Browsing by Author "Bandara, T. M. W. J."

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Effect of reduced graphene oxide on the thermoelectric properties of titanium dioxide: Seebeck coefficient analysis
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Kahawaththe, K. G. D. T. B.; Narangammana, L. K.; Bandara, T. M. W. J.; Subasinghe, N. D.
Researchers worldwide are more focused on finding new ways to utilize waste energy to address increasing global energy demand. Thermoelectricity has attracted significant interest because it can generate electric energy using this waste heat energy. Thermoelectric energy recovery at a temperature range close to the ambient has attracted significant interest because of the usage of numerous heat sources near room temperature such as consumer electronics, solar cells, home heating and wearable devices on human bodies. The properties of thermoelectric materials (TEs) are typically characterized by their figure of merit, Seebeck coefficient, electrical conductivity and thermal conductivity. The conventional TEs such as bismuth and antimony chalcogenide-based materials were toxic and expensive. Therefore, in this study, the thermoelectric properties of nontoxic titanium dioxide (TiO2) were investigated. In order to prepare the TiO2 pellets, RGO and TiO2 were mixed in a mass percentage of 0%, 1%, 3% and 5% was mixed anhydrous acetonitrile using the mortar and pestle until they became fine powder. A compressive force of 40 kN, resulting in a pressure of 301 MPa, was applied for 5 to 7 minutes to prepare the pellets, which have a diameter of 13 mm and a thickness of 4 mm. The pellets were then annealed at 650 °C for approximately 30 minutes. Generated voltages were measured and the Seebeck coefficient was calculated for RGO-added TiO2 pellets by varying the temperature. RGO incorporation improved the Seebeck coefficient of TiO2 pellets and the Seebeck coefficient values were negative over the entire temperature range studied, indicating n-type conduction of this TE material (TEM). The generated voltages of 0%, 1%, 3% and 5% RGO- TiO2 pellets at 373 K were 3.97±0.02, 5.15±0.03, 8.43±0.05 and 7.19±0.04 mV respectively and Seebeck coefficients at 373 K were -0.18±0.01, -0.24±0.01, -0.41±0.02 and -0.36±0.01 mV K-1 respectively. The results indicate that the highest Seebeck coefficient and the maximum generated voltage were observed for the 3% RGO added sample. To the best of our knowledge thermoelectric parameters of bulk TiO2 have not been reported before. This novel TEM shows promising thermoelectric properties and the results indicate that TiO2 is better TEM compared to the widely studied ZnO.
Effect of temperature and pH on the wettability of electrodeposited n-type cuprous oxide films
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Kapukotuwa, K. M. V. Y.; Shakya, M. D. P. A.; Jayathilaka, K. M. D. C.; Bandara, T. M. W. J.; Wijesundera, L. B. D. R. P.
This research considers the temperature effect on wettability properties of electrodeposited n-type cuprous oxide (n-Cu2O) thin films, having focus on the role of bath pH and annealing temperature in their different values. In this research, n-type Cu2O films were produced using a three-electrode electrochemical cell containing an aqueous solution of sodium acetate and cupric acetate at 55°C, with the change in bath pH carried out by adding diluted acetic acid and NaOH. The films were deposited on titanium substrate at -200 mV vs Ag/AgCl for 40 minutes, and after that annealed in an air atmosphere at different temperatures increasing by 50°C increments starting from 100°C. The results of the photoresponse measurements confirmed the n-type nature of cuprous oxide. Crystal structure was determined by X-ray diffraction and the detailed surface morphology of the Cu2O thin films were examined using SEMs, which relate to the wettability characteristics of this material. The sessile drop method, utilizing ImageJ software based on Young's equation, showed that the contact angle measurements of wettability in the n-Cu2O substrates greatly depended on the pH of the electrodeposition bath and annealing temperature. The results revealed that the n-Cu2O films were hydrophilic when films were prepared at pH of 5.6, 6.23, 6.4, and 6.6. Interestingly, at pH 5.8, the contact angles exceeded 90° when the surfaces were annealed in an air atmosphere at temperatures of 100°C and 150°C and then allowed to return to room temperature, indicating the formation of hydrophobic surfaces. At pH 6.0, hydrophobicity was realized under annealing temperatures of 100°C, 150°C, and 200°C. XRD crystallographic analysis supported the formation of Cu2O with a cubic structure, while SEM details gave the surface morphology of the films. It serves as a very strong demonstration of the high degree of intercorrelation between wettability, pH, and annealing temperature in cost-effective routes toward hydrophobic n-Cu2O surfaces. By varying the pH and annealing temperature, it was possible to obtain both hydrophobic and non-hydrophobic surfaces. Knowing the wetting properties of n-type cuprous oxide facilitates many applications, such as the control of corrosion in coating technology and atmospheric water harvesting.
Enhancing quasi solid-state dye-sensitized solar cell performance using mixedpolymer gel electrolytes: the influence of low and high molar-weight polymers
(Faculty of Science, University of Kelaniya Sri Lanka, 2023) Rajakarunarathne, R. D. M. A. C. B.; Wickramasinghe, H. M. N.; Bandara, T. M. W. J.
Gel polymer electrolytes (GPEs) based quasi solid-state dye-sensitized solar cells (DSSCs) have attracted attention due to their relatively high chemical and physical stability, ionic conductivity, better mechanical properties, and enhanced safety. This study investigated the possibility of improving DSSC performances by preparing new GPEs using polyethylene oxide (PEO) with its low molar weight counterpart, polyethylene glycol (PEG). The studied plasticized gel electrolyte included organic solvents, ethylene carbonate (EC) and propylene carbonate (PC), a binary mixture of salts, LiI and Hex4NI, and performance enhancers, 1-methyl-3-propylimidazolium iodide (MPII) and 4-tert-butylpyridine (4TBP), with the polymer matrix, C2nH4n+2On+1, having molar weights 40,000 (PEG) and 4,000,000 (PEO). The electrolyte was synthesized using the hot press method. The correctly weighted chemicals were stirred for about one hour at room temperature and then heated to about 100 °C for 10 min. Then after the sample cooled down to 40 °C iodine was added, and stirring was continued for an hour. The study aimed to optimize the DSSC performance by varying the weight (wt.) ratio of PEO and PEG in the electrolyte. The ionic conductivities of the GPEs were determined using impedance analysis through Nyquist plots. The electrolyte that contains 100 wt% of PEG with respect to the total polymer weight exhibited the highest ionic conductivity (0.826 S m-1) and viscous liquid-type nature. Conversely, the electrolyte with a 100 wt% PEO is in solid form and displayed the lowest ionic conductivity (0.351 S m-1). The mixed polymer electrolyte with a 1:1, PEO:PEG wt. ratio showed an intermediate conductivity and a good gel nature. Also, the conductivity of the GPEs behaves according to the Vogel-Tamman-Fulcher (VTF) relation. The DSSCs were assembled using N719 dye-sensitized TiO2 nano-particle multi-layer photoelectrode and Pt counter electrode. The solar cell characterization results showed that the cells achieved the highest power conversion efficiency (PCE) of 7.09% for the 1:1, PEO:PEG wt. ratio with a Jsc of 13.80 mA cm-2. The PCE values were relatively lower for the 3:1 (6.29%), and 1:3 PEO:PEG wt. ratios (5.99%). The lowest PCE out of the five compositions investigated was observed for the 100 wt% PEO content, which can be a result of the solid nature and poor conductivity of the electrolyte. The results demonstrated a notable advancement in performance with an improvement of 23.86% and 21.61% when compared to single polymer electrolytes comprising of PEO and PEG, respectively. In conclusion, the presence of both low and high-molar-weight polymers in the electrolyte has a significant impact on the performance of DSSCs. The study continues to fine-tune polymer composition and understand the efficiency-enhancing mechanism in mixed-phase gel polymer electrolytes.
Facile synthesis of ZnO particles and the effect of their usage as fillers on the 𝛽 phase content and mechanical properties of PVDF and PVDF-HFP polymers
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Sahajeewa, L. K. N. N.; Bandara, T. M. W. J.; Narangammana, L. K.
Polyvinylidene fluoride (PVDF) and its co-polymers are widely used, especially in wearable devices, because of their flexibility, high mechanical strength, high chemical resistivity, and biocompatibility. They are also easily processable and are of relatively low cost. The 𝛽 phase of PVDF and polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) present outstanding electrical characteristics including piezo, pyro and ferroelectric properties. Zinc oxide (ZnO) nanoparticles are often used as fillers to induce the 𝛽 phase of these polymers. In using these fillers, it is also important to be concerned about their effect on the mechanical strength and flexibility of the polymers. This research focuses on facile low-cost synthesis of ZnO particles, and the incorporation of these particles into PVDF and PVDF-HFP polymers to determine how the size and shape of the ZnO particles affect the 𝛽 phase percentage, strength and flexibility of the above-mentioned polymers. The ZnO synthesis was carried out by the chemical precipitation method using low-cost chemicals, followed separately by microwave irradiation, and thermal decomposition. The sizes and the morphologies of the synthesized samples were assessed using scanning electron microscopy (SEM), and particle size was measured using Image J software. The microwave irradiation synthesis method gave ZnO rods with a mean width of ~177 nm. ZnO granules, synthesized using the thermal decomposition method, using Na2CO3 as the base, gave particles with a mean size of ~75 nm. X-ray diffraction (XRD) was carried out to confirm that the samples synthesized were wurzite ZnO. The preparation of the polymer and polymer/ZnO composite films was carried out using the solvent casting method. Fourier-transform infrared spectroscopy (FTIR) was carried out on the samples with the dual intention of identifying the sample and comparing the effect of the ZnO nanofillers on the 𝛽 phase content of the polymers. The highest percentage increase in 𝛽 fraction, of ~48% over the pure polymer sample, was shown for the Polymer/ZnO composite sample of PVDF/ZnO granules. Mechanical testing was carried out in order to compare Young’s moduli and the tensile strengths of the samples. The highest tensile strength, of ~ 9.2 × 105 𝑁 𝑚-1, among the ZnO/polymer composites, was observed for the PVDF-HFP/ZnO rods sample. The lowest Young’s moduli of ~ 8.8 × 107 𝑁 𝑚-1 , and hence higher flexibility was observed for the PVDF/commercial ZnO.
Incorporation of Sri Lanka’s natural minerals, zircon and apatite, in radiation shielding
(Faculty of Science, University of Kelaniya Sri Lanka, 2022) Ranasinghe, M. U.; Hathnagoda, E. M. D. K. B.; Nanayakkara, D. K. K.; Wijayaratne, K.; Bandara, T. M. W. J.; Jayasinghe, U. J. M. A. L.; Jayalath, C. P.; Sivakumar, V.
With the rapid increase in the application of ionizing radiation, radiation protection has become a predominant factor in ensuring the safety of humans and the environment. Blocking high-energy photon radiation has proven to be much more challenging due to its excessive penetrating power. Lead-based materials are commonly used for shielding due to their high efficiency in attenuating gamma rays and X-rays. However, the cumulative toxicity of lead to the ecosystem, the weight and the stiffness have made it unpopular when portable shielding application is considered. This study aims to investigate the possibilities of using naturally available minerals in Sri Lanka to develop multifunctional shielding devices for various radiation protection applications. In this preliminary work, zircon and appetite were utilized as the primary attenuating materials due to their elemental compositions. Using silicone rubber and epoxy as binding materials 0.5 cm thick composite layers of zircon and apatite were prepared separately. The selection of binders and the weight ratio of the filler to the binder were chosen to fulfil the requirement of flexibility, low-weight and processability. The capability of radiation shielding of each sample was tested for 662 keV gamma radiation emitted from Cs-137 isotope. Radiation was detected by a NaI (Tl) scintillation detector and analysed by a multi-channel analyser. The linear attenuation coefficient of the binders, single layers of zircon and apatite, and the effective linear attenuation coefficient of two-layer systems with possible orders of layer-arrangement were calculated. The linear attenuation coefficient of epoxy was considerably higher than that of silicone rubber. Among the fillers used, zircon showed more attenuation than apatite due to the higher effective atomic number. In addition, the higher electron density of zircon leads to a higher Compton scattering rate compared to apatite. The linear attenuation coefficients of pure zircon and apatite are calculated to be 0.092 and 0.059 cm-1, respectively, for 662 keV photons. It was observed that in the two-layer composite system effective attenuation coefficient depends on the order of the material layer. Out of the two-layer structures studied, apatite-zircon combination with epoxy as the binding material showed better shielding with 18.1% blocking rate where the apatite layer was placed towards the source. The effective linear attenuation coefficient of this composite system is calculated to be 0.087 cm-1 with an effective half-value layer thickness of 7.9 cm.
Investigation of the mixed cation effect and the irradiance level dependence on the efficiency of dye‑sensitized solar cells
(Faculty of Science, University of Kelaniya Sri Lanka, 2023) Wickramasinghe, H. M. N.; Karunathilaka, N. G. A.; Gnanarathne, D. M. T.; DeSilva, L. Ajith; Bandara, K. M. S. P.; Bandara, T. M. W. J.
The development of photoelectrochemical energy conversion devices holds immense significance in addressing the escalating demand for renewable and environmentally benign energy. By harnessing the synergistic effects of salt mixtures that encompass both large and small counter ions, notable advancements in dye-sensitized solar cell (DSSC) performance have been realized. The investigated DSSCs with a novel organic electrolyte complex that contains LiI and (tetrahexylammonium) Hex4NI exhibited significant efficiency enhancement compared to that of their individual salt end components. The ionic conductivity variations and frequency-dependent AC conductivity in the electrolyte and dielectric properties were analyzed using complex impedance data. The conductivity in the electrolyte at room temperature is 11.44 mS cm−1. The investigated DSSCs are comprised of improved TiO2 multilayer photoelectrodes and Pt counter electrodes. Under an irradiance of 1000 W m−2, the energy conversion efficiency of the mixed salt system reached 8.37%, marking an impressive enhancement of 86.83% and 76.21% compared to the Hex4NI and LiI-based single salt counterparts, respectively. Additionally, an impressive efficiency of 10.57% is shown when the light intensity drops to 400 W m−2. The cells exhibited commendable short-term stability, likely attributed to the elimination of volatile solvents in the electrolyte. This study underscores the pivotal role played by mixed counter ions in the electrolyte, as they elicit synergistic effects that amplify DSSC performance enhancements, effectively overshadowing the effects imposed by conductivity variation.
Optimizing concentration of titanium dioxide nano-fillers in PEO gel-polymer electrolytes for enhanced performance of dye-sensitized solar cells
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Chandrika, R. P.; Liyanage, J. P.; Wijayaratne, W. M. K. B. N.; Bandara, T. M. W. J.
The influence of nano-composite gel-polymer electrolytes on the performance of dye-sensitized solar cells (DSSCs) has attracted significant attention recently. In this study, titanium dioxide nanoparticles (TiO2) with varying percentages were incorporated into a gel-polymer electrolyte in order to determine the optimal nanofiller (NF) concentration as well as to study the effect of NFs composition on conductivity in the polymer electrolyte and light to current conversion efficiency of DSSCs. For these purposes, TiO2 NFs with an average particle size of 13 nm were incorporated into polyethylene oxide (PEO) based gel-polymer electrolyte. The TiO2 nano-composite electrolyte series were prepared by varying the TiO2 NF composition from 0.0 to 25.0 wt.% relative to the PEO weight. The DSSCs were assembled by sandwiching NF incorporated polymer electrolyte between a multilayer photoanode sensitized with N719 dye and platinum electrode. The conductivity and light to current conversion efficiency depend on the NF composition in the polymer electrolyte. The electrical conductivity of the electrolyte and efficiency of DSSCs containing nano-composite electrolytes increases with the increase in TiO2 content up to 17.5 wt.% and then decreases with any further increase in TiO2 percentage. Temperature-dependent electrical conductivity of the prepared nanocomposite gel-polymer electrolytes was investigated by gradually increasing the temperature from 20 °C to 80 °C increments of 10 °C. The conductivity increased with rising temperature within this range, and the temperature dependence exhibited VTF (non-Arrhenius) behavior. The optimum TiO2 composition was found to be 17.5 wt.%, with a conductivity of 5.18 mS cm-1 at 20 °C, which increased to 10.43 mS cm-1 when the temperature was raised to 80 °C. Thus the highest recorded conductivity was observed at the temperature of 80 °C, testing temperature was not raised further as higher temperatures cause the release of I2 from the electrolyte. The conductivity enhancement with added TiO2 can be attributed to the change in the morphology of the polymer network. TiO2 NFs contribute to this process by inducing electrostatic interactions/Lewis acid-base interactions between O atoms of the PEO and hydroxyl group of the TiO2 particles. DSSC assembled with the polymer electrolyte containing 17.5 wt.% of TiO2 NFs (the highest conducting electrolyte) exhibited the highest photoelectric conversion efficiency of 7.30%, representing a 28.1% enhancement compared to the reference DSSCs assembled with a filler-free gel-polymer electrolyte, which had an efficiency of (5.70%).
PEDOT: PSS/GO based supercapacitor for energy storage applications
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Ravindran, N. S.; Wijayaratne, W. M. K. B. N.; Bandara, T. M. W. J.
Traditional energy storage devices like batteries and capacitors suffer from low power and poor energy densities, highlighting the need for advancements in this field. Supercapacitors offer a promising alternative as the energy and power densities of supercapacitors are comparably high. In contrast with traditional capacitors the capacitance of the supercapacitors is in the order of farad (F), higher than the electrolytic capacitors (mF) and dielectric capacitors (μF). Especially composite supercapacitors integrating carbon-based materials with pseudocapacitive components like metal oxides or conducting polymers aim to enhance energy density while preserving high power density and long cycle life. Several attempts have been made previously using different combinations of the materials mentioned above. The primary aim of this study was to fabricate a supercapacitor using electrodes made of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate and graphene oxide (PEDOT: PSS/GO) to demonstrate the electrochemical properties of the nanocomposite for energy storage applications. To prepare the electrodes of the supercapacitor, first, GO was synthesized using a modified Hummer’s method. The electrode fabrication process involved depositing the PEDOT: PSS/GO nanocomposite onto a graphite sheet of dimension 1 cm × 2 cm via the drop-casting method. The supercapacitor assembly was achieved by placing filter paper soaked in a 6M potassium hydroxide (KOH) solution between two electrodes made from a composite of PEDOT: PSS and GO on a graphite base. The resulting supercapacitor exhibited a specific capacitance of 18.84 F g-1, with an energy density of 0.65 Wh kg-1 and a power density of 29.2 W kg-1, as determined from the galvanostatic charge-discharge (GCD) curve data at a current of 0.5 mA. When ascorbic acid was added to the nanocomposite, the specific capacitance dropped to 13.04 F g-1, with an energy density of 0.45 Wh kg-1 and a power density of 14.44 W kg-1. This indicates that the supercapacitor without ascorbic acid achieves the highest specific capacitance. The CV results further demonstrated that despite the presence of a polymer, the absence of visible redox peaks shows that the supercapacitor operates as an electric double-layer capacitor (EDLC).