SUPERCAPACITORS AND ENERGY STORAGE From research through industrial applications up to nuclear fusion plants

LOW COST TECHNOLOGIES FOR PRODUCING SUPERCAPACITOR ELECTRODES

M. Federica De Riccardis SSPT-PROMAS-MATAS ENEA

FRASCATI, May 13, 2016

Summary

• SUPERCAPACITORS: MATERIALS AND TECHNOLOGIES

• PREPARATION OF NANOSTRUCTURED MATERIALS FOR SC ELECTRODES

• RESULTS

Supercapacitors: Materials and Technologies

SC technology has experienced an impressive growth in performance thanks to the discovery of new electrode materials, especially nanomaterials, and the design of new hybrid systems that combine faradic and capacitive electrodes

CONFINED DIMENSIONS of NANOSTRUCTURED MATERIALS

unusual electrical, mechanical and surface properties

NEA

R-SU

RFAC

E CH

ARG

E S

TORA

GE

Supercapacitors: Materials and Technologies

Supercapacitance effects

EDLCs store charges electrostatically through ion absorption at the electrode/electrolyte interface (carbon-based active electrode materials with high surface area)

Electrochemical double-layer capacitance Pseudocapacitance

In pseudocapacitors the charge storage occurs by means of fast and

reversible redox reactions at the surface of electroactive materials.

Supercapacitors: Materials and Technologies

Capacitance performance for both carbon-based EDLC electrodes and pseudocapacitor electrodes (including transition metal oxides and conducting polymers).

K. Naoi and P. Simon, The Electrochemical Society Interface • Spring 2008

EDLC

PC

Carbon +

Conducting Polymers

Combining nanostructured carbons with pseudocapacitive materials, the performance of electrodes has been improved.

Conducting Polymers (CPs)

Usually an organic polymer has a low conductivity (10-10–10-5 S/cm). In order to become electrically conductive, it should have delocalized and only partially filled molecular orbitals for a free movement of electrons.

A CP contains alternating single and double bonds, called conjugated double bonds. The bonds between the carbon atoms are alternately single and double. Every double bond is formed by a localized σ bond (strong) and also a π bond (weak) delocalized along the backbone of the polymer.

Applications Transistors Light Emitting Diodes (LEDs) Lasers used in flat televisions Solar cells Corrosion Inhibitors Compact Capacitors …….

The polymer needs to be “doped” by Conjugated polymers, when doped, become conductors (1 – 104 S/cm).

removing electrons from chain => p-doping inserting electrons into chain => n-doping

Hybrid conducting nanocomposites

HYBRID CONDUCTING NANOCOMPOSITES are produced by the combination of conducting polymers and nanostructured materials

Conventional synthesis method: chemical synthesis starting with the aniline monomer New synthesis method: Electropolymerisation (EP) combined with Electrophoretic Deposition (EPD)

EP advantages: - polymerisation of monomers and polymer doping simultaneously - reaction at room temperature - a careful control of reaction rate and oxidation state

+ NEW MATERIAL WITH ENHANCED PROPERTIES

Why PANI? Polyaniline (PANI) has been one of the most studied conducting polymer because of:

easy synthesis electrochromic polymer

low cost good supercapacitive behaviour

environmental stability good anticorrosion properties

different domains of conductivity good electrical conductivity

Each oxidation state can exist in the form of its base or its protonated form (salt) by treatment of the base with an acid. Depending on the oxidation state and the degree of protonation, PANI can be either an insulator or a conductor. y 1-y

y=1 → leucoemeraldine y=0.5 → emeraldine y=0 → pernigraniline

M. F. De Riccardis, et al., Functional Characterisations Of Hybrid Nanocomposite Films Based On Polyaniline And Carbon Nanotubes, Advances in Science and Technology Vol. 79 (2013) pp 81-86 Martina, V., M.F. De Riccardis, et al., Electrodeposition of polyaniline-carbon nanotubes composite films and investigation on their role in corrosion protection of austenitic stainless steel by SNIFTIR analysis, Journal of Nanoparticle Research (2011) 13:6035–6047

Electrosynthesis techniques

ADVANCED MATERIALS: functional and structural coatings, composite and porous materials, functionally graded materials, thin films and nanostructured materials

SECTORS: Nanotechnology Energy Electronic Biomedical Optical Catalytic

ADVANTAGES: versatility to be used with different materials and combinations of materials, cost-effectiveness (simple equipments), high potential for scaling up to large product volumes and variety of product shapes.

EP consists in applying an opportune potential to a working electrode immersed in an electrolyte solution. The electrodeposited film is obtained by electrode reaction from a solution containing the monomer.

EPD is achieved by (i) the migration of charged particles suspended in a liquid medium under the effect of an applied electric field, and (ii) the particles deposition on the opposite charged electrode.

Deposition methods su

bstr

ate

CNT

aniline

PANI+CNT composite

film EP

PANI-CNTs films were electropolymerised starting with an Aniline solution containing CNTs (co-electropolymerisation)

subs

trat

e

CNT

polyaniline

PANI+CNT composite

film

EPD

PANI (in the polymerised form) and CNTs were co-deposited by EPD

1) CNTs were deposited by EPD ->2) PANI was electropolymerised by EP on CNTs

subs

trat

e

CNT CNT film

EPD EP

PANI+CNT composite

film

aniline

subs

trat

e

CNT

aniline

PANI+CNT composite

film EP

The CNTs were incorporated in the PANI matrix during the Electropolymerisation process.

The functionalisation of CNTs by means of PANI occurred through the formation of donor-acceptor complexes. In fact CNTs act as good electron acceptors, while PANI is a good electron donor .

Deposition method-1: EP

0,0 0,2 0,4 0,6 0,8 1,0 1,2-0,02

-0,01

0,00

0,01

0,02

0,03

0,04

(b)

Cur

rent

(A)

Potential (V vs Ag/AgCl)

ELD PANI+0.3% v/v CNT

0,0 0,2 0,4 0,6 0,8 1,0 1,2

-0,010

-0,005

0,000

0,005

0,010

0,015

0,020

0,025

(a)

Curre

nt (A

)

Potential (V vs Ag/AgCl)

ELD PANI

The formation and deposition of PANI-CNTs films were obtained by means of 3 consecutive CV scans from 0.0 V to 1.2 V.

By comparing CV with and without CNTs in ANI, the curves for EP PANI-CNTs exhibit a considerable increase of current intensities at the monomer oxidation region, meaning that the presence of CNTs increases the growth rate of PANI.

PANI PANI+CNTs

Deposition method-1: EP

The length of the fibrils in the composite films are longer than that of PANI fibrils, reminding a shape similar to CNTs

Peak B (0.5 V) represents the transition leucoemeraldine → protonated emeraldine. Peak B (0.8 V) corresponds to the oxidation emeraldine → pernigraniline. Peak A (0.2 V) corresponds to the generation of radical cations.

A typical CV in H2SO4 of PANI-CNTs SE

M im

ages

TE

M im

ages

subs

trat

e

CNT

polyaniline

PANI+CNT composite

film EPD

PANI in the polymerised form and CNTs were co-deposited by EPD

Deposition method-2: EPD

25

35

45

55

65

75

0 0,1 0,2 0,3 0,4

ζ (m

V)

CNT content (%v/v)

High zeta potential means a good stability of suspension and an efficient deposition process.

Deposition method-2: EPD

PANI

CNT

PANI

CNT

10 nm

-1,0 -0,5 0,0 0,5 1,0 1,5-0,004

-0,003

-0,002

-0,001

0,000

0,001

0,002

0,003

0,004

C'

B'

A'

C

BA

Curre

nt (A

)

Potential (V vs Ag/AgCl)

EPD PANI EPD PANI+0.1% v/v CNT EPD PANI+0.2% v/v CNT EPD PANI+0.3% v/v CNT

Deposition method-3: EPD+EP su

bstr

ate

CNT CNT film

EPD

1st step

EP

PANI+CNT composite film

aniline

2nd step 2nd step: PANI was

electropolymerised by EP on CNTs

1st step: CNTs were deposited by EPD

The surface morphology is porous and with many nanofibrils

Deposition method-3: EPD+EP

Results

0,2 0,3 0,4 0,5 0,6 0,7 0,8

-0,006

-0,004

-0,002

0,000

0,002

0,004

0,006

0,008

I (A/

cm2 )

V (V vs Ag/AgCl)

EPD PANI EPD PANI+CNTs

For comparison the voltammograms acquired on pure PANI (both EP and EPD) are reported.

Capacitance [mF/cm2] measured on PANI and PANI-CNTs films obtained by different techniques (3 cycles deposition)

The presence of CNTs in the polymer did not substantially change the electrochemical properties of the polymer, but the closed area of the voltammograms, related to power density provided by the composite film, was significantly changed.

C (mF/cm2) EP EPD+EP EPD

PANI 135 / 123

PANI+CNTs 460 380 350

0,2 0,3 0,4 0,5 0,6 0,7 0,8

-0,04

-0,03

-0,02

-0,01

0,00

0,01

0,02

0,03

0,04

i (A/

cm2 )

V (V vs Ag/AgCl)

ELD PANI on EPD CNTs ELD PANI+CNTs ELD PANI

Conclusions

i. PANI-CNTs films co-electropolymerised by EP are easily deposited, by

one-step process that allows to control the oxidation state of PANI.

ii. PANI-CNTs films co-deposited by EPD are easily deposited, by one-step process, applicable to large areas, but a higher number of chemicals than in EP are used.

iii. PANI films electropolymerised on CNTs previously deposited by EPD, need a two-step process, where both the used electrodeposition techniques, EPD of CNTs and EP of PANI, are simple and easy to control.

iv. Both the EPD and EP have a great potential in producing nanocomposites based on carbon and conducting polymers.