Research On Graphene Paper-based Supercapacitors For Energy Storage

Supercapacitors, also called electrochemical capacitors, are a fast-rising class of electrochemical energy storage devices, due to its extraordinary power density and cycling stability compared with Li-ion batteries. Graphene, with its large specific surface area, good electrical conductivity and mechanical strength, is considered as an ideal electrode material. Particularly, freestanding graphene paper, without binder and conductive additive when as electrode materials, is attracting great research interests.In this thesis, we obtained chemically reduction graphene oxide (C-rGO) by vacuum filtration. Then it was used as electrode materials for supercapacitors and tested in6M KOH electrolyte. The results show that good capacitive performance was obtained when the scan rate was relatively low (150F g-1at10mV s-1). However, as the scan rate increased, here we observed obvious degraded capacitance,71.5F g-1at1000mV s-1. It indicates that the graphene paper obtained through vacuum filtration leads to compact structure, which increases the resistance of ion transport into the graphene layers and impacts the capacitive performance.Considering the disadvantages of compact graphene paper, scanning positive column of atmospheric-pressure glow discharge is proposed toward reduction of graphene oxide (GO) paper as an eco-friendly and cost-effective strategy. As characterized, the plasma-assisted reduction of graphene oxide paper (P-rGO) achieved a number of exposed open channels and the expansion of gaphene layers, leading to unimpeded liquid permeation. Taking above advantages, the P-rGO exhibited better capacitive performance, compared with C-rGO. In1M TEABF4/AN electrolyte, the specific capacitance was181.4F g-1at10mV s-1, while the C-rGO was120F g-1. Meanwhile, the P-rGO exhibited an obvious improved rate performance, which was evidenced by a capacitance retention of ca.77%when current density was increased from1A g-1to50A g-1, while C-rGO’s was only ca.18%.In order to obtain high rate performance graphene paper-based supercapaictors, vertically oriented graphene, with good electrical conductivity and a large number of exposed edges, was used as bridges between active layers and current collector to reduce the contact resistance at the interface, leading to high rate performance for supercapacitors. As a result, the VG-bridged supercapacitor using conventional graphene paper as the active materials exhibited a capacitance maintenance of ca.90%as the CV scan rates increase from20mV s-1to1000mV s-1. What’s more, the VG-bridged supercapacitor showed an ultrahigh power density of112.6kW kg-1(specific capacitance of130F g-1) at a current density of600A g-1.