Yan Xingbin

Nitric Acid Modification of Graphene Nanosheets Prepared by Arc- Discharge Method and Their Enhanced Electrochemical Properties

Large-scale synthesis of few-layer graphene nanosheets (GNSs) with high crystallinity and electrical conductivity (1680 S·m-1) is achieved by an arc-discharge method. The GNSs exhibited good morphologies as observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). However, electrochemical testing showed that the performance of the graphene (GNS) electrodes in supercapacitors was poor. To increase the surface active sites for electrochemical reactions and promote the wettability by aqueous electrolyte of the GNSs, a nitric acid treatment was used to chemically modify their surface. The acid treatment introduced more oxygen/nitrogen-containing functional groups onto the GNS surface, and clearly enhanced the hydrophilicity. The nitric-acid-modified GNSs (H-GNSs) showed vastly better electrode performance, with a maximum specific capacitance of 65.5 F·g-1 (about 30 times that of original GNSs) at a current density of 0.5 A·g-1 in 2 mol·L-1 KOH electrolyte. In addition, the H-GNS electrode showed good cycling stability and lifetime after running 2000 cycles. Therefore, H-GNSs may be an attractive candidate as electrode materials for supercapacitors.

Magnetic and Electrochemical Properties of NiCo 2 O 4 Microbelts Fabricated by Electrospinning

Cobaltate nickel (NiCo2O4) microbelts were fabricated by direct calcination of electrospun precursor samples with an appropriate heating rate. The crystal structure, morphology, magnetic properties, and electrochemical properties of the NiCo2O4 microbelts were investigated by X-ray diffraction, scanning electron microscopy, vibrating sample magnetometry, and electrochemical analysis. The results showed that a heating rate of 1 degrees C.min(-1) resulted in the formation of cubic spinel NiCo2O4 microbelts. After calcination at high temperatures, the microbelts retained their one-dimensional structure. Magnetization results indicated that the NiCo2O4 microbelts were superparamagnetic and their magnetization value at 10 kOe was 6.35 emu.g(-1). Moreover, the electrochemical results suggest that the capacitance of the NiCo2O4 microbelts is typical pseudocapacitive capacitance, and the value of the specific capacitance gradually decreases with increasing discharge current density.

Fabrication and Magnetic Properties of Electrospun Zinc Ferrite Hollow Fibers

Zinc ferrite (ZnFe2O4) hollow fibers have been fabricated by annealing electrospun polyvinylpyrrolidone (PVP)/nitrate salt composite nanofibers at 500 °C for 3 h with a heating rate of 5 °C· min. The composite fibers were initially prepared by electrospinning Zn, Fe salts, and PVP from solution. The structure, morphology, and magnetic properties were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and vibrating sample magnetometry (VSM). The XRD results indicate a spinel phase structure, while SEM and TEM reveal hollow fibers (200-400 nm in diameter) with walls consisting of packed 25 nm nanoparticles. Room temperature VSM of the ZnFe2O4 hollow fibers reveal a superparamagnetic behavior and a magnetization value of 2.03 emu·g-1 at 10 kOe.