Scalable fabrication and electrochemical characterization of binder-free Fe3O4@C films on Cu Current Collector

Abstract

Here we present a scalable strategy for fabrication of nanostructured magnetite (Fe3O4) films directly on a copper (Cu) current collector as potential anodes for energy storage devices. Hydrothermal synthesis was employed in first step to realize Fe3O4 films which were subsequently encapsulated in carbon shell in a controlled way using chemical vapor deposition (CVD) techniques. Through a systematic investigations, it was revealed that lower hydrothermal temperature (80°C) gives rhombus-shaped nanoarchitectures which were primarily composed of α-FeOOH. At higher temperature (120°C), three-dimensional (3D) superstructures comprising of Fe3O4/iron carbonate (FeCO3) composite nanolayers were found. Furthermore, it was revelaed that, irrespective of the composition of hydrothermally synthesized film, each one converted upon calcination to a cubic Fe3O4 without any significant changes in the morphology. A conformal carbon encapsulation allowed to form Fe3O4@C core–shell structures having tunable shell thicknesses and strong interfacial bonding (Fe-O-C). Although structural investigations showed improvement in crystallinity with carbon encapsulation by either CVD techniques, but it was more pronounced in case of microwave plasma CVD (MP-CVD), which also induced partial reduction of Fe3O4 to metallic iron (Fe). The films showed pseudocapacitive behavior in 1M Na2SO4 during electrochemical evaluation, and stored charge at lower scan rates predominantly by a diffusion-controlled process, which decreased with increasing scan rate, leading to a dominant capacitive process for charge storage. The developed binder-free films have a great potential as highly robust anodes for lithium and post-lithium ion batteries (LIBs), supercapacitors, and battery-supercapacitor hybrid devices.