Harnessing the potential of Type-II heterostructures: NiO/TiO2/ZnO fibers for enhanced photocatalytic and electrochemical performance in asymmetric supercapacitors

Abstract

A novel two-step approach, electrospinning followed by wet chemical route, was used for the synthesis of NiO/TiO2/ZnO heterostructure fibers. Structural, morphological, and elemental analyses confirmed the single-phase formation with a unique, one-dimensional furry insect-like morphology, free of impurities. BET analysis revealed a significant increase in the specific surface area from 12.64 to 54.50 m2/g for NiO/TiO2/ZnO heterostructure fibers, indicating the existence of more active sites for catalytic and redox activities. Optical studies demonstrated a reduction in the band gap of NiO in the presence of TiO2 and ZnO, enhancing the photocatalytic properties. The Langmuir-Hinshelwood kinetic model was employed to measure the reaction rate constant, showing improved photocatalytic performance of NiO by enhancing the separation rate of photo-generated electrons and holes on its surface. Furthermore, the electrochemical performance of the prepared fibers-based asymmetric supercapacitors (ASCs) showed a low polarization, attributed to low charge transfer resistance. The NiO/TiO2/ZnO fibers-based ASCs exhibited higher specific capacitance (108 F/g), with a maximum specific energy density of 9.6 Wh/kg at a specific power density of 2000 W/kg indicating excellent performance suitable for finding potential uses in energy storage applications. Various practical and physical tests further certified the efficient performance of the prepared NiO/TiO2/ZnO heterostructure fibers-based asymmetric supercapacitors. The contribution of NiO and TiO2 to the inner surface were ∼52.02 and ∼47.08 %, respectively. In contrast, the NiO/TiO2/ZnO fibers showed a notable difference, with ZnO-NWs contributing ∼4.99 % to the overall surface. This increase in the inner surface contribution to around 95.01 % indicates that the growth of ZnO-NWs provides additional channels for electrochemical reactions during redox processes and enhances adhesion between the ZnO-NWs and NiO/TiO2 heterostructure, facilitating OH− ions transportation.