Papers by Hui (Claire) Xiong
Journal of the American Chemical Society, 2008
Electrochemistry Communications, 2004
Analytical Chemistry, 2007
Analytical Chemistry, 2006
Physical Review Letters, 2013
conducted and analyzed the electrochemical and high pressure experiments and H. Yildirim performe... more conducted and analyzed the electrochemical and high pressure experiments and H. Yildirim performed and analyzed the molecular dynamics simulations.
Journal of Electroanalytical Chemistry, 2009
Scanning electrochemical microscopy (SECM) is developed as a powerful approach to electrochemical... more Scanning electrochemical microscopy (SECM) is developed as a powerful approach to electrochemical characterization of individual one-dimensional (1D) nanostructures under unbiased conditions. 1D nanostructures comprise high-aspect-ratio materials with both nanoscale and macroscale dimensions such as nanowires, nanotubes, nanobelts, and nanobands. Finite element simulations demonstrate that the feedback current at a disk-shaped ultramicroelectrode tip positioned above an unbiased nanoband, as prepared on an insulating substrate, is sensitive to finite dimensions of the band, i.e., micrometer length, nanometer width, and nanometer height from the insulating surface. The electron-transfer rate of a redox mediator at the nanoband surface depends not only on the intrinsic rate but also on the open-circuit potential of the nanoband, which is determined by the dimensions of the nanoband as well as the tip inner and outer radii, and tip-substrate distance. The theoretical predictions are confirmed experimentally by employing Au nanobands as fabricated on a SiO 2 surface by electron-beam lithography, thereby yielding well defined dimensions of 100 or 500 nm in width, 47 nm in height, and 50 μm in length. A 100 nm-wide nanoband can be detected by SECM imaging with ∼2 μm-diameter tips although the tip feedback current is compromised by finite electron-transfer kinetics for Ru(NH 3) 6 3+ at the nanoband surface.
Analytical Chemistry, 2010
Here we report on novel application of scanning electrochemical microscopy (SECM) to enable spati... more Here we report on novel application of scanning electrochemical microscopy (SECM) to enable spatially resolved electrochemical characterization of individual single-walled carbon nanotube (SWNT). The feedback imaging mode of SECM was employed to detect a pristine SWNT (~1.6 nm in diameter and ~2 mm in length) grown horizontally on a SiO 2 surface by chemical vapor deposition. The resulting image demonstrates that the individual nanotube under an unbiased condition is highly active for the redox reaction of ferrocenylmethyltrimethylammonium used as a mediator. Micrometer-scale resolution of the image is determined by the diameter of a disk-shaped SECM probe rather than by the nanotube diameter as assessed using 1.5 and 10 μm-diameter probes. Interestingly, the long SWNT is readily detectable using the larger probe although the active SWNT covers only ~0.05 % of the insulating surface just under the tip. This high sensitivity of the SECM feedback method is ascribed to efficient mass transport and facile electron transfer at the individual SWNT.
Electrolytes are an important component of electrochemical energy storage systems and their optim... more Electrolytes are an important component of electrochemical energy storage systems and their optimization is critical for emerging beyond lithium ion technologies. Here, an integrated computational-experimental approach is used to rank-order and aid the selection of suitable electrolytes for a Naion battery. We present an in silico strategy based on both thermodynamic and kinetic descriptors derived from molecular dynamics simulations to rationally arrive at optimal electrolytes for Na-ion batteries. We benchmarked various electrolytes (pure and binary mixtures of cyclic and acyclic carbonates with NaClO 4 salt) to identify appropriate formulations with the overarching goal of simultaneously enhancing cell performance while meeting safety norms. Fundamental insights from computationally derived thermodynamic and kinetic data considerations coupled with atomistic-level description of the solvation dynamics is used to rank order the various electrolytes. Thermodynamic considerations based on free energy evaluation indicate EC:PC as a top electrolyte formulation under equilibrium conditions. However, kinetic descriptors which are important factors dictating the rate capability and power performance suggest EC:DMC and EC:EMC to be among the best formulations. Experimental verification of these optimized formulations was carried out by examining the electrochemical performance of various electrolytes in Na/TiO 2 nanotubes half cells with NaClO 4 salt. Our rate capability studies confirm that EC:DMC and EC:EMC to be the best formulations. These optimized formulations have low-rate specific capacities ∼120−140 mAh/g whereas the lower ranked electrolytes (EC: DEC) have capacities ∼95 mAh/g. The various electrolytes are also evaluated from a safety perspective. Such results suggest encouraging prospects for this approach in the a priori prediction of optimal sodium ion systems with possible screening implications for novel battery formulations.
Uploads
Papers by Hui (Claire) Xiong