Preparation Of Carbon-based Composite Electrode Material And Assembly Of Flexible Supercapacitors

As a type of semiconductor,gallium nitride（GaN）exhibits high carrier concentration,high thermal conductivity,and good structural stability.However,Ga N manifests relatively low specific capacitance when used as the active material for supercapacitro electrodes.To improve the electrochemical performance of Ga N-based electrode materials,detailed investigations were performed as follows.First,sample electrodes constituted by gallium oxynitride（GON）nanoparticles residing on the carbon cloth（CC）were prepared through a moisture-assisted ammolysis（MAA）method.The sample electrodes were characterized with XRD,CHNO（elemental analysis）,SEM,TEM,XPS,PL,and UV?Vis techniques.Also,the electrochemical properties of sample electrodes were evaluated in a three-electrode and a two-electrode systems,respectively,using cyclovotammogram（CV）,galvanostatic charge/discharge（GCD）,and electrochemical alternating current impedance spectroscopy techniques.The results show:（1）GON nanoparticles,which are different from Ga N,Ga2O3,and Ga N/Ga2O3composite,can be prepared through the MAA approach,using Ga Cl3 as the gallium source.（2）The particle size,band structure,density of states,defect concentration,and N/O ratio with respect to GON can be tuned by varying the nitridation temperature.（3）GON@CC-800 electrode obtained with nitridation at 800°C exhibits excellent electrochemical performance.In a three-electrode system,the areal specific capacitance of GON@CC-800 is628 m F cm^?2 at 10 m A cm^?2,using 1 M H2SO4 as the electrolyte.The capacitance retention retains 100%after 10,000 cycles at 10 mAcm^?2.After 20,000 cycles at current densities varying from 10 to 50 mAcm^?2,the GON@CC-800-based symmetric supercapacitors manifest nearly 100%capacitance retention.At 1mAcm^?2,the supercapacitor device can deliver a specific energy of 21.1μWhcm^?2,with corresponding specific power of 0.5 mWcm^?2.The excellent electrochemical performance of GON@CC-800 is attributed to（i）relatively finer particle size,suitable oxygen defect concentration,and suitable N/O ratio;（ii）the replacement of N by O results in increase in Ga?N length and,hence,the attraction of N towards Ga 3d electrons is decreased.Such a situation is beneficial for decreasing the energy of redox reactions on the electrode surface and,in other words,the pseudocapacitance and electrode kinetics are improved.Second,GON nanoparticles were prepared by nitridizing the hydrolysized product of Ga Cl3.Then,the working electrodes were prepared,using the as-obtained GON nanoparticles as the active material.The defect concentration of sample electrodes was engineered with electrochemical etching.The sample electrodes were characterized with XRD,SEM,TEM,PL,UV?Vis,XPS,and near-edge X-ray absorption fine structure（NEXAFS）spectroscopy techniques.Also,the electrochemical performance of sample electrodes was comparably investigated.The results show:（1）At 0.5 mAcm^?2,the areal specific capacitance of pristine GON nanoparticle-based electrode is only 18 m F cm^?2.After electrochemical in 0.1 M oxalic acid at 20 V for 4?6 min,the electrochemical performance of sample electrodes can be remarkably improved.（2）Sample electrode S-5,which was electrochemically etched in 0.1 M oxalic acid at 20 V for 5 min,manifests superior electrochemical performance.At 0.5 m A cm^?2,the areal specific capacitance of S-5 can reach 792 mF cm^?2,approaching 44 folds of that for pristine GON electrode.At varied current densities ranging from 5 to 50 mAcm^?2,the capacitance retention of electrodes with and without etching is nearly 100%.Also,the S-5-based symmetric supercapacitors retain nearly 100%capacitance retention after 10,000 cycles at consecutive current densities ranging from 5 to 20 mAcm^?2.At 0.5 mAcm^?2,the device can deliver a specific energy of 17.2μWhcm^?2,with corresponding specific powder of 0.25 mWcm^?2.（3）The textural properties of SBET,Vmicropore,and Vtotal can be enhanced.However,the superior electrochemical performance of sample electrodes with electrochemical etching is attributed to the elimination of oxide layer and the suitable gallium vacancy concentrion,rather than the textural properties.