Space charge limited current conduction in thermoelectric electrospun NaCo2O4 nanofibers

Abstract

In this study, NaCo2O4 nanofibers were synthesized via an electrospinning technique. The uniformity and size of these nanofibers were optimized as a function of polyvinylpyrrolidone (PVP) concentration. NaCo2O4 nanofibers were characterized by TG–DTA, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, energy-dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). No crystallinity was observed in the nanofibers when calcined at 100 °C, whereas at 600 °C predominatly γ-phase of NaCo2O4 nanofibers with good crystallinity was achieved. Analysis of XRD and SEM results revealed that PVP concentration and calcination temperature played an important role in the formation of the desired crystalline phase, size, uniformity and porosity of NaCo2O4nanofibers. Temperature-dependent current voltage (IV) characteristics demonstrated the presence of an ohmic region (lower voltage) followed by space charge limited current conduction (SCLC) at intermediate voltage. The presence of surface traps and imperfections can be the possible reason for the SCLC transport. The average value of the Seebeck coefficient “S” was 128 μV/K near room temperature.