Download Supplementary Materials_28.09.16

Supplementary Material
Porous
Polymer
Composite
Membrane
Based
Nanogenerator:
A
Realization of Self-powered Wireless Green Energy Source for Smart
Electronics Applications
Sujoy Kumar Ghosh,1 Tridib Kumar Sinha,2 Biswajit Mahanty,1,3 Santanu Jana,1,4 and
Dipankar Mandal1,a)
1 Organic
Nano-Piezoelectric Device Laboratory (ONPDL), Department of Physics, Jadavpur
University, Kolkata 700032, India
2
3
Department of Physics, Indian Institute of Technology, Kharagpur 721302, India
Department of Electronics and Communication Engineering, Saroj Mohan Institute of
Technology, Guptipara, Hooghly 712512, India
4
Department of Electronics, Netaji Nagar Day College, 170/436 N. S. C Bose Road, Kolkata
700092, India
Author
to
whom
correspondence
should
be
addressed.
Electronic
mail:
[email protected]
S1
Methodology
The systematic study of the Pt-NPs doped P(VDF-HFP) films have been made by adding
different concentration (1.0 and 3.0 wt %) of Pt-salt into PVDF-DMF solutions under same
condition as mentioned in the main article, where 2.0 wt % of Pt-salt was utilized. The free
standing films with 1.0 wt % and 3.0 wt % of Pt-salt are indexed as FTML and FTMH
respectively.
(a)
FTML
40 % porosity
(b)
FTMH
90 % porosity
Figure S1. FE-SEM images of (a) FTML with 40 % porosity and (b) FTMH with 90 % of
porosity. In FTML pores are not formed throughout the surface (not continuous) and pore
diameters are not invariant in size. It is probably due to just initiation of pores, whereas in
some cases complete pore formation are took place. Whereas, FTM (Figure 2b) and FTMH
indicate that the pores formation are complete and invariant. It reveals that concentration of
Pt-salt plays a significant role.
S2
Frequency (counts)
Frequency (counts)
(a)
8
6
4
2
0
0.5
1.0
1.5
2.0
2.5
Pore diameter (m)
3.0
3.5
(b)
6
4
2
0
2
3
4
5
6
Pore height (m)
Figure S2. Histogram profile of pore diameter (a) and pore height (b) of the FTM estimated
from FE-SEM images depicted in Figure 1c of main article. The average pore diameter is 1.3
(a)
1600
(b)
FTML

0.50
FEA ≈ 42 %




1200
800

-1
Wavenumber (cm )
400
Absorbance(a.u.)
Absorbance (a.u.)
μm and pore height is 4.25 μm.
FTMH
FEA ≈ 65 %
0.50





1600
1200

 
800
400
-1
Wavenumber(cm )
S3
Figure S3. FT-IR spectra (in 1600 – 400 cm-1 frequency region) of (a) FTML and (b) FTMH.
The 𝐹𝐸𝐴 of FTML and FTMH are 42 % and 65 % which is relatively lower than FTM. Thus,
may be less suitable as ferroelectric as well as piezoelectric material than FTM.R1-R4
(b)
(a)
A||P
(c)
A||P
(d)
A┴P
A┴P
Figure S4. Optical microscopic images of NPV & FTM in un-polarized (A||P) [(a) &(b)
respectively] & polarized (A┴P) [(c) & (d) respectively] modes. The scale bar, given on the
images represents 50μm. Fig. S4c represents several spherulitic growths (A┴P) originated
from the nucleus in NPV film. These big powerfully birefringent spherulites describe the
prominent presence of α-phase crystals but these spherulitic growths are rapidly diminishes in
FTM (Fig. S4d). This implies that there may present β- or/and γ- spherulites in FTM which
S4
do not show any optical anisotropy in polarizing optical microscopy images due to the weak
birefringence nature. The presence of those mix-up electroactive phases is evidenced in FTIR spectroscopy as described in main article. Optical microscopic images (A‖P) of NPV &
FTM shown in Fig. S4 (a~b) also represent surface morphology but in microscopic level.
These figures indicate not only about smooth surface of NPV film but also about porous
Charging electric field (V/cm)
surface of FTM (marked by dotted circles).
60.0k
(a)
1st cycle
4th cycle
14th cycle
30.0k
(b)
0.0
-30.0k
-60.0k
0
2
4
6
8
10
Time (ms)
Figure S5. (a) Experimentally obtained charging electric field in several numbers of field
cycles as a function of time (ms) ensures the ferroelectret behaviour of FTM (b) schematic
view of the hysteresis process of each half cycle in a single polymer void encapsulate with
high dielectric polymer (i.e., due to ferroelectret character). (A) When the external applied
voltage reaches the threshold value Vth (~ 68.9 V within one micro void by application of
threshold electrical break down field of 38 kV/cm), Paschen breakdown is initiated. (B) At
higher voltages, a second series of discharges may occur. (C) During ramping down the
voltage, the reverse electric field from the trapped space charge may lead to back discharges.
S5
Associate discussion S1: Experimentally we have noticed that the charging electric field as a
function of time shows square shaped electric field though bipolar triangular electric field
was applied. This feature is generally observed in ferroelectret polymer. After more and more
cycling of electric field more charges are trapped in micro-voids (reflected from the Fig.
S3a). In DBDs the micro cavities in FTM are first charged up when high electric field is
applied. By fast internal charging (~ ns) process, perfectly oriented macroscopic “dipoles”
have been created and thus internal breakdown (Paschen breakdown) is initiated when the
voltage within the cavities reaches to the required threshold value (Vth). The Vth within a
single micro-cavity of FTM can be calculated through the equation,
𝜀𝑔
𝑉𝑡ℎ = 𝐸𝑡ℎ (𝜀 𝑑𝑝 + 𝑑𝑔 ) .................................... (1)
𝑝
where, 𝐸𝑡ℎ = 38 kV. cm−1 is the threshold electrical break down field in air, 𝑑𝑝 = 150𝜇𝑚 is
the total thickness of FTM, 𝑑𝑔 = 4.25 𝜇𝑚 is the average height of single micro-cavitie, 𝜀𝑝 =
11 is the permittivity of neat P(VDF-HFP) co-polymer and 𝜀𝑔 = 1, dielectric constant of gas
(air in this case) within the voids.R5 Thus calculation shows that the threshold charging
voltage of a single cavity to be macroscopic “dipoles” is ~ 68 V which is quite low than the
general ferroelectret cellular polymer materials. There are mainly three reasons behind this, i)
low dimensional micro void formation in FTM lead to huge number of microscopic “dipole
density” that increases the space charge effect and eventually decreases the threshold
charging voltage, ii) high dielectric constant of the polymer film needs high external electric
field to produce such low voltage within the voids, and iii) uniform distribution of micro
cavities. However, later Paschen breakdown, charges of opposite polarities are then separated
during the DBDs and are subsequently trapped on the top and bottom surfaces of the voids,
S6
respectively (point A in Fig. S3b). The trapped charges strongly induce an electric field
opposite to the externally applied field and thus eventually extinguish the discharge. In
further increment of applied voltage, DBDs triggered again, i.e., a second series of
breakdown events occur, and the density of the internally trapped charges (i.e. macroscopic
dipoles) strongly increases (point B in Fig. S3b). From this point, induced ferroelectric βcrystals of FTM play the major role. In this process we can ignore the minor contribution
from ferroelectric phase, as at low electric field, polarization of ferroelectric domain is almost
linear with applied external electric field. At higher electric field strength, polarization
increases due to higher order of polarization. Thus, polarization ordering due to ferroelectric
β-phase of FTM in conjunction with second series of breakdown event (point B in Fig. S3b)
(i.e., with high density of internally trapped charges) results saturated spontaneous
polarization (Ps ~ 69 μC.cm-2). However, when the applied voltage is reduced, the electric
field of the trapped charges in the voids may over compensate the applied field. Thus may be
able to trigger back discharges (point C in Fig. S3b) which results polarization as back
discharges only occur after the saturation of polarization. Note that, the back discharge, also
called memory behaviour, is well known in conventional DBDs. Therefore, the direction of
these dipoles can be switched back and forth by cycling the electric field if the field is
stronger than the breakdown field of the gases in the voids. In 14th cycle of electric field we
found that less time was needed to saturate than 4th field cycle.
S7
Stress (MPa)
4000
Y=0.81 GPa
3000
2000
1000
0
0
1
2
3
4
5
Strain (%)
Figure S6. The stress-strain curve of FTM estimates the Young’s modulus, Y ~ 0.81 GPa and
elastic compliance, 𝑠33 ~1.23 × 10−9 m2 N−1.
S8
Table S1
Generated open circuit output voltage (Voc) and short-circuit current (Isc) under
different stresses (σa) when the PPCNG was subject to imparted from different heights
Pressure imparting
Open circuit voltage (V)
Stress (MPa)
Short circuit
current (Isc) (μA)
height (cm)
1
2.7
0.5
2.9
3
6
1.1
6.4
6
10
1.9
10.7
9
15
2.8
16.1
12
23
4.3
24.7
Associate discussion S2: Output Current from theoretical approach:
Considering that our device underwent compressive strain for a quarter of the oscillation
period, the strain rate is taken to be 𝜀̇ = 4𝑓𝜀 × 100 % 𝑠 −1 where average frequency of the
axial stress, 𝑓~ 5 Hz. According to piezoelectric theory, the short circuit peak output current
generated from FTM can be written as,
Isc = d33 YAε̇
i.e., Isc =
4fVoc d33 A
Lg33
........................................... (2)
Thus, generated short circuit peak output current under different stress amplitude is tabulated
in Table S1.
S9
(b)
(a)
FTMH
1
Output voltage (V)
Ouput voltage (V)
FTML
0
-1
0.0
0.8
1.6
2.4
1
0
-1
0.0
Time (s)
0.8
1.6
2.4
Time (s)
Figure S7. Harvested output voltages under σa ~ 1.1 MPa from the nanogenerators made of
(a) FTML consists of 40 % porosity with 𝐹𝐸𝐴 ~ 42% and (b) FTMH consists of 90 %
porosity with 𝐹𝐸𝐴 ~ 65%. It revealed that output performance of the PPCNG composed of
FTM (porosity 85 % and 𝐹𝐸𝐴 ~ 85 %) is highest among the Pt-NPs doped porous P(VDFHFP) films which is described in the main article.
Associate discussion S3:
In the COMSOL model we have indicated in Fig. 4d that the input is applied compressive
stress amplitude of 1.1 MPa. Under pressure the generated pizo-potential distribution inside
the PPCNG is shown by COMSOL model. To perform the finite element method (FEM)
simulation model, a geometrical configuration was considered where fixed constrained is the lower
electrode and the bottom of the PPCNG was electrically grounded (Figure R5). To simplify the
simulation, an external boundary load i.e., stress (~ 1.1 MPa) was applied to the upper electrode and
other boundaries of the PPCNG were considered as symmetric.
S10
Boundary load
Symmetric
boundary condition
Upper electrode
FTM
FTM
Lower electrode
Fixed constraint
Ground
Figure S8. The geometrical configuration of the FEM simulation model.
The piezopotential distribution inside PPCNG during applied stress (~ 1.1 MPa) has been
calculated via FEM simulation using COMSOL Multiphysics software. To conduct the
simulations the following values are employed, such as, Young’s modulus, Y~0.81 GPa,
piezoelectric charge constant, 𝑑33 = −836 pC/N. We solved the following linear mechanical
equation E1 that links the stress T to the applied force F on the PPCNG and the Poisson
equation E2 that links the electric displacement D to the fixed charge density 𝜌𝑉 ,
-𝛻. 𝑇 = 𝐹 ,
(3)
𝛻. 𝐷 = 𝜌𝑉 ,
(4)
The coupling between the structural and electrical domains can be expressed in the form of
a connection between the material stress and its permittivity at constant stress or as a
coupling between the material strain and its permittivity at constant strain. The equations
(3, 4) are coupled to the piezoelectric equations of strain-charge form (5, 6) and stress-charge
form (7, 8) that correlate the stress T tensor, strain S, electric displacement D and the electric
field E using the permittivity ε , elasticity tensor c and piezoelectric coupling tensor e and d.
S11
Strain-Charge form:
The strain-charge form of a piezoelectric material is written as,
𝑆 = 𝑠𝐸 . 𝑇 + 𝑑 𝑇 . 𝐸 ,
(5)
𝐷 = 𝑑. 𝑇 + 𝜀0 . 𝜀𝑟𝑇 𝐸 ,
(6)
The material parameters sE, d, and εrT correspond to the material compliance, coupling
properties, and relative permittivity at constant stress. ε0 is the permittivity of free space.
Stress-Charge form:
The stress-charge form of the piezoelectric material is written as,
𝑇 = 𝑐𝐸 . 𝑆 + 𝑒 𝑇 . 𝐸 ,
(7)
𝐷 = 𝑒. 𝑆 + 𝜀0 . 𝜀𝑟𝑆 . 𝐸 ,
(8)
The material parameters cE, e, and εrS correspond to the material stiffness, coupling
properties, and relative permittivity at constant strain.
Associate discussion S4: The instantaneous piezoelectric energy conversion efficiency
(𝜼𝒑𝒊𝒆𝒛𝒐 ) of PPCNGR6
The instantaneous piezoelectric energy conversion efficiency (𝜂𝑝𝑖𝑒𝑧𝑜 ) of PPCNG is defined
as the ratio of the generated output electrical energy (by the instantaneous compressive axial
stress amplitude, σa ~ 1.1 MPa) (𝐸𝑒𝑙𝑒𝑐 ) to the input mechanical energy (𝐸𝑚𝑒𝑐 ). The optimum
resistance (20 MΩ) was connected with the PPCNG to derive optimized output performance,
and the output voltage per cycle was measured instantaneously, as shown in Fig. 4e and Fig.
S8a.
S12
𝑡
𝐸𝑒𝑙𝑒𝑐
𝑉(𝑡)2
=∫
𝑑𝑡
𝑅
0
The evaluated output energy, 𝐸𝑒𝑙𝑒𝑐 = 1.1 × 10−6 𝐽 .
30
2
2
Output voltge (V )
Output voltage (V)
6
3
0
-3
20
10
0
0.0
0.8
1.6
2.4
1.30
Time (s)
1.35
1.40
1.45
1.50
Time (s)
Figure S9. (a) The measured output voltage at an external load of 20 MΩ. (b) The square of
the output voltage for the integration to obtain the instantaneous electrical output power.
To determine the input mechanical energy (𝐸𝑚𝑒𝑐 ), we have to considered the total axial
deformation of the PPCNG under 1.1 MPa stress as, ∆𝐿 = 𝜀 × 𝐿 .
The axial strain ε, developed in the FTM can be calculated following the equation, 𝜀 =
𝜎𝑎
𝑌
=
1.358 × 10−3.
Thus, the total input mechanical energy per cycle is calculated by, 𝐸𝑚𝑒𝑐 = 𝐹 × ∆𝐿 = 7.6 ×
10−5 J where F is the applied force.
The instantaneous piezoelectric energy conversion efficiency of the BPNG can be written as,
𝐸
𝜂𝑝𝑖𝑒𝑧𝑜 = 𝐸𝑒𝑙𝑒𝑐 × 100 % = 1.45 %.
𝑚𝑒𝑐
S13
1.5
(a)
(b)
20 cm
15 cm
1.0
Voltage (V)
Voltage (V)
0.6
0.3
0.5
0.0
0.0
-0.5
0.0
0.8
1.6
2.4
0.0
Time (s)
12 cm
(c)
(d)
0
-2
0.0
0.8
1.6
2.4
Time (s)
0
-2
0.0
1.6
Time (s)
(f)
2
0
2.4
6 cm
2
0
-2
0.0
0.8
Time (s)
1.6
2.4
0.0
3 cm
(g)
(h)
1.6
2.4
2 cm
Voltage (V)
4
2
0
-2
2
0
-2
0.0
0.8
1.6
2.4
Time (s)
4
0.8
Time (s)
4
Voltage (V)
0.8
4
Voltage (V)
Voltage (V)
2
8 cm
(e)
-2
Voltage (V)
2.4
10 cm
4
2
4
1.6
Time (s)
Voltage (V)
Voltage (V)
4
0.8
0.0
0.8
1.6
2.4
Time (s)
1 cm
(i)
2
0
-2
S14
0.0
0.8
1.6
Time (s)
2.4
Figure S10. The transmitted signals across the receiver when the distances between the
transmitter and receiver were varied, ranging from 1 cm to 20 cm (mentioned in the inset of
the each figure).
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G. H. Kim, S. M. Hong, and Y. Seo, Phys. Chem. Chem. Phys. 11, 10506 (2009).
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S. Maji, P. K. Sarkar, L. Aggarwal, S. K. Ghosh, D. Mandal, G. Sheet, and S. Acharya,
Phys. Chem. Chem. Phys. 17, 8159 (2015).
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R5
M. Lindner, H. Hoislbauer, R. Schwodiauer, S. Bauer-Gogonea, and S. Bauer, IEEE Trans.
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S15