Synthesis and Characterization of 

Conducting Composite Nanoparticles for 

Flow Battery Applications

1Purdue University – West Lafayette, IN

2NIST Center for Neutron Research – Gaithersburg, MD

Austin D. Scherbarth1,2

, Dr. Jeffrey J. Richards2

August 5th, 11:20 am

2015 Summer SURF Student Presentation
Motivation – Demand for energy storage technology

Challenge: Electrical power derived from renewable electrical sources requires storage for 

wide-scale adoption and implementation

Storage technologies that exist today are insufficient to meet capacity demands and cost 

requirements associated with the grid:

Flow batteries are currently being 

developed to address this need for 

low-cost and efficient energy 

storage

2 100% Renewable Energy – The Only Way Forward, theenergycollective.com 01/08/13; 
Flow Batteries

• Redox active fluids are pumped into a flow 

cell from external storage tanks where they 

undergo reversible redox reactions

• Flow cell consists of two electrodes 

separated by a ion exchange membrane

• Typical electrolytes consist of 

...Zinc/bromide or vanadium 

W. Antweiler, Can flow batteries solve the electricity storage problem?, University of British Columbia, 09/28/14 3
• Redox active fluids are pumped into a flow 

cell from external storage tanks where they 

undergo reversible redox reactions

• Flow cell consists of two electrodes 

separated by a ion exchange membrane

• Typical electrolytes consist of 

...Zinc/bromide or vanadium 

Flow Batteries

W. 3 Antweiler, Can flow batteries solve the electricity storage problem?, University of British Columbia, 09/28/14 
Advantages:

• Capacity of the battery is decoupled from the volume of its packaging 

• Scaling up the battery requires only the installation of larger catholyte/anolyte tanks

Disadvantages:

• Energy density limited by solubility of active substances in electrolyte

• These redox materials are often dissolved in highly acidic solvents – makes the 

equipment more expensive

Flow Batteries

• Redox active fluids are pumped into a flow 

cell from external storage tanks where they 

undergo reversible redox reactions

• Typical electrolytes consist of 

zinc/bromide or vanadium 

• Flow cell consists of two electrodes 

separated by a ion exchange membrane

W. 3 Antweiler, Can flow batteries solve the electricity storage problem?, University of British Columbia, 09/28/14 
• Combine high energy density of lithium (Li) with benefits of 

flow batteries

• Suspensions of active solid metal oxides intercalated with 

lithium (e.g., LiCoO2) instead of redox species dissolved in 

electrolyte

• Electrical energy is produced when Li is deintercalated from the 

metal oxide, Li-ion passes through the ion exchange membrane 

and the electron travels through an outside circuit to do work

Semi-Solid Flow Batteries (SSFBs)

• Carbon black (CB) is used to provide electrical 

conductivity and allows for charge transfer from 

material to current collector

• Unfortunately, the electrical percolation of the CB 

particles results in a high viscosity suspension and 

undesirable flow properties

Duduta et al., “Semi-Solid Lithium Rechargeable Flow Battery”, (2011) Advanced Energy Materials, 1, 511-516 4
Replace CB with a conductive polymer 

brush

Our Idea:

CB requires hard sphere contact for electrical 

conductivity 

Mitsubishi Chemical Corporation, Three Main Properties of Carbon Black, (2006) 

Polymer brush only requires close proximity 

for charge transfer

More energy required to break up CB to make it 

flow

Electrical percolation without mechanical 

percolation of composite particles makes flow 

much easier

5

Carbon Black (CB) Hydrated Polymer Brush
+

+

+

+

+

+

+

+

Polystyrene sulfonate (PSS) provides 

colloidal stability and ionic 

conductivity

3,4-ethylenedioxythiophene 

(EDOT)

Our Approach

Metal oxide (MO) particles are positively charged at low pH, and we used cationic silica (SiO2) 

as a model for metal oxides

+

At low pH (3-5)

Cationic SiO2 Polystyrene Sulfonate (PSS) PSS: SiO2 Composite

+

PSS: SiO2 Composite PEDOT:PSS:SiO2

Composite

PEDOT provides electrical 

conductivity

6

-

-

- -

-

-

- -

Fe(III)SO4

NaS2O8
PEDOT:PSS:SiO2

Composite

3.5:1 PSS:EDOT

50 nm 50 nm

3:1 PSS:EDOT

50 nm

1.5:1 PSS:EDOT

Rp = 46.8 +/- 2.9 nm

t = 7.5 +/- 2.0 nm

Rp = 51.9 +/- 5.1 nm

t = 9.0 +/- 5.0 nm

Rp = 54.2 +/- 5.1 nm

t = 9.0 +/- 6.7 nm

7

Proof of Principle:

SiO2

Demonstrated proposed synthesis method is capable of 

coating PEDOT:PSS brush layer on SiO2

Thin films of coated particles were shown to be conductive

Core/shell structure with polymer brush surrounding SiO2 

particles 0.0001

0.0010

0.0100

0.1000

1.0000

3.5:1 3:1 1.5:1

σ (S/cm)

PSS:EDOT Ratio
• Understand the effect of removing unadsorbed PSS from the sample solution on 

the properties of the composite particles 

• What role does the excess (unadsorbed) PSS play in the EDOT reaction?

My Goal

8

PSS: SiO2 Composite

-

-

- -

-

-

- -

PSS: SiO2 Composite 

+ Excess PSS

-

-

- -

-

-

- -

-

-

- -

-

-

- -

-

-

- -

-

-

- -

-

-

- -

-

-

- -

vs.
9

Initial Characterization

Dynamic Light Scattering (DLS) provides information about the size distribution of 

small particles in solution by measuring relaxation time

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

SiO2 PSS:SiO2 +PSS PSS:SiO2 Excess PSS

R

H (nm)
10

Initial Characterization

Zeta potential (ZP) can be thought 

of as simply the surface charge of 

particles in solution. 

The ZP of particles can be 

determined from the electrophoretic 

mobility that is measured when an 

electric field is applied across the 

sample

Samples with excess PSS present 

show more negative surface charge 

at low pH indicating the 

contribution of the unadsorbed PSS 

to particle and solution properties

-80

-60

-40

-20

0

20

40

60

3 5 7 9 11 13

pH

SiO2

PSS:SiO2

-80

-70

-60

-50

-40

-30

-20

-10

0

0 2 4 6 8 10 12

pH

With Excess PSS

No Excess PSS
Cationic SiO2

11

SANS measurements

+

+

+

+

+

+

+

+

Cationic SiO2 vs. PSS

-

-

- -

-

-

- -

vs. 

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

Cationic SiO2

PSS: SiO2 Composite + PSS

-

-

- -

-

-

- -

PSS: SiO2 Composite

vs. 
12

SANS measurements

Particles with and without excess PSS compared with their corresponding shape factors

+

+

+

+

+

+

+

+

Cationic SiO2 vs. PSS: SiO2 Composite Cationic SiO2 vs. 

+

+

+

+

+

+

+

+

PSS: SiO2 Composite + PSS

-

-

- -

-

-

- -
With PSS: SiO2 content fixed, the 

amount of EDOT reacted was 

varied to gain an understanding of 

how the properties of the particles 

were affected

It was determined that particle 

agglomeration was responsible for 

this increase, and for the decrease in 

surface charge above a ratio of 1:4

Particle Size and Surface Charge

13

-80

-70

-60

-50

-40

-30

-20

-10

0

1:1 1:2 1:3 1:4 1:8 1:16 1:20 PSS

ξ (mV)

EDOT:PSS Ratio

1

10

100

1000

1:1 1:2 1:3 1:4 1:8 1:12 1:16 1:20

Radius (nm)

EDOT:PSS Ratio

DLS measurements revealed a 

significant increase in hydrodynamic 

radius as EDOT:PSS ratio went from 

1:4 to 1:1, as would be expected

PSS: SiO2 Composite PEDOT:PSS:SiO2

Composite
14

Conductivity Measurements

0.000001

0.00001

0.0001

0.001

0.01

0.1

1

0 0.5 1 1.5 2 2.5 3 3.5

σ (S/cm)

PSS:EDOT Ratio

The conductivities of thin films of PEDOT:PSS:Silica composites were obtained by measuring 

the resistance of the films with varied EDOT content using Ossilla Variable Channel Length 

substrates
• PEDOT:PSS: SiO2 composite particles were successfully synthesized and 

characterized using various techniques

• Bulk PSS that is not adsorbed to the SiO2 particles likely plays a role in the 

incorporation of PEDOT onto the composite and adsorbs at high EDOT:PSS ratios

• SANS measurements revealed clear differences between pure SiO2 and adsorbed PSS 

on SiO2

• These particles showed conductivity when made into thin films

• At high EDOT:PSS ratios (1:1-1:2), large amounts of agglomeration was observed, 

resulting in a decrease in surface charge in this regime, but further studies and 

analysis must be done at these ratios to truly understand the behavior

• TEM micrographs supported DLS data that suggested the formation of a polymer 

surface layer on the metal oxide particles

Conclusions and Future Work

15
Many thanks to:

-Dr. Jeffrey Richards and Dr. Paul Butler

-Dr. Julie Borchers and all of the SURF Directors

-NSF

-Stacey Cochiara

Acknowledgements
Questions?