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dc.contributor.advisorFalch, A.
dc.contributor.advisorKriek, R.J.
dc.contributor.authorBissen, Tevin Gladwyn
dc.date.accessioned2021-11-25T07:14:37Z
dc.date.available2021-11-25T07:14:37Z
dc.date.issued2021
dc.identifier.urihttps://orcid.org/0000-0002-2061-8102
dc.identifier.urihttp://hdl.handle.net/10394/37994
dc.descriptionMSc (Chemistry), North-West University, Potchefstroom Campusen_US
dc.description.abstractStored energy, as a result of the conversion of renewable resources has resulted in extensive research and development efforts towards water electrolysis. Alkaline water electrolysis, in combination with renewable energy sources, provides a promising sustainable and environmentally friendly means for generating high purity hydrogen. Although alkaline water electrolysis has a hundred-year-long history, advances are still required for the electrode material that catalyses the oxygen evolution reaction (OER) at the anode, as this reaction exhibits sluggish reaction kinetics and ultimately results in cell efficiency losses. To improve OER activity in alkaline water electrolysis, various (NiZnxCry)O electrocatalysts were synthesised by employing a citrate sol-gel method following two different routes (0.4 M and 1 M citric acid). Electrocatalysts were deposited onto glassy carbon electrodes and subjected to electrochemical and physical characterisation. Energy-dispersive x-ray spectroscopy (EDS), scanning electron microscopy ((SEM)-EDS), x-ray diffraction analysis (XRD) and transmission electron microscopy (TEM) were independently employed to evaluate the metal composition, metal phases, crystallite size and morphology of each electrocatalyst. For electrochemical analysis, rotating disk electrode (RDE) techniques were employed which comprised cyclic voltammetry (CV) and linear sweep voltammetry (LSV) before and after five hours of chronopotentiometry (CP) evaluation runs. The study revealed that the change in citric acid concentration resulted in (i) electrocatalysts with the same metal compositions but with different phases, and (ii) a reduction in crystallite size when using higher concentrations of citric acid which lead to electrocatalytic activity improvements. The best-performing electrocatalyst combination was identified as the (NiCr)O electrocatalyst prepared by the two routes ((NiCr)O-1 and (NiCrO)-2)). (NiCr)O-1 not only exhibited the lowest overpotential (405±32 mV at 10 mA.cm-2) with a Tafel slope of 80±30 mV.dec-1 before CP, but also exhibited the lowest overpotential (426±84 mV at 10 mA.cm-2 ) and Tafel slope (58±13 mV.dec-1) after CP. Elementary analysis revealed that leaching of Cr occurred after five hours of CP. However, this did not severely affect the activity of the (NiCr)O electrocatalysts as no great reduction occurred in the polarisation curves. It was found that the incorporation of Zn into NiO and (NiCr)O resulted in severe durability loss as all samples containing Zn exhibited low current densities and were rendered inactive after CP analysis. It is evident from this study that a favourable synergy exists between Ni and Cr and that crystallite size reduction resulted in the realisation of lower overpotentials. Furthermore, the current density was seen to be more reliant on the electrocatalyst composition whereas the overpotential was reliant on crystallite size and electrocatalyst composition.en_US
dc.language.isoenen_US
dc.publisherNorth-West University (South Africa)en_US
dc.subjectSol-gelen_US
dc.subjectElectrocatalysten_US
dc.subjectAlkaline water electrolysisen_US
dc.subjectHydrogenen_US
dc.subjectOxygen evolution reactionen_US
dc.subjectActivityen_US
dc.subjectOverpotentialen_US
dc.subjectStabilityen_US
dc.titleSynthesis and evaluation of (NiZnxCry)O electrocatalysts for the oxygen evolution reactionen_US
dc.typeThesisen_US
dc.description.thesistypeMastersen_US
dc.contributor.researchID20286317 - Falch, Anzel (Supervisor)
dc.contributor.researchID13238477 - Kriek, Roelof Jacobus (Supervisor)


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