Highly conductive pristine graphene electrodes were fabricated by inkjet printing using ethyl cellulose-stabilized ink prepared from pristine graphene. Pristine graphene was generated by exfoliation from graphite using ultrasound-assisted supercritical CO2. The ink, at concentrations up to 1 mg/mL, was stable for more than 9 months and had compatible fluidic characteristics for efficient and reliable inkjet printing. The inkjet printing patterns of the graphene on diverse substrates were uniform and continuous. After 30 printing passes and annealing at 300 °C for 30 min, the printed films developed a high conductivity of 9.24 × 103 S/m. The resistivity of the printed electrodes on the flexible substrates increased by less than 5% after 1000 bending cycles and by 5.3% under a folding angle of 180°. The presented exfoliated pristine graphene and the corresponding efficient methods for formulating the ink and fabricating conductive electrodes are expected to have high potential in applications involving graphene-based flexible electronic devices.

A simple, cost-effective approach is presented for producing exfoliated films of pure graphene or polymer–graphene composite with high yield, high conductivity, and processability. The approach combines supercritical CO2 with ultrasonics. Characterization by Raman spectroscopy combined with atom force field microscopy demonstrates that the graphene sheets were obtained with 24% as monolayers, 44% as bilayers, and 26% as trilayers. The layer number and lateral size of graphene sheets can be controlled by adjusting the process parameters. The yield of graphene sheets with a lateral size of about 0.5–5.0 μm is about 16.7 wt % under optimum conditions, which can be easily raised to 40–50 wt % by repeated exfoliation of the sediment that remained in the reactor. The resultant pure graphene film made by filtration has a high electrical conductivity of 2.8 × 107 S/m. The electrical conductivity of the film of polyvinyl alcohol–graphene composite is 300 S/m.

A facile and general approach was developed to exfoliate layer materials to produce two-dimensional atomic crystals. A single and few layers of BN, MoS2, and WS2 were obtained via directly exfoliating their powder materials using supercritical CO2 assisted with ultrasound. The effects of supercritical CO2 coupled with ultrasound play a key role in the exfoliation process. The layer numbers and sizes of the BN, MoS2, and WS2 can be easily controlled by adjusting the power and the time of ultrasonication. The AFM images suggest single-layered BN, MoS2, and WS2 were produced, respectively. Their lateral sizes are about 0.5–2 μm, and almost 90% of the BN sheets are less than five layers. The electric diffraction patterns demonstrate that the crystallinities of the produced samples remained the same as that of the raw material during the exfoliating process. This novel technique is cost-effective and scalable, and can be widely used in the production of two-dimensional atomic crystals with high quality.

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