Graphene-Based Stretchable Electrodes And Their Applications In Electrochemical Capacitors

Stretchable electrodes are electrodes that can maintain their conductivities with negligible changes at large strains or upon repeated stretching/releasing.They are the fundamental components of stretchable electronics.Graphene possesses high mechanical strength and conductivity,excellent chemical stability and good transparency,making it to be an ideal material for fabricating stretchable electrodes.This thesis focuses on the fabrication of graphene-based stretchable electrodes and their applications in stretchable electrochemical capacitors.The main contents are listed as follows.Wavy graphene oxide(GO)films were formed on an elastic tape substrate via a prestrain/releasing method.Then,this film was reduced by hydroiodic acid to produce a wavy reduced graphene oxide(rGO)/tape composite film.The rGO/tape composite film showed a low sheet resistance(21 ? sq-1)and it maintained its conductivity at a large strain(100% strain),a large bending angle(160o),or upon stretching/releasing or bending/releasing for 1000 cycles.The morphologies of rGO layer kept unchanged after stretching/releasing with a maximum strain of 100% for 1000 cycles.The low resistance and high stability of this composite film is mainly attributed to the utilization of less defective GO and relatively thicker rGO layer.The method of fabricating rGO/elastic tape composite electrodes is facile,cheap,and scalable,without involving film transfer or thermal annealing at high temperatures.More importantly,a freestanding wavy rGO film can be obtained by detaching it from the elastic tape via soaking in ethanol.The freestanding rGO film maintained its elasticity.It can be stretched for 50% and completely recovered to its original shape within 360 ms after releasing.The stress-strain curves of this freestanding wavy rGO film are linear and stable during 100 stretching/releasing cycles at a strain of 50%.The resistance of this film was tested to be increased by only 0.055% at a strain of 50% and by 0.20% after 1000 stretching/releasing cycles.The elasticity of rGO film is mainly attributed to the in-situ reduction of wavy GO film.During the reduction process,the relative locations of graphene sheets in wavy GO film were fixed,and the wavy structure can behave like a spring.Getting rid of the restrain of substrate,this freestanding rGO film became lighter in weight,smaller in size,and more stable in its electrical property.An all-solid-state electrochemical capacitor was fabricated with rGO/elastic tape film as stretchable electrode,rGO layer reduced by ascorbic acid as electrode material and H2SO4-polyvinyl alcohol hydrogel as separator and electrolyte.This electrochemical capacitor showed a large areal specific capacitance up to 67.3 mF cm-2,and excellent electrochemical stability and flexibility.The capacitance kept stable at a strain of 100% or during 1000 stretching/releasing cycles.