Search

A lithium-air battery based on lithium oxide (Li 2 O) formation can theoretically deliver an energy density that is comparable to that of gasoline. Lithium oxide formation involves a four-electron reaction that is more difficult to achieve than the one- and two-electron reaction processes that result in lithium superoxide (LiO 2 ) and lithium peroxide (Li 2 O 2 ), respectively. By using a composite polymer electrolyte based on Li 10 GeP 2 S 12 nanoparticles embedded in a modified polyethylene oxide polymer matrix, we found that Li 2 O is the main product in a room temperature solid-state lithium-air battery. The battery is rechargeable for 1000 cycles with a low polarization gap and can operate at high rates. The four-electron reaction is enabled by a mixed ion–electron-conducting discharge product and its interface with air.

Dual-site models were constructed to represent manganese nitride (Mn4N)-supported Ni3 and Fe3 clusters for NH3 synthesis. Density functional theory calculations produced an energy barrier of approximately 0.55 eV for N-N bond activation at the interfacial nitrogen vacancy sites (Nv); also, the hydrogenation and removal of interfacial N is promoted by earth-abundant Ni and Fe metals. Steady-state microkinetic modeling revealed that the turnover frequencies of NH3 production follow an order of Fe3@Mn4N ≈ Ni3@Mn4N > Mn4N > Fe ≫ Ni. Moreover, we present clear evidence that, before NH3 formation, NH migrates from Nv onto the metallic sites. Using N binding energy (BEN) and the transition-state energy of N2 activation (ETS) as descriptors, we concluded that the beneficial effects owing to interfacial Nv sites are the most pronounced when BEN is either too strong or too weak while ETS is high; otherwise, excessive Nv sites may hinder catalyst performance.

Experimental evidence has demonstrated that the presence of water in non-aqueous electrolytes significantly affects Li–O2 electrochemistry. Understanding the reaction mechanism for Li2O2 formation in the presence of water impurities is important to understand Li–O2 battery performance. A recent experiment has found that very small amounts of water (as low as 40 ppm) can significantly affect the product formation in Li–O2 batteries as opposed to essentially no water (1 ppm). Although experimental as well as theoretical work has proposed mechanisms of Li2O2 formation in the presence of much larger amounts of water, none of the mechanisms provide an explanation for the observations for very small amounts of water. In this work, density functional theory (DFT) was utilized to obtain a mechanistic understanding of the Li–O2 discharge chemistry in a dimethoxyethane (DME) electrolyte containing an isolated water and no water. The reaction pathways for Li2O2 formation from LiO2 on a model system were carefully evaluated with different level of theories, i.e. PBE (PW), B3LYP/6-31G(2df,p), B3LYP/6-311++G(2df,p) and G4MP2. The results indicate that the LiO2 disproportionation reaction to Li2O2 can be promoted by the water in DME electrolyte, which explains why there is a significant difference compared to when no water is present in the experimentally observed discharge product distributions. Ab initio molecular dynamics calculations were also used to investigate the disproportionation of LiO2 dimer in explicit DME. This work adds to the fundamental understanding of the discharge chemistry of a Li–O2 battery.

Three-dimensionally ordered macro-/mesoporous carbon (OMMC)-supported Ag nanoparticles (Ag/OMMC) with homogeneously dispersed Ag particles are prepared and investigated as effective electrocatalysts for oxygen reduction reaction (ORR) in alkaline aqueous system. The obtained Ag/OMMC catalyst displays smaller Ag particle size, higher Ag dispersion, and enhanced catalytic activity and durability compared with the carbon black Vulcan XC-72R supported Ag (Ag/XC-72R). The sizes of Ag particles supported on the OMMC and XC-72R are 4.3 and 6.5 nm, respectively. The prepared Ag/OMMC catalyst shows a positive half-wave potential of 0.79 V vs. RHE and a large diffusion-limited current of 5.6 mA cm−2 at 0.4 V, superior to Ag/XC-72R catalyst. The better ORR performance of the Ag/OMMC is probably ascribed to the unique 3D ordered interconnected macro-/mesoporous structure, which contributes to facilitating the mass/charge transport, improving the Ag particle dispersion, and preventing the Ag particle growth and aggregation.

Dual-site models were constructed to represent manganese nitride (Mn

Experimental evidence has demonstrated that the presence of water in non-aqueous electrolytes significantly affects Li-O2 electrochemistry. Understanding the reaction mechanism for Li2O2 formation in the presence of water impurities is important to understand Li-O2 battery performance. A recent experiment has found that very small amounts of water (as low as 40 ppm) can significantly affect the product formation in Li-O2 batteries as opposed to essentially no water (1 ppm). Although experimental as well as theoretical work has proposed mechanisms of Li2O2 formation in the presence of much larger amounts of water, none of the mechanisms provide an explanation for the observations for very small amounts of water. In this work, density functional theory (DFT) was utilized to obtain a mechanistic understanding of the Li-O2 discharge chemistry in a dimethoxyethane (DME) electrolyte containing an isolated water and no water. The reaction pathways for Li2O2 formation from LiO2 on a model system were carefully evaluated with different level of theories, i.e. PBE (PW), B3LYP/6-31G(2df,p), B3LYP/6-311++G(2df,p) and G4MP2. The results indicate that the LiO2 disproportionation reaction to Li2O2 can be promoted by the water in DME electrolyte, which explains why there is a significant difference compared to when no water is present in the experimentally observed discharge product distributions. Ab initio molecular dynamics calculations were also used to investigate the disproportionation of LiO2 dimer in explicit DME. This work adds to the fundamental understanding of the discharge chemistry of a Li-O2 battery.

Metal-organic frameworks (MOFs) are promising materials for electrocatalysis; however, lack of electrical conductivity in the majority of existing MOFs limits their effective utilization in the field. Herein, an excellent catalytic activity of a 2D copper (Cu)-based conductive MOF, copper tetrahydroxyquinone (CuTHQ), is reported for aqueous CO

In this paper, a novel heat pump system is proposed, which operates as a heat-source-tower heat pump with no frosting in winter, and as a hybrid refrigerant system consisting of a conventional chiller combined with a liquid desiccant dehumidification and evaporative cooling subsystem in summer. A validated mathematical model of the proposed system operating in summer is established to investigate the effects of key parameters, including solution to refrigerant flow ratio (FR), condensation heat recovery ratio (Rcond) and ambient parameters, on the cooling performance. Besides, this paper analyzes key factors that should be considered in designing the heat exchange area of the solution-cooled condenser (SCC). The results show that the maximum COP and ECOP of the heat pump system are 13.4% and 10.3% higher than those of conventional vapor compression refrigerant systems under the typical summer condition of Nanjing, respectively. The recommended range of FR is from 1.2 to 6 and that for Rcond is from 16% to 40%. Moreover, the proposed system is more superior to conventional ones when applied in hot and humid regions.

Cyclic step-catalysis enables intermittent, atmospheric ammonia production, and can be integrated with sustainable and renewable energy sources. By employing metal (e.g., Mn) nitride, a nitrogen ca...

Three-dimensionally (3D) ordered macro-/mesoporous (3DOM/m) materials, which combine the advantages of high surface area of the mesopores, efficient mass transport within the macropores, and strong structural stability of the 3D interconnected porous frameworks, have shown remarkable performances in a wide range of applications. Herein, we demonstrate a novel dual-hard-templating technique as a general synthetic strategy for constructing the 3DOM/m materials by nanocasting mesoporous silica confined within the regular voids of a silica colloidal crystal (opal). Through this method, various materials, such as 3DOM/m Pt, Pd, Ni2P, carbon and N/P codoped carbon (NPC), have been successfully synthesized. The as-prepared 3DOM/m Ni2P and NPC are demonstrated to exhibit outstanding electrocatalytic performance for the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR), respectively.

Lithium-oxygen batteries are among the most attractive alternatives for future electrified transportation. However, their practical application is hindered by many obstacles. Due to the insulating nature of Li

Electrochemical reduction of furfural (ECRFF) emerges as an efficient and sustainable means to obtain high-value chemicals and biofuels with the activity and product selectivity being sensitive to cathode materials. In this work, elementary steps describing furfuryl alcohol (FA) and 2-methylfuran (MF) production routes in ECRFF are studied by using periodic density functional theory on Ag, Pb, and Ni, as alternative cathode materials. The established Bronsted–Evans–Polanyi (BEP) relationship has been proven to be reliable to estimate energy barriers of C–O bond cleavage. The intrinsic characters of Ag, Pb, and Ni are then summarized in free energy diagrams to reflect the FA and MF production trends as future guidelines to evaluate ECRFF activity and selectivity on these metals. On all metal surfaces, at both terrace and stepped sites, the first C–H or O–H hydrogenation step, producing respective mh6 or mh7 intermediates, influences overall FA production. On Ag and Pb, pathways involving the mh6 intermedia...

In the past thirty years, molecular simulation techniques centred on density functional theory (DFT) calculations have quickly become a powerful research and technology development instrument. In p...

Glycerol is an extremely versatile platform molecule for chemical and fuel production, as evidenced by successful demonstrations in electrochemical and thermochemical processes, where key catalytic chemistries occur at the solid-liquid interface. Despite the remarkable progress made in enriching the first-principles-based computational tool set to reveal and characterize solvent structures in the past decade, techniques for realistic and efficient molecular-level modeling to study aqueous-phase glycerol chemistry are still far from mature. Many aqueous-phase catalytic systems are deemed too complex for routine modeling because of their highly correlated structures at the heterogeneous solid-liquid interface. This invited feature article merges recent developments in quantum mechanical solvation models and oxygenated hydrocarbon conversion chemistry by revisiting the molecular interactions of adsorbed glycerol and its dehydrogenation intermediates at the water-metal interface. Explicit participation of water through the establishment of water-adsorbate, water-water, and water-metal interactions on Pt(111) was investigated using density functional theory. In periodic models, the adsorption favors networklike structures with adsorbates as nodal points linked by coadsorbed water molecules. We also showed that these adsorption patterns actually preserve the original bond-order-based scaling relationship framework established without the consideration of solvent. This behavior can be exploited to improve computational efficiency for future analysis of catalytic polyol conversions in the aqueous-phase environment.

Metal-organic frameworks (MOFs) are promising materials for electrocatalysis; however, lack of electrical conductivity in the majority of existing MOFs limits their effective utilization in the field. Herein, an excellent catalytic activity of a 2D copper (Cu)-based conductive MOF, copper tetrahydroxyquinone (CuTHQ), is reported for aqueous CO2 reduction reaction (CO2 RR) at low overpotentials. It is revealed that CuTHQ nanoflakes (NFs) with an average lateral size of 140 nm exhibit a negligible overpotential of 16 mV for the activation of this reaction, a high current density of ≈173 mA cm-2 at -0.45 V versus RHE, an average Faradaic efficiency (F.E.) of ≈91% toward CO production, and a remarkable turnover frequency as high as ≈20.82 s-1 . In the low overpotential range, the obtained CO formation current density is more than 35 and 25 times higher compared to state-of-the-art MOF and MOF-derived catalysts, respectively. The operando Cu K-edge X-ray absorption near edge spectroscopy and density functional theory calculations reveal the existence of reduced Cu (Cu+ ) during CO2 RR which reversibly returns to Cu2+ after the reaction. The outstanding CO2 catalytic functionality of conductive MOFs (c-MOFs) can open a way toward high-energy-density electrochemical systems.

Three-dimensionally ordered mesoporous carbon sphere array (OMCS)-supported Pt nanoparticles (Pt/OMCS) were synthesized and studied as electrocatalysts for the methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR). In the Pt/OMCS, the Pt particles with a mean size of ∼1.6 nm are homogeneously dispersed on the mesopore walls of the carbon spheres. The Pt/OMCS catalyst exhibits smaller Pt particle size, greater Pt dispersion, larger specific electrochemically active surface area (ECSA), higher activity for MOR and ORR, and better electrocatalytic stability than the carbon black (Vulcan XC-72R)-supported Pt and commercial Pt/C catalysts.

Three dimensionally ordered macro-/mesoporous (3DOM/m) Pt catalysts are fabricated by chemical reduction employing a dual-templating synthesis approach combining both colloidal crystal (opal) templating (hard-templating) and lyotropic liquid crystal templating (soft-templating) techniques. The macropore walls of the prepared 3DOM/m Pt exhibit a uniform mesoporous structure composed of polycrystalline Pt nanoparticles. Both the size of the mesopores and Pt nanocrystallites are in the range of 3–5 nm. The 3DOM/m Pt catalyst shows a larger electrochemically active surface area (ECSA), and higher catalytic activity as well as better poisoning tolerance for methanol oxidation reaction (MOR) than the commercial Pt black catalyst.

Nowadays, the social competition is becoming fiercer and fiercer, the competition pressures and working pressures of the working group obviously increased. With the increase of pressure in the working group, the occupational groups in all walks have different levels of job burnout,not excepting the civil servants. Grass-roots civil servants are the basic management of the public affairs, which is the direct power of the government functions.Their works are complicated, and a considerable part of people are in the high work pressure environment, physical and mental fatigue, which is harmful to the health and affects the organization efficiency. Therefore, we need to give much attention to the problem of occupational burnout, and explore the reasonable intervention measures to effectively protect the physical and mental health of the grass-roots civil servants, and promote the scientific development and orderly conduct of basic public management.

A facile biomolecule-assisted hydrothermal route has been demonstrated to grow γ-MnS multipods at 130 °C for 10 h in distilled water when l -cystine was used as both the sulfur source and complexing agent. The products were characterized by XRD, SEM, TEM and photoluminescence. The results indicate that the as-synthesized γ-MnS multipods are composed of single-crystal, hexagonal and prism-like rods with a size of ca. 300–800 nm and a length of 2–4 μm. The room-temperature photoluminescence spectrum exhibits a peak centered at 419 nm corresponding to the band edge emission when the sample was excited with a wavelength of 358 nm. A possible formation mechanism for the γ-MnS multipods was also discussed based on the time-dependent experiments.

Chain-like MoS2 assemblies consisting of hexagonal MoS2 nanoparticles (20–60 nm) have been successfully synthesized in a Triton X-100/cyclohexane/hexanol/water W/O reverse microemulsion in the presence of (NH4)2MoS4 as the molybdenum source and NH2OH·HCl as the reducing agent. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and UV-vis diffuse reflectance absorption spectra. The influence of synthetic parameters such as acidity, water/oil ratio (ω0), aging time and annealing temperature on the formation of MoS2 assemblies was investigated. TEM analysis showed that these synthetic factors played important roles in controlling the size of MoS2 nanoparticles and the length of the chain-like MoS2 assemblies. XRD analysis indicated that the well-crystallized MoS2 nanoparticles could be obtained by annealing the precursors at 700°C for 2 h under a flow of N2 atmosphere. In addition, the as-prepared chain-like MoS2 nanoparticles exhibited excellent photocatalytic H2 activity in Ru(bpy)32+-MoS2-H2A three-component molecular systems under visible light irradiation.

High-aspect-ratio of worm-like Ag 2 S nanocrystal with length up to several micrometers and a diameter of 25–50 nm has been successfully prepared by a Triton X-100/cyclohexane/hexanol/water W/O reverse microemulsion in the presence of TAA (Thioacetamide) as a sulfur source and EDTA (ethylene diamine tetraacetic acid) as a chelating ligand. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and UV–vis diffuse reflectance absorption spectra. The results indicate that the morphology and size of Ag 2 S nanocrystal can be readily controlled by modulating the mole ratio of Ag + to EDTA, the molar ratio of water to surfactant (ω 0 ), and the aging time.

Furfural is a significant platform compound derived from biomass. Electrocatalytic reduction of furfural on transition metals emerges as a sustainable approach compared to heterogeneous catalysis to obtain valuable chemicals and fuels, such as furfuryl alcohol (FA) and 2-methylfuran (MF). Although the product selectivity was shown to be strongly depended on the intrinsic properties of the transition metal electrodes, similar as CO2 reduction, the complex chemical nature of furfural presents challenges to investigate the reaction mechanisms, which are still under debate. Density functional theory (DFT) calculations have been performed for electrocatalytic reduction of furfural to FA and MF on the close-packed (111) and stepped (211) surfaces of Cu, Ag, Pb, and Ni electrodes. The elementary reaction steps have been evaluated based on computational hydrogen electrode (CHE) model. A novel Brønsted–Evans–Polanyi (BEP) relationship has been established for C-O bond cleavage which is necessary for MF production. On Cu, Ag, Pb, and Ni, at both terrace and stepped sites, the first hydrogenation step of C=O, leading to mh6 or mh7 formation, influences the overall reaction activity and product selectivity. It has been found that the pathway via mh6 is more competitive than that via mh7 for FA formation on Cu, Ag, and Pb, whereas on Ni, both mh6 and mh7 routes are competitive due to strong interactions between the furan ring and the substrate. The C-O bond cleavages of furfural, the partially hydrogenated intermediates (mh6 and mh7) and FA were considered as the parallel pathways to produce MF besides FA formation pathways. It is well-known that solvation can facilitate the hydrogenation reactions involving proton-electron pairs. In this work, solvation was confirmed to decrease the C-O bond cleavage energy barriers, which could boost MF production and potentially tune the product selectivity on transition metal electrodes.

In recent years, with the seriously ecological pollution, environmental problem has become one of the concerns about the topic. Hebei province is a region of high energy consumption, high pollution, in order to guarantee the quality of people's living environment, the ecological environment in Hebei province sustainable research is imperative. Through the evaluation and analysis of ecological environment of Hebei province, promote the sustainable development of the ecological environment in the region. This paper selects indicators for the sustainable development of ecological environment, establishes the suitable index system, combines with the data which are premised on the Chinese Environment Yearbook 2009-2013, and applies the gray correlation degree analysis method to calculate the index correlation coefficient and weighted incidence degree. Finally, it can get the index ranking of sustainable ability of ecological environment of Hebei Province for nearly five years. Combining with source data analysis and comparison results to find the reason for ecological environment advantages and disadvantage. Finally,according to the conclusion that ecological environment is unsustainable to put forward countermeasures. This study provides a theoretical guidance to strengthen the construction of ecological environment, to promote the harmonious development of economy, society and the environment.

In recent years,with the rapid development of network information,the ways of people contacting and paying attention to the political news are more much and available.The corruption has become a focus problem of the society,and numerous official corruption also frequently reported through the media.Considering the huge damage to the government and the society, the central government also pay more attention to the anti-corruption work, and promote anti-corruption.To the problem of civil servants corruption, this paper uses the method of dynamic game and analyses the two civil servants and government's costs and expected returns in the process of civil servants corruption,Nash equilibrium of the main benefit maximization. According to the basic conclusions,we put forward the policy suggestion of the prevention of corruption to echo government work better and purify officialdom atmosphere.

The developing of the globalization of the world economy and regional economic integration, makes China, which is in the period of social transformation, have the situation such as: professional norms empty, professional norms confliction, professional norms unclear, professional norms dysfunctional. With the fuzzy mathematics theory, the paper sets up a quantitative model .in the process of establishing the model, through experts scoring, using the analytic hierarchy process confirms the weight of each index system,finally the paper calculates the evaluation result.Then we apply the above results into a score P, which measure the organizational human resource professional norms system is sound and reasonable or not,in order to provide guidance and reference for building an excellence professional norms system. Using this method not only realizes the professional norms transformation from quantitative research to qualitative research,so that the model is more scientific、 authoritative、maneuverability,and avoid the subjective factors playing a leading role in establishing the professional norms system. KeyWords-Human Resources;professional norms ;Fuzzy Comprehensive Evaluation Model;experts scoring;analytic hierarchy process

Novel magnetic Co chains with lengths of up to 10–100 μm, self-assembled by cross-linked hexagonal Co microflakes with an average diameter of 2–10 μm and a thickness of about 130 nm, have been solvothermally prepared in the mixed solution of ethylene glycol and ethylenediamine with polyvinyl pyrrolidone (PVP) and dodecanethiol as surfactant. The products were characterized by XRD, EDS, SEM, TEM, HRTEM and SQUID methods. The Co microchains exhibit a ferromagnetic characteristic with the coercivity of 148.8 Oe at room temperature, over fourteen orders of magnitude larger than that of bulk Co counterpart. The simple and high yield synthetic technique can be applied to the fabrication of other metals with complex hierarchical structures.