Probing, Charging and Discharging of Single Nanopores in a Supercapacitor Pingshan Wang Electrical and Computer Engineering Department, Clemson University Jim Rui Mechanical Engineering Department Clemson University
Contents Background Probing the fundamental processes in electrochemical capacitors (EC) On-chip dielectric spectroscopy with microfluidic and nanofluidic channels Dielectric spectroscopy with planar micro/nanofluidic channels for EC process probing Nanofluidic channel fabrication Dielectric spectroscopy methods Molecular dynamics simulation 1/21/2009 Capacitor Consortium Planning Meeting 2
Background: Wetting and ion transport in ECs ++++++++++++++ + + + + + + + + + + + + + + + + + + + + + + + + + + + Wetting characteristics in nanopores Ion transport: electrolytes for performance Nanoscale systems Pores: 0.5 3 nm in size) * Modified from Fig. 16 on p. 55 of Basic Research Needs for Electrical Energy Storage 1/21/2009 Capacitor Consortium Planning Meeting 3
Background: Charging and discharging at atomic level Correlation between pore size, ion size, surface area, surface chemistry and EC performance Solvation dynamics, molecular interactions at the interfaces Electrolyte/electrode interface during charging/discharging at molecular and atomic levels Calibrated and valibrated predictive models for capacitive energy systems: nm to mm and picosecond to microsecond. - + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + * Modified from Fig. 16 on p. 49 of Basic Research Needs for Electrical Energy Storage 1/21/2009 Capacitor Consortium Planning Meeting 4
Background: on-chip dielectric spectroscopy with micro/nanofluidic channels Dielectric spectroscopy (Impedance spectroscopy) Network analyzer Dielectric spectroscopy is complementary to Nuclear magnetic resonance (NMR) Neutron scattering Mechanical spectroscopy Debye relaxation Sample holder nm W( μm ) where e is the permittivity ty at the high frequency limit,, is the static, low frequency Nanofluidic channel permittivity, and τ is the characteristic relaxation time of the medium. 1/21/2009 Capacitor Consortium Planning Meeting 5
The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again. Background: micro/nano fluidic channels G S G Glass wafer 10 µm Si Silicon MUT Si R L C G C G Water flow video 1/21/2009 Capacitor Consortium Planning Meeting 6
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Background: microfluidic channels and results Microfluidic channels Measurement setup Permittivity (Imaginary Part t) 60 55 50 45 40 15 20 25 30 35 40 45 50 55 60 65 Permittivity (Real Part) Water dielectric permittivity ~ 50 kv/cm electric field Slightly different from ordinarily accepted 80 1/21/2009 Capacitor Consortium Planning Meeting 8
Proposal: probing fundamental process in ECs with 1-1000 nm planar micro/nanofluidic channels + + + + + + + + + + + + + + + + + + + + + + + + + + + + 1 nm Wetting R L C C G G - + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + Charging and discharging On-chip dielectric spectroscopy py Different electrolytes (bulk vs. confined) 1/21/2009 Capacitor Consortium Planning Meeting 9
Microfluidic channels: fine. Nanofluidic channels: is it possible? ~ 4 nm 5 µm Surface roughness ~60µm AFM 3D_AFM ~14 nm Silicon transmission lines 1/21/2009 Capacitor Consortium Planning Meeting 10
Proposal: probing fundamental process in ECs with 1-1000 nm planar micro/nanofluidic channels + + + + + + + + + + + + + + + + + + + + + + + + + + + + 1 nm Wetting R L C G C G + - + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + Charging and discharging 1 M quaternary ammonium bis(oxalato) borates (QABOBs)/propylene py carbonate solutions 1 M Et4NBF4/propylene carbonate 1/21/2009 Capacitor Consortium Planning Meeting 11
Long term goals and 1-year deliverables Long term goals Understand wetting, charging and discharging processes of ECs at the atomic level Establish corresponding models Understand the interactions charged electrodes and electrolytes Help identify the properties of perfect electrolytes for ECs First year deliverables Microfluidic channels and dielectric characterization of two electrolytes: 1 M quaternary ammonium bis(oxalato) borates (QABOBs)/ propylene carbonate solutions, and 1M Et4NBF4/propylene carbonate. Planar nanofluidic channels with ~ 1 nm (silicon and SiO2 surface) Initial results on wetting and charging and discharging models 1/21/2009 Capacitor Consortium Planning Meeting 12