A surface engineering approach was adopted for the preparation of a core-shell structure of bimetallic PtCo nanoparticles to improve catalytic activity for methanol oxidation on a mass basis. Synthesis of core-shell Co@Pt nanocomposite catalysts with different Pt content was carried out by reducing platinum precursors using ethylene glycolcitrate (EG) in aqueous solution containing previously formed Co/C. Characterizations were carried out using transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectra (XPS) and electrochemical techniques. The synthesized core-shell Co@Pt nanocomposite catalysts showed enhanced catalytic activity in the methanol oxidation reaction. The enhancement may result from favorable strain effects related to the thickness of Pt shell formed on the non-noble metal substrate. Moreover, the electrocatalytic activity was optimized by tuning shell thickness. This result confirms that changing the Pt shell thickness has a significant effect on the catalytic activities of nonnoble core-noble shell bimetallic nanoclusters. The developed surface-modification method (i.e. by fine-tuning the thickness of Pt shell on the non-noble metal substrate) has great potential application for producing highly active electrochemical catalysts for methanol oxidation on a large scale. The work thus paves the way for further investigating the strain effect in core-shell bimetallic catalysts.

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Porous Ni(OH)2 nanoflakes are directly grown on the surface of nickel foam supported Ni3Se2 nanowire arrays using an in situ growth procedure to form 3D Ni3Se2@Ni(OH)2 hybrid material. Owing to good conductivity of Ni3Se2, high specific capacitance of Ni(OH)2 and its unique architecture, the obtained Ni3Se2@Ni(OH)2 exhibits a high specific capacitance of 1689 µAh cm−2 (281.5 mAh g−1) at a discharge current of 3 mA cm−2 and a superior rate capability. Both the high energy density of 59.47 Wh kg−1 at a power density of 100.54 W kg−1 and remarkable cycling stability with only a 16.4% capacity loss after 10 000 cycles are demonstrated in an asymmetric supercapacitor cell comprising Ni3Se2@Ni(OH)2 as a positive electrode and activated carbon as a negative electrode. Furthermore, the cell achieved a high energy density of 50.9 Wh L−1 at a power density of 83.62 W L−1 in combination with an extraordinary coulombic efficiency of 97% and an energy efficiency of 88.36% at 5 mA cm−2 when activated carbon is replaced by metal hydride from a commercial NiMH battery. Excellent electrochemical performance indicates that Ni3Se2@Ni(OH)2 composite can become a promising electrode material for energy storage applications.

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NixCoy alloy pompoms formed by the aggregation of nano ultrathin sheets were prepared by simultaneous reduction of NiCl2 and CoCl2 with NaBH4via a liquid-liquid interface reaction. Ni1Co3 pompoms produced markedly higher activity and stability as hydrazine oxidation catalysts than Ni, Co and other NixCoy pompom catalysts.