TiC_(x)is an excellent composite strengthening particle and grain refiner for Al alloys.However,the stability of TiC_(x)is poor when solute Si exists in Al alloy melts,which significantly depresses its strengthening a...TiC_(x)is an excellent composite strengthening particle and grain refiner for Al alloys.However,the stability of TiC_(x)is poor when solute Si exists in Al alloy melts,which significantly depresses its strengthening and grain refining effects.In this work,the destabilization mechanisms of the TiC_(x)particles in Al-Si alloy melt with a composition of Al-7Si-7.5TiC were explored via experiments,first-principles calculations and thermodynamic calculations.The experimental results show that Si atoms diffuse into TiC_(x)and Ti atoms are released into the Al melt to form a Ti-rich transition zone during the insulation of TiC_(x)in Al-Si melt,and the TiAlySiz and Al_(4)C_(3)phases are solidified in the Ti-rich zone and at Ti-rich zone/TiC_(x)interface,respectively.The first principles calculations show that the low formation energy of C vacancies facilitates the rapid diffusion of Si atoms in TiC_(x),while the doping of Si atoms reduces the energy barrier of diffusion of Ti atoms in TiC_(x)and promotes the formation of Ti-rich zones.The thermodynamic calculations show that the wide crystallization temperature range of the destabilized product TiAlySiz phase is the key to continuous decomposition of TiC_(x)particles.In addition,the driving force of the main destabilization reaction of TiC_(x)in the Al-Si alloys is about 44 times higher than that in the Al alloys without Si addition.This indicates that the presence of solute Si remarkably promotes the subsequent decomposition process of TiC_(x)in the Al-Si alloy melts.展开更多
Two-dimensional(2D)transition metal carbide MXene-based materials hold great potentials applied for new electromagnetic wave(EMW)absorbers.However,the application of MXenes in the field of electromagnetic wave absorpt...Two-dimensional(2D)transition metal carbide MXene-based materials hold great potentials applied for new electromagnetic wave(EMW)absorbers.However,the application of MXenes in the field of electromagnetic wave absorption(EMA)is limited by the disadvantages of poor impedance matching,single loss mechanism,and easy oxidation.In this work,MoO_(3)/TiO_(2)/Mo_(2)TiC_(2)T_(x)hybrids were prepared by the annealing-treated Mo_(2)TiC_(2)T_(x)MXene and uniform MoO_(3)and TiO_(2)oxides in-situ grew on Mo_(2)TiC_(2)T_(x)layers.At the annealing temperature of 300℃,the minimum reflection loss(RLmin)value of MoO_(3)/TiO_(2)/Mo_(2)TiC_(2)T_(x)reaches-30.76 dB(2.3 mm)at 10.18 GHz with a significantly broadening effective absorption bandwidth(EAB)of 8.6 GHz(1.8 mm).The in-situ generated oxides creating numerous defects and heterogeneous interfaces enhance dipolar and interfacial polarizations and optimize the impedance matching of Mo_(2)TiC_(2)T_(x).Considering the excellent overall performance,the MoO_(3)/TiO_(2)/Mo_(2)TiC_(2)T_(x)hybrids can be a promising candidate for EMA.展开更多
MXene is a promising electrode material for both high volumetric capacitance and high-rate performance in supercapacitors.However,the current study has mainly focused on the monometallic element Ti_(3)C_(2)T_(x) MXene...MXene is a promising electrode material for both high volumetric capacitance and high-rate performance in supercapacitors.However,the current study has mainly focused on the monometallic element Ti_(3)C_(2)T_(x) MXene until now,while the bimetallic and multimetallic MXene have received comparatively less attention.In this work,we demonstrate that the electronic structure of the Mo_(2)TiC_(2)T_(x) MXene could be regulated by fine-tuning the content of doped Nb atoms.The enhanced electron cloud density of surface–O termination and the electron spin of the Mo atoms in the Mo_(2)TiC_(2)T_(x) MXene,leads to the boost of electric double-layer capacitor(EDLC)and improvement of pseudocapacitance.As a consequence,the electrochemical performance of Nb-doped Mo_(2)TiC_(2)T_(x) MXene(Nb-0.3-MXene)demonstrates a capacitance of 398 F·cm^(−3),roughly doubling that of the pristine Mo_(2)TiC_(2)T_(x) MXene electrode at 197 F·cm^(−3) in the 3 M H_(2)SO_(4) electrolyte.At the same time,the Nb-0.3-MXene could even maintain a capacitance of 82.75% at 200 mV·s−1,with high cyclic stability for 19,000 cycles at 10 A·g−1.Additionally,Nb-0.3-MXene-based hybrid supercapacitors deliver a remarkable volumetric energy density of 48.1 W·h·L^(−1)at 230.7 W·L^(−1),and 34.4 W·h·L^(−1)at a high power density of 82.6 kW·L^(−1).There exists a balance between the volumetric capacitance and rate performance with different ratios of Nb atoms in the Nb-doped MXene due to the strong interaction between the Nb-doped MXene and the intercalated protons.Therefore,optimizing the electronic structure of MXene through heteroatom doping is of great potential for enhanced supercapacitor performance.展开更多
基金the financial supported from the Key R&D Program of Shaanxi Province,China(No.2020ZDLGY13-01)the innovation team program of material developing and application of key engine components(No.K20220185)the National Natural Science Foundation of China(Nos.52101049,52234009 and 52071262).
文摘TiC_(x)is an excellent composite strengthening particle and grain refiner for Al alloys.However,the stability of TiC_(x)is poor when solute Si exists in Al alloy melts,which significantly depresses its strengthening and grain refining effects.In this work,the destabilization mechanisms of the TiC_(x)particles in Al-Si alloy melt with a composition of Al-7Si-7.5TiC were explored via experiments,first-principles calculations and thermodynamic calculations.The experimental results show that Si atoms diffuse into TiC_(x)and Ti atoms are released into the Al melt to form a Ti-rich transition zone during the insulation of TiC_(x)in Al-Si melt,and the TiAlySiz and Al_(4)C_(3)phases are solidified in the Ti-rich zone and at Ti-rich zone/TiC_(x)interface,respectively.The first principles calculations show that the low formation energy of C vacancies facilitates the rapid diffusion of Si atoms in TiC_(x),while the doping of Si atoms reduces the energy barrier of diffusion of Ti atoms in TiC_(x)and promotes the formation of Ti-rich zones.The thermodynamic calculations show that the wide crystallization temperature range of the destabilized product TiAlySiz phase is the key to continuous decomposition of TiC_(x)particles.In addition,the driving force of the main destabilization reaction of TiC_(x)in the Al-Si alloys is about 44 times higher than that in the Al alloys without Si addition.This indicates that the presence of solute Si remarkably promotes the subsequent decomposition process of TiC_(x)in the Al-Si alloy melts.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.U2004177 and U21A2064)Outstanding Youth Fund of Henan Province(No.212300410081)Support Plan for Scientific and Technological Innovation Talents in Colleges and Universities of Henan Province(No.22HASTIT001)。
文摘Two-dimensional(2D)transition metal carbide MXene-based materials hold great potentials applied for new electromagnetic wave(EMW)absorbers.However,the application of MXenes in the field of electromagnetic wave absorption(EMA)is limited by the disadvantages of poor impedance matching,single loss mechanism,and easy oxidation.In this work,MoO_(3)/TiO_(2)/Mo_(2)TiC_(2)T_(x)hybrids were prepared by the annealing-treated Mo_(2)TiC_(2)T_(x)MXene and uniform MoO_(3)and TiO_(2)oxides in-situ grew on Mo_(2)TiC_(2)T_(x)layers.At the annealing temperature of 300℃,the minimum reflection loss(RLmin)value of MoO_(3)/TiO_(2)/Mo_(2)TiC_(2)T_(x)reaches-30.76 dB(2.3 mm)at 10.18 GHz with a significantly broadening effective absorption bandwidth(EAB)of 8.6 GHz(1.8 mm).The in-situ generated oxides creating numerous defects and heterogeneous interfaces enhance dipolar and interfacial polarizations and optimize the impedance matching of Mo_(2)TiC_(2)T_(x).Considering the excellent overall performance,the MoO_(3)/TiO_(2)/Mo_(2)TiC_(2)T_(x)hybrids can be a promising candidate for EMA.
基金supported by the National Natural Science Foundation of China(No.52272242)the Provisional Key Research and Development Program of Henan Province(No.231111240600)+1 种基金the Natural Science Foundation of Henan Province(No.242300421428)the Start-up Funding for Scientific Research of Zhengzhou University(No.32310221).
文摘MXene is a promising electrode material for both high volumetric capacitance and high-rate performance in supercapacitors.However,the current study has mainly focused on the monometallic element Ti_(3)C_(2)T_(x) MXene until now,while the bimetallic and multimetallic MXene have received comparatively less attention.In this work,we demonstrate that the electronic structure of the Mo_(2)TiC_(2)T_(x) MXene could be regulated by fine-tuning the content of doped Nb atoms.The enhanced electron cloud density of surface–O termination and the electron spin of the Mo atoms in the Mo_(2)TiC_(2)T_(x) MXene,leads to the boost of electric double-layer capacitor(EDLC)and improvement of pseudocapacitance.As a consequence,the electrochemical performance of Nb-doped Mo_(2)TiC_(2)T_(x) MXene(Nb-0.3-MXene)demonstrates a capacitance of 398 F·cm^(−3),roughly doubling that of the pristine Mo_(2)TiC_(2)T_(x) MXene electrode at 197 F·cm^(−3) in the 3 M H_(2)SO_(4) electrolyte.At the same time,the Nb-0.3-MXene could even maintain a capacitance of 82.75% at 200 mV·s−1,with high cyclic stability for 19,000 cycles at 10 A·g−1.Additionally,Nb-0.3-MXene-based hybrid supercapacitors deliver a remarkable volumetric energy density of 48.1 W·h·L^(−1)at 230.7 W·L^(−1),and 34.4 W·h·L^(−1)at a high power density of 82.6 kW·L^(−1).There exists a balance between the volumetric capacitance and rate performance with different ratios of Nb atoms in the Nb-doped MXene due to the strong interaction between the Nb-doped MXene and the intercalated protons.Therefore,optimizing the electronic structure of MXene through heteroatom doping is of great potential for enhanced supercapacitor performance.
