Pure tungsten powder (W, 200 mesh, 99%), hydrogen peroxide solution (H2O2, 30%), ethanol (99.8%), nickel (II) nitrate hexahydrate (Ni(NO3)2·6H2O, 98%), urea (CON2H4, 99%) and propylene carbonate (C4H6O3) were all obtained from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, ...