Date of Award
Master of Science (MS)
Dr.Ram K. Gupta
Dr. Serif Uran
Dr. Khamis Siam
An access to reliable, sustainable, eco-friendly and cost-effective energy supply is being challenged by the global increase in population and the rapid technological advancement. Sophisticated systems, machinery and various devices being innovated, require the steady energy supply for their operations and applicability. To have reliable energy, numerous researches are being conducted through various approaches across the world. In this research work, the facile approach in investigating and tuning the materials properties was employed to improve energy properties of metal oxides. Nanostructured NiFe-oxide and CoFe-oxide were synthesized using a facile coprecipitation method. It was revealed that; nanostructured materials have favorable structures which promote their electrochemical efficiency. The oxides structural and electrochemical properties were studied. To further investigate their properties, they were sulfurized and phosphorized using hydrothermal and thermal process, respectively. The sulfides and phosphides showed impressive property improvement as compared to their respective oxides. NiFe-oxide showed impressive oxygen evolution reaction and hydrogen evolution reactions with 298 mV and 54 mV overpotentials, respectively. After doped with sulfur, their results were further improved, with the exception of NiFe-oxide nanocubes (NiFe-NCs), whose HER overpotential was increased from 54 mV to 177 mV after sulfurization; while the rest of samples showed improvement of OER and HER overpotentials; from 298 mV for NiFe-NCs to 241 mV for NiFeS-NCs in OER, 258 mV for NiFe-oxide nanoparticles (NiFe-NPs) to 216 mV for NiFeS-NPs in OER; and 187 mV for NiFe-NPs to 152 mV for NiFeS-NPs in HER. Likewise, the materials specific capacitance increased from 69 F/g to 605 F/g for sulfurized NiFe-NCs and 186 F/g to 515 F/g for sulfurized NiFe-NPs. The energy density of materials increased from 2 Wh/kg to 20 Wh/kg for NiFe-NCs and NiFeS-NCs, and from 6 Wh/kgto 17 Wh/kg for NiFe-NPs and NiFeS-NPs respectively, at 1 A/g.
CoFe-oxide samples revealed good electrocatalytic and storage behavior. Their overpotentials decreased from 113 mV for Cofe- nanocubes (CoFe-NCs) to 52 mV for CoFeS-NCs and from 161 mV for CoFe- nanoparticles (CoFe-NPs) to 122 mV for CoFeS-NPs and their specific capacitance was increased; where by 123 F/g specific capacitance of CoFe-NCs increased to 484 F/g for CoFeS-NCs and 161 F/g of CoFe-NPs to 244 F/g for CoFeS-NPs. The energy density of CoFe-NCs increased from 4 Wh/kg to 17 Wh/kg after sulfurization, whereas for CoFe-NPs; the energy density increased from 5 Wh/kg to 8 Wh/kg, at 1 A/g.
Upon phosphorization, the overpotentials values of 300, 330, 340, and 360 mV for phosphorized NiFe-nanoparticles (NiFeP-NPs), phosphorized CoFe-nanocubes (CoFeP-NCs), phosphorized NiFe-nanocubes (NiFeP-NCs) and phosphorized CoFe-nanoparticles (CoFeP-NPs) respectively, were observed, with some deviations from their unphosphorized counterparts which showed 256, 300, 298, and 300 mV overpotentials, respectively. The overpotentials for HER seemed to decrease when compared to their unphosphorized counterparts, where by the 135, 121, 118, and 84 mV were determined for NiFeP-NPs, NiFeP-NCs, CoFeP-NPs and CoFeP-NCs as compared to their unphosphorized samples overpotentials of 187, 54, 161, and 113 mV respectively. Specific capacitances of phosphorized samples were significantly improved; whereby for CoFe-NCs, it increased from 123 to 248 F/g, 161 to 464 F/g for CoFe-NPs, 69 to 424 F/g for NiFe-NCs, and 186 to 214 F/g for NiFe-NPs. On another hand, the energy densities increased after phosphorization as shown in the following order; from 4 Wh/kg for CoFe-NCs to 9 Wh/kg forCoFeP-NCs, from 5 Wh/kg for CoFe-NCs to 16 Wh/kgfor CoFeP-NPs, from 2 Wh/kg for NiFe-NCs to 15 Wh/kg for NiFeP-NCs, and from 6 Wh/kg for NiFe- NPs to 7 Wh/kgfor NiFeP-NPs.
The research study suggests that, facile sulfurization and phosphorization of nanostructured NiFe oxides and CoFe oxides, could significantly improve their electrocatalytic and capacitive behavior.
Nkhama, Alfred, "FACILE SYNTHESIS OF METAL OXIDES, SULPHIDES, AND PHOSPHIDES FOR ENHANCED ENERGY APPLICATIONS" (2021). Electronic Theses & Dissertations. 369.