Cation vacancies can bring numerous surprising characters due to its multifarious electron and orbit distribution.In this work,d-MnO_(2) with alkali-ion(K,Na,Li)associated manganese(Mn)vacancies is fabricated by a sim...Cation vacancies can bring numerous surprising characters due to its multifarious electron and orbit distribution.In this work,d-MnO_(2) with alkali-ion(K,Na,Li)associated manganese(Mn)vacancies is fabricated by a simple hydrothermal reaction,and the correlation between their electronic structure and pseudocapacitance are systematically investigated.FESEM/TEM images have shown that the morphology of MnO_(2) is obviously changed after the introducing of cation vacancies.The position of alkali-ion in MnO_(2) structure can be controlled by adjusting the ion concentration.XRD patterns and Raman spectra demonstrate that the alkali-ion is embedded in Mn vacancies at low concentration,while entered the interlayer of MnO_(2) at high concentration.The existence of Mn vacancies will resulting in the distortion of neighboring atoms,leading to the electronic delocalization,and thus enhancing the conductivity,pseudocapacitance and rate capability of MnO_(2).Accordingly,the specific capacitances of optimized 0.4 KMO,0.4 NaMO and 0.4 LiMO samples are enhanced about 1.9,1.6 and 1.6 times compared to pure MnO_(2).Meanwhile,the rate performance has also been improved about 76%,46%and 42%,respectively.Theoretical calculations further confirm that the Mn vacancies can generate additional occupancy states and cause an increase in carrier concentration,which will improve the conductivity and further boost the pseudocapacitance of MnO_(2).This result open up a promising approach to explore active and durable electrode materials.展开更多
Superlubricity means non-sticky and frictionless when two bodies are set contacting motion.Although this occurrence has been extensively investigated since 1859 when Faraday firstly proposed a quasiliquid skin on ice,...Superlubricity means non-sticky and frictionless when two bodies are set contacting motion.Although this occurrence has been extensively investigated since 1859 when Faraday firstly proposed a quasiliquid skin on ice,the mechanism behind the superlubricity remains uncertain.This report features a consistent understanding of the superlubricity pertaining to the slipperiness of ice,self-lubrication of dry solids,and aqueous lubricancy from the perspective of skin bond-electron-phonon adaptive relaxation.The presence of nonbonding electron polarization,atomic or molecular undercoordination,and solute ionic electrification of the hydrogen bond as an addition,ensures the superlubricity.Nonbond vibration creates soft phonons of high magnitude and low frequency with extraordinary adaptivity and recoverability of deformation.Molecular undercoordination shortens the covalent bond with local charge densification,which in turn polarizes the nonbonding electrons making them localized dipoles.The locally pinned dipoles provide force opposing contact,mimicking magnetic levitation and hovercraft.O:H−O bond electrification by aqueous ions has the same effect of molecular undercoordination but it is throughout the entire body of the lubricant.Such a Coulomb repulsivity due to the negatively charged skins and elastic adaptivity due to soft nonbonding phonons of one of the contacting objects not only lowers the effective contacting force but also prevents charge from being transited between the counterparts of the contact.Consistency between theory predictions and observations evidences the validity of the proposal of interface elastic Coulomb repulsion that serves as the rule for the superlubricity of ice,wet and dry frictions,which also reconciles the superhydrophobicity,superlubricity,and supersolidity at contacts.展开更多
基金supported by Zhejiang Provincial Natural Science Foundation of China under Grant No.LQ18E030005,LY18E060005,LY19E020006,LY18E020007National Natural Science Foundation of China(No.51902301)。
文摘Cation vacancies can bring numerous surprising characters due to its multifarious electron and orbit distribution.In this work,d-MnO_(2) with alkali-ion(K,Na,Li)associated manganese(Mn)vacancies is fabricated by a simple hydrothermal reaction,and the correlation between their electronic structure and pseudocapacitance are systematically investigated.FESEM/TEM images have shown that the morphology of MnO_(2) is obviously changed after the introducing of cation vacancies.The position of alkali-ion in MnO_(2) structure can be controlled by adjusting the ion concentration.XRD patterns and Raman spectra demonstrate that the alkali-ion is embedded in Mn vacancies at low concentration,while entered the interlayer of MnO_(2) at high concentration.The existence of Mn vacancies will resulting in the distortion of neighboring atoms,leading to the electronic delocalization,and thus enhancing the conductivity,pseudocapacitance and rate capability of MnO_(2).Accordingly,the specific capacitances of optimized 0.4 KMO,0.4 NaMO and 0.4 LiMO samples are enhanced about 1.9,1.6 and 1.6 times compared to pure MnO_(2).Meanwhile,the rate performance has also been improved about 76%,46%and 42%,respectively.Theoretical calculations further confirm that the Mn vacancies can generate additional occupancy states and cause an increase in carrier concentration,which will improve the conductivity and further boost the pseudocapacitance of MnO_(2).This result open up a promising approach to explore active and durable electrode materials.
基金Financial supports from the National Natural Science Foundation of China(Nos.21273191 and 11502223)and inspiring discussion with Professor Ya-Pu Zhao are gratefully acknowledged.
文摘Superlubricity means non-sticky and frictionless when two bodies are set contacting motion.Although this occurrence has been extensively investigated since 1859 when Faraday firstly proposed a quasiliquid skin on ice,the mechanism behind the superlubricity remains uncertain.This report features a consistent understanding of the superlubricity pertaining to the slipperiness of ice,self-lubrication of dry solids,and aqueous lubricancy from the perspective of skin bond-electron-phonon adaptive relaxation.The presence of nonbonding electron polarization,atomic or molecular undercoordination,and solute ionic electrification of the hydrogen bond as an addition,ensures the superlubricity.Nonbond vibration creates soft phonons of high magnitude and low frequency with extraordinary adaptivity and recoverability of deformation.Molecular undercoordination shortens the covalent bond with local charge densification,which in turn polarizes the nonbonding electrons making them localized dipoles.The locally pinned dipoles provide force opposing contact,mimicking magnetic levitation and hovercraft.O:H−O bond electrification by aqueous ions has the same effect of molecular undercoordination but it is throughout the entire body of the lubricant.Such a Coulomb repulsivity due to the negatively charged skins and elastic adaptivity due to soft nonbonding phonons of one of the contacting objects not only lowers the effective contacting force but also prevents charge from being transited between the counterparts of the contact.Consistency between theory predictions and observations evidences the validity of the proposal of interface elastic Coulomb repulsion that serves as the rule for the superlubricity of ice,wet and dry frictions,which also reconciles the superhydrophobicity,superlubricity,and supersolidity at contacts.
