The preparation process of the graphene/CNT composite
lms 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
ml1) (Fig. 2b). The target lms were then fabricated by separately
spraying the resulting suspensions onto clean stainless
steel substrates by means of a spray gun in a nitrogen ow of
0.2 MPa (Fig. 2a and c). Lastly, the obtained lms were heated at
50 C in a nitrogen ow to remove residual solvent.