Probing, Charging and Discharging of Single Probing, Charging and Discharging of Single SSNanoporesNanopores in a in a SupercapacitorSupercapacitor

Pingshan WangElectrical and Computer Engineering Department Clemson UniversityDepartment, Clemson University

Jim RuiMechanical Engineering DepartmentClemson Universityy

ContentsContents

Background– Probing the fundamental processes in electrochemicalProbing the fundamental processes in electrochemical

capacitors (EC)– On-chip dielectric spectroscopy with microfluidic and nanofluidic

channelschannels

Dielectric spectroscopy with planar micro/nanofluidic channels for EC process probing– Nanofluidic channel fabrication– Dielectric spectroscopy methods– Molecular dynamics simulationy

1/21/2009 Capacitor Consortium Planning Meeting 2

Background: Wetting and ion transport in ECsBackground: Wetting and ion transport in ECs

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• Wetting characteristics in nanoporesWetting characteristics in nanopores• Ion transport: electrolytes for performance

Nanoscale systems

* Modified from Fig. 16 on p. 55 of Basic Research Needs for Electrical Energy Storage

yPores: 0.5–3 nm in size)

1/21/2009 Capacitor Consortium Planning Meeting 3

Background: Charging and discharging at atomic levelBackground: 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 andcharging/discharging at molecular and atomic levels

• Calibrated and valibrated predictive models for capacitive energy systems: nm to mm

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and picosecond to microsecond.

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1/21/2009 Capacitor Consortium Planning Meeting 4

* Modified from Fig. 16 on p. 49 of Basic Research Needs for Electrical Energy Storage

Background: onBackground: on--chip dielectric spectroscopy with chip dielectric spectroscopy with micro/micro/nanofluidicnanofluidic channelschannels

Dielectric spectroscopy (Impedance spectroscopy)

micro/micro/nanofluidicnanofluidic channelschannels

Dielectric spectroscopy is complementary to• Nuclear magnetic resonance (NMR)• Neutron scatteringNetwork

analyzer • Mechanical spectroscopy• Debye relaxation

analyzer

μmnm

W(       ) where is the permittivity at the high frequency

Sample holder

nm e e s t e pe tt ty at t e g eque cylimit, , is the static, low frequency permittivity, and τ is the characteristic relaxation time of the medium.

Nanofluidic channel

1/21/2009 Capacitor Consortium Planning Meeting5

Background: micro/Background: micro/nanonano fluidic channelsfluidic channels

Glass wafer

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G

10 µmG

S

Silicon

MUT

Si

G’ L R C’

MUT

Si

C G

Water flow video

1/21/2009 6Capacitor Consortium Planning Meeting

1/21/2009 7Capacitor Consortium Planning Meeting

Background: Background: microfluidicmicrofluidic channels and resultschannels and results

60t)

Microfluidic channels Measurement setup

45

50

55

60

(Imag

inar

y Pa

rt

• ~ 50 kV/cm electric field• Slightly different from ordinarily

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45

15 20 25 30 35 40 45 50 55 60 65

Perm

ittiv

ity (

Permittivity (Real Part)

• Slightly different from ordinarily accepted 80

Water dielectric permittivity

1/21/2009 8Capacitor Consortium Planning Meeting

Proposal: probing fundamental process in ECs with 1Proposal: probing fundamental process in ECs with 1--1000 nm planar micro/nanofluidic channels1000 nm planar micro/nanofluidic channels1000 nm planar micro/nanofluidic channels 1000 nm planar micro/nanofluidic channels

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1 nm

Wetting

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G’ L

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R C’

G +C G

On-chip dielectric spectroscopy

Charging and discharging

Different electrolytes

1/21/2009 Capacitor Consortium Planning Meeting 9

p p py y(bulk vs. confined)

Microfluidic channels: fine.Microfluidic channels: fine.Nanofluidic channels: is it possible?Nanofluidic channels: is it possible?Nanofluidic channels: is it possible?Nanofluidic channels: is it possible?

5 µm~ 4 nm

Surface roughness

~ 60 µm

Surface roughness

~ 60 µm

~14 nmAFM 3D_AFMSilicon transmission lines

1/21/2009 Capacitor Consortium Planning Meeting 10

Silicon transmission lines

Proposal: probing fundamental process in ECs with 1Proposal: probing fundamental process in ECs with 1--1000 nm planar micro/nanofluidic channels1000 nm planar micro/nanofluidic channels1000 nm planar micro/nanofluidic channels 1000 nm planar micro/nanofluidic channels

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1 nm

Wetting

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- 

G’ L

C

R C’

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Charging and discharging1 M quaternary ammonium bis(oxalato) borates (QABOBs)/propylene carbonate solutions

1/21/2009 Capacitor Consortium Planning Meeting 11

q y ( ) ( ) p py1 M Et4NBF4/propylene carbonate

Long term goals and 1Long term goals and 1--year deliverablesyear deliverables

Long term goals– Understand wetting charging and discharging processes of ECsUnderstand wetting, charging and discharging processes of ECs

at the atomic level– Establish corresponding models

Understand the interactions charged electrodes and electrolytes– 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