For electrodes synthesis, we have prepared the materials which are listed in Table(2.1.1). 1.25 g Gallic acid, 1.1366 g CuCl2•2H2O, 1 g Polyethyleneimine and not quantitative Sodium hydroxide are needed in the preparation. First of all, Gallic acid and CuCl2•2H2O were dissolved into 30 mL deionized water under 40 ℃ separately. Likewise, Polyethyleneimine was dissolved into 70 mL deionized water. Subsequently, the Polyethyleneimine solution was added to the mixture of CuCl2•2H2O and Gallic acid. After synthesizing the solution of three materials, we added Sodium hydroxide to the solution in order to adjust the pH to 8. After that, we cooled down the solution to room temperature and the turbid substance was precipitated. Lastly, we removed the residue by suction filtration and obtained the dark green powder as the electrode material.