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XAFS studies on the well-defined fuel cell model catalysts
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| Title: | XAFS studies on the well-defined fuel cell model catalysts |
| Other Titles: | 燃料電池モデル触媒の XAFS 研究 |
| Authors: | DONG, Kaiyue Browse this author |
| Issue Date: | 28-Jun-2024 |
| Publisher: | Hokkaido University |
| Abstract: | To meet the target of carbon neutralization society and solve the critical issue arising from the depletion of traditional fossil storage and high demand for renewable energy resources, fuel cell technology provides a promising solution to the problems. Oxygen reduction reaction (ORR) at cathode side of fuel cells is the crucial rate determining step, which is accelerated by the monometallic Pt and bimetallic Pt-based PtM (M=Pd, Au, etc) alloy nanoparticles (NPs) catalysts supported on porous carbons. In order to increase the activity and durability and to further contribute to the development of fuel cell, it is significantly important to investigate the relationship between the electronic and geometric structures of Pt (PtM) nanoparticles and their activities. Nevertheless, these porous carbon powder catalyst supports usually exhibit an ill- defined structure, which is hard to give an exact description of structure and related active sites. An alternative way is to use a model catalyst system to make it possible to apply surface science techniques to reveal the detailed structures at atomic scales. Furthermore, in situ characterization must be necessary to obtain precise insights into real reaction processes. X-ray absorption fine structure (XAFS) is the most suitable surface science technique, which allows us to carry out in situ characterization of electronic and geometric structures of Pt (PtM) NPs on atomic level. However, when I tried to apply it to the model systems, new developments in XAFS techniques are needed. In this work I developed three new XAFS techniques: a bent crystal Laue analyzer + back illuminated / high energy resolution fluorescence detection X-ray absorption fine structure (BCLA+BI/HERFD-XAFS), BCLA enhanced polarization-dependent total reflection fluorescence XAFS (BCLA+PTRF-XAFS) technique, and in situ electrochemical PTRF-XAFS (EC-PTRF- XAFS) technique. These new XAFS techniques are applied to the Pt-based model systems. I found several new and important concepts for the development of noble metal Pt-based ORR catalysts. The first chapter gave a general introduction. The second chapter described experimental methods and analysis details, which included model catalyst preparation for monometallic (Pt) and bimetallic Pt-based (PtM) model catalyst systems, development of in-situ electrochemical XAFS apparatus, and related surface science characterizations. The third chapter described the investigation of model catalyst structure for monometallic Pt NPs in a small amount (~ 1015 Pt atoms cm-2) supported on the flat HOPG. A novel BCLA/HERFD-BI-XAFS method was applied for the structure study under in-situ conditions which corresponded to the ORR reactions. Structure framework and surface adsorbates were successfully investigated. The fourth chapter focused on the development of in-situ EC-BCLA+PTRF-XAFS measurement apparatus for structure studies of diluted noble metals supported by single crystal surfaces. The limited target element amount and enormous elastic scatterings arises from solutions hinders the in-situ EC-XAFS studies. The applications of BCLA perfectly solved abovementioned problems with delicate adjustment between the BCLA position and X-ray footprints, especially for EXAFS of bimetallic PtAu system under solution free case, for which elements possess a close absorption energy edge. Nevertheless, the application of BCLA in for diluted PtAu model catalyst system under solution condition didn’t significantly choose the target Pt fluorescence signals because of huge contribution of inelastic scatterings arise from solutions was too large to be easily removed by simply application of BCLA monochromator. Further improvements should be considered to eliminate the negative solution effect in in-situ XAFS measurement. In the fifth chapter, I challenged to apply the developed in-situ PTRF-XAFS technique to track the formation process of spontaneously deposited [PtCl4]2- species under in-situ conditions. The as-prepared sample with a very limited Pt amount (~ 0.2 ML) formed via self-deposition method, where a planar structure [PtCl4]2- was assumed in Feff8 theoretical simulation. In the sixth chapter, I successfully applied the in-situ EC-PTRF-XAFS method to the bimetallic Pt-based model catalyst system of Pt sub-ML supported by Au (111), and confirmed the strain effect in this model system. The Pt-Pt bond distance in this model catalyst was expanded to Au-Au in Au foil as 2.88 Å, which was induced by Au (111) underlying substrate because of lattice constant between Pt and Au species. The seventh chapter gave the general conclusion of the dissertation. I successfully developed three XAFS methods suitable for structure investigation of monometallic and bimetallic Pt-based model catalysts for ORR under in-situ conditions. The developed XAFS apparatus will be contribute to the catalyst fundamental research, which is possible to establish the relationship between the Pt-based catalyst and corresponding ORR catalytic activities and further providing an essential guiding line for ORR catalyst design. |
| Conffering University: | 北海道大学 |
| Degree Report Number: | 甲第16043号 |
| Degree Level: | 博士 |
| Degree Discipline: | 工学 |
| Examination Committee Members: | (主査) 教授 加美山 隆, 教授 柴山 環樹, 教授 高草木 達 (触媒科学研究所), 名誉教授 朝倉 清高 |
| Degree Affiliation: | 工学院（量子理工学専攻） |
| Type: | theses (doctoral) |
| URI: | http://hdl.handle.net/2115/92731 |
| Appears in Collections: | 学位論文 (Theses) > 博士 （工学）
課程博士 (Doctorate by way of Advanced Course) > 工学院(Graduate School of Engineering)
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