Research progress of transition metal compounds as bifunctional catalysts for zinc-air batteries

Zinc-air batteries(ZABs)are widely studied because of their high theoretical energy density,high battery voltage,environmental protection,and low price.However,the slow kinetics of oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)on the air electrode limits the further application of ZABs,so that how to develop a cheap,efficient,and stable catalyst with bifunctional catalytic activity is the key to solving the development of ZABs.Transition metal compounds are widely used as cathode materials for ZABs due to their low cost,high electrocatalytic activity,and stable structure.This review summarizes the research progress of transition metal compounds as bifunctional catalysts for ZABs.The development history,operation principle,and mechanism of ORR and OER reactions are introduced first.The application and development of transition metal compounds as bifunctional catalysts for ZABs in recent years are systematically introduced,including transition metal oxides(TMOs),transition metal nitrides(TMNs),transition metal sulfides(TMSs),transition metal carbides(TMCs),transition metal phosphates(TMPs),and others.In addition,the shortcomings of transition metal compounds as bifunctional catalysts for ZABs were summarized and reasonable design strategies and improvement measures were put forward,aiming at providing a reference for the design and construction of high-performance ZABs cathode materials.Finally,the challenges and future in this field are discussed and prospected.

A Review on Engineering Transition Metal Compound Catalysts to Accelerate the Redox Kinetics of Sulfur Cathodes for Lithium–Sulfur Batteries

Engineering transition metal compounds(TMCs)catalysts with excellent adsorption-catalytic ability has been one of the most effec-tive strategies to accelerate the redox kinetics of sulfur cathodes.Herein,this review focuses on engineering TMCs catalysts by cation doping/anion doping/dual doping,bimetallic/bi-anionic TMCs,and TMCs-based heterostructure composites.It is obvious that introducing cations/anions to TMCs or constructing heterostructure can boost adsorption-catalytic capacity by regulating the electronic structure including energy band,d/p-band center,electron filling,and valence state.Moreover,the elec-tronic structure of doped/dual-ionic TMCs are adjusted by inducing ions with different electronegativity,electron filling,and ion radius,resulting in electron redistribution,bonds reconstruction,induced vacancies due to the electronic interaction and changed crystal structure such as lat-tice spacing and lattice distortion.Different from the aforementioned two strategies,heterostructures are constructed by two types of TMCs with different Fermi energy levels,which causes built-in electric field and electrons transfer through the interface,and induces electron redistribution and arranged local atoms to regulate the electronic structure.Additionally,the lacking studies of the three strategies to comprehensively regulate electronic structure for improving catalytic performance are pointed out.It is believed that this review can guide the design of advanced TMCs catalysts for boosting redox of lithium sulfur batteries.

Examination of Polymeric Azomethine Compounds and Their Transition Metal Complexes by Using XRF and XRD Technique

In this study,the electronic transition properties and structural analysis of the metal complexes(Ni(Ⅱ),Co(Ⅱ),Cu(Ⅱ)and Mn(Ⅱ))of three different polymer ligands were performed by using XRF and X-ray diffraction(XRD)techniques,respectively.The structural analysis of the polymers and their complexes were performed by XRD technique and some of the polymers were found to be in the face-centred cubic(fcc)structure.In addition,the values of the present K X-ray intensity ratios are significantly greater than the values reported in literature.

Spontaneous Magnetic Transitions and Corresponding Magnetoelastic Properties of Intermetallic Compounds RMn_2Ge_2(R=Gd, Tb and Dy)

The spontaneous magnetic transitions and corresponding magnetoelastic properties of intermetallic compounds RMn2Ge2（R=Gd, Tb and Dy） were investigated by using the X-ray diffraction method and magnetic measurement. The results showed that the compounds experience two magnetic transitions, namely the second-order paramagnetic to antiferromagnetic transition at temperature TN（TN=368, 423 and 443 K for Gd Mn2 Ge2, Tb Mn2 Ge2 and Dy Mn2 Ge2, respectively） and the first-order antiferromagnetic-ferrimagnetic transition at temperature Tt（Tt=96, 80 and 40 K for Gd Mn2 Ge2, Tb Mn2 Ge2 and Dy Mn2 Ge2, respectively） as the temperature decreases. The temperature dependence of the lattice constant a（T） displays a negative magnetoelastic anomaly at the second-order transition point TN and, at the first-order transition Tt, a increases abruptly for Gd Mn2 Ge2 and Tb Mn2 Ge2, Da/a about 10^（-3）. Nevertheless, the lattice constant c almost does not change at these transition points indicating that such magnetoelastic anomalies are mainly contributed by the Mn-sublattice. The transitions of the magnetoelastic properties are also evidenced on the temperature dependence of magnetic susceptibility χ. The first-order transition behavior at Tt is explained by the Kittel mode of exchange inversion.

CHARACTERIZATION OF SOME SCHIFF BASES OF HETEROCYCLIC COMPOUNDS AND THEIR TRANSITION METAL COMPLEXES

Some new Schiff bases were synthesized by the condensation of equimolar quantities of salicylaldehyde and 2-amino-5-phenylazo-pyridine or its derivatives in dry benzene(1):Metal complexes of the type ML_2and M'L_3 where M=Cu^(2+),Co^(2+),Ni^(2+),Mn^(2+)Pd^(2+),M'=Fe^(3+)and L=different newly synthesized monobasic Schiff bases were prepared in absolute ethanolic medium(2)and characterized by elementary analysis,conductance measurements,infrared spectra,electronic spectra,magnetic moments studies.

Electrocatalytic oxygen evolution activities of metal chalcogenides and phosphides:Fundamentals,origins,and future strategies

The development of inexpensive and efficient electrocatalysts is key to commercializing energy-related electrocatalytic techniques such as water electrolyzers and metal-air batteries.In particular,novel oxygen evolution reaction(OER)pre-catalysts,such as transition metal chalcogenides(TMCs)and phosphides(TMPs),have evolved in recent years from traditional stable OER electrocatalysts,which show superior OER electrocatalytic performance compared with transition metal oxides(TMOs)or(oxy)hydroxides(TMOHs).In this feature article,we summarize recent advances in the development of TMCand TMP-based OER electrocatalysts,as well as approaches to improve the OER performance in terms of morphology,structure,composition,surface engineering,lattice-strained and in-situ transformation in the electrolysis process.In particular,the electrochemical stability of TMCs and TMPs in alkaline electrolytes and the evolution of morphology,structure and composition under OER conditions are discussed.In the last section,we discuss the challenges that need to be addressed in this specific area of research and the implications for further research.

Mechanism research progress on transition metal compound electrode materials for supercapacitors

Supercapacitors(SCs)have remarkable energy storage capabilities and have garnered considerable interest due to their superior power densities and ultra-long cycling characteristics.However,their comparatively low energy density limits their extensive application in large-scale commercial applications.Electrode materials directly affect the performance of SCs.Thus,the development of cutting-edge electrode materials and modification of their morphological and structural properties are vital for advancing the performance of SCs.Transition metal compounds have a high specific capacity and good cycling durability,making them the most promising electrode active materials for high-energy density SCs.Nevertheless,their inadequate conductivity,unfavorable ion diffusion rates,substantial volume expansion and phase transitions during charging and discharging are obstacles to their stable and efficient integration into SCs.To address these challenges,this study provides a comprehensive summary of the current advancements in transition metal nanomaterials as electrode materials for SCs,an overview of the current research status,and the prevailing challenges.Furthermore,this study highlights synthetic techniques and management strategies for electrode materials derived from transition metal compounds,targeting the resolution of the aforementioned challenges.Finally,a concise discussion is provided on the future directions of SC development,with an emphasis on the utilization of transition metal compound electrode materials.

Magnetocaloric effects in Fe_4MnSi_3B_x interstitial compounds

The magnetic properties and magnetocaloric effect in Fe4MnSi3B~ compounds with x=0, 0.05, 0.10, 0.15, 0.20, 0.25 have been investigated. X-ray diffraction study shows that all these compounds investigated crystallize in the MnsSi3-type structure with space group P63/mcm. Boron insertion in the host ternary silicide Fe4MnSi3 does not change the crystal symmetry, only leads to an increase of the lattice parameters, indicating the B atoms entered the interstitial sites. With increasing B content, the Curie temperature shifts to higher temperatures. The maximal magnetic-entropy changes of the Fe4MnSi3Bx compounds with x=0, 0.10 and 0.20 are about 1.8 J/（kg.K）, 1.8 J/（kg-K） and 1.6 J/（kg.K）, respectively, for a field change from 0 to 1.5 T.

Recent progress of two-dimensional metal-base catalysts in urea oxidation reaction

Urea oxidation reaction(UOR)is an auxiliary water electrolysis hydrogen production technology developed in recent years to replace oxygen evolution reaction and reduce energy consumption,which can produce hydrogen more efficiently by low theoretical potential,reduce the average cost of electrochemical hydrogen production,and is a frontier research hotspot for renewable hydrogen energy.Two-dimensional(2D)nanomaterials as electrocatalysts have many favorable potential,such as it can effectively reduce the resistivity of materials and increase the specific surface area with certainty.This paper reviews the application of 2D materials in UOR in alkaline electrolytes.And a cross-sectional comparison of various material performance data including overpotential,Tafel slope,electrochemical active surface area(ECSA)and it stability test was conducted,which could illustrate the differences between materials composed of different elements.In addition,the main challenges hindering the progress of research on 2D materials in urea electrocatalysis processes and promising materials in this field in future are summarized and prospected.It is believed that this review will contribute to designing and analyzing highperformance 2D urea electrocatalysts for water splitting.

The band structures of some transition metals and their NaCl-type compounds

The band structures of Group IVB (Ti, Zr, Hf), VB (V, Nb, Ta) and VIE (Cr, Mo, W) transition metals and some of their carbides and nitrides (TiN, ZrN, HfN, VC, NbC, TaC, VN, NbN, TaN) with NaCl-type (B1-type) structure have been calculated by using the tight-binding method within the Extended Huckel approximation (EHT). The energy bands, densities of states and crystal orbital overlap populations are given. The relationship between the bonding properties and the superconducting transition temperatures (T-c) of them is discussed. The influences of various kinds of metallic atoms and changes of bond lengths on T-c are also discussed.

Recent progresses of micro-nanostructured transition metal compound-based electrocatalysts for energy conversion technologies

The rapid consumption of fossil fuels has caused increasingly climatic issues and energy crisis,which leads to the urgent demand for developing sustainable and clean energies.Electrocatalysts play a key role in the development of electrochemical energy conversion and storage devices.Especially,developing efficient and cost-effective catalysts is important for the large-scale application of these devices.Among various electrocatalyst candidates,earth abundant transition metal compound(TMC)-based electrocatalysts are being widely and rapidly studied owing to their high electrocatalytic performances.This paper reviews the recent and representative advances in efficient TMC-based electrocatalysts(i.e.,oxides,sulfides,selenides,phosphides,carbides and nitrides)for energy electrocatalytic reactions,including hydrogen evolution reaction(HER),oxygen evolution reaction(OER)and oxygen reduction reaction(ORR).Different compounds with different applications are summarized and the relative mechanisms are also discussed.The strategies for developing earth-abundant and low-cost TMC-based electrocatalysts are introduced.In the end,the current challenges and future perspectives in the development of TMC research are briefly discussed.This review also provides the latest advance and outlines the frontiers in TMC-based electrocatalysts,which should provide inspirations for the further development of low-cost and high-efficiency catalysts for sustainable clean energy technologies.

Doping transition metal ions as a method for enhancement of ablation rate in femtosecond laser irradiation of silicate glass

We present a doping method to improve the femtosecond laser ablation rate and promote ablation selectivity. Doping transition metal ions, Co2＋ or Cu2＋, in silicate glass apparently change absorption spectroscopy and induce resonant absorption at wavelengths of 600 and 800 nm, respectively. Comparing with femtosecond laser processing of the same glass without doping, we find that the threshold fiuenee decreases and the ablation rate increases in resonant absorption in doped silicate glass. Resonant absorption effectively increases multiphoton ionization for seed-free electron generation, which in turn enhances avalanche ionization.

Structural stability and electrical properties of AlB_2-type MnB_2 under high pressure

The structural stability and electrical properties of AlB2-type MnB2 were studied based on high pressure angledispersive x-ray diffraction, in situ electrical resistivity measured in a diamond anvil cell(DAC) and first-principles calculations under high pressure. The x-ray diffraction results show that the structure of AlB2-type MnB2 remains stable up to 42.6 GPa. From the equation of state of MnB2, we obtained a bulk modulus value of 169.9±3.7 GPa with a fixed pressure derivative of 4, which indicates that AlB2-type MnB2 is a hard and incompressible material. The electrical resistance undergoes a transition at about 19.3 GPa, which can be explained by a transition of manganese 3d electrons from localization to delocalization under high pressure.

Structure and Magnetocaloric Effect in Tb(Co_(1-x)Sn_x)_2 Alloys

The phases and magnetocaloric effect in the alloys Tb（Co1-xSnx）2 with x = 0, 0.025, 0.050, 0.075, 0. 100 were investigated by X-ray diffraction analysis and magnetization measurement. The substitution of Sn in TbCo2 was limited. The cubic MgCu2-type structure for the sample of TbCo2 was confirmed by the results of X-ray powder diffraction and the rest samples consist of the TbCo2 phase mainly, together with some TbCo3 and Tb5Sn3 impurity phases. The impurity phases increase with the increase of Sn contents. The magnetic phase transition in all samples keeps second-order transition. Tc increases slightly by Sn substitution from 230 K of the alloy with x = 0 to 233 K of the alloy with x = 0.050 and then a slight decrease for higher concentration of x. The maximum magnetic entropy change in the samples Tb （Co1- x Snx）2 with x =0, 0.025, 0.050, 0.075 are 3.44, 2.29, 1.64, 1.16 J·kg^-1·K^-1, respectively, with the applied field change from 0 to 2.0 T.

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.

Structure and Magnetic Properties of Fe1-xCx Solid Solution Prepared by Mechanical Alloying

Supersaturated solid solutions Fe1-xCx （0≤x≤0.9 ） of wide composition range have been prepared by mechanical alloying process. Nanocrystalline phase was formed for 0 ≤ x ≤ 0.67 and a large grain phase for 0.75 ≤ x ≤ 0.9. The large fraction of graphite volume puts off formation of nanocrystalline phase for high carbon content. In the large grain phase, magnetization follows simple magnetic dilution, and eoereivity He is mainly due to dissolution of carbon at grain boundaries. In the nanocrystalline phase the alloying effect of carbon is revealed by a distinct reduction of average magnetic moment. The increasing lattice constant with increasing carbon content is observed for x ≤ 0.5, suggesting that the high carbon concentration may enhance diffusion of carbon into the Fe lattice. It shows a discontinuity in the Hc variation with a grain size D of nanocrystalline phase. For small grain D below the critical value, Hc increases with D. For a large grain D, Hc decreases with increasing D. The solubility limit of carbon in a-Fe extended by nanocry- stalline phase formation is discussed.

Insight into the boosted activity of TiO2–CoP composites for hydrogen evolution reaction:Accelerated mass transfer,optimized interfacial water,and promoted intrinsic activity

The use of abundant elements in the earth as electrocatalytic hydrogen production catalysts is of great significance for hydrogen energy cycling.Herein,we report amorphous TiO_(2)-decorated CoP/NF(TiO_(2)–CoP/NF)as an excellent electrocatalyst for alkaline hydrogen evolution reaction(HER).The welldispersed amorphous TiO_(2)on nanoneedle-like CoP arrays preserves the crystal structure of CoP and changes its electronic structure by interfacial charge transfer.Compared to CoP/NF catalyst,the Ti O_(2)–CoP/NF composite catalyst exhibits high HER activity with an overpotential of 61 mV at 10 mA cm^(-2)and high stability.Importantly,it almost maintains the Volmer step as a rate-determining step(RDS)and the Tafel slope at a wide cathodic potential range showing the fast kinetics under large polarization regions.Theoretical simulations reveal that the combination of TiO_(2)and CoP selectively accelerates the hydrated K+diffusion,regulates the interfacial water orientation to adapt to the subsequent smooth water dissociation,and optimizes*H adsorption/H_(2)desorption.The strengthened coupling of HER multi-scale-processes on transition metal compound composites catalysts is the underlying mechanism for improving HER activity.

Magnetocaloric Effect in MnCo_(1-x)Al_xGe Compounds

The effects of substitution of AI for Co on magnetic and magnetocaloric properties of MnCo1-xAlxGe （x=0.00, 0.03, 0.05, 0.08, 0.10, 0.13, 0.15, and 0.20） compounds have been investigated by X-ray diffraction （XRD） and magnetization measurements. XRD exhibits that MnCo1-xAlxGe compounds crystallize in the orthorhombic TiNiSi-type structure for x〈0.03 and in the hexagonal Ni2In-type crystal structure for x〉0.03. Magnetic measurements show that the Curie temperature can be tuned between 286 and 347 K by changing the Co/Al ratio. The maximum magnetic entropy change determined from the isothermal magnetization measurement by Maxwell relation reaches 1.52 J/（kgK） for x=0.08 in a field change from 0 to 1.5 T around 310 K.

Highly efficient and magnetically separable nano-CuFe_2O_4 catalyzed S-arylation of thiourea by aryl/heteroaryl halides

The non-toxic and magnetically separable nano-CuFeOcatalyzed synthesis of symmetrical aryl sulfides by the reaction of thiourea with a wide variety of aryl halides,including aryl chlorides has been reported.Excellent yields of products have been obtained under ligand-free conditions and without the use of any expensive catalyst,such as palladium.

Nucleation growth quenching for superior cluster catalysts

Cluster catalysts are rapidly growing into an important sub-field in heterogeneous catalysis,owing to their distinct geometric structure,neighboring metal sites,and unique electronic structure.Although the thermodynamics and kinetics of the formation of nanoparticles have been largely investigated,the precise synthesis of clusters in wet chemical methods still faces great challenges.In the study,a quenching strategy of asymmetric temperature in solution for the rapid generation of vacancy-defect rich clusters is reported.The quenching process can be used to synthesize multitudinous metal compound clusters,including metal oxides,fluorides,oxygen-sulfur compounds,and tungstate.For oxygen evolution reaction(OER),IrO_(2)clusters with abundant oxygen vacancies were obtained and uniformly dispersed in the solution.Compared to commercial IrO_(2),the prepared IrO_(2)cluster can be directly loaded on carbon paper and used as binder-free electrodes,which exhibit higher OER activity and long-term operational stability in alkaline electrolytes.The quenching strategy provides a simple and efficient method for the synthesis of clusters,which has tremendous potential for industrial-scale preparation and application,especially can be further applied to flow electrochemical generators.