Two-dimensional titanium carbonitride MXene as a highly efficient electrocatalyst for hydrogen evolution reaction

In this paper,we report,for the first time,on the electrochemical catalytic activity of 2D titanium carbonitride MXene for hydrogen evolution reaction(HER).According to our study,2D titanium carbonitride exhibited much higher electrocatalytic activity than its carbide analogues,achieving an onset overpotential of 53 mV and Tafel slope of 86 mV dec^(-1),superior to the titanium carbide with onset overpotential of 649 mV and Tafel slope of 303 mV dec^(-1).The obtained onset overpotential for 2D titanium carbonitride is lower than those of all the reported transition metal carbides MXene catalysts without additives,so far.Density functional theory calculations were conducted to further understand the electrochemical performance.The calculation results show that a greater number of occupied states are active for Ti_(3)CNO_(2),revealing free energy for the adsorption of atomic hydrogen closer to 0 than that of Ti_(3)C_(2)O_(2).Both experimental and calculation studies demonstrate the excellent electrocatalytic behavior of titanium carbonitride.The investigation of 2D titanium carbonitride opens up a promising paradigm for the conscious design of high-performance non-precious metal catalyst for hydrogen generation.

Precipitation and Solid Solution of Titanium Carbonitride Inclusions in Hypereutectoid Tire Cord Steel

The properties of titanium carbonitride Ti（CxN1-x） inclusions precipitated during solidification of tire cord steels and the thermodynamic conditions for their decomposition and solid solution during billet heating were investigated using a thermodynamics method. The solid solution of Ti（CxN1-x） inclusions during high-temperature heating was also studied experimentally. The results revealed that： （1） the higher the content of carbon in the tire cord steel is, the greater the value of .r in the Ti（CxN1-x） inclusions is; （2） the higher the content of carbon in the tire cord steel is, the earlier the Ti（CxN1-x） inclusions precipitated during the solidification process and the lower the solidification front temperature is during precipitation; （3） when an 82A steel sample was heated to 1087℃, the Ti（CxN1-x） inclusions possess the thermodynamic conditions of decomposition and solid solution; and （4） when 82A samples were heated to 1150 and 1 250℃, the total number of Ti（CxN1-x） inclusions larger than 5μm in diameter decreased by 55.0% and 70.3%, respectively. In addition, although smaller inclusions with diameter less than 2 μm continued to decompose when the sample was heated at 1 250℃ for 2 h and then cooled to 1000℃ in the furnace, the number of inclusions larger than 5 μm in diameter increased.

Synthesis of new two-dimensional titanium carbonitride Ti_(2)C_(0.5)N_(0.5)T_(x)MXene and its performance as an electrode material for sodium-ion battery

Two-dimensional(2D)layered transition metal carbides/nitrides,called MXenes,are attractive alternative electrode materials for electrochemical energy storage.Owing to their metallic electrical conductivity and low ion dif-fusion barrier,MXenes are promising anode materials for sodium-ion batteries(SIBs).Herein,we report on a new 2D carbonitride MXene,viz.,Ti_(2)C_(0.5)N_(0.5)T_(x)(T_(x) stands for surface terminations),and the only second carbonitride after Ti_(3) CNT_(x) so far.A new type of in situ HF(HCl/KF)etching condition was employed to synthesize multilayer Ti_(2)C_(0.5)N_(0.5)T_(x) powders from Ti_(2)AlC_(0.5)N_(0.5).Spontaneous intercalation of tetramethylammonium followed by sonication in water allowed for large-scale delamination of this new titanium carbonitride into 2D sheets.Multilayer Ti_(2)C_(0.5)N_(0.5)T_(x) powders showed higher specific capac-ities and larger electroactive surface area than those of Ti_(2)CT_(x) powders.Multi-layer Ti_(2)C_(0.5)N_(0.5)T_(x) powders show a specific capacity of 182 mAh g^(-1) at 20 mA g^(-1),the highest among all reported MXene electrodes as SIBs with excellent cycling stability.

Effect of titanium content on the refinement of coarse columnar austenite grains during the solidification of peritectic steel

The effect of titanium content on the refinement of austenite grain size in as-cast peritectic carbon steel was investigated by fast directional solidification experiments with simulating the solidification and growth of surface and subsurface austenite in continuously cast slabs.Transmission electron microscope(TEM)and scanning electron microscope(SEM)were used to analyze the size and distribution of Ti(C,N)precipitates during solidification.Based on these results,the pinning pressure of Ti(C,N)precipitates on the growth of coarse columnar grains(CCGs)was studied.The results show that the austenite microstructure of as-cast peritectic carbon steel is mainly composed of the regions of CCGs and fine columnar grains(FCGs).Increasing the content of titanium reduces the region and the short axis of the CCGs.When the content of titanium is 0.09wt%,there is no CCG region.Dispersed microscale particles will firstly form in the liquid,which will decrease the transition temperature from FCGs to CCGs.The chain-like nanoscale Ti(C,N)will precipitate with the decrease of the transition temperature.Furthermore,calculations shows that the refinement of the CCGs is caused by the pinning effect of Ti(C,N)precipitates.

Preparation and properties of ultra-fine TiCN matrix cermets by vacuum microwave sintering

Ultra-fine titanium carbonitride （TiCN） matrix materials with a grain size less than 1μm were successfully prepared by vacuum microwave sintering. The milling process for raw TiCN particles and the microstructure and properties of cermets produced with a composition of 15wt.%WC-17wt.%（Co＋Ni）-9wt.%Mo2C-59wt.%Ti0.TN0.3 and sintered by vacuum microwave were analyzed by scanning electron microscopy （SEM） and X-ray diffraction （XRD）. The results show that a ball-to-powder mass ratio of 8：1 and a milling time of 50 h provided appropriate conditions for the production of ultra-fine TiCN solid solution powders. The use of vacuum microwave sintering produced cermets with much finer grain and black core structures and higher relative density and hardness than those produced by vacuum sintering technology.

Sliding wear behaviour of Fe/316L/430-Ti(C,N)composites prepared via spark plasma sintering and subsequent heat treatment

A series of novel steel-Ti(C,N)composites was fabricated by spark plasma sintering(SPS)and subsequent heat treatment.The hardness,indentation fracture resistance,and wear behaviour of the steel-Ti(C,N)composites were compared with those of the unreinforced samples,and their potentials were assessed by comparison with traditional cermet/hardmetal systems.The results showed that with the addi-tion of 20wt%Ti(C,N),the wear rates of the newly examined composites reduced by a factor of about 2 to 4 and were comparable to those of cermets and hardmetals.The martensitic transformation of the steel matrix and the formation of in situ carbides induced by heat treatment en-hanced the wear resistance.Although the presence of excessive in situ carbides improved the hardness,the low indentation fracture resistance(IFR)value resulted in brittle fracture,which in turn resulted in poor wear property.Moreover,the operative wear mechanisms were investig-ated.This study provides a practical and cost-effective approach to prepare steel-Ti(C,N)composites as potential wear-resistant materials.

Effects of Different Carbon Sources and NaBr-KCl on Synthesis of Ti(C,N)

Ti（ C, N） was synthesized with the starting materials of 76. 9% titania white and 23. 1% carbon black （graphite or activated carbon ）, or 40% titania white and 60% amylum, with or without 10% NaBr - KCl, dry moulding and carbon embedded firing at i 300 ℃ and 1 400 ℃ for 3 h, respectively. Phase composition and microstructure of the synthesized Ti （C, N） were analyzed by XRD, SEM and EPMA. Effects of different carbon sources and NaBr-KCl on the synthesis of Ti（ C, N） were investigated. The results show that： （1） Ti （C, N） can be synthesized by using carbon black, graphite, activated carbon or amylum as carbon source separately; （2） Additive NaBr - KCl is more favorable for accelerating the carbothermal reduction reaction using carbon black or amylum as carbon source; （3） In the presence of NaBr - KCl, particle size of the synthesized Ti（ C, N） is 5 -8μm using carbon black as carbon source fired at 1 300 ℃ for 3 h, while that is only 1 - 3 μm using graphite, activated carbon or amylum fired at 1 400 ℃ for 3 h.

Influence of residual stress on the phase equilibrium of Ti(C_xN_y) thin films

In order to provide a theoretic basis for the research of Ti(C_xN_y) thinfilms, the thermodynamic database of Ti-C-N ternary system is established and the phase diagramsections are calculated. In addition to the assessed thermodynamic properties of Ti-C-N system, theinfluence of the residual strain energy of Ti(C_xN_y) thin films on the phase equilibria isanalyzed. The classical formula for calculating the elastic strain energy is expressed into aRedlich-Kister form in order to perform the thermodynamic and equilibrium calculations using theThermo-Calc software. Isothermal sections at 900 and 1100 K are calculated with this database andcompared with those calculated without considering the residual stress. As a result, with theaddition of strain energy delta-fcc Ti(C_xN_y) phase area shrinks. It is therefore concluded thatwith the influence of the residual stress in Ti(C_xN_y) thin solid film, the precipitation of puredelta film requires more precise control of composition.

Ti_(3)AICN MAX for tailoring MgH_(2) hydrogen storage material:from performance to mechanism

Many MXenes are efficient catalysts for MgH_(2)hydrogen storage material.Nevertheless,the synthesis of MXenes should consume a large amount of corrosive HF to etch out the Al layers from the transition metal aluminum carbides or nitrides(MAX) phases,which is environmentally unfriendly.In this work,Ti_(3)AlCN MAX without HFetching was employed directly to observably enhance the kinetics and the cycling stability of MgH_(2).With addition of10 wt% Ti_(3)AlCN,the onset dehydrogenation temperature of MgH2 was dropped from 320 to 205℃,and the rehydrogenation of MgH2 under 6 MPa H2 began at as low as50℃.Furthermore,at 300℃,it could provide 6.2 wt% of hydrogen in 10 min.Upon cycling,the composite underwent an activation process during the initial 40 cycles,with the reversible capacity increased from 4.7 wt% to 6.5 wt%.After that,the capacity showed almost no attenuation for up to 100 cycles.The enhancing effect of Ti_(3)AICN on MgH_(2) was comparable to many MXenes.It was demonstrated that Ti_(3)AICN did not destabilize MgH_(2) but acted as an efficient catalyst for MgH_(2).Ti_(3)AICN was observed to be the active sites for the nucleation and growth of MgH_(2)and might also help in dissociation and recombination of hydrogen molecules.Such two factors are believed to contribute to the improvement of MgH_(2).This study not only provides a promising strategy for improving the hydrogen storage performances of MgH_(2) by using noncorrosive MAX materials,but also adds evidence of nucleation and growth of MgH_(2) on a catalyst.

Precipitates in Steels With Ti Additive Produced by CSP Process

Hot strips of low carbon steels with Ti additive [-contain C 0.04 % -0. 07 % , Si≤0.6%, Mn≤0.6%, Ti 0. 060/00- 0.14% （mass percent）] prodvced by EAF-CSP （Electric Arc Furnaces-Compact Strip Production） process were examined by TEM, HREM and XRD. Carbonitrides with different N/C ratio were found in the sam- ples. The varying composition of the Ti-carbonitrides resulted from the supersaturation of Ti and temperature at which the compound was formed. In the tested steel, total mass fraction of the precipitates including cementite, carbonitride and a small quantity of Fe3O4, AO2O3 , Ti2 CS and A1N was about 0. 305 %. XRD results showed that about a quarter of the powder extracted by electrolysis was titanium nitrides, carbonitrides and carbides. Particle arrays formed by interphase precipitation could be observed either in slabs or in hot strips. The dominant reaction mecha- nisms were discussed. Compared with the conventional cold charge process, small amount of Ti addition would be more effective for orecipitation of fine orecioitates in the steels oroduced by CSP process.