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Facile Synthesis of Mixed Metal Oxygen Evolution Reaction Catalysts
AuthorLindstrom, Mary L.
Chemical and Materials Engineering
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Global energy demand is projected to increase at a rapid rate in the followingdecades. This poses a challenge for researchers to develop innovative and cost effectivemethods to harvest sustainable energy and prevent a rise in greenhouses gas emissionsdue to carbon-based fuel consumption. Electrolytic water splitting offers energy storageand conversion opportunities, yet the slow kinetics of the oxygen evolution reactionrequires the development of efficient electrocatalysts.To date, the most efficient oxygen evolution reaction catalysts are expensive andrare platinum-group oxides in acidic media. It is highly desirable to synthesize efficientcatalysts from low cost, abundant materials for industrial applications. This thesisreports the facile synthesis of novel, cost-effective mixed transition metalelectrocatalysts for the oxygen evolution reaction. Mixed transition metal oxides ofMonel 400 alloy and nickel, iron, and cobalt precursors were synthesized using a onestep,hydrothermal process and investigated for their catalytic activity.The catalysts presented in this work are self-supported and do not requireadditional electrode preparation steps before use as the working electrode in a alkalinewater splitting cell and these materials can be quickly commercialized. The oxidized,transition metal-based electrodes were characterized using a variety of techniques.Scanning electron microscopy, electron dispersive spectroscopy, X-ray diffraction,Raman spectroscopy, and X-ray photoelectron spectroscopy were used to evaluate thesurface composition. Electrochemical techniques, including linear sweep voltammetryand electrochemical impedance spectroscopy, were used to compare the catalyticactivity and stability of the synthesized mixed metal oxides to the as-received metals andsimilar catalysts in the literature. Oxides that formed on the surface of Monel 400 alloyafter exposure to subcritical water showed an ~3-fold increase in catalytic activity forthe OER when compared to the as-received material. Nickel and cobalt containingcomplexes that were formed during hydrothermal synthesis exhibited a 30% increase incatalytic activity when compared to nickel metal. The catalyst that exhibited the highestOER activity was a ternary nickel-iron-cobalt catalyst. The hydrothermal synthesis ofthe nickel-iron-cobalt catalyst was optimized during this research and the resultingelectrode exhibited a current density of 110 mA cm-2 at 1.8 V vs RHE and a lowoverpotential of 0.31 V at a current density of 10 mA cm-2. These are extremelycompetitive characteristics compared to those in the literature and this supports thehypothesis that this method may be feasible to produce viable catalysts for industrialapplications in the near future, which may aid in the development of sustainable energytechnologies.