DESIGN AND MANUFACTURING of DimensionALLY ControLlED Graphene Based HYBRID Structures By CORE-SHELL Electrospinning for ENERGY STORAGE SYSTEMS

Leila Haghighi Poudeh
Materials Science and Engineering, PhD Dissertation, 2018

Thesis Jury

Prof. Dr Mehmet Yıldız (Thesis Advisor),

Doç. Dr. Burcu Saner Okan (Thesis Co-advisor)

Doç. Dr. Fevzi Çakmak Cebeci

Dr. Öğr.Üyesi Eralp Demir

Prof. Dr. Halit Türkmen

Dr. Öğr. Üyesi Bertan Beylergil

Date & Time: 30th July, 2018 –  10:00AM

Place: KTMM, 3rd floor, Seminar room

Keywords : Graphene, energy storage systems, electrospinning, electrospraying, hybrid electrodes

Abstract

In the first part of study, two-dimensional (2D) graphene oxide sheets were converted into 3D hollow and filled microspheres by using different carrying polymers through one-step core-shell electrospraying technique. Electrospraying process prevents the aggregations and crumbling of graphene sheets by constructing 3D interconnected framework, provides homogeneous dispersion of graphene sheets in polymer solution under electric field. The proper polymer concentration and solution viscosity were determined by using Mark-Houwink-Sakurada equation. The hollowness of spheres was controlled by changing the core solvents.

Later on, Platinum (Pt) decorated graphene-based sphere, foam, and fibers with controlled dimensionality were successfully fabricated through the same technique and their electorchemical performances were investigated in details. In this work, graphene-based foam was produced for the first time by utilizing core-shell electrospraying technology instead of available chemical vapor deposition techniques. Among three different electrodes, Pt supported 3D graphene-based spheres exhibited the highest specific capacitance as well as cyclic stability owing to its unique structure and small size of Pt particles.

At the final step, to further improve the electrochemical performance of graphene-based fibers, a novel and hierarchical hybrid structure was constructed by the addition of manganese oxide and polyaniline. Graphene/polyaniline/manganese oxide carbon fibers showed a high specific capacitance of 454 F/g at a scan rate of 1 mV/s. The produced electrodes exhibited a high cycling stability whereby only 11% of capacitance lost after 1000 cycles of charging-discharging. This study especially brings a new insight to the fabrication of high-performance hybrid electrodes for energy storage devices.