Electrospun conductive polyanilinepolyaniline-carbon black composite nanofibrous mat for conductive electrode applications Sujith Kalluri, Asha A.M, Anjali P, Vani R, Sivakumar N, K. R. V. Subramanian, A. Sreekumaran Nair, Shantikumar V Nair*, A. Balakrishnan* *Corresponding authors: avinash.balakrishnan@gmail.com, nairshanthi@gmail.com Nano Solar Division, Division, Amrita Centre for Nanosciences and Molecular medicine, Amrita Viswa Vidyapeetham University, KochiKochi-682 041, India Abstract
The study reports the first example for use of available PANI-CB composite to develop electrospun conductive nanofiber mats using an optimized amount of PVA as a carrier solution, which was sublimated at 230 ºC to attain a complete conducting nanofiber network. The samples are characterized using SEM, FTIR, UV spectroscopy and SECM for surface morphology, phase transformation, porosity and electrical conductivity respectively. The heat-treated fibers showed specific conductance values four times higher than the as-prepared fibers with percolation threshold in both. It is hypothesized the possible Schottky nanocontacts between PANI and CB. It can find wide applications in the area of in DSSC and Supercapacitors.
Experiment
Introduction 1. Optimization of polymeric blend of PANI-CB and PVA.
PANI when blended with fillers like CB (20 wt.%) show combined properties of both with novel functionality. Formation of high specific surface area nanofibers from electrospinning of PANI-CB can improve electrical conductivity. Fig1: Schematic representation of possible electron transfer pathways in PANI-CB composite (a) initial current raise and (b) after Schottky barrier overcome.
2. Electrospinning of polymeric blend. 3. Electrospun sample is calcined at 230 ºC to sublimate PVA Fig 2: Electrospinning setup
Characterization Diameter (nm) Refractive index
1. Surface Morphology of processed nanofibers using SEM.
PUV (%)
Thickness (µm)
Surface pore size (µm)
2. Porosity is confirmed with UV-VIS spectrophotometer.
As-prepared
250±10
1.35±0.005
41±1.2
42±10
0.3±0.02
3. SECM study is carried out in 0.1M LiClO4 for as-prepared and heat treated
Heat treated
160±50
1.21±0.01
70±2
34±7
1.8±0.7
Table 1. Physical and optical properties of as-prepared and heat treated fiber mats.
samples. 4. Phase transformation and cross-linkages are confirmed by FTIR.
Results
Fig 4: Surface current distribution of electrospun PANI-C as-prepared and heat treated fiber mats Fig 3: SEM images of electrospun PANI-C composite (a) thin fibers with beads (PVA: PANI-C 4:1), (b) as-prepared fibers & (c) heat treated fibers.
Fig 5: Plot of fiber diameter distribution (a) as-prepared and (b) heat treated samples.
Fig 6: Surface profilometry showing thickness of samples (a) as-prepared and (b) heat treated.
Weibull statistics showed higher values for heat treated samples (0.14 ± 0.05) µS/cm2 compare to as-prepared samples (0.03 ± 0.005) µS/cm2
Fig 7: Comparison of I-V curves of electrospun PANI-CB as-prepared and heat treated fiber mats.
Fig 8: Weibull plot comparison of the specific conductance of electrospun PANI-CB asprepared and heat treated fiber mats.
Conclusion It is hypothesized that the presence of “metallic” carbon black in the polymer matrix possibly generates a nanoscale Schottky contacts with the “semiconducting” PANI. These nanoscale Schottky contacts with the PANI may play a key role in determining the possible conduction pathways as shown in Fig.1
Electrospinning of PANI-CB in combination with PVA resulting in structurally stable fibers, which were heat treated at 230ºC for highly porous network. The porosity measurements showed twice increase in values for heat treated samples. Weibull plot showed the mean specific conductance values obtained for heat treated fibers to be about four times higher than that of the as-prepared fibers. SECM studies showed the percolation threshold value for as-prepared samples at ~1.8 V, while the heat treated samples showed linearity with less prominent percolation threshold (~0.6 V) in I-V curves indicating the formation of possible nanoscale Schottky contacts between CB and PANI.
Acknowledgements: Ministry of New and Renewable Energy (MNRE) and Department of Science and Technology (DST), Government of India is gratefully acknowledged for their financial support under the NATAG program monitored by Dr G.Sundararajan.