Electrodes Design Based On Graphene 3D Networks (G3DN) And Their Electrochemical Performance

Graphene is one kind of carbon materials with a large theoretical surface area,which has high electrical conductivity,good chemical inertness,excellent mechanical property and high thermal conductivity.Therefore,graphene has a variety of applications,such as energy storage,catalysis and thermal applications.Especially,due to its high electrical conductivity,high chemical stability and excellent mechanical property,it often functions as the substrate for electrochemical electrodes.Nevertheless,most of them are used in powder form so far.So there are stilla series of issues,such as complicated and time-consuming fabrication process of electrodes,the need of Nafion for the immobilization of catalyst nanoparticles on electrodes,and lack of solution diffusion channels,lack of exposure of catalyst nanoparticles to the electrolyte and especially lack of precise quantification of the catalysts on electrodes.Fortunately,graphene 3D network(G3DN)can perfectly overcome the shortcomings of the graphene used in powder form and the electrodes based on G3 DN even have other advantages,such as simple fabrication process,rich pores for electrolyte diffusion and stable structure without Nafion.Therefore,in this thesis we selected G3 DN for detailed study,with the aim to explore and develop new electrochemical electrodes with excellent performance for fuel cell,glucose sensor and electrochemical energy storage,and to expand the synthesis methods of electrochemical electrodes.The details of this research are described as follows:(1)We synthesized a G3 DN on a Si substrate,which is used as Pt nanoparticle support for effective electrocatalytic oxidation of methanol and ethanol.The controllable Pt loading on the G3 DN is conducted by a facile,repeatable and environmentally friendly approach.The electrocatalytic properties of the Pt/G3 DN electrodes for methanol and ethanol oxidation are investigated.The influence of graphene architecture on electrocatalytic activities is comparatively investigated by loading same amount of Pt on the G3 DN and commercial graphene sheets(CGS).The Pt/G3DN(0.01 mg Pt cm-2)catalyst electrode shows a tremendous electrocatalytic activity of 910.11 mA mg Pt-1 and 246.69 mA mgPt-1 for the oxidation of methanol and ethanol respectively owing to the high density of three-dimensional active sites,wavy sheet-network channels and synergistic effect of Pt and graphene.The ratio of the forward to backward scan peak current density is 2.79 and 0.65 for methanol and ethanol respectively for the Pt/G3DN(0.01 mgPt cm-2)electrode.The results reveal excellent characteristics of the Pt/G3 DN,such as easy to be prepared,high catalytic activity,stability and tolerance toward poisoning effects for electrooxidation of methanol.(2)Due to the fact that catalytic oxidation of glucose only takes place on the surface of catalysts,increasing the specific surface of catalysts is an effective way to achieve high catalytic performance.Herein,we have developed an effective and extremely simple method to prepare a highly sensitive,Nafion-free and non-enzymatic glucose sensor with precisely quantified catalyst,which is prepared by in-situ growth of Cu2 O nanoparticles on a G3 DN grown on carbon paper(G3DN/CP).The sensitivity,detection limit,response time and linear range of the sensor are(2.31±0.03)×103 μA mM-1 cm-2,0.14±0.01 μM,1.6 s and 0.48 μM~1813 μM,respectively.In addition,the sensor can retain 95.5% of its initial sensitivity even after 10 days.Specifically,due to the precise quantification of Cu2 O nanoparticles deposited on G3 DN,it is beneficial to mass production and precisely controlling the performance of the glucose sensor devices for public healthcare and industry.This approach could be used for other electrochemical sensors.(3)Owing to the faradaic oxidation and reduction reactions mainly taking place on surface,enlarging the specific surface of redox materials is one of the most effective ways to achieve excellent electrochemical performance.Here we report a binder-free three dimensional(3D)architecture electrode consisting of a G3 DN structure growing on flexible carbon paper by chemical vapor deposition and NiO nanoparticles growing on the G3 DN by in-situ thermal decomposition for high rate battery and high-performance electrochemical capacitors.Such a nanostructure provides a large specific surface and fast electronic transmission channels.The unique structure design for this electrode enables outstanding performance,showing high specific capacity of 89.1 mAh cm-2(119.2 mAh/g)at current density of 0.5 mA cm-2(0.67 A/g)with the NiO loading of 0.7471 mg cm-2.Meanwhile the electrode displays excellent rate capability and cycling stability,which keeps 85.5% of initial capacity after 3000 deep-discharge cycles.Furthermore,a solid-state symmetric electrochemical capacitor based on two NiO/G3DN/CP electrodes with an area of 4 cm2 each is fabricated,and two pieces of them in series can light up 100 green LEDs for 2 min.The architecture of G3 DN loaded with NiO might be generally applied to different kinds of nanomaterials for high-rate energy storage to improve their overall electrochemical performance.