Investigation of Electronic Structure Effects of Transition Metal Oxides toward Water Oxidation and CO2 Reduction Catalysis
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2016
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ndltd-OhioLink-oai-etd.ohiolink.edu-osu14628686232021-08-03T06:36:39Z Investigation of Electronic Structure Effects of Transition Metal Oxides toward Water Oxidation and CO2 Reduction Catalysis Fugate, Elizabeth Anne Chemistry metal oxides carbon dioxide reduction water oxidation photocatalysis electrocatalysis acetate copper iron oxide X-ray Absorption Spectroscopy ion chromatography Energy conversion and storage technologies are often limited by the stability and selectivity of catalysts. One reaction of great importance in the energy conversion process is CO2 reduction. For CO2 reduction, selectivity is often influenced by the structure of the catalyst material. Also, catalysts need to be selective for CO2 reduction over the hydrogen evolution reaction. Recent studies have shown that the selectivity of catalysts to high energy dense products is dependent on the band gap of the catalyst materials. This approach has also shown potential to be used to outcompete the hydrogen evolution process. Earth abundant metal oxides have narrow band gaps that would be energetically favorable for this process. These materials such as CuFeO2 and Cu2O have narrow band gaps (Eg) and Fermi levels (EF) that are suitable for reducing CO2 as well as the oxidation of water. By investigating the electronic structure of these catalysts, we can better understand how electron transfer impacts the selectivity of different products. To this end catalysts that are selective to high energy density products can be produced. Thus by investigating metal oxides of varying electronic structure, we can elucidate trends in product selectivity. We have produced Fe2O3, CuO, and CuFeO2 catalysts by electrodeposition to investigate the photoelectrocatalysis of CO2 reduction. Only the CuFeO2 mixed phase catalyst produced selective photocurrent under CO2 reduction conditions. Our CuFeO2 was able to produce acetate at approximately 70% faradaic efficiency as confirmed by standard addition method using Ion Chromatography and Nuclear Magnetic Resonance Spectroscopy. By looking at the structure using X-ray Photoelectron Spectroscopy, we conclude that our catalyst has an iron rich surface that we believe to be responsible for this high selectivity under CO2 reduction conditions. We believe there is a metal to metal charge transfer from the Fe to the Cu where the hole is localized to Cu 3d orbitals in the valence band and the electron is localized to Fe 3d orbitals in the conduction band. This state results in a long-lived Fe2+ excited state that we hypothesize is responsible for the reduction of CO2. In the near future, we plan to probe charge transfer dynamics of this material via soft X-ray transient absorption spectroscopy, which is oxidation state and element specific. Additionally, we have produced NiOx, CoOx, and MnOx catalysts. Cyclic voltammetry was used to investigate trends in the overpotential for the water oxidation reaction at pH 7 and pH 13. Both NiOx and CoOx have significantly lower overpotentials than any of the other oxides with the overpotential corresponding to 3d orbital occupancy. Additionally, nickel doping of Fe2O3 lowers the overpotential significantly, with a 10% nickel molar ratio in the electrolyte being optimal. By investigating the ground and excited state x-ray spectra of these oxides, we can determine how electronic structure and the band gap of these materials correlate with the overpotential for water oxidation. 2016-09-01 English text The Ohio State University / OhioLINK http://rave.ohiolink.edu/etdc/view?acc_num=osu1462868623 http://rave.ohiolink.edu/etdc/view?acc_num=osu1462868623 unrestricted This thesis or dissertation is protected by copyright: some rights reserved. It is licensed for use under a Creative Commons license. Specific terms and permissions are available from this document's record in the OhioLINK ETD Center. |
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NDLTD |
| language |
English |
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NDLTD |
| topic |
Chemistry metal oxides carbon dioxide reduction water oxidation photocatalysis electrocatalysis acetate copper iron oxide X-ray Absorption Spectroscopy ion chromatography |
| spellingShingle |
Chemistry metal oxides carbon dioxide reduction water oxidation photocatalysis electrocatalysis acetate copper iron oxide X-ray Absorption Spectroscopy ion chromatography Fugate, Elizabeth Anne Investigation of Electronic Structure Effects of Transition Metal Oxides toward Water Oxidation and CO2 Reduction Catalysis |
| author |
Fugate, Elizabeth Anne |
| author_facet |
Fugate, Elizabeth Anne |
| author_sort |
Fugate, Elizabeth Anne |
| title |
Investigation of Electronic Structure Effects of Transition Metal Oxides toward Water Oxidation and CO2 Reduction Catalysis |
| title_short |
Investigation of Electronic Structure Effects of Transition Metal Oxides toward Water Oxidation and CO2 Reduction Catalysis |
| title_full |
Investigation of Electronic Structure Effects of Transition Metal Oxides toward Water Oxidation and CO2 Reduction Catalysis |
| title_fullStr |
Investigation of Electronic Structure Effects of Transition Metal Oxides toward Water Oxidation and CO2 Reduction Catalysis |
| title_full_unstemmed |
Investigation of Electronic Structure Effects of Transition Metal Oxides toward Water Oxidation and CO2 Reduction Catalysis |
| title_sort |
investigation of electronic structure effects of transition metal oxides toward water oxidation and co2 reduction catalysis |
| publisher |
The Ohio State University / OhioLINK |
| publishDate |
2016 |
| url |
http://rave.ohiolink.edu/etdc/view?acc_num=osu1462868623 |
| work_keys_str_mv |
AT fugateelizabethanne investigationofelectronicstructureeffectsoftransitionmetaloxidestowardwateroxidationandco2reductioncatalysis |
| _version_ |
1719440236134531072 |