Transition-metal oxides have attracted increased attention in the application of high-performance lithium ion batteries(LIBs), owing to its higher reversible capacity,better structural stability and high electronic conductivity.Herein, CoWO_4 nanoparticles wrapped by reduced graphene oxide(CoWO_4–RGO) were synthesized via a facile hydrothermal route followed by a subsequent heat-treatment process. When evaluated as the anode of LIB, the synthetic CoWO_4–RGO nanocomposite exhibits better Li^+ storage properties than pure CoWO_4 nanostructures synthesized without graphene oxide(GO). Specifically, it delivers a high initial specific discharge capacity of1100 mAh·g^(-1) at a current density of 100 mA·g^(-1), and a good reversible performance of 567 mAh·g^(-1) remains after the 100th cycle. Moreover, full battery using CoWO_4–RGO as anode and commercial LiCoO_2 powder as cathode was assembled, which can be sufficient to turn on a 3 V,10 mW blue light emitting diode(LED). The enhanced electrochemical performance for lithium storage can be attributed to the three-dimensional(3D) structure of the CoWO_4–RGO nanocomposite, which can accommodate huge volume changes, and synergetic effect between CoWO_4 and reduced graphite oxide(RGO) nanosheets,including an increased conductivity, shortened Li^+ diffusion path.
Gaining insight into the structure evolution of transition-metal phosphides during anodic oxidation is significant to understand their oxygen evolution reaction(OER) mechanism, and then design highefficiency transition metal-based catalysts. Herein, NiCo_2P_x nanowires(NWs) vertically grown on Ni foam were adopted as the target to explore the in-situ morphology and chemical component reconstitution during the anodic oxidation. The major factors causing the transformation from NiCo_2P_x into the hierarchical NiCo_2P_x@CoNi(OOH)_x NWs are two competing reactions: the dissolution of NiCo_2P_x NWs and the oxidative re-deposition of dissolved Co^(2+) and Ni^(2+) ions, which is based primarily on the anodic bias applied on NiCo2 Px NWs. The well balance of above competing reactions, and local pH on the surface of NiCo_2P_x NW modulated by the anodic oxidation can serve to control the anodic electrodeposition and rearrangement of metal ions on the surface of NiCo_2P_x NWs, and the immediate conversion into CoNi(OOH)_x. Consequently, the regular hexagonal CoNi(OOH)_x nanosheets grew around NiCo_2P_x NWs.Benefiting from the active catalytic sites on the surface and the sufficient conductivity, the resultant NiCo_2P_x@CoNi(OOH)_x arrays also display good OER activity, in terms of the fast kinetics process, the high energy conversion efficiency, especially the excellent durability. The strategy of in-situ structure reconstitution by electrochemical reaction described here offers a reliable and valid way to construct the highly active systems for various electrocatalytic applications.
Xue BaiZhiyu RenShichao DuHuiyuan MengJun WuYuzhu XueXiaojun ZhaoHonggang Fu
