*2.1. Materials*

GNPs were purchased from UChees Co. (Taiwan, China) with 1~10 nm thickness, 0.5–20 μm lateral dimension and surface area of 400–700 m2/g. MWCNTs, grown by CVD, were purchased from Conjutek Co. Taiwan with the diameter in the range of 10–50 nm, length of 100–200 μm, surface area of 400–700 m2/g, and purity >98.5%. Both of GNPs and MWCNTs were used as received without any modification.
