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Degenerate antiferromagnetic states in spinel oxide LiV2O4

Chinese Physics B 2020年第7期29卷 542-547页

作者：龚本超杨焕成金魁刘凯卢仲毅 Department of Physics and Beijing Key Laboratory of Opto-electronic Functional Materials&Micro-nano Devices Renmin University of ChinaBeijing 100872China Beijing Computational Science Research Center Beijing 100193China Beijing National Laboratory for Condensed Matter Physics Institute of PhysicsChinese Academy of SciencesBeijing 100190China Collaborative Innovation Center of Quantum Matter Beijing 100190China

The magnetic and electronic properties of spinel oxide LiV2O4 have been systematically studied by using the spin-polarized first-principles electronic structure calculations.We find that a series of magnetic states,in which the ferromagnetic(FM)V4 tetrahedra are linked together through the corner-sharing antiferromagnetic(AFM)V4 tetrahedra,possess degenerate energies lower than those of other spin configurations.The large number of these energetically degenerated states being the magnetic ground state give rise to strong magnetic frustration as well as large magnetic entropy in LiV2O4.The corresponding band structure and density of states of such a typical magnetic state in this series,i.e.,the ditetrahedron(DT)AFM state,demonstrate that LiV2O4 is in the vicinity of a metal-insulator transition.Further analysis suggests that the t2g and eg orbitals of the V atoms play different roles in the magnetic exchange interactions.Our calculations are consistent with previous experimental measurements and shed light on understanding the exotic magnetism and the heavy-fermion behavior of LiV2O4.

关键词： spinel oxide magnetic properties heavy fermion first-principles calculations

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Highly active and durable triple conducting composite air electrode for low-temperature protonic ceramic fuel cells

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Nano Research 2023年第7期16卷 9280-9288页

作者： Qi Huang Shanshan Jiang Yujia Wang Jingjing Jiang Yubo Chen Jiahuan Xu Hao Qiu Chao Su Daifen Chen School of Energy and Power Jiangsu University of Science and TechnologyZhenjiang 212100China Institute of Analysis and Testing Beijing Academy of Science and Technology(Beijing Center for Physical and Chemical Analysis)Beijing 100089China School of Material Science and Engineering Nanyang Technological University50 Nanyang AvenueSingapore 639798Singapore School of Science Jiangsu University of Science and TechnologyZhenjiang 212100China

Protonic ceramic fuel cells(PCFCs)are more suitable for operation at low temperatures due to their smaller activation energy(Ea).Unfortunately,the utilization of PCFC technology at reduced temperatures is limited by the lack of durable and high-activity air electrodes.A lot number of cobalt-based oxides have been developed as air electrodes for PCFCs,due to their high oxygen reduction reaction(ORR)activity.However,cobalt-based oxides usually have more significant thermal expansion coefficients(TECs)and poor thermomechanical compatibility with electrolytes.These characteristics can lead to cell delamination and degradation.Herein,we rationally design a novel cobalt-containing composite cathode material with the nominal composition of Sr_(4)Fe_(4)Co_(2)O_(13)+δ(SFC).SFC is composed of tetragonal perovskite phase(Sr_(8)Fe_(8)O_(23)+δ,I4/mmm,81 wt.%)and spinel phase(Co_(3)O_(4),Fd3m,19 wt.%).The SFC composite cathode displays an ultra-high oxygen ionic conductivity(0.053 S·cm^(-1)at 550℃),superior CO_(2)tolerance,and suitable TEC value(17.01×10^(-6)K^(-1)).SFC has both the O_(2)^(-)/e^(-)conduction function,and the triple conducting(H^(+)/O_(2)^(-)/e^(-))capability was achieved by introducing the protonic conduction phase(BaZr_(0.2)Ce_(0.7)Y_(0.1)O_(3-δ),BZCY)to form SFC+BZCY(70 wt.%:30 wt.%).The SFC+BZCY composite electrode exhibits superior ORR activity at a reduced temperature with extremely low area-specific resistance(ASR,0.677Ω·cm^(2)at 550℃),profound peak power density(PPD,535 mW·cm^(-2)and 1.065 V at 550℃),extraordinarily long-term durability(>500 h for symmetrical cell and 350 h for single cell).Moreover,the composite has an ultra-low TEC value(15.96×10^(-6)K^(-1)).This study proves that SFC+BZCY with triple conducting capacity is an excellent cathode for low-temperature PCFCs.

关键词： protonic ceramic fuel cells spinel oxide composition tuning triple-conducting

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Magnetic field induced synthesis of(Ni, Zn)Fe2O4 spinel nanorod for enhanced alkaline hydrogen evolution reaction

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Progress in Natural Science:Materials International 2023年第2期33卷 172-177页

作者： Mingkun Xia Yan zhang Jiangyue Xiao Peng Zhao Zhongjun Hou Fanglin Du Dawei Chen Shuo Dou College of Material Science and Engineering Qingdao University of Science and Technology Key Laboratory of Bio-Based Material Science and Technology of Ministry of Education Northeast Forestry University

Recently, the introduction of external fields(light, thermal, magnetism, etc.) during electrocatalysis reactions gradually becomes a new strategy to modulate the catalytic activities. In this work, an external magnetic field was innovatively employed for the synthesis progress of(Ni, Zn)Fe2O4spinel oxide(M-(Ni, Zn)Fe2O4). Results indicated the magnetic field(≤250 m T) would affect the morphology of catalyst due to the existing Fe ions, inducing the M-(Ni, Zn)Fe2O4nanosphere particles to be uniform and coral-like nanorods. In addition, the electronic structure of the catalyst was regulated by the valence state of Fe, changing the bonding of metal to oxygen atoms in different spinel sites. The results manifested that the M-(Ni, Zn)Fe2O4requires a lower overpotential of only 67m V to deliver 10 m A cm-2for hydrogen evolution reaction(HER) in alkaline electrolyte. Moreover, M-(Ni, Zn)Fe2O4respectively as the anode and cathode electrode for the overall water splitting, the catalysis system requires a cell voltage of only 1.76 V to gain a current density of 50 m A cm-2, combining with an excellent discharging stability after 10 h. This work provides a facile synthesis strategy toward the design of efficient non-noble metal catalysts for alkaline HER and overall water splitting.

关键词： Hydrogen evolution reaction Magnetic field Water splitting spinel oxide Electron modulation

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Coexistence of magnetic and ferroelectric properties in Y_(0.1)Co_(1.9) MnO_4

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Chinese Physics B 2010年第7期19卷 497-500页

作者：刘毅 College of Science Guizhou University

The magnetic, conductivity, and dielectric properties have been investigated in single-phase polycrystalline Y0.1Co1.9MnO4. The temperature-dependent magnetisation reveals the ferromagnetic transition in sample at a low temperature （～186 K）. Magnetisation as a function of field H （M H loop） indicated the weak ferromagnetism of the sample at room temperature. The constant e and dielectric loss tg5 measurements represent a ferroelectric phase transition at a higher temperature （~650 K）, while the conductivity shows an insulator-metallic transition. The ferro- electric hysterisis loops and capacitance voltage measurements confirm the ferroelectric nature of the sample at room temperature. The observed ferromagnetism and ferroelectric nature in this material suggests a potential multiferroic application.

关键词： spinel oxide dielectric conductivity magnetic

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Boosting Electrocatalytic Oxygen Evolution by Cation Defect Modulation via Electrochemical Etching

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CCS Chemistry 2021年第1期3卷 675-685页

作者： Xiang Chen Meng Yu Zhenhua Yan Weiyi Guo Guilan Fan Youxuan Ni Jiuding Liu Wei Zhang Wei Xie Fangyi Cheng Jun Chen Renewable Energy Conversion and Storage Center Key Laboratory of Advanced Energy Materials Chemistry(Ministry of Education)Engineering Research Center of High-efficiency Energy Storage(Ministry of Education)College of ChemistryNankai UniversityTianjin 300071

Defects engineering is an efficient strategy to enhance the performance of electrode materials by modulating the local electronic structure but usually requires costly and complicated processing.Here,an electrochemical reduction etching method has been developed for controllable tailoring of the cationic defects in iron-based oxides under mild conditions.The optimized defective spinel-type iron nickel oxide exhibits an overpotential as low as 270 mV at 10 mA cm−2 and a Tafel slope of only 33.8 mV dec−1 for the oxygen evolution reaction(OER),outperforming the benchmark RuO2 and pristine oxide.Experiments and theoretical calculations reveal that Fe vacancies can enhance Ni–O covalency,increase the density of active sites,and optimize the surface electronic structure,which promote the water adsorption/activation and moderate oxygen intermediate species adsorption,thus significantly enhancing OER activity.This work provides a promising approach to create cation deficiency and mechanistic insight to understand the vacancy-induced enhancement of oxygen electrocatalysis.

关键词： defect chemistry electrochemical synthesis spinel oxide oxygen evolution metal–oxygen covalency

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