Evaporation induced electricity generation in freestanding and flexible carbon-based hybrid film

Energy harvesting from ambient environment attracts widespread interest for its great potential in green and sustainable development. Very recently, evaporation, a ubiquitous process existing in nature was demonstrated as a reliable process, which can convert low-grade thermal energy in environment into electricity. Evaporation-driven water flow within a piece of carbon black sheet or printed porous carbon film could generate sustainable direct-current electricity with open-circuit voltage (V_oc) up to 1 V, and with lifetime over hundreds of hours. However, both the flame-deposited carbon black sheets and all-printed porous carbon films need to be deposited or printed on rigid substrates (e.g., silica glass and Al₂O₃ plate) in the previous work, which has deceased the effective evaporation area and occupied excessive space, thus limiting the application of this new energy harvesting strategy as a practical power source. In this work, we present the fabrication of a flexible and freestanding carbon nanoparticles/glass fiber hybrid film (CNGF) for electricity generation via evaporation-driven water flow within it. The CNGF hybrid film has a structure of reinforced concrete, thus exhibits good flexibility and mechanical properties. The carbon film with the size of 1 cm×4.5 cm×0.13 mm and glassfiber/carbon nanoparticle mass ratio of 0.6, has a max tensile stress of 4.9 MPa. The electrical resistance of the carbon film keeps nearly unchanged after 10000 bends at a max bending angle of 90°, indicating its excellent flexibility. Without the limit of rigid substrates, the double-side evaporation enables higher water flow rate through the film. The freestanding carbon film thus has higher electrical power output than the carbon films reported before. A device with the size of 1 cm×4.5 cm×0.13 mm generates an open-circuit voltage of ~1 V and current of ~ 0.86 μA under ambient condition. The hybrid carbon film can also be easily scaled-up. We demonstrated a carbon film with the maximum width of 40 cm, which has an output current of ~28 μA. Furthermore, the excellent flexibility allows the film to be rolled up to save space, even with a high power output. To demonstrate the application of carbon film, we successfully degraded methylene blue (MB) by using our device as power source. Given the simple fabrication, robust mechanical property, high electricity output, such a freestanding and flexible carbon-based hybrid film shows great potential in environmental energies harvesting for green and sustainable development.