Jinhuan Yao

Density Functional Theory Investigations on the Structure and Electronic Properties of Normal Spinel ZnFe2O4

The structure and electronic properties of normal spinel ZnFe2O4 have been investigated using density functional theory (DFT) within the generalized-gradient approximation (GGA) and the local density approximation (LDA). The calculation results show that GGA/RPBE with ultrasoft pseudopotential method is a good method in predicting the crystal structures of the normal spinel ZnFe2O4. The results also indicate that the normal spinel ZnFe2O4 is direct gap semiconductor. There is a very strong hybridization between the Fe 3d state and the O 2p state, and a very strong hybridization between the Zn 3d state and O 2p state. The Zn−O bonds and Fe−O bonds have a covalent character.

Facile synthesis of nanocrystalline-assembled nest-like NiO hollow microspheres with superior lithium storage performance

Interconnected nest-like NiO hollow microspheres assembled from nanocrystallites are prepared by a facile hydrothermal method followed by annealing at 700 °C in air. It is noteworthy that the NiO hollow microspheres exhibit a very significant pseudocapacitive effect which makes a great contribution to the enhanced lithium storage performance. Benefiting from the advantages of unique nest-like nanoarchitecture and pseudocapacitive effect, the NiO hollow microspheres show high reversible capacity, superior cyclic performance, and excellent high rate capability. When used as anode materials for lithium ion batteries, the NiO hollow microspheres maintain a capacity of 650 mA h g−1 after 100 cycles at a current density of 1 A g−1. The capacity retention is 93%, which corresponds to a very small capacity decay of 0.07% per cycle. In particular, even at an ultra-high current density of 10 A g−1, the NiO electrode still delivers a stable discharge capacity of 457 mA h g−1.

First-Principles Study of the Geometric and Electronic Structures of Zinc Ferrite with Vacancy Defect

The effects of Zn-vacancy (Zn7Fe16O32), Fe-vacancy (Zn8Fe15O32), and O-vacancy (Zn8Fe16O31) on the geometric and electronic structures of normal spinel ZnFe2O4 (Zn8Fe16O32) are studied by using a first-principles method based on density functional theory (DFT) at a generalized gradient approximation (GGA) level. Compared with perfect ZnFe2O4, the lattice parameters of ZnFe2O4 with Zn-vacancy or Fe-vacancy increase slightly, while the lattice parameters of ZnFe2O4 with O-vacancy decrease significantly. All the vacancy defects induce the distortion of the unit cell structure, especially for the O-vacancy. Zn-vacancy, Fe-vacancy, and O-vacancy in ZnFe2O4 cannot be formed spontaneously, but Zn-vacancy is the most prone to form, followed by Fe-vacancy and O-vacancy under the condition of external energy supply. Zn-vacancy, Fe-vacancy, and O-vacancy change the properties of ZnFe2O4 from a semiconducting character to a metallic character. Either ZnFe2O4 or ZnFe2O4 has various vacancy defects, the strength of the O-Zn bond is stronger than that of the O-Fe bond, and both of them have a covalent bond character. Zn-vacancy enhances the strength of O-Fe bonds and slightly weakens the strength of O-Zn bonds around Zn-vacancy. Fe-vacancy induces a significant increase of the strength of O-Fe bonds and O-Zn bonds around Fe-vacancy. O-vacancy leads to a significant decrease in the strength of O-Zn bonds and to a slight increase in the strength of O-Fe bonds around O-vacancy.

First-Principles Investigation on the Electronic Structure and Stability of In-Substituted ZnFe2O4

The geometric structure, electronic structure, and stability of In-substituted ZnFe2O4 (Zn7InFe16O32 and Zn8Fe15InO32) are investigated by the density functional theory at generalized gradient approximation level. Compared with the perfect ZnFe2O4 (Zn8Fe16O32), the unit cell volume of In-substituted ZnFe2O4 increases and the structure deforms slightly. The formation energy of In substitution for Zn is smaller than that of In substitution for Fe, indicating that Zn7InFe16O32 is easier to be formed than Zn8Fe15InO32. In substitution changes the properties of ZnFe2O4 from semiconducting character to metallic character. For ZnFe2O4 and In-substituted ZnFe2O4, the strength of O–Zn bond is stronger than O–Fe bond and both of them have a covalent bond character. The strength of O-In bond is similar to that of O–Zn bond in Zn7InFe16O32, but weaker than O–Fe in Zn8Fe15InO32. In substitution for Zn causes the strength of O–Fe bonds around In atom to weaken. In substitution for Fe causes the strength of O–Zn bonds around In atom to weaken obviously, while the strength of O–Fe bonds strengthen slightly.

Experimental and Theoretical Study of the Electron Transfer Through Alkanedithol Molecules

The electron transport property of alkanedithiol molecules was investigated using conducting atomic force microscopy and first-principles calculations. The measured Current-voltage (I-V) curves show sigmoidal behavior and an exponential attenuation with molecular length, characteristic of nonresonant tunneling. The length-dependent decay parameter, β, is found to be approximately 1.15 per carbon atom (C−1) and is independent of applied bias (over a voltage range of ±1.0 V). The measured I-V characteristics of alkanedithiols are in excellent qualitative agreement with the results from first-principles calculations. The β value (0.97 per carbon atom) obtained from first-principles calculations is also independent of applied bias but slightly smaller than that from AFM measurement. The electron transmission spectra of alkanedithiol junctions are also analyzed to gain more insight into the length-dependent I-V curves.

Preparation of ZnFe2O4/α-Fe2O3 Nanocomposites From Sulfuric Acid Leaching Liquor of Jarosite Residue and Their Application in Lithium-Ion Batteries

Recycling Zn and Fe from jarosite residue to produce high value-added products is of great importance to the healthy and sustainable development of zinc industry. In this work, we reported the preparation of ZnFe2O4/α-Fe2O3 nanocomposites from the leaching liquor of jarosite residue by a facile chemical coprecipitation method followed by heat treatment at 800°C in air. The microstructure of the as-prepared ZnFe2O4/α-Fe2O3 nanocomposites were characterized by X-ray diffraction (XRD), Mössbauer spectroscopy, scanning transmission electron microscope (STEM), and X-ray photoelectron spectrum (XPS). The results demonstrated that the ZnFe2O4/α-Fe2O3 composites are composed of interconnected ZnFe2O4 and α-Fe2O3 nanocrystals with sizes in the range of 20–40 nm. When evaluated as anode material for Li-ion batteries, the ZnFe2O4/α-Fe2O3 nanocomposites exhibits high lithium storage activity, superior cyclic stability, and good high rate capability. Cyclic voltammetry analysis reveals that surface pseudocapacitive lithium storage has a significant contribution to the total stored charge of the ZnFe2O4/α-Fe2O3, which accounts for the enhanced lithium storage performance during cycling. The synthesis of ZnFe2O4/α-Fe2O3 nanocomposites from the leaching liquor of jarosite residue and its successful application in lithium-ion batteries open up new avenues in the fields of healthy and sustainable development of industries.

Synthesis and lithium storage performance of ZnFe2O4/C composites with the assistance of P123

ABSTRACT To improve the lithium storage performance of ZnFe2O4 as anode material for LIBs, ZnFe2O4/C composites were prepared by using a homogeneous precipitation method with the assistant of block copolymer P123, followed by annealing in argon atmosphere at 900°C. The series of ZnFe2O4/C samples prepared with P123 additive quantity of 0 wt.%, 2 wt.%, 5 wt.%, 8 wt.% and 10 wt.% (denoted as ZFO, ZFO/C-2%, ZFO/C-5%, ZFO/C-8% and ZFO/C-10%, respectively) were analyzed by physical characterizations and electrochemical characterizations. The results reveal that ZFO and ZFO/C-2% shares relatively smaller particles among the five samples. The surface of ZFO/C-2% has some obvious small pores, which can improve the infiltration of electrolyte and shorten the diffusion path of lithium ion. Compared with the pure ZFO, ZFO/C-2% exhibits much higher electrochemical activity, better rate performance, much improved cycling stability. After 50 charge/discharge cycles under a current density of 120 mA g−1, ZFO/C-2% electrode can retain a specific discharge capacity of 578 mAh g−1, much higher than that (433 mAh g−1) of ZFO. However, excessive adding P123 (ZFO/C-5%, ZFO/C-8% and ZFO/C-10%) during synthesis process induces an obvious agglomeration of particles, leading to significantly inferior lithium storage performance of ZnFe2O4.

First-principles study of the geometric and electronic structures of Mn-substituted ZnFe2O4

ABSTRACT The structure and electronic properties of Mn-substituted ZnFe2O4 were investigated by the first-principles method based on density functional theory (DFT). After Mn substitution, the unit cell volume of ZnFe2O4 decreases and the property of ZnFe2O4 changes from semiconducting character to metallic character. In the Mn−substituted ZnFe2O4, the strength of O−Mn bond is the strongest of all, next is O−Zn bonds and O−Fe bonds, and all of them have a covalent bond character. After Mn substitution, the strength of O−Fe bonds around Mn atom weakens obviously.

Theoretical Investigation on the Electron Transport Behavior of Fe-Porphyrin Complexes

The electron transport behaviors of oxygen and carbon monoxide complexes of Fe-porphyrin (FeP) are investigated by nonequilibrium Greens function techniques combined with Density Functional Theory calculations. The results show that the molecular current of FeP decreases dramatically after adsorptions of oxygen and carbon monoxide. The molecular current decreases with a order of FeP > FeP+O2 complex > FeP+CO complex. This change of the molecular current after adsorption of oxygen or carbon monoxide can be potentially used to design a molecular sensor or a molecular switch.