Minzae Lee

Preparation of energy storage material derived from a used cigarette filter for a supercapacitor electrode.

We report on a one-step method for preparing nitrogen doped (N-doped) meso-/microporous hybrid carbon material (NCF) via the heat treatment of used cigarette filters under a nitrogen-containing atmosphere. The used cigarette filter, which is mostly composed of cellulose acetate fibers, can be transformed into a porous carbon material that contains both the mesopores and micropores spontaneously. The unique self-developed pore structure allowed a favorable pathway for electrolyte permeation and contact probability, resulting in the extended rate capability for the supercapacitor. The NCF exhibited a better rate capability and higher specific capacitance (153.8 F g(-1)) compared to that of conventional activated carbon (125.0 F g(-1)) at 1 A g(-1). These findings indicate that the synergistic combination of well-developed meso-/micropores, an enlarged surface area and pseudocapacitive behavior leads to the desired supercapacitive performance. The prepared carbon material is capable of reproducing its electrochemical performance during the 6000 cycles required for charge and discharge measurements.

A biodegradable gel electrolyte for use in high-performance flexible supercapacitors.

Despite the significant advances in solid polymer electrolytes used for supercapacitors, intractable problems including poor ionic conductivity and low electrochemical performance limit the practical applications. Herein, we report a facile approach to synthesize a NaCl-agarose gel electrolyte for use in flexible supercapacitors. The as-prepared agarose hydrogel consists of a three-dimensional chemically interconnected agarose backbone and oriented interparticular submicropores filled with water. The interconnected agarose matrix acts as a framework that provides mechanical stability to the gel electrolyte and hierarchical porous networks for optimized ion transport. The developed pores with the water filler provide an efficient ionic pathway to the storage sites of electrode. With these properties, the gel electrolyte enables the supercapacitor to have a high specific capacitance of 286.9 F g(-1) and a high rate capability that is 80% of specific capacitance obtained in the case of a liquid electrolyte at 100 mV s(-1). In addition, attributed to the simple procedure and its components, the gel electrolyte is highly scalable, cost-effective, safe, and nontoxic. Thus, the developed gel electrolyte has the potential for use in various energy storage and delivery systems.

Interfacial Synthesis of Two-Dimensional Dendritic Platinum Nanoparticles Using Oleic Acid-in-Water Emulsion.

Here we propose facile and scalable synthesis of two-dimensional (2D) dendritic platinum nanoparticle at room temperature by exploiting an oil-in-water emulsion. The interfacial synthesis selectively provides platinum nanoparticle with 2D structure in high yield by controlling key reactants such as the amount of oleic acid and the concentration of block copolymer. Electrocatalytic activity of 2D dendritic platinum nanoparticle for oxygen reduction and methanol oxidation reaction is also examined.

Real-Time Optical Monitoring of Pt Catalyst Under the Potentiodynamic Conditions.

In situ monitoring of electrode materials reveals detailed physicochemical transition in electrochemical device. The key challenge is to explore the localized features of electrode surfaces, since the performance of an electrochemical device is determined by the summation of local architecture of the electrode material. Adaptive in situ techniques have been developed for numerous investigations; however, they require restricted measurement environments and provide limited information, which has impeded their widespread application. In this study, we realised an optics-based electrochemical in situ monitoring system by combining a dark-field micro/spectroscopy with an electrochemical workstation to investigate the physicochemical behaviours of Pt catalyst. We found that the localized plasmonic trait of a Pt-decorated Au nanoparticle as a model system varied in terms of its intensity and wavelength during the iterations of a cyclic voltammetry test. Furthermore, we show that morphological and compositional changes of the Pt catalyst can be traced in real time using changes in quantified plasmonic characteristics, which is a distinct advantage over the conventional electrochemistry-based in situ monitoring systems. These results indicate the substantial promise of online operando observation in a wide range of electrical energy conversion systems and electrochemical sensing areas.

The dependence of the interband exciton transitions on the annealing temperature and time in In0.53Ga0.47As/InP multiple quantum wells with a SiNx capping layer

Abstract Photoluminescence (PL) measurements have been performed to investigate the compositional intermixing of In 0.53 Ga 0.47 As/InP multiple quantum wells (MQWs) grown by using chemical beam epitaxy. A SiN x capping layer together with a thermal annealing process was introduced to create the energy shift of the exciton transition from the first electronic subband to the first heavy hole (E 1 -HH 1 ) in the In 0.53 Ga 0.47 As/InP MQWs. The blue shift of the (E 1 -HH 1 ) transition is attributed to the interdiffusion of the P in the InP barrier and the As in the In 0.53 Ga 0.47 As quantum well. These results indicate that the value of the (E 1 -HH 1 ) shift can be effectively adjusted by the annealing temperature and the annealing time in the energy range of 87 meV and that the intermixing method of In 0.53 Ga 0.47 As/InP MQWs by using a SiN x capping layer together with a annealing process holds promise for practical applications in the intergrated photonic devices.