Mn-doped ZnO nanocrystals are synthesized by a wet chemical route and treated in H_2/Ar atmosphere with different H_2/Ar ratios.It is found that hydrogen annealing could change the coordination environment of Mn in ZnO lattice and manipulate the magnetic properties of Mn-doped ZnO.Mn ions initially enter into interstitial sites and a Mn^(3+)O_6 octahedral coordination is produced in the prepared Mn-doped ZnO sample,in which the nearest neighbor Mn^(3+) and O^2 ions could form a Mn^(3+)-O^(2-)-Mn^(3+) complex.After H_2 annealing,interstitial Mn ions can substitute for Zn to generate the Mn^(2+)O_4tetrahedral coordination in the nanocrystals,in which neighboring Mn^(2+) ions and H atoms could form a Mn^(2+)-O^(2-)-Mn^(2+)complex and Mn-H-Mn bridge structure.The magnetic measurement of the as-prepared sample shows room temperature paramagnetic behavior due to the Mn^(3+)-O^(2-)-Mn^(3+) complex,while the annealed samples exhibit their ferromagnetism,which originates from the Mn-H-Mn bridge structure and the Mn-Mn exchange interaction in the Mn^(2+)-O^(2-)-Mn^(2+)complex.
Sodium-ion batteries(SIBs) recently have received a worldwide attention due to the resource abundance of sodium and similar battery chemistry with lithium-ion batteries(LIBs). However, search for suitable anodes for SIBs still remains a challenge since graphitized carbon, the anode for commercial LIBs, usually exhibits low electrochemical Na-storage activity. In this work, a unique graphene-reinforced Ni_3S_2 thin film(Ni_3S_2/G) has been constructed and investigated as a promising anode for SIBs. The Ni_3S_2 thin film has a thickness of 200–300 nm and is composed of small sized crystals of around 100 nm. The graphene has a wrinkled surface profile which offers three-dimensional networks for electron conductivity and structural reinforcement. The Ni_3S_2/G thin film exhibits high capacity, excellent cycling stability and good rate capability due to the introduction of wrinkled graphene. Ni_3S_2/G can deliver a high initial capacity of 791 m Ah g^(-1)at 50 m A g^(-1). The capacity can be maintained at 563 m Ah g^(-1)after 110 cycles.This work provides a unique design for high-performance SIBs anodes.
In this work, a facile, one-pot route has been applied to synthesize nanohybrids based on mixed oxide Ni Fe2O4 and reduced graphene oxide(r GO). The hybrid is constructed by nanosized Ni Fe2O4 crystals confined by fewlayered r GO sheets. The formation mechanism and microstructure of the hybrids have been clarified by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy.Electrochemical tests show that the performance of Ni Fe2O4 can be considerably improved by r GO incorporation. The performance improvement can be attributed to the two-dimensional conductive channels and the unique hybrid structure r GO constructed. The easy synthesis and good electrochemical performance of Ni Fe2O4/r GO hybrid make it a promising anode material for Li-ion batteries.
A Co3O4 nanorod supported Pd electro-catalyst for the methanol electro-oxidation(MEO) has been fabricated by the combination of hydrothermal synthesis and microwave-assisted polyol reduction processes. The crystallographic property and microstructure have been characterized using XRD, SEM and TEM. The results demonstrate that Pd nanoparticles(Pd NPs) with a narrow particle size distribution(3-5 nm) are uniformly deposited onto the surface of Co3O4 nanorods. Electrochemical measurements show that this catalyst having a larger electrochemically active surface area and a more negative onset-potential exhibits enhanced catalytic activity of 504 m A/mg Pd for MEO comparing with the Pd/C catalyst(448 m A/mg Pd). The dependency of log I against logv reveals that MEO on Pd-Co3O4 electrode is under a diffusion control.Electrochemical impedance spectroscopy(EIS) measurement agrees well with the CV results. The minimum charge transfer resistance of MEO on Pd-Co3O4 is observed at-0.05 V, which coincides with the potential of MEO peak.
Yanbiao RenShichao ZhangHua FangXin WeiPuheng Yang
Pd@Ru bimetallic nanoparticles deposited on carbon black electro-catalysts have been fabricated by microwave-assisted polyol reduction method and investigated for methanol electro-oxidation(MEO). The structure and electro-catalytic properties of the as-prepared catalysts were characterized by XRD, SEM, TEM and cyclic voltammetry(CV) techniques. The results showed that the introduction of Ru element(2-10 wt%) into Pd 20 wt%/C(hereafter, denoted as Pd/C) produced a series of core-shell structured binary catalysts. Pd@Ru 5 wt%/C(hereafter, denoted as Pd@Ru5/C) catalyst displayed the highest catalytic activity towards MEO. And the mass activity of Pd@Ru5/C electrode catalyst at E =-0.038 V(vs. Hg/HgO) was 1.42 times higher than that of Pd/C electrode catalyst. In addition, the relationship between the catalytic stability for MEO on Pd@Ru/C catalysts and the value of Jbp/Jfp(the ratio of MEO peak current density in the negative scan and positive scan) were also investigated. The result demonstrated that Pd@Ru5/C offering the smallest value of Jbp/Jfpdisplayed the best stable catalytic performance.
用溶胶-凝胶法结合高温煅烧过程制备富锂正极材料Li_(1.2)Mn_(0.54)Ni_(0.13)Co_(0.13)O_2,对800°C和900°C煅烧后得到的2种材料(标记为S8和S9)进行物相和形貌表征以及电化学测试。电化学测试结果表明,样品S9具有较高的放电容量、较好的循环稳定性和较小的电荷转移电阻。样品S9在0.1 C(25 m A·g^(-1))时的首次充电容量为345.0 m A·h·g^(-1),首次放电容量为273.9 m A·h·g^(-1),首次库伦效率为79.4%。1 C时,首次放电容量为188.1 m A·h·g^(-1),循环30周后放电容量为173.3 m A·h·g^(-1),容量保持率为92.1%。结果表明,尽管富锂正极材料R-3m层状结构在800°C煅烧后已经形成,但仍需要经过更高温度煅烧,以提高锂离子和过渡金属离子在各自层中的有序度,从而有效地提高材料的电化学性能。
