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We report the microstructure and thermoelectric properties of composite nanofiber webs, which were fabricated by dual-electrospinning of polyacrylonitrile (PAN) and sodium cobalt oxide (NaCo2O4) precursor solutions with different input compositions and following heat-treatment at 600–900 °C for simultaneous carbonation and calcination. The SEM and EDS mapping images revealed that PAN-derived carbon nanofibers (CNFs) and NaCo2O4-based ceramic nanofibers coexisted in the composite nanofiber webs and that their relative contents could be controlled by the input compositions. The Seebeck coefficient increased from ~26.77 to ~73.28 μV/K and from ~14.83 to ~40.56 μV/K with increasing the relative content of NaCo2O4 nanofibers in the composite nanofiber webs fabricated at 700 and 800 °C, respectively. On the other hand, the electrical conductivity of the composite nanofiber webs increased with the decrement of the relative content of NaCo2O4 nanofibers as well as the increment of the heat-treatment temperature. Owing to the opposite contributions of NaCo2O4 nanofibers and CNFs to the Seebeck coefficient, electrical conductivity and thermal conductivity, a maximum power factor of ~5.79 μW/mK2 and a figure of merit of ~0.01 were attained for CNF/NaCo2O4-based composite nanofiber webs fabricated at 45 wt% input composition of NaCo2O4 and at heat-treatment of 700 °C.

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We report the microstructure and electrochemical performance of poly(azomethine ether) (PAME)-derived carbon nanofibers (CNFs), which were fabricated by a facile two-step process of electrospinning and carbonization, as self-standing and binderfree supercapacitor electrode materials. The SEM images showed that the average diameter decreased noticeably from $293.9 nm of as-spun nanofibers to $150.3 nm of CNFs after the carbonization at 1000 C. The EDS, XPS, Raman, and XRD analyses demonstrated that PAME-derived CNFs have a nitrogen self-doped graphitic structure. Accordingly, PAME-derived CNFs were characterized to have relatively high electrical conductivity of $3.1 S/cm and excellent wettability to water. The cyclic voltammetry and galvanostatic charge/discharge tests revealed that PAME-derived CNFs have a high specific capacitance of 298 F/g at 0.3 A/g, energy density of 3.3 to 13.9 Wh/kg, power density of 37.5 to 250.0 W/kg, and capacity retention of $94% after 1000 cycles.