Physico-Chemical Characteristics and Application Potential of Advanced Nickel Titanate and Nickel Cobaltite Nanofibers

Abstract

Nickel titanate (NTO) and nickel cobaltite (NCO) nanofibers were synthesized by sol-gel electrospinning process using poly(styrene-co-acrylonitrile) [SAN] as a polymeric binder. The as-synthesized precursor nanofibers were pyrolyzed at different pyrolysis conditions based on the results of thermal analysis, such that there was no impurity or phase separation in the obtained inorganic nanofibers. Both pyrolysis soaking temperature (T) and time (t), being the influential factors in crystallite and particle growth kinetics by diffusion, play a vital role in morphological and structural evolution of nanostructures. At an isochronal t = 2 h, NTO nanofibers were synthesized at three different T (viz., 773, 973, and 1173 K) to correlate the difference in their physico-chemical properties as a function of T and to optimize the same for proposed applications. Besides, NCO nanofibers were synthesized at three different t (i.e., 2, 4, and 6 h) for isothermal T = 773 K. The morphological, structural, electrochemical, electrical, and magnetic properties of the obtained inorganic nanofibers were characterized using various techniques. It was observed that as the pyrolysis conditions (T and t) were varied the properties of resultant inorganic nanofibers also changed. This in turn influenced their performance and ability in the applications studied. The applicability of NTO nanofibers was explored as bifunctional electrocatalysts for water splitting. The NCO nanofibers developed were used in non-enzymatic sensing of glucose and H2O2. In addition, their water splitting ability was also studied. The properties of these nanostructures are relevant to their synthesis routes and particle/fiber shape, as the surface atoms play key role in electrocatalytic reactions, magnetic anisotropies, and electrical conduction mechanism. Furthermore, the results showed that the residues from SAN (binder) degradation and the degradation kinetics itself can impact the properties of as-prepared inorganic nanofibers, which helps in tailoring the structure, composition, and morphology of NTO and NCO nanofibers. Also, a comparative study on NCO nanofibers obtained using precursor nanofibers collected on rotating disc and rotating drum collectors suggest that the former is best suited for metal oxides synthesis to obtain optimal electrospun nanofibers.