HYBRID MATERIALS FOR ENERGY STORAGE · HYBRID MATERIALS FOR ENERGY STORAGE Marilena RE, M. Federica...
Transcript of HYBRID MATERIALS FOR ENERGY STORAGE · HYBRID MATERIALS FOR ENERGY STORAGE Marilena RE, M. Federica...
HYBRID MATERIALS FOR ENERGY STORAGE
Marilena RE, M. Federica De Riccardis, Daniela Carbone ENEA- SSPT PROMAS MATAS
NANOITALY 2015
Rome, September 21-24, 2015
Conducting Polymers (CPs)
Polymers → Molecules that form long chains, repeating themselves
Usually an organic polymer, either semiconductor or insulant, 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 :
1- CPs consist of alternating single and double bonds, called conjugated double bonds [The bonds between the carbon atoms are alternately single and double. Every double bond contains a localized σ bond, a strong chemical bond, and also a weaker π bond delocalized along the backbone of
the polymer] 2- The polymer needs to be “doped” by removing electrons from (oxidation, p-doping) or inserting them into (reduction, n-doping) the material
Conjugated polymers, when doped,
become conductors (1 – 104 S/cm)
Conducting Polymers (CPs)
Polypyrrole (Ppy) Polythiophene (PT) Polyfuran (PFFU) Polyaniline (PANI) Polyethylene dioxythiophene (PEDOT)
Applications
Transistors Light Emitting Diodes (LEDs) Lasers used in flat televisions Solar cells Corrosion Inhibitors Compact Capacitors …….
Only some of the CPs
Electropolymerisation
CPs can be produced through an electrochemical process which induces not only the polymerization of monomers but also polymer doping. In this way a conductive polymer coating can be deposited on an electrode.
Some advantages of this polymerization process respect to chemical process are: ― reaction at room temperature ― a careful control of the reaction rate and of
oxidation state
Why PANI? Among all CPS Polyaniline (PANI) has been one of the most studied for its characteristics:
easy synthesis electrochromic polymer
low cost good supercapacitive behaviour
environmental stability good anticorrosion properties
different domains of conductivity good electrical conductivity
Depending on the oxidation state and the
degree of protonation, PANI can be either
an insulator or a conductor with different
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. y= 1 → leucoemeraldine
y= 0.5 → emeraldine
y= 0 → pernigraniline
y 1-y
POLIANILINE
But its mechanical stability is not so much good
• M. F. De Riccardis, et al, Advances in Science and Technology Vol. 79 (2013), 81
• Martina, V., M.F. De Riccardis, et al., Journal of Nanoparticle Research Vol. 13 (2011),
:6035
HYBRID CONDUCTING NANOCOMPOSITES
HYBRID CONDUCTING NANOCOMPOSITES are produced by the combination of conducting polymers and nanoparticles
Applications: sensors, actuators, touch screens, electrode for supercapacitors, etc..
Conventional synthesis method: electrochemical synthesis starting with the aniline monomer
+
NEW MATERIAL WITH ENHANCED PROPERTIES
Here some experimental results are reported on different methods used to produce a film of PANI+CNT with interesting properties
Electrosynthesis techniques
ELECTROLYTIC DEPOSITION ELECTROPHORETIC DEPOSITION
To form advanced materials: functional and structural ceramic coatings, composite and porous materials, functionally graded materials, thin films, and nanostructured materials
Applications in several 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.
DC power supply
ELD 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 salt solution.
+ _
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.
ELECTROLYTIC DEPOSITION (ELD) ELECTROPHORETIC DEPOSITION (EPD)
Electrosynthesis techniques
Deposition methods su
bst
rate
CNT
aniline
PANI+CNT composite
film ELD
1° METHOD: ELD
PANI-CNTs films were electropolymerised by ELD starting with an Aniline solution containing CNTs
2° METHOD: EPD
sub
stra
te
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, then 2) PANI was electropolymerised by ELD on CNTs
sub
stra
te
CNT CNT film
EPD
3° METHOD: EPD + ELD
ELD
PANI+CNT composite
film
aniline
sub
stra
te
CNT
aniline
PANI+CNT composite
film ELD
Deposition method-1: ELD
PANI-CNTs nanocomposites film is electrochemical co-deposited starting with an Aniline solution containing CNTs: it is formed during the electropolymerisation – deposition of the polymer just near the electrode surface
CNTs are functionalised by PANI in the solution 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: ELD
The formation and deposition of PANI-CNTs films on carbon paper were obtained by means of 3 consecutive CV scans from 0.0 V to 1.2 V (scan rate of 20 mV/s).
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)
Cu
rre
nt (A
)
Potential (V vs Ag/AgCl)
ELD PANI+0.3% v/v CNT
By comparing CV with and without CNTs in ANI, the curves for ELD PANI-CNTs exhibit a considerable increase of current intensities at the monomer oxidation region and a peak shift at less anodic potential, meaning that the presence of CNTs accelerates the growth rate of PANI. 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)
Cu
rren
t (A
)
Potential (V vs Ag/AgCl)
ELD PANI
Electrochemical characterization
-0,2 0,0 0,2 0,4 0,6 0,8 1,0 1,2
-0,004
-0,003
-0,002
-0,001
0,000
0,001
0,002
0,003
0,004
C'
B'
A'
C
BA
i (A
/cm
2) V (V vs Ag/AgCl)
A typical CV in 0.5 M H2SO4 of PANI-CNTs
Peak A (0.25 V) represents the transition leucoemeraldine → protonated emeraldine
Peak C (0.8 V) corresponds to the oxidation emeraldine → pernigraniline
Peak B corresponds to the generation of radical cations.
Morphological characterization
The length of the fibrils in the composite films are longer than that of PANI fibrils, reminding a shape similar to CNTs
PANI PANI+CNTs
SEM images
TEM images
PANI+CNT composite film
sub
stra
te
CNT
polyaniline
EPD
PANI in the polymerised form and CNTs were co-deposited by EPD
Deposition method-2: EPD
PANI and CNT are suspended together and then deposited on the electrode A fundamental step for EPD deposition is the production of the suitable and very stable suspension with particles well dispersed in the liquid medium
Preparation of EPD suspension
Liquid medium = CHCl3/EtOH DBSA (dodecylbenzensulphonic acid) donates H+ to PANI making it protonated, whereas DBSA remains negatively charged
m-cresol as a co-solvent straightens the PANI chains and is therefore responsible for increasing the mean molecular area per PANI unit
Possible interactions between PANI and CNTs that do not neutralize the total positive charge of PANI chains
+ DBSA
+ m - cresol
+ +
+
+
+
+
+
+
+
-
-
-
-
-
- -
+ +
+
+
+
+ +
+
+ CNT +
-
-
-
+
+
+
+ +
PANI
OH
O -
O
NH
p-stacking
hydrogen bonding
O -
O
NH +
electrostatic interaction
25
35
45
55
65
75
0 0,1 0,2 0,3 0,4
z (m
V)
CNT content (%v/v)
PANI is effectively positively charged. After adding CNTs to PANI suspension, the zeta potential increased in positive correlation with the CNTs content.
High zeta potential means a good stability of suspension and an efficient deposition process.
Deposition method-2: EPD
Electrochemical characterization
-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
Cu
rren
t (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
A typical CV in 0.5 M H2SO4 of PANI-CNTs obtained by EPD with 3 different contents of CNTs
A typical CV in 0.5 M H2SO4 of PANI-CNTs obtained by ELD (0.3% CNTs)
Morphological characterization
PANI
CNT
10 nm
PANI
CNT
Deposition method-3: EPD+ELD
sub
stra
te
CNT CNT film
EPD
1st step
ELD
PANI+CNT composite
film
aniline
2nd step
1st step: CNTs were deposited by EPD
2nd step: PANI was electropolymerized by ELD on CNTs
Morphological characterization
The surface morphology is porous and with many nanofibrils
By looking in an internal part of the nanocomposite film different morphological features can be seen
Electrochemical characterization
CVs in 0.5 M H2SO4 obtained for the different nanocomposite systems: • 1st scan of PANI ELD
on CNTs (CV01) • 2nd scan of PANI ELD
on CNTs (CV02) • 3rd scan of PANI ELD
on CNTs (CV03) • PANI ELD (CV05) • CNT ELD (CV04)
Electrochemical characterisation
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
/cm
2)
V (V vs Ag/AgCl)
ELD PANI on EPD CNTs
ELD PANI+CNTs
ELD PANI
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
/cm
2)
V (V vs Ag/AgCl)
EPD PANI
EPD PANI+CNTs
For comparison the voltammograms acquired on pure PANI (both ELD and EPD) are reported.
CVs areas [VA/cm2] measured on PANI and PANI-CNTs films obtained by different techniques
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.
ELD EPD+ELD EPD
PANI 0.00852 0.00852 0.00198
PANI+CNTs 0.01509 0.01242 0.00242
Δ% 77.1 45.8 22.2
Conclusions
I. The hybrid conducting polymer nanocomposite CNT + PANI, obtained by three electrosynthesis methods, shows better performance of the electrochemical properties respect to pure PANI (an increased power density).
II. PANI-CNTs films co-electropolymerised by ELD are easily deposited, by one-step
process that allows to control the oxidation state of PANI. The process is reproducible but not applicable on large areas.
III. 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 ELD are used.
IV. PANI films electropolymerised on CNTs previously deposited by EPD, need a two-step process, where both the used electrodeposition techniques, EPD of CNTs and ELD of PANI, are simple and easy to control.
Work in progress….
Measurements of specific conductivity of the PANI+CNTs nanocomposites obtained by ELD, by EPD and by the combined processes
More experiments in order to optimize process parameters…..
• Variation of process parameters…. • Evaluations of the electrochemical properties ……….. • Morphological characterizations……..
New and more complex structures of hybrid conducting polymer nanocomposite can be properly tailored for energy applications
Thank you very much!