*2.3. Preparation of CNF, CNF–CNT and CNF–GnP Aerogels*

CNTs or GnPs were added to CNF dispersions with various mass ratios of CNF to carbon nanomaterial (1:0, 3:1, 1:1, 1:3 and 0:1). The final concentration of all the mixtures was controlled to be 6 mg mL<sup>−</sup>1. The mixtures were sonicated by ultrasonic cell disruptor (SCIENTZ, IID, Ningbo, China) at 600 W for 30 min in an ice bath. Each sample was frozen at −21 ◦C for 4 h in a 15 mL polypropylene centrifuge tube followed by freeze-drying at −50 ◦C. The CNF–CNT and CNF–GnP hybrid aerogels were obtained. Pure CNF aerogel also was obtained via the same method from a CNF suspension of 6 mg mL<sup>−</sup>1.
