Sunmoon Yu

Electrospun nanofibers as a platform for advanced secondary batteries: a comprehensive review

Poor electrochemical performances of materials in commercial lithium-ion batteries (LIBs) make it difficult to realize battery technologies for future electric power applications such as energy storage systems and electric vehicles. To reach beyond the horizon of state-of-the-art LIBs, the exploration of next generation batteries composed of rationally designed nanomaterials in consideration of the structure, phase and element influencing the battery performance is critical. By virtue of the simple set-up, versatility, size controllability and mass-productivity of electrospinning, one-dimensional (1D) nanofibers (NFs) produced via electrospinning are attractive candidates for the construction of advanced secondary batteries. A comprehensive review of the forefront in the development of electrospun NFs as advanced materials of next generation LIBs, sodium-ion batteries (NIBs), lithium–sulfur batteries and lithium–air batteries with particular emphasis on synthesis and improved energy and power density, and cyclability is presented. In this review, we highlight the recent advancements in electrospun 1D nano-architectures with large surface area to volume ratios and controllable morphologies as anodes, cathodes, separators, electrolytes and even catalytic materials. Furthermore, current challenges and prospects of electrospun NFs in both academia and industry are also discussed. We expect that this review opens up new research activities in a variety of research fields including advanced rechargeable batteries.

Rational Design of Efficient Electrocatalysts for Hydrogen Evolution Reaction: Single Layers of WS2 Nanoplates Anchored to Hollow Nitrogen-Doped Carbon Nanofibers.

To exploit the benefits of nanostructuring for enhanced hydrogen evolution reaction (HER), we employed coaxial electrospinning to synthesize single-layered WS2 nanoplates anchored to hollow nitrogen-doped carbon nanofibers (WS2@HNCNFs) as efficient electrocatalysts. For comparison, bulk WS2 powder and single layers of WS2 embedded in nitrogen-doped carbon nanofibers (WS2@NCNFs) were synthesized and electrochemically tested. The distinctive design of the WS2@HNCNFs enables remarkable electrochemical performances showing a low overpotential with reduced charge transfer resistance, a small Tafel slope, and excellent durability. The experimental results highlight the importance of nanostructure engineering in electrocatalysts for enhanced HER.

Nanoscale PdO Catalyst Functionalized Co3O4 Hollow Nanocages Using MOF Templates for Selective Detection of Acetone Molecules in Exhaled Breath

The increase of surface area and the functionalization of catalyst are crucial to development of high-performance semiconductor metal oxide (SMO) based chemiresistive gas sensors. Herein, nanoscale catalyst loaded Co3O4 hollow nanocages (HNCs) by using metal-organic framework (MOF) templates have been developed as a new sensing platform. Nanoscale Pd nanoparticles (NPs) were easily loaded on the cavity of Co based zeolite imidazole framework (ZIF-67). The porous structure of ZIF-67 can restrict the size of Pd NPs (2-3 nm) and separate Pd NPs from each other. Subsequently, the calcination of Pd loaded ZIF-67 produced the catalytic PdO NPs functionalized Co3O4 HNCs (PdO-Co3O4 HNCs). The ultrasmall PdO NPs (3-4 nm) are well-distributed in the wall of Co3O4 HNCs, the unique structure of which can provide high surface area and high catalytic activity. As a result, the PdO-Co3O4 HNCs exhibited improved acetone sensing response (Rgas/Rair = 2.51-5 ppm) compared to PdO-Co3O4 powders (Rgas/Rair = 1.98), Co3O4 HNCs (Rgas/Rair = 1.96), and Co3O4 powders (Rgas/Rair = 1.45). In addition, the PdO-Co3O4 HNCs showed high acetone selectivity against other interfering gases. Moreover, the sensor array clearly distinguished simulated exhaled breath of diabetics from healthy peoples breath. These results confirmed the novel synthesis of MOF templated nanoscale catalyst loaded SMO HNCs for high performance gas sensors.

2D WS2-edge functionalized multi-channel carbon nanofibers: effect of WS2 edge-abundant structure on room temperature NO2 sensing

Transition metal dichalcogenides (TMDs), such as molybdenum disulfide (MoS2) and tungsten disulfide (WS2), have been studied intensively in recent years due to wide range of potential applications. TMD gas sensors have been developed and intensively explored for their promising applications. In recent times, it has been reported that edge sites of TMDs can contribute to highly enhanced gas adsorption properties. Herein, superior room temperature gas sensing properties of WS2 edge functionalized carbon nanofibers (CNFs) with multiple tubular pores (WS2@MTCNFs) have been demonstrated. A copolymer-electrospinning route, which uses poly(styrene-acrylonitrile) as sacrificial templates and WS2 precursor containing poly(acrylonitrile) as carbon matrix, offered facile synthesis of CNFs having high gas permeability with single-layered WS2 edge-rich surface. As a result, WS2@MTCNFs based sensors exhibited notable gas response (15% at 1 ppm of NO2) at room temperature compared to pristine CNFs (2% at 1 ppm of NO2), which can be attributed to the synergistic effects that originated from enhanced surface area and open porosity with numerous elongated pore channels of MTCNFs as well as remarkably increased active spots on the surface from WS2 edge sites.

Metal Chelation Assisted In Situ Migration and Functionalization of Catalysts on Peapod-Like Hollow SnO2 toward a Superior Chemical Sensor.

Rational design of nanostructures and efficient catalyst functionalization methods are critical to the realization of highly sensitive gas sensors. In order to solve these issues, two types of strategies are reported, i.e., (i) synthesis of peapod-like hollow SnO2 nanostructures (hollow 0D-1D SnO2 ) by using fluid dynamics of liquid Sn metal and (ii) metal-protein chelate driven uniform catalyst functionalization. The hollow 0D-1D SnO2 nanostructures have advantages in enhanced gas accessibility and higher surface areas. In addition to structural benefits, protein encapsulated catalytic nanoparticles result in the uniform catalyst functionalization on both hollow SnO2 spheres and SnO2 nanotubes due to their dynamic migration properties. The migration of catalysts with liquid Sn metal is induced by selective location of catalysts around Sn. On the basis of these structural and uniform functionalization of catalyst benefits, biomarker chemical sensors are developed, which deliver highly selective detection capability toward acetone and toluene, respectively. Pt or Pd loaded multidimensional SnO2 nanostructures exhibit outstanding acetone (R air /R gas = 93.55 @ 350 °C, 5 ppm) and toluene (R air /R gas = 9.25 @ 350 °C, 5 ppm) sensing properties, respectively. These results demonstrate that unique nanostructuring and novel catalyst loading method enable sensors to selectively detect biomarkers for exhaled breath sensors.

Improved high temperature integration of Al2O3 on MoS2 by using a metal oxide buffer layer

We deposited a metal oxide buffer layer before atomic layer deposition (ALD) of Al2O3 onto exfoliated molybdenum disulfide (MoS2) in order to accomplish enhanced integration. We demonstrate that even at a high temperature, functionalization of MoS2 by means of a metal oxide buffer layer can effectively provide nucleation sites for ALD precursors, enabling much better surface coverage of Al2O3. It is shown that using a metal oxide buffer layer not only allows high temperature ALD process, resulting in highly improved quality of Al2O3/MoS2 interface, but also leaves MoS2 intact.