Theses and Dissertations

Synthesis and characterization of graphene-gold nanocomposite counter electrodes for dye-sensitized solar cell application

Fri, 01 Jan 2021 00:00:00 GMT

Synthesis and characterization of graphene-gold nanocomposite counter electrodes for dye-sensitized solar cell application Ngumbi, Paul K. With the increasing global demand for alternative energy, photovoltaic (PV) technology has undergone remarkable evolution extending over four PV generations. Currently, dye-sensitized solar cells (DSSCs), which fall within the 3rd generation are more versatile and relatively less costly compared to the dominant crystalline silicon (Si) technologies. These DSSCs bear the hope of becoming the future solution to the energy crisis. However, the poor catalysis within the electrodes makes DSSCs relatively inefficient hence ineffective for full commercial utilization. This study investigated the use of composite counter electrodes (CEs) by incorporating graphene (Gr) and/or plasmonic gold (Au) nanoparticles (NPs) with the aim to improve the efficiency of the conventional platinum (Pt) based DSSCs. Gold nanoparticles (AuNPs) in colloidal form with an average size of ~12 nm were prepared by chemical reduction method. The size evaluation was done using the resulting localized surface plasmon resonance (LSPR) peak wavelength values (518- 520 nm) based on the UV-Vis spectra data. Graphene modules prepared by chemical vapor deposition (CVD) on a glass/Fluorine-doped tin oxide (FTO) were used as electrode substrates in this work. These modules depicted G and 2D bands at 1380 and 1700 cm-1 respectively under Raman spectroscopy, indicating low defect state of the Gr. Four different sets of composite CE modules namely FTO/Pt (CE1), FTO/Gr/Pt (CE2), FTO/Gr/AuNPs (CE3) and FTO/Gr/AuNPs/Pt (CE4) were prepared. The CEs recorded transmittance above 70% under UV-Vis spectroscopy, meeting requirements for back-electrode application in DSSCs. Photoanode (PA) modules consisting of titanium dioxide (TiO2) on the FTO/Gr substrate were prepared by the doctor-blade method. Three DSSC modules were assembled based CEs CE2, CE3 and CE4 and their PV performance compared to the reference cell based on CE1. Both Gr and AuNPs were found to possess PV properties and enhanced the resulting DSSCs by 13.4 and 10.1% respectively. The DSSCs containing Pt (CE1, CE2, and CE4) performed better in terms of power conversion efficiency (PCE) due to the increased short circuit current densities (Jsc) and fill factors (FF). However, change in the open-circuit voltage (Voc) was negligible. The CE4 based cell design presented the best PCE at 4.62%, In this composite DSSC, the Jsc (9.92 mA/cm2 ), Voc (0.68 V) and FF (0.69) values recorded representing 13.9%, 0.8% and 9.0% increase respectively compared to CE1. This represented a 24.9% PCE enhancement, which is the synergistic effect of Gr and AuNPs as a composite. This remarkable performance could be due to increased electrocatalytic activity resulting from the graphene matrix within the electrodes. It is also partly attributed to the suppressed carrier recombination resulting from the LSPR property of the Au contacts anchored on the Gr surface in the CE structure. Doctor of philosophy in physics, 2021

Spatio-temporal variations in physicochemical water quality and the impact of land use/land cover change In River Athi Basin, Kenya.

Wed, 01 Jan 2025 00:00:00 GMT

Spatio-temporal variations in physicochemical water quality and the impact of land use/land cover change In River Athi Basin, Kenya. Ogbonna, Vincent A. The growing impacts of natural processes and human activities on water quality at global, regional, and local scales are raising concerns. The River Athi Basin natural gravitational flow toward lower elevations, ultimately reaching the Indian Ocean, facilitates waste disposal practices among the residence located along the river bank. This study sought to determine the Spatiotemporal Variations in Physicochemical Water Quality and the Impact of Land Use/Land Cover Change in the Mid Reaches of River Athi Basin, Kenya by; 1) examining the influence of land use/land cover change in river Athi Basin from 2015 to 2023. (2) Determining seasonal variation in the physicochemical water quality of the river Athi Basin. (3) Assessing the spatial variation in physicochemical water quality of the river Athi Basin. The study examined the influence of LULC changes from 2015 to 2023 using Landsat 8 imagery, GIS, remote sensing, and GPS technologies for data extraction, image processing, and LULC analysis. Pearson correlation analysis assessed spatial differences of land use land cover impacts on water quality across six sampling stations in the basin. Interview survey was used to supplement the water quality dataset. The studies applied multivariate analysis for spatial and temporal reduction of the multidimensional dataset and identification of pollution sources. Seasonal variations in the physico-chemical water quality of River Athi Basin was determined using eight physicochemical parameters (pH, EC, TDS, NO₃, K, PO₄, BOD, and COD) and two heavy metals (Cd and Cr). Data collection was carried out during two distinct seasonal periods: the short dry and rainy season (August-September for dry, November-December for rainy) in 2023, and the long dry and rainy season (January-February for dry, April-May for rainy) in 2024. An independent T-test was used to compare the mean levels of water quality parameters between dry and rainy seasons. The study assessed spatial variation in the physicochemical water quality of the river basin, covering six sampling stations. One way analysis of variance (ANOVA) compared the mean values of variables of the sampling stations. Multiple linear regression tested the influence of pH, EC, TDS, NO3, K, and PO4 on BOD and COD (oxidation parameters) and cadmium and chromium (heavy metals). The Pearson Product-Moment Correlation Coefficient (PPMCC) assessed the relationships between water physicochemical parameters and heavy metals in seasonal and spatial variations in water quality of the river basin. The findings on LULC analysis show notable shifts in land use from 2015 to 2023. Between these periods, the overall built-up increased to 0.29%, bare-lands declined by 7.06%. Farmlands, forests, and grasslands were elevated by 0.52%, 4.54%, and 2.77%, with decline in open waters by 1.24%. Spatial LULC difference with correlation analysis reveal higher amounts of EC, TDS, Cd, Cr, NO3, and PO4 influencing water quality. Interview survey revealed settlements, agriculture, and climate conditions as the main causes of degradation of water quality. Seasonal finding reveal significant fluctuations in pollution, with the dry season exhibiting higher pollution levels. February demonstrate proliferated temporal pollution, characterized by high concentrations of EC, TDS, BOD, and COD. Spatial finding demonstrated significantly higher pollution signatures in Athi River Town, Stony Athi, and NYS stations, while NYS contribute to higher levels of nutrients, organic pollutants, and heavy metals. In contrast, the control station and Kibwezi Bridge station demonstrates effective self-purification processes. Multivariate analysis revealed pollution sources over time and space in the River Basin. The stable pH levels over time and space was influenced by the buffering capacity. Multiple regression analysis indicates that physicochemical parameters, such as pH, EC, TDS, NO₃, K, and PO₄, explain 62% of BOD variation and 70% of COD variation, as well as 36% of both Cd and Cr variations. Pearson correlation analysis shows strong links between EC, TDS, BOD, and heavy metals (Cd, Cr), with significant associations among nutrients and other water quality indicators. Natural and anthropogenic activities are pivotal drivers of the water quality degradation of River Athi Basin over time and space. This study recommends that the National Environmental Management Authority (NEMA) and the National Environmental Policy (NEP) strengthen regulations on environmental management, water resource conservation, sustainable land use, public health protection, irrigation control, forest preservation, and aquatic ecosystem conservation in order to support global efforts toward achieving Sustainable Development Goals (SDGs). Doctor of Philosophy (Ph.D.) In Environmental Management

Socio-economic impact of women enterprise fund in Kitui Central Sub County, Kitui County, Kenya

Wed, 01 Jan 2025 00:00:00 GMT

Socio-economic impact of women enterprise fund in Kitui Central Sub County, Kitui County, Kenya Njeri, Nzuki Evaline This study assessed the socio-economic impact of the Women Enterprise Fund (WEF) in Miambani Ward, Kitui County, Kenya. WEF was introduced to expand women’s access to affordable credit and promote empowerment, yet its effectiveness at the community level has not been fully established. The study was guided by the following objectives; to describe the socio-demographic status of women who access the Women Enterprise Fund, to examine the effects of the fund on women socio-economic status and to identify the challenges women, face in accessing and utilization of Women Enterprise Fund. The study was justified by the need to generate localized evidence to guide policy and improve women’s access to finance in rural areas. A cross-sectional research design within a mixed- method approach was adopted. The target population comprised 152 women in 8 women groups, from which 64 were sampled using probability proportional to size. Data were collected using questionnaires, focus group discussions, and key informant interviews. Additional insights were obtained from a WEF officer, a local bank officer, and a spouse of a beneficiary. Findings indicated that WEF improved women’s ability to pay school fees, meet household needs, and initiate small businesses, enhancing welfare, confidence, and participation in decision-making. However, small loan amounts, strict repayment schedules, and group defaults limited outcomes. Education, age, and marital status strongly influenced access and utilization. The study concludes that WEF positively contributes to women’s socio-economic empowerment but faces structural and socio-cultural barriers. It recommends larger loans, flexible repayment terms, and enhanced training and monitoring. The study was limited to Miambani Ward, which may constrain generalizability, but it provides valuable insights into WEF’s role in similar rural contexts. Master of Arts in Gender and Development Studies, 2025

Financial inclusion and growth of deposit-taking SACCOS in Eastern Region, Kenya

Wed, 01 Jan 2025 00:00:00 GMT

Financial inclusion and growth of deposit-taking SACCOS in Eastern Region, Kenya Wambua, Miriam N Deposit taking Savings and Credit Cooperative Societies have increasingly adopted financial inclusion practices, yet many continue to exhibit poor growth as evidenced by declining membership, assets, loan repayment rates, and operational efficiency. Recent data indicates significant drops in withdrawable deposits, net income, and overall financial performance, compounded by high default rates and non-remitted funds. These trends highlight persistent challenges in leveraging financial inclusion to drive growth. The primary goal of this study was to evaluate the impact of financial inclusion practices on the growth of deposit-taking SACCOs in the Eastern Region of Kenya. Specifically, the study sought to examine the influence of financial literacy, Loan accessibility, digital financial services and branch network on the growth of deposit taking SACCOs in the Eastern Region of Kenya. The study was anchored on the financial inclusion theory as the main theory supported by the financial intermediation theory, and agency theory. The study used an explanatory research design. The respondents were the heads of finance, marketing, operations, and information technology. A total number of 104 management respondents was used in the study. Primary data used was collected using structured questionnaire. Validity and reliability of the data collection instruments were determined before conducting data collection. Data analysis was done using descriptive and inferential statistics with the aid of SPSS. Financial literacy had statistically significant effect on the growth of deposit taking SACCOs (β=.266, P=0.009<0.05). Similarly, loan accessibility had statistically significant effect on the growth of deposit taking SACCOs (β=.216, P=0.007<0.05). Additionally, digital financial services had statistically significant effect on the growth of deposit taking SACCOs in the Eastern region of Kenya (β=0.165, P=0.012<0.05). Further, branch networks had significant effect on the growth of deposit taking SACCOs (β=0.247, P=0.001<0.05. It is recommended that SACCOs should regularly update and customize their financial literacy programs to address evolving financial trends and challenges. Also the management of the deposit- taking SACCOs should continue upholding and improving transparency in loan processing and maintain competitive interest rates. They are recommended to continue investing in modern, user-friendly, and secure digital platforms that cater to the diverse needs of the members. Additionally, SACCOs should expand their physical branch networks in order to expand their market reach. Master of Business Administration, 2025