Porous activated carbon materials from Triphala seed stones for high-performance supercapacitor applications

Porous activated carbon materials derived from biomass could be the suitable materials for high-rate performance electrochemical supercapacitors as it exhibits high surface area due to well-defined pore structure. Here, we report the novel porous activated carbon from Triphala seed stones by chemical activation with zinc chloride at different carbonization temperature (400-700 °C) under the nitrogen gas atmosphere. The activated carbon was characterized by Fourier transform-infrared (FTIR) spectroscopy, Raman scattering and scanning electron microscopy (SEM). Nitrogen adsorption-desorption measurements was used to study the surface properties (effective surface areas, pore volumes and pore size distributions). The electrochemical measurements were performed in an aqueous 1 M sulphuric acid (H2SO4) solution in a three-electrode cell set up. Triphala seed stones-derived porous carbon materials with well-defined micro- and mesopores exhibit high specific surface area ranges from 878.7 to 1233.3 m2 g-1 and total pore volume ranges from 0.439 to 0.626 cm3 g-1. The specific capacitance obtained by electrochemical measurement experiment was 208.7 F g-1 at 1 A g-1. These results indicate that the prepared nanoporous activated carbon material from Triphala seed stones would have significant possibility as supercapacitor electrode material for high-energy-storage supercapacitor applications

Irreversibility of the antiferroelectric to ferroelectric phase transition in (Pb<SUB>0.90</SUB>Ba<SUB>0.10</SUB>)ZrO<SUB>3</SUB> ceramics

Dielectric and x-ray diffraction evidences are presented to show that the antiferroelectric to ferroelectric phase transition in (Pb0.90Ba0.10)ZrO3 ceramics is not reversible during the cooling cycle. It is shown that the stable antiferroelectric phase recovers from the metastable ferroelectric matrix on aging at room temperature. The kinetics of recovery of the antiferroelectric phase is very sluggish. It is pointed out that this type of irreversibility occurs in field induced antiferroelectric to ferroelectric transitions also. This may have serious implications for the actuator applications of these materials. It is proposed that the large transformation strains associated with the antiferroelectric orthorhombic to ferroelectric rhombohedral phase transition is responsible for this irreversibility

Dielectric studies of phase transitions in (Pb<SUB>1-x</SUB>Ba<SUB>x</SUB>)ZrO<SUB>3</SUB>

Phase transitions in semiwet derived (Pb1-xBax)ZrO3 ceramics for the composition range 0=x=0.30 have been investigated by dielectric measurements at various frequencies during heating and cooling cycles. The paraelectric (PE) to ferroelectric (FE) to antiferroelectric (AFE) sequence of phase transitions is observed for 0&#8804;x&#171;0.20. On increasing the Ba2+ content from x=0 to x=0.05, the thermal hysteresis associated with the AFE-FE phase transition increases from 11 to 100&#176;C. This is attributed to the increase in the piezoelectric coupling between the strain and polarization. For x=0.20, the FE phase does not transform into the AFE phase on cooling. Pronounced deviations from the regular FE behavior are observed on increasing the Ba2+ content to x=0.25. For x=0.30, the temperatures corresponding to the peak values of the real and imaginary parts of the dielectric constant become frequency dependent indicating relaxor FE behavior. It is shown that the polar clusters present in the PE phase undergo Vogel-Fulcher type relaxational freezing in the relaxor FE phase. The results of temperature dependent polarization measurements confirm the findings of the dielectric studies. It is proposed that Ba2+ substitution modifies the AFE and FE interactions of the PbZrO3 matrix in such a manner that their strengths become comparable for x=0.30 leading to the glassy or relaxor behavior

High temperature X-ray diffraction studies on antiferroelectric and ferroelectric phase transitions in (Pb<SUB>1-x</SUB>Ba<SUB>x</SUB>)ZrO<SUB>3</SUB> (x=0.05,0.10)

We have carried out high temperature x-ray diffraction studies on (Pb1-xBax)ZrO3(PBZ) to correlate the large thermal hysteresis (~100 &#176;C for x=0.05) and irreversibility (for x=0.10) of the antiferroelectric (AFE)-ferroelectric (FE) phase transition observed in dielectric measurements with structural changes. It is shown that for both the compositions, the sequence of phase transitions during heating is orthorhombic antiferroelectric (AO) to rhombohedral ferroelectric (FR) and then to cubic paraelectric (PC). The wide phase coexistence region (~80 &#176;C for x=0.05 and ~160 &#176;C for x=0.10) and the arrest of the FR to AO transition for x=0.10 during cooling strongly indicate first order character of the AO-FR transition. It is shown that the transformation strains associated with the AO to FR transition increases with Ba2+ concentration from a value of 0.6% for x=0 to 0.9% for 0.10. Similarities of the AO-FR transition in PBZ with nonthermoelastic martensitic transformations are pointed out. The FR to PC transition is also shown to be first order but with a small thermal hysteresis (~10 &#176;C) and a small discontinuous change in the cell volume (~0.5%)

Demonstration of Reentrant Relaxor Ferroelectric Phase Transitions in Antiferroelectric-Based (Pb0.50Ba0.50)ZrO3 Ceramics

Herein we demonstrate a novel (Pb0.50Ba0.50)ZrO3 (PBZ50) ceramic that exhibits a reentrant relaxor ferroelectric phase transition in an antiferroelectric-based perovskite system. The dielectric measurement has confirmed that the imaginary part of the dielectric constant for the reentrant phase is nearly frequency independent below the freezing temperature. The reentrant behavior could be scaled to a phenomenological equation involving the Vogel–Fulcher relationship. These results were further complemented by the polarization measurements. The PBZ50 was fabricated using a semi-wet synthetic route involving a solid-state thermochemical reaction. We believe this unusual phase transition sequence in the PBZ50 material would be highly useful in high-density data storage devices

Rhombohedral superlattice structure and relaxor ferroelectric behavior of (Pb<SUB>0.70</SUB>Ba<SUB>0.30</SUB>)ZrO<SUB>3</SUB> ceramics

Superlattice reflections observed in the neutron powder-diffraction patterns of (Pb<SUP>0.80</SUP>Ba<SUB>0.20</SUB>)ZrO<SUB>3</SUB> (PBZ20) and (Pb<SUB>0.70</SUB>Ba<SUB>0.30</SUB>)ZrO<SUB>3</SUB> (PBZ30) are explained in terms of doubled rhombohedral cell (R3c). A Rietveld analysis of the neutron data reveals that the displacements of Pb<SUP>2+</SUP>/Ba<SUP>2+</SUP> and Zr<SUP>4+</SUP> decrease with increasing Ba<SUP>2+</SUP> content while the thermal parameter for Pb<SUP>2+</SUP>/Ba<SUP>2+</SUP> increases and becomes similar to ferroelectric relaxors. Dielectric studies indeed confirm relaxor behavior in PBZ30 with Vogel-Fulcher type relaxational freezing

<i>Phyllanthus emblica</i> Seed-Derived Hierarchically Porous Carbon Materials for High-Performance Supercapacitor Applications

The electrical double-layer supercapacitance performance of the nanoporous carbons prepared from the Phyllanthus emblica (Amala) seed by chemical activation using the potassium hydroxide (KOH) activator is reported. KOH activation was carried out at different temperatures (700–1000 °C) under nitrogen gas atmosphere, and in a three-electrode cell set-up the electrochemical measurements were performed in an aqueous 1 M sulfuric acid (H2SO4) solution. Because of the hierarchical pore structures with well-defined micro- and mesopores, Phyllanthus emblica seed-derived carbon materials exhibit high specific surface areas in the range of 1360 to 1946 m2 g−1, and the total pore volumes range from 0.664 to 1.328 cm3 g−1. The sample with the best surface area performed admirably as the supercapacitor electrode-material, achieving a high specific capacitance of 272 F g−1 at 1 A g−1. Furthermore, it sustained 60% capacitance at a high current density of 50 A g−1, followed by a remarkably long cycle-life of 98% after 10,000 subsequent charging/discharging cycles, demonstrating the electrode’s excellent rate-capability. These results show that the Phyllanthus emblica seed would have significant possibilities as a sustainable carbon-source for the preparing high-surface-area activated-carbons desired in high-energy-storage supercapacitors