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Study on the Effect of Mn Structure and Valency on Water Oxidation Catalysis
망간의 구조와 산화수가 산소 발생 촉매 작용에 미치는 영향에 대한 연구

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dc.contributor.advisor남기태-
dc.contributor.author박지민-
dc.date.accessioned2017-07-14T03:06:43Z-
dc.date.available2017-07-14T03:06:43Z-
dc.date.issued2014-02-
dc.identifier.other000000017227-
dc.identifier.urihttps://hdl.handle.net/10371/123278-
dc.description학위논문 (석사)-- 서울대학교 대학원 : 재료공학부, 2014. 2. 남기태.-
dc.description.abstractThe development of a water oxidation catalyst has been a demanding challenge for the realization of overall water-splitting systems. The asymmetric geometry and flexible ligation of the biological Mn4CaO5 cluster are important properties for the function of photosystem II, and these properties can be applied to the design of a new inorganic water oxidation catalyst. In part I, we identified a new crystal structure, Mn3(PO4)2-3H2O, that precipitates spontaneously in aqueous solution at room temperature and demonstrated its superior catalytic performance at neutral pH. Computational analysis indicated that phosphate ligations in our crystal make Mn-O bonding longer and more distorted than in other Mn-based oxides. Such structural flexibility can stabilize Jahn-Teller distorted Mn(III) and thus facilitate Mn(II) oxidation, as monitored by electron paramagnetic resonance spectroscopy.
Moreover, although intensive studies have explored the role of Mn element in water oxidation catalysis, it has been difficult to understand whether the catalytic capability originates mainly from either the Mn arrangement or the Mn valency. In part II, to decouple these two factors and to investigate the role of Mn valency on catalysis, we selected a new pyrophosphate-based Mn compound (Li2MnP2O7), which has not been utilized for water oxidation catalysis to date, as a model system. Due to the monophasic behavior of Li2MnP2O7 with the delithiation, the Mn valency of Li2-xMnP2O7 (x = 0.3, 0.5, 1) can be controlled with negligible change in crystal framework (e.g. volume change ~ 1 %). Interestingly, we observed that as the averaged oxidation state of Mn in Li2-xMnP2O7 increases from 2 to 3, the catalytic performance is enhanced in the series Li2MnP2O7 < Li1.7MnP2O7 < Li1.5MnP2O7 < LiMnP2O7. Moreover, Li2MnP2O7 itself exhibits superior catalytic performance compared with MnO or MnO2 because of the highly distorted Mn geometry in Li2MnP2O7.
In summary, we selected Mn3(PO4)2-3H2O and Li2-xMnP2O7 compounds as artificial platforms for understanding the effect of Mn structure and valency on water oxidation catalysis, respectively. We think that this study presents valuable guidelines for developing an efficient Mn-based catalyst which can be comparable with the biological Mn4CaO5 cluster in photosystem II under neutral conditions with controlled Mn valency and atomic arrangement.
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dc.description.tableofcontentsList of Tables 10
List of Figures 11
Chapter 1 Introduction 17
1.1 Energy Crisis and Demand for renewable energy 17
1.2 Water splitting 19
1.3 Oxygen Evolution reaction(OER) 21
1.3.1 Noble metal based OER electrocatalysts 24
1.3.2 Transition metal (Co,Ni,Cu,Fe) based OER electrocatalysts 26
1.4 Manganese based OER electrocatalysts 30
1.4.1 Photosystem II in biological system 30
1.4.2 Bio-inspired Mn based OER electrocatalysts 31
1.4.3 Bottleneck in Mn based electrocatalysts in OER 36
1.4.4 Importance for understanding the effect of Mn valency And Structure on water oxidation catalysis 37
Chapter 2 Mn3(PO4)2-3H2O : Effect on Mn structure 41
2.1 Experimental and Procedure 41
2.1.1 Synthesis and Materials 41
2.1.2 Characterization 42
2.1.2.1 Powder X-ray diffraction 42
2.1.2.1 ICP/MS 42
2.1.2.2 Rietveld analysis 43
2.1.2.3 Scanning electron microscopy(SEM) analysis 43
2.1.2.4 Transmission electron microscopy (TEM) analysis 44
2.1.2.5 BrunauerEmmettTeller (BET) method 44
2.1.3 Electrochemical analysis 46
2.1.3.1 Cyclic Voltammetry (CV) 46
2.1.3.2 Gas Chromatography (GC) 47
2.1.3 Electron paramagnetic resonance (EPR) spectroscopy 49
2.1.4 DFT calculation 51
2.2 Results and Discussions 52
2.2.1 Structural Characterization of Mn3(PO4)2-3H2O 52
2.2.2 Electrochemical analysis of Mn3(PO4)2-3H2O 64
2.2.3 Mechanistic studies of Mn3(PO4)2-3H2O 75
Chapter 3 Li2-xMnP2O7 (x= 0~1): Effect on Mn Valency 81
3.1 Experimental and Procedure 81
3.1.1 Synthesis and Material 81
3.1.2 Characterization 81
3.1.2.1 ICP/MS 82
3.1.2.2 Powder X-ray diffraction, Full-pattern matching 82
3.1.2.3 X-ray photon spectroscopy (XPS) 82
3.1.2.4 Transmission electron microscopy (TEM) analysis 83
3.1.2.5 BrunauerEmmettTeller (BET) method 83
3.1.3 Electrochemical analysis 84
3.1.4 DFT calculation 86
3.2 Results and Discussion 87
3.2.1 Structural Characterization of Li2-xMnP2O7 (x=0~1) 87
3.2.2 Electrochemical analysis of Li2-xMnP2O7 (x=0~1) 93
3.2.3 Mechanistic studies of Li2-xMnP2O7 (x=0~1) 112
Chapter 4 Conclusion 128
References 130
국문초록 138
감사의 글 (Acknowledgement) 140
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dc.formatapplication/pdf-
dc.format.extent3600951 bytes-
dc.format.mediumapplication/pdf-
dc.language.isoen-
dc.publisher서울대학교 대학원-
dc.subjectwater splitting-
dc.subjectoxygen evolution reaction-
dc.subjectMn3(PO4)2-3H2O-
dc.subjectLi2MnP2O7-
dc.subjectNeutral condition-
dc.subjectMn structure and valency-
dc.subject.ddc620-
dc.titleStudy on the Effect of Mn Structure and Valency on Water Oxidation Catalysis-
dc.title.alternative망간의 구조와 산화수가 산소 발생 촉매 작용에 미치는 영향에 대한 연구-
dc.typeThesis-
dc.contributor.AlternativeAuthorJimin Park-
dc.description.degreeMaster-
dc.citation.pages146-
dc.contributor.affiliation공과대학 재료공학부-
dc.date.awarded2014-02-
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College of Engineering/Engineering Practice School (공과대학/대학원)Dept. of Material Science and Engineering (재료공학부) Theses (Master's Degree_재료공학부)
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