Interconversion of nickel hydroxides studied using dynamic electrochemical impedance

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dc.contributor.authorAiyejuro, Victor Omoatokwe
dc.contributor.supervisorHarrington, David A.
dc.date.accessioned2020-08-28T04:28:07Z
dc.date.available2020-08-28T04:28:07Z
dc.date.copyright2020en_US
dc.date.issued2020-08-27
dc.degree.departmentDepartment of Chemistry
dc.degree.levelMaster of Science M.Sc.en_US
dc.description.abstractThe interconversion of α- and β-Ni(OH)₂ was studied using cyclic voltammetry and dynamic electrochemical impedance (dEIS). Holding experiments were done at 0.5 V, 0.6 V, 0.8 V and 1.0 V while subsequent cathodic holds were applied in selected experiments at -0.1, -0.2, -0.25 V. The number of thickness of Ni(OH)₂ formed increased with increasing anodic potential. After α-Ni(OH)₂ was formed (< 0.5 V), it was easily reduced by sweeping down to -0.15 V. However, sweeping further (> 0.5 V) resulted in its "irreversible" conversion to β-Ni(OH)₂. Since β-Ni(OH)₂ was not reduced by sweeping to -0.15 V, the current, capacitance and the conductance at the α-Ni(OH)₂ peak (at 0.2 V) decreased as a result. However, β-Ni(OH)₂ was shown to be reducible during potential holds at -0.2 V or lower. In contrast, holding at -0.1 V only resulted in partial reduction. Eventually, a link was established between the reduction of β-Ni(OH)₂ and hydrogen evolution. The relatively slow reduction of the β-Ni(OH)₂ to metallic nickel appears to inhibit the capacitance increase at -0.15 V which occurs when the potential is kept under 0.5 V. The retention of a low capacitance while β-Ni(OH)₂ persists suggests a blocking mechanism. A concerted adsorption-desorption step which generates adsorbed hydrogen prior to hydrogen evolution was proposed. An exponential increase in current and capacitance occurred during the potential hold at -0.2 V. The capacitance increase suggests a reversal of the blocking (low capacitance at -0.15 V) caused by the persistence of β-Ni(OH)₂. Additionally, the exponential current decay during the hold at -0.2 V was significantly slower than the conversion of α- to β-Ni(OH)₂ at 0.8 V. This further demonstrates the possibility of a slow step involving surface blocking during the reduction of β-Ni(OH)₂. These observations provide new information on the mechanism and kinetics of the interconversion of α-Ni(OH)₂ into β-Ni(OH)₂ and the interaction of the latter in the hydrogen evolution reaction.en_US
dc.description.scholarlevelGraduateen_US
dc.identifier.urihttp://hdl.handle.net/1828/12044
dc.languageEnglisheng
dc.language.isoenen_US
dc.rightsAvailable to the World Wide Weben_US
dc.subjectImpedanceen_US
dc.subjectNickel hydroxideen_US
dc.subjectInterconversion of Nickel hydroxidesen_US
dc.subjectDynamic Electrochemical Impedanceen_US
dc.subjectInterconversion of Nickel Hydroxides Studied using Dynamic Electrochemical Impedanceen_US
dc.subjectDynamic Impedanceen_US
dc.subjectdEISen_US
dc.subjectNickel hydroxides studied using Dynamic Electrochemical Impedanceen_US
dc.subjectusing Dynamic Electrochemical Impedanceen_US
dc.subjectNickelen_US
dc.titleInterconversion of nickel hydroxides studied using dynamic electrochemical impedanceen_US
dc.typeThesisen_US

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