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Core-shell Ni(OH) 2 @CuO electrodes grown on three-dimensional copper foams were synthesized by a facile thermal oxidation and chemical bath deposition method. The electrochemical experiments present that the Ni(OH) 2 @CuO electrode delivers large areal capacitance (1.625 F cm À 2 at 3 mA cm À 2 ), excellent rate capacity (1.285 F cm À 2 at 30 mA cm À 2 ), and brilliant cycling stability (retaining 96.4 % after 5000 cycles). In addition, an asymmetric supercapacitor (ASC) device was designed taking Ni (OH) 2 @CuO electrode and active carbon (AC) as a positive and negative electrode, respectively. The ACS device exhibits a high voltage of 1.6 V and remarkable energy density up to 58.59 Wh kg À 1 at a power density of 686.45 W kg À 1 . This work may serve to develop new areas of low-cost materials for energy storage and conversion system.

In order to further improve the photocatalytic performance of BiFeO3 (BFO), novel Au-induced hierarchical nanofibers/nanoflakes structured BiFeO3 homojunctions (Aux-BFO, x = 0, 0. 6, 1.2, 1.8, 2.4 wt%) were in situ synthesized through a simple reduction method with assist of sodium citrate under the analogous hydrothermal environment. The effect of loading amount of Au nanoparticles (NPs) on the physicochemical properties and photocatalytic activity was investigated in detail. The Au1.2-BFO NFs sample show the best photocatalytic activity (85.76%), much higher than that for pure BFO samples (49.49%), mainly due to the hierarchical nanofibers/nanoflakes structured homojunction, the surface plasmon resonance (SPR) effect of Au NPs, as well as the presence of defects (Fe2+/Fe3+ pairs and oxygen vacancy). Furthermore, the possible formation mechanism of the unique homojunction and the enhanced photocatalytic mechanism for the degradation of methylene blue (MB) dye are proposed. It is proven that holes (h+) play the decisive role in the photocatalytic process. The present work provides a fascinating way to synthesize efficient homojunctions for the degradation of organic pollutes.