| In recent years, carbon nanofibers(CNFs) have gradually attracted much attention around the world, due to the excellent tensile strength, thermostability, conductivity and catalytic activity. However, the brittleness and poor flexural properties critically restrict their practical applications in the field of composite materials. To overcome these disadvantages in this paper, polyacrylonitrile(PAN), polyvinylpyrrolidone(PVP) and aluminum hydroxyacetate(Al(OH)C4H6O4) were prepared as precursor first of all, then PAN/PVP/Al(OH)C4H6O4 composite nanofibers films were fabricated by facile electrospinning with different mass ratio of 1.6 : 1, 2.4 : 1, 3.2 : 1, 4.0 : 1(Al(OH)C4H6O4 : PAN). The morphologies, diameter distributions and chemical components of composite nanofibers with different Al(OH)C4H6O4 content were investigated, and 700 °C was confirmed to be preliminary carbonization temperature according to the result of thermo- gravimetric analysis(TGA).Subsequently, CNFs and alumina(Al2O3)/carbon(C) composite nanofibers films(ACNFs) were obtained by pre-oxidation and carbonization of PAN/PVP and PAN/PVP/ Al(OH)C4H6O4, respectively. The samples were characterized by field emission scanning electron microscopy(FE-SEM), transmission electron microscopy(TEM), X-ray diffraction(XRD), fourier transform infrared spectra(FT-IR), multi-purpose tensile tester and four-point probes. The results showed that the surfaces of CNFs were smooth and many micropores could be observed on the surfaces of nanofibers. CNFs showed serious brittleness in fracture experiment. The surfaces of ACNFs were rough and two different phases could be observed clearly between γ-Al2O3 and CNFs. The surfaces of CNFs were covered by γ-Al2O3. With the increase of γ-Al2O3 content, both flexural rigidity and flexural modulus of ACNFs decreased drastically, indicating that flexibility of ACNFs was improved while conductivity of ACNFs was decreased. The main reason for the improved flexibility of CNFs was attributed to γ-Al2O3 with its nature of flexibility. After consideration of flexibility and conductivity, the mass ratio of Al(O H)C4H6O4 : PAN was determined by 2.4 : 1. The flexural rigidity, flexural modulus and resistivity of composite carbon nanofibers film was 65.42 ± 0.67 mN·mm2, 10.90 ± 0.11 MPa and 16.264 Ω·cm, respectively.Furthermore, the mechanical properties and electrical properties influenced by different carbonation temperature were investigated. The results revealed that with the increase of carbonization temperature, the average diameter of ACNFs decreased and the diameter distribution tended to be uniform. With the increase of carbonization temperature, the flexibility of ACNFs decreased slightly but the conductivity of ACNFs improved obviously. After consideration of flexibility and conductivity, the carbonization temperature of ACNFs was determined by 800 °C. The flexural rigidity, flexural modulus and resistivity of composite carbon nanofibers film was 70.38 ± 1.28 mN·mm2, 13.60 ± 0.25 MPa and 12.104 Ω·cm, respectively.Finally, the mass ratio of Al(OH)C4H6O4 : PAN and carbonization temperature was determined by 2.4 : 1 and 800 °C, respectively. The obtained composite carbon nanofibers film was used as counter electrode for flexible dye-sensitized solar cells(FDSSC) and the performances of FDSSC were characterized. In addition, the photoanode of FDSSC was investigated at the same time. The photoanode titanium oxide(TiO2) particles were well-distributed in spite of some conglobated particles. The crystallization of photoanode TiO2 was good. The curves obtained by cyclic voltammetry showed good redox peaks, indicating that ACNFs had excellent redox for I3-/I- redox couple. The photoelectric conversion efficiency(η) of FDSSC was 2.26%. |
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