ZIF-8 was synthesized via TEA-assisted procedure . Typically, TEA (14 mmol) was added to a zinc nitrate solution (0.8 mL, 0.67 mmol), followed by the addition of 2.3 mL of Hmim solution (6.9 mmol). The product was separated via centrifugation, washed with water (2 × 20 mL) and ethanol (2 × 20 mL), and dried overnight at 85 o C. ZnO@N-doped C was synthesized via the carbonization of ZIF-8 at 600 o C for three h with a heating rate of 10 o C/min. The carbonized material was washed with water and ethanol. It was dried overnight at 85 o C.