Electrochemical exfoliation of two-dimensional layered black phosphorus and applications

With the discovery of graphene,black phosphorus(BP)has been rediscovered as a two-dimensional(2 D)layered material.Since its first preparation in 2014,2 D BP has elicited immense interest,and has exhibited excellent properties,such as distinct pleated structures in layers,adjustable direct bandgap,high carrier mobility,moderate on/off ratio,large specific surface area,and various interesting in-layer anisotropies.However,the realization of these excellent properties depends on the preparation of highquality 2 D BP sheets.Electrochemical exfoliation methods are typically performed under mild conditions,thus,these methods are convenient,controllable,and can produce high-quality 2 D BP sheets.This review summarizes research progress in BP sheets preparation through anodic,cathodic,and electrolyte exfoliation in recent years.Different exfoliating methods affect the quality of 2 D BP sheets.Moreover,possible exfoliating mechanisms and the potential applications of different exfoliating methods are summarized and discussed in detail.Lastly,the shortcomings of existing research on electrochemical exfoliation are presented,and suggestions and prospects for future research on the electrochemical exfoliation of 2 D BP are proposed.

Optimization of Process Parameters of Laser Cladding 304L Alloy Powder Based on Orthogonal Experiment

In order to find the optimal combination of process parameters for laser cladding 304L alloy powder on the surface of 45 steel,a combination method of single factor test and multi-factor orthogonal experiment was used to perform the single pulse laser cladding experiment.The effects of process parameters(pulse current A,pulse width B,pulse frequency C,defocus distance D,scan velocity E)on the morphology and performance of cladding layer was studied by range analysis,and the optimal combination of cladding parameters is calculated by fuzzy comprehensive evaluation.The results show that different process parameters have different effects on the morphology of the cladding layer and scanning velocity E and defocus distance D are the most important influencing factor of cladding morphology.The effect on cladding width is D>C>A>B>E and the effect on cladding height is E>A>C>D>B.The optimal combination of cladding width is A4B4C4D4E2.The optimal combination of cladding high is A2B1C1D4E1.The comprehensive optimal process parameters are pulse current 210A,pulse width 3.6ms,pulse frequency 16Hz,defocus distance+10mm and scanning speed 240mm/min.The average hardness of the cladding layer,melting pool,heat-affected zone and substrate under the optimal process parameters is 406.2 HV0.5,470.8 HV0.5,230.5HV0.5 and 202.0HV0.5,respectively.The 304L cladding layer on 45 steel surface is stable in width,height and surface quality under comprehensive optimal parameters.

Techno-Economic Study on an Energy System in Northwest China

A combined system of heating, power and biogas (CHPB) system has been developed and tested in a single building in MinQin County, Gansu Province, China. The proposed system satisfies the user’s demand of power, heat, and gas. The CHPB system can effectively overcome seasonal, climate and many other factors which affect the production of the renewable energy. For this purpose, experiments were conducted extensively during the winter period from November 2014 to March 2015. Compared with conventional energy supply systems meets the test household indoor temperature level, the system can reduce the consumption of standard coal 5819.30 kg/year, and save energy costs 11,046.20 yuan/year, the system’s payback period of 4.37 years, also can save 27.03 tons of carbon dioxide emissions. As a result, the CHPB system have been successfully tested for single building, use solar energy and biomass as input and produce power, heat, and gas steadily. These results contributed to the construction of energy supply systems.

Dynamics of non-metal-regulated FeCo bimetal microenvironment on oxygen reduction reaction activity and intrinsic mechanism

The change in the coordination environment of the active sites of a fuel cell cathode catalyst provides a new modulation strategy for stimulating the catalyst’s oxygen reduction reaction activity.The thermodynamic and electronic properties of the FeCoN5A and FeCoN6A catalyst structures with nonmetallic A-doped(A=B,N,O,P,and S)coordination were calculated and analyzed based on density functional theory.The modulation order of G*OH by different A-doped FeCo bimetal pairs(BMPs)was as follows:S>P>O>N/C>B.There was a dynamic distribution of charges in the coordination environment during the adsorption of OH,which resulted in inversely proportional relationship with the charge transfer between the adsorbate OH,active site,first coordination layer,and second coordination layer in turn.Descriptors of the orbital energy levels of neighboring nonmetal atoms were constructed based on the p-electron number and electronegativity of the doped nonmetal A.The change of the orbital energy levels of the first coordination atom during the adsorption process caused the structure to exhibit different adsorption energies.This study provides new insights on the non-metallic modulation of the M-N-C coordination environment to improve the oxygen reduction reaction activity.

Progress in research on metal-based materials in stabilized Zn anodes

Aqueous zinc-ion batteries(ZIBs) combine the benefits of metallic Zn anodes with those of aqueous electrolytes and are well suited for large-scale energy storage because of their inherent high safety, cost-effectiveness, and eco-friendliness. Currently, the practical application of such batteries is hindered by the poor cycling performance of Zn anodes due to uncontrolled dendrite formation and severe side reactions, although recent reports suggest that these problems can be mitigated through the modification of Zn anodes with metal-based materials.Given that the mechanisms of improving Zn deposition and the structural evolution of metal-based materials have not been systematically reviewed, we herein systematically overview the metal-based materials used to stabilize Zn anodes, starting with a brief summary of the anode working mechanism and the challenges faced by stabilized Zn anodes. Subsequently, the design principles of Zn anodes stabilized by metal-based materials and the related recent progress are reviewed, and the key challenges and perspectives for the future development of such Zn anodes are proposed.

Thermal-Hydraulic Characteristics of Twisted Elliptical Tube Bundle in Staggered Arrangement

Based on experimental data,numerical simulations by turbulent air flowing across staggered tube bundle composed of twisted elliptical tube(TET)with constant tube wall temperature are conducted in present study.Parametric study on the thermal-hydraulic characteristics of air crossflow in TET bundles is investigated with physical parameters and Reynolds number(Re).The results show that spiral channels created by spiral deformation of TETs have a diversion effect on the air flow,which changes the flow direction of the air near the tube wall.The air in the near wall region is a three-dimensional flow,consisting of a flow perpendicular to the normal direction of the elliptical cross section and a spiral flow along the helicoid on the downstream side and the upstream side.And the interaction of the spiral channels makes the two flows and their mixing more complicated.The excellent heat transfer performance of staggered TET bundles is confirmed by the comparison of the comprehensive heat transfer performance with that of circular tube bundles.The average Nusselt number(Nu)increases with the increase of the aspect ratio(A/B)and with the increase of Re while decreases as the twist pitch(S)increases.The average Euler number(Eu)increases as A/B increases,while it decreases as Re increases and as S increases.Due to the fact that the suitable correlations for staggered TET bundles are not reported,correlations for Nu and Eu obtained from experimental data and numerical results are presented in the multiple forms.

Research progress on electrolytes for fast-charging lithium-ion batteries

Fast-charging is considered to be a key factor in the successful expansion and use of electric vehicles.Current lithium-ion batteries(LIBs)exhibit high energy density,enabling them to be used in electric vehicles(EVs)over long distances,but they take too long to charge.In addition to modifying the electrode and battery structure,the composition of the electrolyte also affects the fast-charging capability of LIBs.This review provides a comprehensive and in-depth overview of the research progress,basic mechanism,scientific challenges and design strategies of the new fast-charging solution system,focusing on the influences that the compositions of liquid and solid electrolytes have on the fast-charging performance of LIBs.Finally,new insights,promising directions and potential solutions for the electrolytes of fast-charging systems are proposed to stimulate further research on revolutionary next-generation fastcharging LIB chemistry.