近室壓X光光電子能譜術 (APXPS) 由於能夠在毫巴等級的壓力下執行 X 光光電子能譜的量測，已被認知是一個提供界面電子結構信息和識別各種界面處化學狀態的不可或缺的工具。作為在同步輻射研究中心建設近室壓X光光電子能譜術實驗站(台灣光源源 光束線24A)的早期團隊成員之一，我有幸使用實驗站進行了博士論文研究的實驗。
在此論文中，我將討論藉由近室壓X光光電子能譜術研究的兩種不同表面反應所獲得的結果。第一個主題是關於環境氣體和太陽光照射所誘導的三陽離子鹵化鉛鈣鈦礦的降解。有機無機混合鈣鈦礦太陽能電池的快速發展取得了顯著成功，其太陽能電池的性能在短短幾年內達到了商業門檻。但儘管如此，鈣鈦礦太陽能電池在大氣下操作的穩定性還是一個有待解決的重要問題。值得注意的是，最近研究發現，將不同類型的陽離子摻入鈣鈦礦晶胞中可以顯著提高元件的穩定性。為了闡明為什麼多陽離子鈣鈦礦會提高元件穩定性，我們著手研究 Cs0.1(FA0.83MA0.17)0.9Pb(I0.83Br0.17)3在暴露於不同氣體環境且也光照時材料性質的變化。具體來說，我們採用近室壓X光光電子能譜術研究了三陽離子鈣鈦礦薄膜在 0.5 kW/m2 太陽輻射照射下並在 1 mbar 壓力下暴露於 H2O 和/或 O2 氣體的化學成分變化。水氣和氧分子以不同的方式影響鈣鈦礦的降解過程。鈣鈦礦暴露於水氣和光下會產生鹵化鉛和金屬鉛，而鈣鈦礦上暴露於氧氣和光下會導致氧化鉛的形成。當氧分子與被光激發的鈣鈦礦接觸時形成的超氧離子(O2-)可能是導致鈣鈦礦高度氧化的可能。且在氧氣和光暴露的環境下，發現鈣鈦礦表面的碘化物和溴化物都大量消失，但對於水氣暴露的情況則沒有此狀況。有趣的是，水氣和氧氣的共存對鈣鈦礦造成的損害比純氧要小，這可能是由於在鈣鈦礦表面形成了惰性水合層，從而延緩了超氧化物的形成，從而提供了更好的保護。
第二個主題是關於單層石墨烯覆蓋的 Bi5O7Br0.5I0.5 表面上的光催化氮氣還原反應，此研究探討氧缺陷在反應中所扮演的關鍵作用。光催化氮氣還原反應對於以永續能源發展的方式進行人工合成氨是一重要的策略。與傳統的哈伯法工業製氨相比，光催化法提供了一種低能耗、低二氧化碳排放的替代方案。但是，需要跨越低轉換效率的障礙。但是，其需要跨越低轉換效率的障礙。根據其他研究顯示，鹵氧化鉍化合物系列(BixOyXz, X = Cl, Br, I)在光催化氮氣還原反應中的轉換效率很高。其高轉換效率歸因於材料表面在反應中易於形成的氧缺陷，此缺陷不但增強了氮氣的吸附也激活吸附的氮氣分子，從而提高了氨的產率。在本主題中，將會在接近真實反應條件下，藉由近室壓X光光電子能譜術探討Bi5O7Br0.5I0.5表面上存在的氧缺陷對氮氣還原反應的影響，藉由偵測存在的表面物質且追蹤表面反應中間物的演變，來推倒氮氣還原反應的反應機制。APXPS O 1s 數據顯示在可見光照射下，鹵氧化鉍表面產生了氧缺陷的明確證據。APXPS N 1s 數據表明氮分子的吸附在有可見光照射下增強，隨後在表面形成部分氫化的氮產物，證明了 Bi5O7Br0.5I0.5光催化劑的高反應性。此外，通過對表面反應中間物的形態分析，可得出結論，在Bi5O7Br0.5I0.5上光催化氮氣還原反應的反應機制很可能遵循締合交替途徑(associative alternating pathway)。

Thanks to its ability to perform X-ray photoelectron spectroscopy at a pressure higher than mbar, ambient pressure X-ray photoelectron spectroscopy (APXPS) has proven to be an indispensable tool in providing the interfacial electronic structure information and identifying the chemical state present at various interfaces. As one of the earlier team members in constructing the APXPS endstation at NSRRC, I have the privilege of using the endstation to conduct the experiments detailed in this dissertation to partially fulfill the Ph. D. requirement.
Herein, I will report the results obtained from investigating two different surface reactions using the APXPS technique available at BL24A of Taiwan Light Source. The first topic is related to the degradation of triple-cation lead halide perovskite induced by gas exposure and solar-light illumination. The rapid development in hybrid perovskite solar cells has been a remarkable success with the device performance reaching a commercial threshold in a few short years. Nonetheless, one important problem related to device’s operational stability remains to be solved. A recent finding that the incorporation of different types of cations into the perovskite unit cell can significantly increase the device stability is worth noting. To shed light on why the multi-cation perovskite yields improved device stability, we set up to investigate the changes in material properties of Cs0.1(FA0.83MA0.17)0.9Pb(I0.83Br0.17)3 when exposed to different gas ambient in conjunction with light illumination. Specifically, we employed APXPS technique to study the chemical composition change of triple-cation perovskite thin films illuminated with 0.5 kW/m2 solar radiation and exposed to gases of H2O and/or O2 at 1 mbar pressure. Water vapor and molecular oxygen affect the degradation process in a different way. The perovskite exposed to water vapor and light produces lead halide and metallic lead, whereas oxygen exposure with light illumination on the perovskite results in the formation of lead oxide. The high degree of oxidation is made possible by the superoxide ion formed when molecular oxygen contacts the photoexcited perovskites. A large disappearance of both iodide and bromide is found for oxygen exposed and light-illuminated perovskite, but not for water vapor exposure case. Interestingly, a co-presence of water vapor and oxygen causes less damage to the perovskite than the pure oxygen, presumably due to the formation of an inert hydration layer on the perovskite surface that retards the superoxide formation and hence offers better protection.
The second topic is related to photocatalytic nitrogen reduction reaction on monolayer graphene-covered Bi5O7Br0.5I0.5 surface with an emphasis given to assess the critical role played by oxygen vacancy. The photocatalytic nitrogen reduction plays a critically important role in realizing the artificial synthesis of ammonia in a sustainable energy economy. Compared with the traditional industrial ammonia production via the Haber-Bosch process, the photocatalytic method offers an attractive alternative of low energy consumption and low emission of carbon dioxide. However, the hurdle of low conversion efficiency needs to be crossed. A series of bismuth oxyhalide compounds (BixOyXz, X = Cl, Br, I) have been reported to exhibit high yields in photocatalytic reduction of nitrogen. The high yield is attributed to readily available oxygen vacancies in the materials that in turn enhance the nitrogen adsorption and activate the nitrogen molecules, leading to an increasing ammonia production rate. In this topic, APXPS, capable of identifying surface species present under near-real reaction conditions, has been used to assess the influence of oxygen vacancies present on the Bi5O7Br0.5I0.5 on NRR, to track the evolution of surface reaction intermediates, and to delineate the reaction mechanism of NRR. APXPS O 1s data offer clear evidence of oxygen vacancy creation via visible light illumination. APXPS N 1s data evidence an enhancement of molecular nitrogen adsorption followed by the formation of partially hydrogenated products on the surface, attesting to the high reactivity of Bi5O7Br0.5I0.5 photocatalyst. In addition, after the speciation of reaction intermediates on the surface, one can conclude that the reaction mechanism of NRR on Bi5O7Br0.5I0.5 is likely to follow the associative alternating pathway.

I. Chapter 1: Ambient pressure X-ray photoelectron spectroscopy 1
I-1 Performing XPS in elevated pressure: APXPS 1
I-2 APXPS endstation in BL24A of Taiwan Light Source 4
I-3 APXPS applications 10
I-3-1 Gas/ solid interfaces 11
I-3-2 Solid/liquid interfaces 14
I-3-3 Liquid/ vapor interfaces 18
I-4 Reference 22
II. Chapter 2: Degradation of triple cations lead halide perovskite induced by light and ambient gases 27
II-1 High efficiency solar cell materials: metal halide perovskites 27
II-1-1 Characterization of metal halide perovskite 28
II-1-2 Understanding the instability of metal halide perovskite 32
II-1-3 Mixing cations to improve the stability of metal halide perovskite 38
II-2 Motivation 39
II-3 Experimental section 41
II-3-1 Preparation of samples, triple-cation perovskite on PEDOT:PSS/ FTO, for APXPS experiments 41
II-3-2 Experimental setup for in-situ APXPS measurements 42
II-4 Results and discussion 43
II-4-1 Characterization of Cs0.1(FA0.83MA0.17)0.9PbI0.83Br0.17 43
II-4-2 Aging by water vapor and light illumination 45
II-4-3 Aging by oxygen and light illumination 50
II-4-4 Aging by water vapor – oxygen mixture and light illumination 53
II-4-5 Degradation of single-cation perovskite: MAPbI3 and FAPbI3 56
II-4-6 Possible degradation mechanism for triple-cation perovskite 59
II-4-7 Progressive p-doping in degraded Cs0.1-PSK 62
II-5 Conclusion 65
II-6 Reference 67
III. APXPS investigation of photocatalytic nitrogen reduction reaction in Bi5O7Br0.5I0.5: the critical role played by oxygen vacancy 74
III-1 A visible approach for efficient nitrogen reduction reaction: photocatalysis 74
III-1-1 Basic understanding of bismuth oxyhalides 76
III-1-2 Importance of oxygen vacancies in bismuth oxyhalides 77
III-1-3 Nitrogen reduction reaction mechanism derived from DFT calculation 80
III-2 Motivation 82
III-3 Experimental section 82
III-3-1 Material preparation 82
III-3-2 Synthesis of Bi5O7Br0.5I0.5 photocatalyst 83
III-3-3 Preparation of graphene/Bi5O7Br0.5I0.5 pellet for APXPS experiment 83
III-4 Results and discussion 84
III-4-1 Characterization of synthesized Bi5O7Br0.5I0.5 84
III-4-2 Chemical analysis of as-prepared graphene/Bi5O7Br0.5I0.5 pellet 92
III-4-3 Controlling the density of oxygen vacancies on the surface of Bi5O7Br0.5I0.5 with atomic hydrogen 94
III-4-4 In-situ investigation of NRR 100
III-5 Conclusion 109
III-6 Reference 110

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