Xianfeng Hao

One-pot synthesized mesoporous Ni–Co hydroxide for high performance supercapacitors

AbstractMesoporous Ni(OH)2/Co(OH)2 electrode materials were synthesized via a simple one-pot procedure by combining homogeneous precipitation and stepwise precipitation method. The configuration of the porous Ni(OH)2/Co(OH)2 electrode materials synthesized provides 3D electron transmission channels through a high conductive Co(OH)2 distributed in the peripheral nanolayer of the composites, which is beneficial to rate capability and cycle stability. The Ni(OH)2/Co(OH)2 electrode materials have a specific surface area of 229xa0m2xa0g−1, which is approximately 40% higher than that of Ni(OH)2 (163xa0m2xa0g−1). Their specific capacitance is up to 1202 and 1022xa0Fxa0g−1 at the current densities of 10 and 20xa0Axa0g−1, respectively. Furthermore, the capacitance retention of the electrode materials at the current density of 10xa0Axa0g−1 is 98% after 5000xa0cycles. The synthesis method provides a novel simple route to fabricate heterostructure materials for capacitors with high electrochemical performance.n Graphical abstractᅟ

Negligible spin-orbit coupling effect in the Mott-insulating antiferromagnet KRuO4

A comprehensive investigation of the electronic and magnetic properties of KRuO4 has been performed using the first-principles calculations in order to clarify the importance of Coulomb interaction and spin-orbit coupling effect. The results indicate that its ground state is of a G-type Mott-insulating antiferromagnet with nearest-neighbor antiferromagnetic coupling, and the computed magnetic moment of Ru7+ ion is 0.50 μB, in nice agreement with the observed value of 0.57(7) μB. In addition, the electronic structure near the Fermi level is dominated by strong hybridized Ru 4d and O 2p states. In sharply contrast with KOsO4, the significantly weaker spin orbit coupling of Ru 4d electrons has negligible impact on the electronic and magnetic properties of KRuO4, and the orbital contribution to the total moment is minor. On the other hand, the on-site Coulomb repulsion affects the band structure significantly, and is indispensable for appraising the electronic properties, opening the band gap, establishing th...

Pressure induced structural and spin state transitions in Sr3Fe2O5

We report on a first-principles study of the effect of pressure on the structural, electronic and magnetic properties of the two-legged spin ladder structure Sr3Fe2O5, using density functional theory within the generalized gradient approximation (GGA)+U method. The theoretical results showed that a first order structural transition with the space-group change from Immm to Ammm is found around 33 GPa, which is in fair agreement with the experimental value (30 GPa). Furthermore, a spin state cross from the high spin state (S = 2) to the intermediate spin state (S = 1) has been demonstrated in the four-fold square-planar FeO4 coordination, when further pressure is applied. The spin collapse is accompanied by a magnetic configuration transition (antiferromagnetic to ferromagnetic) and an electronic transition (insulating to metallic). However, the predicted pressure for spin state transition is considerably larger than the experimental value. The reason for this discrepancy originates from the constant Hubbard U value we adopted. Furthermore, the transition mechanism underlined has been uncovered in terms of density of states analysis and the evolution of the lattice parameters under the pressure.