Showing papers by "Yue Wu published in 2016"

Electrochemical activation of carbon cloth in aqueous inorganic salt solution for superior capacitive performance

Abstract: Carbon cloth (CC) is an inexpensive and highly conductive textile with excellent mechanical flexibility and strength; it holds great promise as an electrode material for flexible supercapacitors. However, pristine CC has such a low surface area and poor electrochemical activity that the energy storage capability is usually very poor. Herein, we report a green method, two-step electrochemical activation in an aqueous solution of inorganic salts, to significantly enhance the capacitance of CC for supercapacitor application. Micro-cracks, exfoliated carbon fiber shells, and oxygen-containing functional groups (OFGs) were introduced onto the surface of the carbon filament. This resulted in an enhancement of over two orders of magnitude in capacitance compared to that of the bare CC electrode, reaching up to a maximum areal capacitance of 505.5 mF cm−2 at the current density of 6 mA cm−2 in aqueous H2SO4 electrolyte. Electrochemical reduction of CC electrodes led to the removal of most electrochemically unstable surface OFGs, resulting in superior charging/discharging rate capability and excellent cycling stability. Although the activated CC electrode contained a high-level of surface oxygen functional groups (∼15 at%), it still exhibited a remarkable charging–discharging rate capability, retaining ∼88% of the capacitance when the charging rate increased from 6 to 48 mA cm−2. Moreover, the activated CC electrode exhibited excellent cycling stability with ∼97% capacitance remaining after 10 000 cycles at a current density of 24 mA cm−2. A symmetrical supercapacitor based on the activated CC exhibited an ideal capacitive behavior and fast charge–discharge properties. Such a simple, environment-friendly, and cost-effective strategy to activate CC shows great potential in the fabrication of high-performance flexible supercapacitors.

Atomic-Level Characterization of Dynamics of Copper Ions in CuAgSe

Abstract: To examine the ionic migrations on atomic level in metal chalcogenide phonon glasses, 63Cu solid state nuclear magnetic resonance (NMR) spectroscopy was performed in an archetype CuAgSe compound. The observed characteristic motional narrowing effect in the superionic state provide clear evidence for the model of single ion-hopping instead of free-ion-like motion. We further find, for the first time, that thermal conductivity is strongly correlated with cation dynamics revealed by NMR within the range of temperatures investigated. This investigation provides better understanding how microscopic structure affects thermal transport properties which is of current interest in transition-metal chalcogenide based fast ion conductors.