Synthesis and Characterization of Znmn2o4 and Pvdf/Ca-Al LDH Nanofibers for Sustainable Energy Applications

Abstract

ZnMn2O4 (ZMO) and PVDF/Ca-Al LDH (PCAL) nanocomposite nanofibers were synthesized from using electrospinning technique. For the synthesis of ZMO nanofibers styrene-acrylonitrile random copolymer (SAN) was used as the sacrificial polymeric binder and the nanofibers were calcined at three different temperatures (773, 873, and 973 K). Structural, morphological and optical properties of these ceramic nanofibers were characterized. X-ray diffraction and X-ray photoelectron spectroscopy results revealed the presence of hexagonal ZnMnO3 and MnO phases in the ZMO nanofibers produced. Based on the findings, a plausible mechanism of formation of ZMO nanofibers was proposed. The nanofibers calcined at 773 K exhibited a specific surface area of 79.5 m2.g-1, which is higher than that of the zinc manganite nanofibers synthesized hitherto by sol-gel electrospinning. The suitability of ZMO nanofibers was investigated as bifunctional electrocatalysts for water splitting towards Oxygen Evolution Reaction (OER) and Hydrogen Evolution Reaction (HER). The results demonstrate that ZMO nanofibers are promising candidate as bifunctional electrocatalysts for water-splitting applications. A new synthetic route for Ca-Al layered double hydroxide (LDH) nanosheets was adapted and these two-dimensional nanosheets were used as filler for poly(vinylidene fluoride) (PVDF) to produce composite nanofibers by electrospinning. The polymorphism, crystallinity, and the interaction between PVDF and LDH were studied by Fourier transform infrared spectroscopy, X-ray diffraction, and differential scanning calorimetry. The synergetic effect of PVDF-LDH interaction and in situ stretching due to electrospinning facilitates the nucleation of electroactive β phase up to 82.79%, which makes it a suitable material for piezoelectric-based nanogenerators. The piezoelectric performance of PCAL nanofibers was demonstrated by hand slapping and frequency-dependent mechanical vibration modes, which delivered a maximum open-circuit output voltage of 4.1 and 5.72 V, respectively. Moreover, the applicability of PCAL nanofibers was explored in lithium-ion batteries (LIBs) as gel polymer electrolyte (GPE). The PCAL based GPE exhibited enhanced electrochemical properties, such as high ionic conductivity, optimal Li-ion transference number, and improved electrolyte uptake due to the presence of a highly interconnected porousstructure. They exhibited improved charge-discharge profile compared to pristine PVDF and commercial Celgard® 2400 separator membrane. Along with high electrochemical performance, the PCAL based GPE showed superior mechanical and low thermal shrinkage properties, indicating its suitability in battery separator application.