Browsing by Author "Kibona, Talam Enock"
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Item Application of WRF Mesoscale Model for Prediction of Wind Energy Resources in Tanzania(Elsevier, 2020-01-30) Kibona, Talam EnockThis study gives an overview of the wind energy resource distribution within and of the coast of Tanzania. Wind speed predictions using WRF model at 60 m a.g.l, which is typically the height of turbine hub, are compared with the wind speed values obtained by extrapolating Final Analysis (FNL) wind speed data at 10m a.g.l using power law. The WRF Model is used for 72-hours wind speed and direction forecasting where the initial boundary of the model is provided by Final Analysis data (FNL) available at UCAR with resolution of 1 × 1 degree. The WRF model has good results in comparison to power law because the variation is very small. At 1200 and 1800 hours over the areas near the land WRF predicts low wind speed than power law. WRF model predicts more offshore wind strength in the night than the noon. At 1300 to 1400 hrs the wind speed in the offshore part of Tanzania is mostly below 9 m/s as predicted by WRF model. Based on the limited studies, it has been observed that the wind energy potential exists in the offshore zones of Tanzania. This study encourage exploring the possibilities of harnessing the offshore wind energy potentials available in Tanzania. The approach adopted could be configuring WRF models with high horizontal resolution and many domains and carrying out detailed theoretical assessment of the wind energy resources, supplemented by actual measurements of the wind pattern using met-masts at different locations across and offshore of Tanzania.Item Biomass-based carbon electrode materials for capacitive deionization: a review(Springer, 2019-06-27) Elisadiki, Joyce; Kibona, Talam Enock; Machunda, Revocatus L.; Saleem, Muhammad Wajid; Kim, Woo-Seung; Jande, Yusufu A. C.Capacitive deionization (CDI) is a promising water purification technology which works by removing salt ions or charged species from aqueous solutions. Currently, most of the research on CDI focuses on the desalination of water with low or moderate salt concentration due to the low salt adsorption capacity of the electrodes. The electrosorption capacity of CDI relies on the structural and textural characteristics of the electrode materials. The cost of electrode materials, the complicated synthesis methods, and the environmental concerns arising from material synthesis steps hinder the development of large-scale CDI units. By considering the good electrical conductivity, high specific surface area (SSA), porous structure, availability, mass production, and cost, porous carbon derived from biomass materials may be a promising CDI electrode material. This review presents an update on carbon nanomaterials derived from various biomasses for CDI electrodes. It covers different synthesis methods and the electrosorption performance of each material and discusses the impact of the SSA and porous structure of the materials on desalination. This review shows that a variety of biomass materials can be used to synthesize cost-effective CDI electrode materials with different structures and good desalination performance. It also shows that diverse precursors and synthesis routes have significant influences on the properties and performance of the resulting carbon electrodes. Additionally, the performance of CDI does not depend only on BET surface area and pore structure but also on the applied voltage, initial concentration of the feed solution, and mass, as well as the capacitance of the electrodes.Item Effect of biogas-slurry pyrolysis temperature on specific capacitance(Elsevier, 2018) Kibona, Talam Enock; King’ondu, Cecil K.; Pogrebnoi, AlexanderThe purpose of this study was to investigate the effect of carbonization temperature of biogas slurry on specific capacitance. The biogas derived mesoporous carbon materials were synthesized through carbonization of biogas slurry at 450, 550, and 650 °C followed by activation using KOH at 700 °C for 1 h. The physical characterization done by nitrogen adsorption and desorption, scanning electron microscope, transmission electron microscope and X-ray diffraction shows that pyrolysis temperature has influence on the textural and structural properties of the biogas slurry derived carbon. BET specific surface area of 567, 521 and 499 m2 g-1 were obtained for samples carbonized at 450, 550, and 650 °C, respectively. The electrochemical performance of the samples in 6 M KOH electrolyte exhibited high gravimetric capacitance of 262, 272, and 238 F g-1 for samples carbonized at 450, 550 and 650 °C, correspondingly at scan rate of 5 mV s-1. Moderate carbonization temperature of 550 °C therefore afforded the highest capacitance.Item Fish bladder-based activated carbon/Co3O4/TiO2 composite electrodes for supercapacitors(Elsevier, 2019) Sirengo, Keith; Jande, Yusufu Abeid Chande; Kibona, Talam Enock; Hilonga, Askwar; Muiva, Cosmas; King'ondu, Cecil KCobalt oxide/titanium dioxide/activated carbon (Co3O4/TiO2/Ac) composite was synthesized using simple sol-gel method before annealing at 300 °C. Fish bladder derived porous carbon used for the composite was synthesized by pyrolysis followed by chemical activation. Both scanning electron microscopy (SEM) and X-ray diffraction displayed Co3O4 and TiO2 phases well embedded onto the carbon matrices. Cyclic voltammetry in 6 M KOH electrolyte demonstrated that the composite has an excellent specific capacity of 946 Fg-1 for Co3O4/TiO2/Ac as compared to Co3O4/Ac, TiO2/Ac, and Ac with specific capacitances of 845, 340, and 308 F g−1, respectively at 5 mVs−1. Impedance spectroscopy reveals that the composite has good capacitive behavior with a series resistance of 0.6 Ω. Besides, Co3O4/TiO2/Ac maintains 89.7% of the initial capacitance after 2000 cycles. This study shows that the synergistic effect of the metal oxides and the carbon in the composite can enhance capacitance for practical supercapacitor applications.Item Highly mesoporous Parinari Curatellifolia carbon nanomaterials for supercapacitors(Elsevier, 2020-04-01) Kibona, Talam Enock; Achola, Laura; Kerns, Peter; Macharia, John; King'ondu, Cecil K; Suib, StevenHigh surface area nanostructured electrodes are essential for understanding charge storage mechanisms in high capacitance supercapacitors. Additionally, a growing number of studies provide credible evidence that the highest capacitance in carbon nanomaterials is attainable only when the pore size is in micropore range. In this study therefore, micropore-dominatedcarbon materials derived from Parinari curatellifolia (PC) waste seeds are prepared via pyrolysis and subsequent chemical activation with KOH. SEM, EDAX, TEM, Raman, and XRD studies show that the microstructure and composition of the as-prepared microporous carbon materials are influenced by adjusting the KOH to carbon mass ratio. Sorption studies demonstrate a very high BET surface area of 1898 m2 g−1, type I isotherm, and 99% micropore content in all the samples. The BET surface area, S, V, and total volume increased with increasing KOH content during activation. The fabricated electrodes exhibit high specific capacitances of 423 F g−1 at 5 mV s−1 and cyclic stability of 98% after 50000 cycles both of which are indicative of our carbon materials huge potential in making high performance supercapacitors. The specific capacitance increased with the micropore content in the samples signifying that the pores enhanced diffusion and hence the charge storage. The PC carbon materials deliver high specific capacitance due to the enhancement of diffusion and charge storage stemming from the synergetic interplay of the aforementioned textural parameters. The PC carbon materials therefore provide good prospects for supercapacitor applications.Item Highly microstructured porous carbon derived from vitex mombassae for high specific capacitance supercapacitors(Spinger, 2019-08-26) Kibona, Talam EnockThis study reports on producing highly porous carbon materials by carbonization and activation of biomass (Vitex mombassae) seed wastes. The pore textural properties and microstructures of the synthesized materials are controlled by adjusting the activation temperature from 600 to 800 °C. X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, Raman and nitrogen adsorption and desorption are used to study the physical characteristics of the synthesized materials. The Brunauer–Emmet–Teller surface area, micropore surface area and pore volume increase with activation temperature. At activation temperature of 700 °C, the porous carbon acquires high specific area (2044 m2 g−1). The pore volume increases with increase in activation temperature 0.8–1.1 cm3 g−1 with high self-doping oxygen content. As a result of good physical characteristics, the prepared electrodes exhibit excellent performance with the specific capacitance up to 437 F g−1 at 5 mV s−1 in 6 M KOH electrolyte. The good capacitive behavior of the synthesized porous carbon depends on high surface area, micropore pore volume as well as moderate microstructures. The synthesized sample demonstrates high cyclic stability with capacitance retention of over 90% after 50,000 cycles.Item Highly porous biomass-based capacitive deionization electrodes for water defluoridation(2019-12-09) Elisadiki, Joyce; Jande, Yusufu; Kibona, Talam Enock; Machunda, RevocatusThe high concentration of fluoride (F−) in water sources is the main challenge in major fluoride belts. Though capacitive deionization (CDI) with porous carbon electrodes is the promising alternative in removing charged species from aqueous solution, little has been presented on the usefulness of CDI with biomass-based electrodes in removing F− from natural water existing together with other ions such as Ca2+ and Mg2+. This study investigated the feasibility of using biomass-based electrodes for natural water defluoridation application. Porous carbon was synthesized from jackfruit peels (JFAC) through potassium hydroxide (KOH) activation. Surface morphology, pore structure, and electrochemical properties of the JFAC were investigated. The textural properties of the synthesized carbon and electrochemical characteristics of the fabricated electrodes were found to be influenced by activation temperature. Brunauer-Emmett-Teller (BET) surface area, pore diameter, pore volume, and pore surface area increased with an increase in activation temperature and KOH to carbon ratio. It was further confirmed that as the applied voltage increased from 1.2 to 2 V, the amount of adsorbed anions increased without significantly affecting the pH of the water. At 2.0 V, the electrodes showed a maximum F− adsorption efficiency and electrosorption capacity of 62% and 0.13 mg/g respectively. The electrosorption capacity depends on the initial concentration of the ion in the feed water. It was further observed that natural organic substances contained in the natural water might inhibit JFAC electrode surface and decrease its adsorption efficiency. This study provides cost-effective CDI electrode material prepared from biomass for water defluoridation.Item Mesoporous Electrodes for Supercapacitors(CRC Press (Taylor & Francis Group), 2019-12) Shao, Godlisten N.; Kibona, Talam EnockMesoporous electrodes with desirable properties for supercapacitors are very fascinating and their ubiquitous attraction to scientists and engineers is indisputably incessant. Conversely, supercapacitors are highly researched energy storage materials due to their promising potentials to solve the energy storage demands for high-performance energy applications. Investigation of materials with suitable properties for mesoporous electrodes for supercapacitors is mainly carried out to improve their power density and energy density. This chapter highlights the recent investigations and advances toward the development of mesoporous electrodes for supercapacitors.Item Porous carbon derived from Artocarpus heterophyllus peels for capacitive deionization electrodes(Elsevier, 2019) Elisadiki, Joyce; Jande, Yusufu Abeid Chande; Machunda, Revocatus Lazaro; Kibona, Talam EnockSustainable clean water for human use can be attained through cost effective water purification technologies where by capacitive deionization (CDI) technology is among them. To attain high CDI performance porous carbon materials with good electrical conductivity, high surface area, specific capacitance and good chemical stability are essential. In this study high surface area porous carbon has been synthesized through carbonization of agricultural waste jackfruit peels (Artocarpus heterophyllus) followed by KOH activation at 600, 700, and 800 °C for 1 h. It was found that, the activation temperature significantly increased the BET surface area of the synthesized carbon from 607 m2/g to 1955 m2/g. Desalination experiments were carried out with 30–500 mg/L NaCl solution in batch mode at a flow rate of 2.5 ml/min while applying voltage of 1.2, 1.4 and 2.0 V to the cell. The electrosorption capacity and salt-removal efficiency increased with increasing BET Surface area and applied potential. Specifically, ACJF1:1-700 exhibited highest specific capacitance of 307 F/g, high salt removal efficiency and electrosorption capacity of 5.74 mg/g when voltage of 2 V was applied. These results indicated that the Artocarpus heterophyllus can be promising CDI electrode materials for low salinity water desalination.Item Specific capacitance–pore texture relationship of biogas slurry mesoporous carbon/MnO2 composite electrodes for supercapacitors(Elsevier, 2019-02) Kibona, Talam Enock; Shao, Godlisten N.; Kim, Hee Taik; King’ondu, Cecil K.Here, we report synthesis of biogas slurry mesoporous carbon/MnO2 composites by simple co-precipitation route followed by thermal treatment at 250 °C for 6 h. The texture, morphology, crystal structure, and microstructure of the composites are investigated by nitrogen sorption studies, FESEM, HRTEM, X-ray diffraction, and Raman spectroscopy. All samples exhibit type IV isotherms. The BET surface area decreased from 514 to 110 m2 g−1 while total pore volume decreased from 0.52 to 0.17 cm3 g−1 for samples loaded with 2×10−5 and 2×10−3 moles of Mn. The electrodes fabricated exhibit high specific capacitance of 709 F g−1 at scan rate of 5 mV s−1. The specific capacitance at scan rate of 5 mV s−1 increases with increasing MnO2 content. However, at 50 mV s−1, specific capacitance decreases with increasing MnO2 content. Varying the MnO2 content and hence the textural parameters, strongly influences the specific capacitances of the composite electrodes.Item Synthesis of NiCo2O4/mesoporous carbon composites for supercapacitor electrodes(Springer, 2020) Kibona, Talam EnockIn this study, nickel cobaltite/mesoporous carbon composites are synthesized by reacting CoCl2, Ni (NO3)2 and nitric acid-treated biogas slurry mesoporous carbon using urea as hydrolyzing agent and hexadecyltrimethylammonium bromide (CTAB) as surfactant. The presence of Ni, Co, C and O peaks in the EDX results confirm that the composites are successfully synthesized. Interestingly at 350 °C, the composite surface morphology switched to cross-linked nanoflake structures interconnected with mesoporous carbon. The X-ray diffraction analysis of the NiCo2O4/mesoporous carbon composites reveals that the spinel structure of the NiCo2O4 is maintained in the composites. The nitrogen uptake increases with increasing annealing temperature to 300 °C then decreases at higher temperature (400 °C). The type IV isotherms are exhibited by all the composites. The contribution of mesopores increases with increasing annealing temperature: 32% for BC-NCo-200, 41% for BC-NCo-250, 56% for BC-NCo-300, 66% for BC-NCo-350 and 86% for BC-NCo-400. The NiCo2O4/mesoporous carbon composites exhibit high specific capacitance of 835 F g−1 at scan rate of 5 mV s−1 for sample annealed at 350 °C. The cyclic stabilities of the electrodes are above 90% after 50,000 cycles indicating that the synthesized composites are suitable candidates for supercapacitors.