced Ag-doped ZnO.Interesting features of electronic mixing states were detected in the valence band XPS of ZnO:Ag,suggesting the strong coupling or interaction of Ag and ZnO in the sample rather than their simple mixture.The Ag-doped ZnO also showed a narrower bandgap and a decrease in thermal diffusion coefficient compared to the pure ZnO,which would be beneficial to thermoelectric performance.

Formation and emission characteristics of VOCs from a coal-fired power plant

On-site measurements of volatile organic compounds(VOCs)in different streams of flue gas were carried out on a real coal-fired power plant using sampling bags and SUMMA canisters to collect gas samples,filters to collect particle samples.Gas chromatography-flame ionization detector/mass spectrometry and gas chromatography-mass spectrometry was the offline analysis method.We found that the total mass concentration of the tested 102 VOC species at the outlet of wet flue gas desulfuration device was(13456±47)μg·m^(-3),which contained aliphatic hydrocarbons(57.9%),aromatic hydrocarbons(26.8%),halogen-containing species(14.5%),and a small amount of oxygen-containing and nitrogencontaining species.The most abundant species were 1-hexene,n-hexane and 2-methylpentane.The top ten species in terms of mass fraction(with a total mass fraction of 75.3%)were mainly hydrocarbons with a carbon number of 6 or higher and halogenated hydrocarbons with a lower carbon number.The mass concentration of VOC species in the particle phase was significantly lower than that in the gas phase.The change of VOC mass concentrations along the air pollution control devices indicates that conventional pollutant control equipment had a limited effect on VOC reduction.Ozone formation potential calculations showed that aromatic hydrocarbons contributed the highest ozone formation(46.4%)due to their relatively high mass concentrations and MIR(maximum increment reactivity)values.

Effects of calcium on the evolution of nitrogen during pyrolysis of a typical low rank coal

This study aims to investigate the effects of calcium on the migration of nitrogen in coal(coal-N)to N-containing gas species,particularly,NH3 and HCN(volatile-N)in volatiles,as well as the chemical transformation of the N in char during coal pyrolysis under different temperatures.The pyrolysis experiments of Shengli brown coal and its derived coal samples loaded with different contents of calcium were conducted under 600–800°C in a novel fluidized bed reactor.The experimental results showed that during coal pyrolysis,the generation of NH3 is mainly derived from secondary reactions among volatiles,tar and char with the catalytic effect of mineral matter,especially calcium in coal.Increasing pyrolysis temperature from 600 to 800°C could enhance the release of N in coal to volatiles.Meanwhile,the increased pyrolysis temperature could also inhibit the generation of NH3 while facilitating the formation of HCN.The release of HCN is more sensitive to pyrolysis temperatures.Specifically,under higher pyrolysis temperatures,more N-containing structures in coal would become thermally unstable and crack into HCN;On the other hand,higher pyrolysis temperature could also enhance the decomposition of N in coal to N-containing species in tar or N2,thus reducing the release of HCN and NH3.Nitrogen in tar could either undergo secondary decomposition reactions,generating NH3,HCN,N2 and other N-containing species in gas phase,or experience condensation polymerization by forming macromolecular structure and be retained in char at high pyrolysis temperatures.Calcium could significantly restrain the release of N from coal,thus reducing the yields of NH3 and HCN.During coal pyrolysis,calcium catalytically enhances the fracture and combination of chemical bonds,generating abundant free radicals.These free radicals could continuously attack N-containing structures and consequently release the N-containing gaseous products,such as NH3,HCN,N2 etc.,resulting in the decrease of N in char.Calcium also plays important roles in nitrogen transformation in char during coal pyrolysis by catalytically intensifying the transformation of N in char from pyridinic nitrogen(N-6)and pyrrolic nitrogen(N-5)to quaternary type nitrogen(N-Q)during coal pyrolysis.

Emission Behaviors of Submicron Particles(PM_(1))Generated by the Combustion of Sesame Stalk after Combined Water Washing and Carbonization Pretreatment

Pretreatment before biomass combustion is significant for its efficient utilization and that combined water washing and carbonization can be efficient.An agricultural processing residues sesame stalk was selected and carried out two pretreatments separately,i.e.,water washing-torrefaction(W-T)and torrefaction-water washing(T-W),to explore the effect on the fuel properties,combustion characteristics and particulate matter(PM)emission.The obtained biochar was also combusted under air and oxy50(CO_(2):O_(2)=50:50)conditions for the sake of investigating the effect of pretreatment and combustion atmosphere.The results indicate that,W-T and T-W both not only have great effect on the improvement of fuel properties but also reduce the content of water-soluble elements like K,Cl,etc.Due to the difference in hydrophobicity,the biochar obtained by W-T have the optimal fuel properties.At the same time,the pretreatment also hinder the combustion in a certain extent in which the comprehensive combustion characteristics(SN)show a downward trend.Furthermore,both two pretreatments have obvious benefit on the reduction of PM_(1)emission and W-T have the best effect related to the higher removal efficiency of inorganic elements(especially K+Na+Cl+S).Under oxy50 condition,the oxygen concentration and combustion temperature is higher,improving the sulfation of K and vaporization of Ca,P and Mg which result in weakening in the pretreatment reduction effect on PM_(1)emission.

Advances of machine learning in materials science: Ideas and techniques

In this big data era, the use of large dataset in conjunction with machine learning (ML) has been increasingly popular in both industry and academia. In recent times, the field of materials science is also undergoing a big data revolution, with large database and repositories appearing everywhere. Traditionally, materials science is a trial-and-error field, in both the computational and experimental departments. With the advent of machine learning-based techniques, there has been a paradigm shift: materials can now be screened quickly using ML models and even generated based on materials with similar properties;ML has also quietly infiltrated many sub-disciplinary under materials science. However, ML remains relatively new to the field and is expanding its wing quickly. There are a plethora of readily-available big data architectures and abundance of ML models and software;The call to integrate all these elements in a comprehensive research procedure is becoming an important direction of material science research. In this review, we attempt to provide an introduction and reference of ML to materials scientists, covering as much as possible the commonly used methods and applications, and discussing the future possibilities.

Stable Cycling of All-Solid-State Lithium Batteries Enabled by Cyano-Molecular Diamond Improved Polymer Electrolytes

The interfacial instability of the poly(ethylene oxide)(PEO)-based electrolytes impedes the long-term cycling and further application of all-solid-state lithium metal batter-ies.In this work,we have shown an effective additive 1-adaman-tanecarbonitrile,which con-tributes to the excellent per-formance of the poly(ethylene oxide)-based electrolytes.Owing to the strong interaction of the 1-Adamantanecarboni-trile to the polymer matrix and anions,the coordination of the Li^(+)-EO is weakened,and the binding effect of anions is strengthened,thereby improving the Li^(+)conductivity and the electrochemical stability.The diamond building block on the surface of the lithium anode can sup-press the growth of lithium dendrites.Importantly,the 1-Adamantanecarbonitrile also regulates the formation of LiF in the solid electrolyte interface and cathode electrolyte interface,which contributes to the interfacial stability(especially at high voltages)and protects the electrodes,enabling all-solid-state batteries to cycle at high voltages for long periods of time.Therefore,the Li/Li symmetric cell undergoes long-term lithium plating/stripping for more than 2000 h.1-Adamantanecarbonitrile-poly(ethylene oxide)-based LFP/Li and 4.3 V Ni_(0.8)Mn_(0.1)Co_(0.1)O_(2)/Li all-solid-state batteries achieved stable cycles for 1000 times,with capacity retention rates reaching 85%and 80%,respectively.

Inventory of CO2 emissions driven by energy consumption in Hubei Province： a time-series energy input-output analysis

Based on an input-output analysis, this paper compiles inventories of fuel-related CO2 emissions of Hubei economy in the years of 2002, 2005, and 2007. Results show that calculated total direct CO2 emissions rose from 114,462.69 kt （2002） to 196,650.31 kt （2005）, reaching 210,419.93 kt in 2007, with an average 22.50% rate of increase. Raw coal was the dominant source of the direct emissions throughout the three years. The sector of Electric Power, Heat Production, and Supply was the main direct emissions contributor, with the largest intensities observed from 2002 （1192.97 g/CNY） to 2007 （1739.15 g/ CNY）. From the industrial perspective, the secondary industry, which is characterized as manufacture of finished products, was still the pillar of the Hubei economy during this period concerned, contributing more than 80% of the total direct emissions. As a net exporter of embodied CO2 emissions in 2002 and 2007, Hubei reported net-exported emissions of 4109.00 kt and 17,871.77 kt respectively; however, Hubei was once a net importer of CO2 emissions in 2005 （2511.93 kt）. The CO2 emissions embodied in export and fixed capital formation had the two leading fractions of emissions embodied in the final use. The corresponding countermeasures, such as promoting renew- able and clean energy and properly reducing the exports of low value added and carbon-intensive products are suggestions for reducing CO2 emissions in Hubei.

Review of the role of ionic liquids in two-dimensional materials

Ionic liquids(ILs)are expected to be used as readily available“designer”solvents,characterized by a number of tunable properties that can be obtained by modulating anion and cation combinations and ion chain lengths.Among them,its high ionicity is outstanding in the preparation and property modulation of two-dimensional(2D)materials.In this review,we mainly focus on the ILs-assisted exfoliation of 2D materials towards large-scale as well as functionalization.Meanwhile,electric-field controlled ILs-gating of 2D material systems have shown novel electronic,magnetic,optical and superconducting properties,attracting a broad range of scientific research activities.Moreover,ILs have also been extensively applied in various field practically.We summarize the recent developments of ILs modified 2D material systems from the electrochemical,solar cells and photocatalysis aspects,discuss their advantages and possibilities as“designer solvent”.It is believed that the design of ILs accompanying with diverse 2D materials will not only solve several scientific problems but also enrich materials design and engineer of 2D materials.

Building the bridge of small organic molecules to porous carbons via ionic solid principle

Replacing traditional polymer-based precursors with small molecules is a promising pathway toward facile and controllable preparation of porous carbons but remains a prohibitive challenge because of the high volatility of small molecules.Herein,a simple,general,and controllable method is reported to prepare porous carbons by converting small organic molecules into organic molecular salts followed by pyrolysis.The robust electrostatic force holding organic molecular salts together leads to negligible volatility and thus ensures the formation of carbons under high-temperature pyrolysis.Meanwhile,metal moieties in organic molecular salts can be evolved into in-situ templates or activators during pyrolysis to create nanopores.The modular nature of organic molecular salts allows easy control of the porosity and chemical doping of carbons at a molecular level.The sulfur-doped carbon prepared by the ionic solid strategy can serve as robust support to prepare small-sized intermetallic PtCo catalysts,which exhibit a high mass activity of 1.62 A·mgPt^(−1)in catalyzing oxygen reduction reaction for fuel cell applications.

Determination of the embedded electronic states at nanoscale interface via surface-sensitive photoemission spectroscopy

The fabrication of small-scale electronics usually involves the integration of different functional materials.The electronic states at the nanoscale interface plays an important role in the device performance and the exotic interface physics.Photoemission spectroscopy is a powerful technique to probe electronic structures of valence band.However,this is a surface-sensitive technique that is usually considered not suitable for the probing of buried interface states,due to the limitation of electron-mean-free path.This article reviews several approaches that have been used to extend the surface-sensitive techniques to investigate the buried interface states,which include hard X-ray photoemission spectroscopy,resonant soft X-ray angle-resolved photoemission spectroscopy and thickness-dependent photoemission spectroscopy.Especially,a quantitative modeling method is introduced to extraa the buried interface states based on the film thickness-dependent photoemission spectra obtained from an integrated experimental system equipped with in-situ growth and photoemission techniques.This quantitative modeling method shall be helpful to further understand the interfacial electronic states between functional materials and determine the interface layers.

Physicochemical and adsorption properties of biochar from biomass-based pyrolytic polygeneration:effects of biomass species and temperature

Biochar obtained from a biomass pyrolytic polygeneration technology exhibits great potential as an adsorbent,because of its renewability,porosity and desirable surface chemical properties.Pyrolysis temperature and feed are important elements in the preparation of biochar.Thus,the effects of these factors on the physicochemical properties of biochar were investigated in this study.The adsorption of biochar was evaluated using water,CO_(2),phenol,and methylene blue(MB)as adsorbates.The correlation between adsorption capacity and physicochemical properties was determined using the Pearson correlation.Results indicated that temperature could significantly affect the structure of biochar.The effects of biomass species were also noticeable as well.The number of macropores and their contribution to the total surface area for cotton stalk,bamboo,and rapeseed stalk increased with an increase in temperatures,meanwhile,the number of micropores decreased at high tem-peratures.At the same temperature,the macropore,mesopore,and micropore components of biochar produced by different species were markedly different.The water adsorption and CO_(2) adsorption of biochar were close to those of commercial activated carbon(AC),whereas the adsorption capacity of untreated biochar on phenol and MB was less than that of AC.Porosity exerted more significant effects on the adsorption capacity of biochar,compared with functional groups.The surface area of the micropores exhibited a significant positive correlation with the adsorption of CO_(2),phenol,and MB.The hydroxyl group was positively correlated with water adsorption.

Accelerating electron transport in Eosin Y by bidentately bridging on BaSnO_(3)for noble-metal-free photocatalytic H 2 production

The separation and transport of photogenerated carriers is regarded as a curial factor in photocatalytic H_(2)pro-duction.As known in solar cells and photoelectron-chemistry,to strengthen the electron conduction for effective utilization of carriers,the electron transport material(ETM)is widely applied.Herein,inspired by the function of ETM,we adopted barium stannate(BaSnO_(3),labeled as BSO)as an excellent ETM which had the merits of high electron mobility,suitable conduction band position and simple preparation,to adjust the carrier kinetics of dye Eosin Y(EY)-sensitized photocatalytic system.Detailly,the photocatalytic system with the spatial sepa-ration sites of photogenerated carriers excitation and water reduction reaction was elaborately constructed,that was,dye EY-sensitized BSO(EY/BSO)for photocatalytic H_(2)production.The photocatalytic H_(2)-production rate of EY/BSO(257𝜇mol·h^(−1)·g EY^(−1))in the absence of noble metals was 28.6 times higher than that of single EY(∼9𝜇mol·h^(−1)·g EY^(−1))under visible-light irradiation.With systematic and comprehensive characterizations,the formed electron transport channel by the bidentate bridging of EY on BSO could accelerate the transfer of photogenerated electrons from EY to BSO,promoting the effective separation of photogenerated carriers for the enhanced pho-tocatalytic performance.Moreover,the water reduction reaction for H_(2)production proceeded on the surface of BSO that acted as the H_(2)-evolution cocatalyst,avoiding the use of high-cost noble metals.Furthermore,based on the well-proved ETM-based concept in the EY/BSO system,La-doped BaSnO_(3)(LBSO)with better electron trans-port ability was adopted to construct EY/LBSO system(344𝜇mol·h^(−1)·g EY^(−1))which showed better photocatalytic activity than EY/BSO.

The accelerating nanoscale Kirkendall effect in Co films–native oxide Si(100)system induced by high magnetic fields

The morphology evolution and magnetic properties of Co films–native oxide Si(100)were investigated at 873,973,and 1073 K in a high magnetic field of 11.5 T.Formation of Kirkendall voids in the Co films was found to cause morphology evolution due to the difference in diffusion flux of Co and Si atoms through the native oxide layer.The high magnetic fields had considerable effect on the morphology evolution by accelerating nanoscale Kirkendall effect.The diffusion mechanism in the presence of high magnetic fields was given to explain the increase of diffusion coefficient.The morphology evolution of Co films on native oxide Si(100)under high magnetic fields during annealing resulted in the magnetic properties variation.

Asymmetrical Transport Distribution Function: Skewness as a Key to Enhance Thermoelectric Performance

How to achieve high thermoelectric figure of merit is still a scientific challenge.By solving the Boltzmann transport equation,thermoelectric properties can be written as integrals of a single function,the transport distribution function(TDF).In this work,the shape effects of transport distribution function in various typical functional forms on thermoelectric properties of materials are systematically investigated.It is found that the asymmetry of TDE,characterized by skewness,can be used to describe universally the trend of thermoelectric properties.By defining symmetric and asymmetric TDF functions,a novel skewness is then constructed for thermoelectric applications.It is demonstrated,by comparison with ab initio calculations and experiments,that the proposed thermoelectric skewness not only perfectly captures the main feature of conventional skewness but also is able to predict the thermoelectric power accurately.This comparison confirms the unique feature of our proposed thermoelectric skewness,as well as its special role of connection between the statistics of TDF and thermoelectric properties of materials.It is also found that the thermoelectric performance can be enhanced by increasing the asymmetry of TDF.Finally,it is also interesting to find that the thermoelectric transport properties based on typical quantum statistics(Fermi-Dirac distributions)can be well described by typical shape parameter(skewness)for classical statistics.

Tunable metamaterial absorber based on resonant strontium titanate artificial atoms

Dynamic control of the absorption frequency and intensity of metamaterial absorbers has attracted considerable attention,and many kinds of tunable metamaterial absorbers have been proposed.Unfortunately,due to the integration of separate resonant unit and tunable unit,these designed metamaterial absorbers suffer from complex structure and low sensitivity.We numerically and experimentally demonstrate a tunable metamaterial absorber composed of artificial dielectric atoms as both resonant and tunable unit arrayed periodically in the background matrix on the metallic plate.Polarization insensitive and wide incident angle absorption band with simulated and experimental absorptivity of 99%and 96%at 9.65 GHz are achieved at room temperature.The absorption frequency can be gradually modulated by temperature,however,the absorption intensity at working frequency remains near unity.The dielectric atoms based tunable metamaterial absorbers with simple structure have potential applications as tempe rature sensors and frequency selective thermal emitters.