Browsing by Author "Monama, Gobeng Release"

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    Hierarchiral 4-tetranitro copper(II)phthalocyanine based metal organic framework hybrid composite with improved electrocatalytic efficiency towards hydrogen evolution reaction
    (Elsivier, 2019) Monama, Gobeng Release
    A novel hybrid-hybrid nanocomposite based on 4-tetranitro copper(II)phthalocyanine (TNCuPc) grown on metal organic frameworks (MOF) as a noble metal-free catalyst for hydrogen evolution reaction (HER) was developed by a simple impregnation method. The structure, surface area and the morphology of the bare MOF, TNCuPc and the TNCuPc/MOF composite were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, Brunauer-Emmet-Teller, scanning electron microscopy, transmission electron microscopy and simultaneous thermal analysis. The electrocatalytic activity of the samples towards the HER was evaluated using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry, exchange current density, i0, Tafel slope value, b, as well as charge transfer coefficient, α. The spectroscopic analyses indicated a successful synthesis of TNCuPc and its composite. The morphological results showed the development of rod-like structures of TNCuPc on the surface of the MOF. The composite exhibited an onset potential of about −0.713 V vs. Ag/AgCl in 0.1 M TBAP/DMSO and 0.3 M H2SO4 solutions, which is 44 mV and 9 mV more positive than that of MOF and TNCuPc respectively. The composite showed the rate determining step (RDS) to be the Volmer reaction in conjunction with either Heyrovsky or Tafel reaction as the RDS due to the Tafel slope value of 147 mV/dec and an α of 0.4. The i0 value of the TNCuPc/MOF composite was about 1.6 times that of the bare MOF. The EIS results showed the charge transfer resistance (Rct) of 12.6 kΩ for the TNCuPc/MOF composite as compared to MOF and TNCuPc values of 41 and 18.6 kΩ, respectively, demonstrating an excellent conductivity of the composite. In addition, Rct values of materials follow the sequence, blank < MOF < TNCuPc < TNCuPc/MOF. The fabricated composite displayed high activity towards the HER, high thermal stability, and excellent tolerance. Therefore, TNCuPc/MOF non-noble electrocatalyst can be a promising electrochemical catalyst to replace Pt-based catalysts for electrochemical hydrogen production.
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    Nanoelectrocatalytic dynamics of lithium zirconium oxide perovskites containing sequentially incorporated palladium oxide, samarium and terbium
    (Univeristy of the Western Cape, 2024) Monama, Gobeng Release; Iwuoha, Emmanuel
    The usage of fossil fuels as energy source has an undesirable impact on the environment and they cannot be recycled. It is projected that at some point, they will run out. With the rapid rise in energy demand and ever-escalating environmental risks, the need for transition from fossil fuel to renewable energy sources is of utmost importance. Thus, a need for a renewable, clean and abundant source of energy is urgent. Hydrogen, as a high-grade clean and renewable energy carrier, is gradually considered as one of the most promising candidates for the fuel of the future. The thesis presents the platinum-metal free electrochemical hydrogen evolution reaction (HER) electrocatalyst based on perovskite oxide, lithium zirconium oxide (Li2ZrO3) doped with palladium, samarium and terbium. This work is motivated by the ongoing research for a pursuit of different materials to replace the scarce and high costly platinum based electrocatalyst. Li2ZrO3 which is identified as a good candidate as it possesses outstanding absorption property, is lightweight with ease of preparation and high catalytic activity. However, the usage of this material as an electrocatalyst is limited by poor electrical conductivity and less electrochemical stability. In order to improve these properties, incorporation of precious and lanthanides metal is needed. In this study, we focus on developing a novel all inorganic perovskites oxide that is Pt-free for HER application.
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    Terbium- and samarium-doped li2zro3 perovskite materials as efficient and stable electrocatalysts for alkaline hydrogen evolution reactions
    (Springer Nature, 2024) Monama, Gobeng Release; Ramoroka, Morongwa Emmanuel; Ramohlola, Kabelo Edmond; Iwuoha, Emmanuel Iheanyichukwu
    The preparation of highly active, rare earth, non-platinum-based catalysts for hydrogen evolution reactions (HER) in alkaline solutions would be useful in realizing green hydrogen production technology. Perovskite oxides are generally regarded as lowactive HER catalysts, owing to their unsuitable hydrogen adsorption and water dissociation. In this article, we report on the synthesis of Li2ZrO3 perovskites substituted with samarium and terbium cations at A-sites for the HER. LSmZrO3 (LSmZO) and LTbZrO3 (LTbZO) perovskite oxides are more afordable materials, starting materials in abundance, environmentally friendly due to reduced usage of precious metal and moreover have potential for several sustainable synthesis methods compared to commercial Pt/C. The surface and elemental composition of the prepared materials have been confrmed by X-ray photoelectron spectroscopy (XPS). The morphology and composition analyses of the LSmZO and LTbZO catalysts showed spherical and regular particles, respectively. The electrochemical measurements were used to study the catalytic performance of the prepared catalyst for hydrogen evolution reactions in an alkaline solution. LTbZO generated 2.52 mmol/g/h hydrogen, whereas LSmZO produced 3.34 mmol/g/h hydrogen using chronoamperometry. This was supported by the fact that the HER electrocatalysts exhibited a Tafel slope of less than 120 mV/dec in a 1.0 M alkaline solution. A current density of 10 mA/ cm2 is achieved at a potential of less than 505 mV. The hydrogen production rate of LTbZO was only 58.55%, whereas LSmZO had a higher Faradaic efciency of 97.65%. The EIS results demonstrated that HER was highly benefcial to both electrocatalysts due to the relatively small charge transfer resistance and higher capacitance values.