The preparation process of the graphene/CNT composite
flms was as follows: the graphene, the CNTs and their mixtures
with difference mass ratios of graphene to CNTs were separately
dispersed into acetone with the aid of ultrasonication for 3 h to
obtain a series of homogeneous and dark suspensions (0.1 mg
ml-1) (Fig. 2b). The target flms were then fabricated by separately
spraying the resulting suspensions onto clean stainless
steel substrates by means of a spray gun in a nitrogen flow of
0.2 MPa (Fig. 2a and c). Lastly, the obtained flms were heated at
50 C in a nitrogen flow to remove residual solvent.