Surface/interface engineering of high-efficiency noble metal-free electrocatalysts for energy-related electrochemical reactions

To date,much efforts have been devoted to the high-efficiency noble metal-free electrocatalysts for hydrogen-and oxygen-involving energy conversion reactions,due to their abundance,low cost and nultifunctionally.Surface/interface engineering is found to be effective in achieving novel physicochemical properties and synergistic effects in nanomaterials for electrocatalysis.Among various engineering strategies,heteroatom-doping has been regarded as a most promising method to improve the electrocatalytic performance via the regulation of electronic structure of catalysts,and numerous works were reported on the synthesis method and mechanism investigation of heteroatom-doping electrocatalysts,though the heteroatom-doping can only provide limited active sites.Engineering of other defects such as vacancies and edge sites and construction of heterostructure have shown to open up a potential avenue for the development of noble metal-free electrocatalysts.In addition,surface functionalization can attach various molecules onto the surface of materials to easily modify their physical or chemical properties,being as a promising complement or substitute for offering materials with catalytic properties.This paper gives the insights into the diverse strategies of surface/interface engineering of the highefficiency noble metal-free electrocatalysts for energy-related electrochemical reactions.The significant advances are summarized.The unique advantages and mechanisms for specific applications are highlighted.The current challenges and outlook of this growing field are also discussed.

Regulating non-precious transition metal nitrides bifunctional electrocatalysts through surface/interface nanoengineering for air-cathodes of Zn-air batteries

Zn-air batteries(ZABs),especially the secondary batteries,have engrossed a great interest because of its high specific energy,economical and high safety.However,due to the insufficient activity and stability of bifunctional electrocatalysts for air-cathode oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)processes,the practical application of rechargeable ZABs is seriously hindered.In the effort of developing high active,stable and cost-effective electrocatalysts,transition metal nitrides(TMNs)have been regarded as the candidates due to their high conductivity,strong corrosion-resistance,and bifunctional catalytic performance.In this paper,the research progress in TMNs-based material as ORR and OER electrocatalysts for ZABs is discussed with respect to their synthesis,chemical/physical characterization,and performance validation/optimization.The surface/interface nanoengineering strategies such as defect engineering,support binding,heteroatom introduction,crystal plane orientation,interface construction and small size effect,the physical and chemical properties of TMNs-based electrocatalysts are emphasized with respect to their structures/morphologies,composition,electrical conductivity,specific surface area,chemical stability and corrosion resistance.The challenges of TMNs-based materials as bifunctional air-cathode electrocatalysts in practical application are evaluated,and numerous research guidelines to solve these problems are put forward for facilitating further research and development.

Polar interface and surface optical vibration spectra in multi-layer wurtzite quantum wires： transfer matrix method

The polar interface optical （IO） and surface optical （SO） phonon modes and the corresponding Froehlich electron phonon-interaction Hamiltonian in a freestanding multi-layer wurtzite cylindrical quantum wire （QWR） are derived and studied by employing the transfer matrix method in the dielectric continuum approximation and Loudon＇s uniaxial crystal model. A numerical calculation of a freestanding wurtzite GaN/AlN QWR is performed. The results reveal that for a relatively large azimuthal quantum number m or wave-number kz in the free z-direction, there exist two branches of IO phonon modes localized at the interface, and only one branch of SO mode localized at the surface in the system. The degenerating behaviours of the IO and SO phonon modes in the wurtzite QWR have also been clearly observed for a small kz or m. The limiting frequency properties of the IO and SO modes for large kz and m have been explained reasonably from the mathematical and physical viewpoints. The calculations of electron-phonon coupling functions show that the high-frequency IO phonon branch and SO mode play a more important role in the electron phonon interaction.

Elastic behavior of disclination dipole near nanotube with surface/interface effect

In this paper, we present an analytical solution of the interaction of the nanotube （NT） with a wedge disclination dipole in nanotube-based composites. The corresponding boundary value problem is solved exactly by using complex potential functions. The explicit expression of the force exerted on disclination dipole is given by using the generalized Peach- Koehler formula. As a numerical illustration, both the equilibrium position and the stability of the disclination dipole are evaluated for different material combinations, relative thickness of an NT, surface/interface effects, and the features of the disclination dipole. The results show that as the thickness of the NT layer increases, the NT has a relatively major role in the force acting on the disclination dipole in the NT-based composite. The cooperative effect of surface/interface stresses and the NT becomes considerable as the increase of NT layer thickness. The equilibrium position may occur, even more than one, due to the influences of the surface/interface stress and the NT thickening. The influences of the surface/interface stresses and the thickness of the NT layer on the force are greatly dependent on the disclination angle.

Geometric shapes of the interface surface of bicomponent flows between two concentric rotating cylinders

In this paper, the shape problem of interface of bicomponent flows between two concentric rotating cylinders is investigated. With tensor analysis, the problem is reduced to an energy functional isoperimetric problem when neglecting the effects of the dissipative energy caused by viscosity. We derive the associated Euler-Lagrangian equation, which is a nonlinear elliptic boundary value problem of the second order. Moreover, by considering the effects of the dissipative energy, we propose another total energy functional to characterize the geometric shape of the interface, and obtain the corresponding Euler-Lagrangian equation, which is also a nonlinear elliptic boundary value problem of the second order. Thus, the problem of the geometric shape is converted into a nonlinear boundary value problem of the second order in both cases.

Contribution of Surface Defects to the Interface Conductivity of SrTiO_3/LaAlO_3

Based on the first-principles method, the structural stability and the contribution of point defects such as O, Sr or Ti vacancies on two-dimensional electron gas of n- and p-type LaAlO3/SrTiO3 interfaces are investigated. The results show that O vacancies at p-type interfaces have much lower formation energies, and Sr or Ti vacancies at n-type interfaces are more stable than the ones at p-type interfaces under O-rich conditions. The calculated densities of states indicate that O vacancies act as donors and give a significant compensation to hole carriers, resulting in insulating behavior at p-type interfaces. In contrast, Sr or Ti vacancies tend to trap electrons and behave as acceptors. Sr vacancies are the most stable defects at high oxygen partial pressures, and the Sr vacancies rather than Ti vacancies are responsible for the insulator-metal transition of n-type interface. The calculated results can be helpful to understand the tuned electronic properties of LaAlO3 /SrTiO3 heterointerfaces.

Regulating interfacial chemistry and kinetic behaviors of F/Mo co-doping Ni-rich layered oxide cathode for long-cycling lithium-ion batteries over-20°C-60°C

Ni-rich layered oxide cathodes have shown promise for high-energy lithium-ion batteries(LIBs)but are usually limited to mild environments because of their rapid performance degradation under extreme temperature conditions(below0°C and above 50 °C).Here,we report the design of F/Mo co-doped LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)(FMNCM)cathode for high-performance LIBs from-20 to 60°C.F^(-) doping with high electronegativity into the cathode surface is found to enhance the stability of surface lattice structure and protect the interface from side reactions with the electrolyte by generating a LiF-rich surface layer.Concurrently,the Mo^(6+) doping suppresses phase transition,which blocks Li^(+)/Ni^(2+) mixing,and stabilizes lithium-ion diffusion pathway.Remarkably,the FMNCM cathode demonstrates excellent cycling stability at a high cutoff voltage of 4.4 V,even at 60°C,maintaining 90.6%capacity retention at 3 C after 150 cycles.Additionally,at temperatures as low as-20°C,it retains 77.1%of its room temperature capacity,achieving an impressive 97.5%capacity retention after 500 cycles.Such stable operation under wide temperatures has been further validated in practical Ah-level pouch-cells.This study sheds light on both fundamental mechanisms and practical implications for the design of advanced cathode materials for wide-temperature LIBs,presenting a promising path towards high-energy and long-cycling LIBs with temperatureadaptability.

Tailoring the surface and interface structures of photocatalysts to enhance hydrogen production

Photocatalytic water splitting using semiconductor photocatalysts is a promising approach for the production of carbon-neutral,sustainable and clean hydrogen fuel.However,the separation and transport of photoinduced carriers are generally considered to be rate-limiting steps,and their low efficiency remains a major challenge.Therefore,much effort has been devoted to developing new strategies in surface/interface engineering of photocatalysts to improve the dynamics of charge separation/transport.This feature article briefly summarizes recent advances in photocatalyst surface/interface engineering by our research group,which have been achieved through the design of various novel photocatalysts,including interfacial modulation,heterostructure construction,heteroatom doping,single atom and diatom sites.The article is divided into three parts:first,we briefly introduce the three key processes involved in solar water splitting and reveal relationships between the properties of nanostructural photocatalysts and the fundamentals of water splitting;second,we detail methods and strategies for surface and interfacial structures to improve the efficiency of the fundamental processes,especially charge separation;finally,we explore prospects for photocatalytic water splitting applications.This article provides a valuable resource and strategies for researchers currently working in the field of photocatalytic water splitting.

First-principles calculations on Si(220) located 6H–SiC(10■0)surface with different stacking sites

6H-SiC （1010） surface and Si （220）/6H-SIC （1010） interface with different stacking sites are investigated using first-principles calculations. Surface energies of 6H-SiC （1010） （case I, case II, and case III） are firstly studied and the surface calculation results show that case II and case III are more stable than case I. Then, the adhesion energies, fracture toughness values, interfacial energies, densities of states, and electronic structures of Si （220）/6H-SIC （1010） interfaces for three stacking models （AM, BM, and CM） are calculated. The CM model has the highest adhesion energy and the lowest interracial energy, suggesting that the CM is stronger and more thermodynamically stable than AM and BM. Densities of states and the total charge densities give evidence that interfacial bonding is formed at the interface and that Si-Si and Si-C are induced due to the hybridization of C-2p and Si-3p. Moreover, the Si-C is much stronger than Si-Si at the interface, implying that the contribution of the interfacial bonding mainly comes from Si-C rather than Si-Si.

Effects of nano-voids and nano-cracks on the elastic properties of a host medium: xfem modeling with level-set function and free surface energy

This work deals with the influences of nano-heterogeneities in the form of voids/cavities or cracks on the elastic (please confirm which word is correct. effective or elastic? According to the title of paper, I choose elastic.) properties of a host medium. With a relatively large ratio of apparent-surface to volume and particularly strong physical interactions with the surrounding medium at nano-scale, nano-heterogeneities can potentially affect the elastic(effective or elastic?) properties of the parent medium (matrix) containing them in a significant manner. This has been reported by various theoretical and experimental studies, some of them are discussed in the present paper. To describe the positive (reinforcement) or negative (degradation) effect of the nano-heterogeneities from the modeling perspective, it is necessary to take into account the energy of interfaces/surfaces between nano-heterogeneities and the matrix which, by the fact of the relatively large extent of their apparent surface and their strong physical interaction with their neighborhood, can no longer be neglected compared to those of the volume energy. Thus, to account for the effects of interfaces/surfaces in a nanostructured heterogeneous medium, the coherent interface model is considered in the present investigation within a periodic homogenization procedure. In this interface/surface model, the displacement vector is assumed to be continuous across the interface while the stress vector is considered to be discontinuous and satisfying the Laplace-Young equations. To solve these equations coupled to the classical mechanical equilibrium problem, a numerical simulation tool is developed in a two-dimensional (2D) context using the eXtended Finite Element Method (XFEM) and the Level-Set functions. The developed numerical tool is then used to carry out a detailed analysis about the effect of nano-heterogeneities on the overall mechanical properties of a medium. The nano-heterogeneities are present in the medium initially as cylindrical cavities (circular in 2D) before being reduced to plane cracks (line in 2D) by successive flattenings.

Ultrasonic image restoration based on support vector machine for surfacing interface testing

In order to restore the degraded ultrasonic C-scan image for testing surfacing inteoface, a method based on support vector regression （SVR） network is proposed. By using the image of a simulating defect, the network is trained and a mapping relationship between the degraded and restored image is founded. The degraded C-scan image of Cu-Steel surfacing inteoface is processed by the trained network and improved image is obtained. The result shows that the method can effectively suppress the noise and deblur the defect edge in the image, and provide technique support for quality and reliability evaluation of the surfacing weld.

Optimizing the electronic spin state and delocalized electron of NiCo_(2)(OH)_(x)/MXene composite by interface engineering and plasma boosting oxygen evolution reaction

The electrocatalytic activity of transition-metal-based compounds is closely related to the electronic configuration.However,optimizing the surface electron spin state of catalysts remains a challenge.Here,we developed a spin-state and delocalized electron regulation method to optimize oxygen evolution reaction(OER)performance by in-situ growth of NiCo_(2)(OH)_(x) using Oswald ripening and coordinating etching process on MXene and plasma treatment.X-ray absorption spectroscopy,magnetic tests and electron paramagnetic resonance reveal that the coupling of NiCo_(2)(OH)_(x) and MXene can induce remarkable spin-state transition of Co^(3+)and transition metal ions electron delocalization,plasma treatment further optimizes the 3 d orbital structure and delocalized electron density.The unique Jahn-Teller phenomenon can be brought by the intermediate spin state(t2 _(g)^(5) e_(g)^(1))of Co^(3+),which benefits from the partial electron occupied egorbitals.This distinct electron configuration(t2_(g)^(5) e_(g)^(1))with unpaired electrons leads to orbital degeneracy,that the adsorption free energy of intermediate species and conductivity were further optimized.The optimized electrocatalyst exhibits excellent OER activity with an overpotential of 268 m V at 10 m A cm^(-2).DFT calculations show that plasma treatment can effectively regulate the d-band center of TMs to optimize the adsorption and improve the OER activity.This approach could guide the rational design and discovery of electrocatalysts with ideal electron configurations in the future.

Tailoring interphase structure to enable high-rate, durable sodium-ion battery cathode

Na-based layered transition metal oxides with O_(3)-type structure have been considered to be promising cathodes for Na-ion batteries. However, the intrinsically limited Na-ion conductivity induced by the Otype Na-coordinate environment compromises their rate and cycle capability, hindering their practical application. Here, we report an interphase-structure tailoring strategy that improves the electrochemical properties of O_(3)-type layered cathodes achieved through surface coating and doping processes.Specifically, a Zr-doped interphase structure is designed in the model compound NaNi_(1/3)Mn_(1/3)Fe_(1/3)O_(2) using the ionic conductor Na_(3)Zr_(2)Si_(2)PO_(12) as the surface coating material and Zr-dopant provider. We discover that the modified NaNi_(1/3)Mn_(1/3)Fe_(1/3)O_(2)cathode shows a stable Na-storage structure as well as an enhanced rate/cycle capability. Combined with theoretical calculations, it is suggested that the superior electrochemical performances originate from the Zr-doped interphase structure, which has an enlarged Na layer spacing that forms favorable Na-ion diffusion channels. This work highlights a general material interface optimization method which opens a new perspective for fabricating high-performance electrodes for Na-ion batteries and beyond.

Effect of nano-oxide layers on the magnetoresistance of ultrathin permalloy films

Ta/NiFe/Ta ultrathin films with and without nano-oxide layers （NOLs） were prepared by magnetron sputtering followed by a vacuum annealing process. The influence of NOLs on the magnetoresistance （MR） ratio of ultrathin permalloy films was studied. The results show that the influence of grain size and textures on the MR ratio becomes weak when the thickness of the NiFe layer is below 15 nm. A higher MR ratio was observed for the thinner （〈 15 nm） NiFe film with NOLs. The MR ratio of a 10 nm NiFe film can be remarkably enhanced by NOLs. The enhanced MR ratio for these ultrathin films can be attributed to the enhanced specular reflection of conduction electrons.

Microstructure and mechanical properties of hot isostatically pressed cermets with TiN coatings

To increase the adhesion strength between the coating and the substrate, sintered Ti（C,N）-based cermets were selected and deposited with monolayer TiN using a multiarc ion-plating technique; subsequently, hot isostatic pressing （HIPhag） treatment was performed at 1000℃ using nitrogen pressure up to 110 MPa. The mechanical properties of cermets after a coating process and subsequent HIPing treatment have been evaluated with respect to the hardness, the residual stress, and the coating adhesion. The results show that atter the HIPing process, there was a higher increase ha critical load ha the TiN-coated cermets with lower surface roughness compared with those with higher surface roughness. In all cases, the residual stress was found to be compressive. The effects of substrate surface roughness and posttreatment on the adhesion strength of the coatings were thus investigated. It was also fotmd that the HIPing posttreatment process is well suited for hacreasing the adhesion strength between the coating and the substrate.

Surface/interface engineering of noble-metals and transition metal-based compounds for electrocatalytic applications

Surface/interface engineering plays an important role in improving the performance and economizing the cost and usage of electrocatalysts.In recent years,substantial progress has been achieved in designing and developing highly active electrocatalysts with the deepening understanding of surface and interface enhanced mechanism.In this review,recent development about optimizing the surface and interfacial structure in promoting the electrocatalytic activity of noble-metals and transition metal compounds is presented and the chemical enhancements are also described in detail.The relationship between the surface/interface structures(both atomic and electronic configuration)and the electrochemical behaviors has been discussed.Finally,personal perspectives have been proposed,highlighting the challenges and opportunities for future development in tuning the surface/interface active sites of electrocatalysts.We believe that this timely review will be beneficial to the construction of highly active and durable electrode materials through optimizing surface atomic arrangement and interfacial interaction,which can largely promote the development of next-generation clean energy conversion technologies.

Optimal interface surface determination for multi-axis freeform surface machining with both roughing and finishing

In the current practice of multi-axis machining of freeform surfaces, the interface surface between the roughing and finishing process is simply an offset surface of the nominal surface. While there have already been attempts at minimizing the machining time by considering the kinematic capacities of the machine tool and/or the physical constraints such as the cutting force, they all target independently at either the finishing or the roughing process alone and are based on the simple premise of an offset interface surface. Conceivably, since the total machining time should count that of both roughing and finishing process and both of them crucially depend on the interface surface, it is natural to ask if, under the same kinematic capacities and the same physical constraints, there is a nontrivial interface surface whose corresponding total machining time will be the minimum among all the possible（infinite） choices of interface surfaces, and this is the motivation behind the work of this paper. Specifically, with respect to the specific type of iso-planar milling for both roughing and finishing, we present a practical algorithm for determining such an optimal interface surface for an arbitrary freeform surface. While the algorithm is proposed for iso-planar milling, it can be easily adapted to other types of milling strategy such as contour milling. Both computer simulation and physical cutting experiments of the proposed method have convincingly demonstrated its advantages over the traditional simple offset method.

Research on Effect of Adding Nanomaterial to Propellant on Gun Barrel

The barrel lifes of three small caliber rifles were tested by using the propellant with nanomaterial and the standard propellant respectively. The test results show that the service life increases observably due to adding nanomaterial to the propellant. Then, the influence of the nanomaterial on the tube was researched by splitting the two barrels tested and detecting their inner surfaces. It was found that the erosion of the barrel bore is reduced observably by using the propellant with nanomaterial. And it makes the volume and the size of the gun chamber change less. Therefore, the barrel life can be prolonged by adding the nanomaterial in the propellant.

Surface and interface chemistry in metal‐free electrocatalysts for electrochemical CO_(2) reduction

The electrochemical reduction of carbon dioxide(CO_(2))into value‐added fuels and chemicals presents a sustainable route to alleviate CO_(2) emissions,promote carbon‐neutral cycles and reduce the dependence on fossil fuels.Considering the thermodynamic stability of the CO_(2) molecule and sluggish reaction kinetics,it is still a challenge to design highly efficient electrocatalysts for the CO_(2) reduction reaction(CO_(2)RR).It has been found that the surface and interface chemistry of electrocatalysts can modulate the electronic structure and increase the active sites,which is favorable for CO_(2) adsorption,electron transfer,mass transport,and optimizing adsorption strength of reaction intermediates.However,the effect of surface and interface chemistry on metal‐free electrocatalysts(MFEs)for CO_(2)RR has not been comprehensively reviewed.Herein,we discuss the importance of the surface and interface chemistry on MFEs for improving the electrochemical CO_(2)RR performance based on thermodynamic and kinetic views.The fundamentals and challenges of CO_(2)RR are firstly presented.Then,the recent advances of the surface and interface chemistry in improving reaction rate and overcoming reaction constraints are reviewed from regulating electronic structure,active sites,electron transfer,mass transport,and intermediate binding energy.Finally,the research challenges and prospects are proposed to suggest the future designs of advanced MFEs in CO_(2)RR.

Control Method for Steel Strip Roughness in Two-stand Temper Mill Rolling

How to control surface roughness of steel strip in a narrow range for a long time has become an important question because surface roughness would significantly influence the appearance of the products. However, there are few effective solutions to solve the problem currently. In this paper, considering both asperities of work roll pressing in and squeezing the steel strip, two asperity contact models including squeezing model and pressing in model in a two-stand temper mill rolling are established by using finite element method（FEM）. The simulation investigates the influences of multiple process parameters, such as work roll surface roughness, roll radius and roll force on the surface roughness of steel strip. The simulation results indicate that work rolls surface roughness and roll force play important roles in the products; furthermore, the effect of roll force in the first stand is opposite to the second. According to the analysis, a control method for steel strip surface roughness in a narrow range for a long time is proposed, which applies higher work roll roughness in the first stand and lower roll roughness in the second to make the steel strip roughness in a required narrow range. In the later stage of the production, decreasing the roll force in the first stand and increasing the roll force in the second stand guarantee the steel strip roughness relatively stable in a long time. The following experimental measurements on the surface topography and roughness of the steel strips during the whole process are also conducted. The results validate the simulation conclusions and prove the effect of the control method. The application of the proposed method in the steel strip production shows excellent performance including long service life of work roll and high finished product rate.