IOCAS-IR
WO3的能带调控与改性及其光电化学阴极保护性能的研究
田景
Subtype博士
Thesis Advisor陈卓元
2021-11-05
Degree Grantor中国科学院大学
Place of Conferral中国科学院海洋研究所
Abstract

近年来,随着我国海洋事业的迅速发展,服役于海洋环境的钢铁材料的腐蚀问题也越来越受到重视。光电化学阴极保护技术作为一种新兴的腐蚀防护技术得到了广泛关注,其只需要利用太阳光照射下半导体的光电转换效应,将半导体上激发产生的光生电子转移到被保护金属上,使金属发生阴极极化而得到保护。在此过程中,半导体本身不会被消耗,也不会对环境造成危害,具有清洁、高效、无污染的优点,应用前景非常广阔。氧化钨(WO3由于具有电子迁移率高、光响应范围广、制备方法简单、无毒以及低成本等优点而被认为是一种很有潜力的光电化学阴极保护材料。然而,WO3存在光生电子的还原能力不足,光生载流子的分离效率低等缺点,这极大限制了其在光电化学阴极保护领域的应用。本文通过钼(Mo)元素掺杂拉负WO3的导带电位,提高WO3的光生电子的还原能力,再通过相结的构建以及修饰导带电位较负的半导体材料,拉负复合光电极的准费米能级,促进光生载流子的分离,最终实现在NaCl溶液中为被保护金属提供光电化学阴极保护。具体的研究内容包括:

1.采用Mo元素掺杂对WO3进行能带调控。Mo元素掺杂没有改变WO3的形貌及光吸收特性,但是使WO3的导带负移,大大提升了光生电子的还原能力,从而解决了其光生电子的还原能力不足的问题。同时,Mo元素的掺杂大大提高了WO3的电导率,使得其光生电子的迁移能力和光生载流子的分离能力大大提高,从而提高了其光电转换效率。因此,0.3%Mo-WO3304不锈钢304 SS的光电化学阴极保护性能相较纯的WO3大大提升,光生电流密度可以达到38.0 μA·cm-2,为304 SS提供234.5 mV的阴极极化。

2. 通过调控WO3的形貌和晶相组成对其能带结构进行调控。在水热过程中,随着钨酸钠的添加量的增多,WO3的形貌由光滑的纳米片状结构变为多孔纳米板结构,再变为多孔纳米棒结构,最后变为类方糖结构。同时,单斜晶相在混合相(六方晶相和单斜晶相)中的比例也随着钨酸钠添加量的增大而增大。其中,钨酸钠的添加量为0.56 gWO3-3304 SS的光电化学阴极保护性能最佳,其在模拟太阳光照射下的光生电流密度为32.1 μA·cm-2,可以为304 SS提供369.1 mV的阴极极化。光电化学阴极保护性能提升的原因:一方面是WO3-3多孔纳米棒光电极的比表面积较大,导致其暴露更多的反应活性位点;另一方面,WO3-3中的六方晶相和单斜晶相的WO3会形成相结,可以有效地加速光生电子和空穴的定向分离;此外,近垂直于钛基底的纳米棒结构有利于光生电子沿纳米棒的方向的定向传输,使得光生载流子的传输路径变短并减少了光生载流子复合的可能性。

3. 虽然通过形貌调控和元素掺杂后的WO3光电极的光电化学阴极保护性能得到很大提升,但仍然不能实现在纯NaCl溶液中为304 SS提供阴极保护。因此,首先通过在Mo-WO3表面水热生长导带电位较负的CdZnS进行改性。CdZnS的复合可以大大拓宽Mo-WO3/CdZnS光电极的光吸收阈值,使其能吸收太阳光谱中更多的能量。同时,二者间形成的异质结电场可以加速光生载流子分离,使更多的光生电子可以定向的迁移到被保护金属上对其进行阴极保护。此外,CdZnS具有较负的导带电位,有利于光生电子向偶联金属的迁移。因此,Mo-WO3/CdZnS光电极可以实现在纯NaCl溶液的光电化学阴极保护,在模拟太阳光照射下,具有最优性能的Mo-WO3/CdZnS-2光电极可以为304 SS提供约39.5 μA·cm-2的光生电流密度,将其阴极极化334.3 mV

4.由于CdZnS中的Cd元素有毒性,而且CdZnS本身容易发生光腐蚀,因此,进一步选择同样具有较负的导带电位的ZnIn2S4WO3进行改性,并进一步研究了WO3/ZnIn2S4复合光电极的延时阴极保护性能。在WO3/ZnIn2S4复合光电极体系中,外层的ZnIn2S4可以增强光吸收性能,同时,WO3/ZnIn2S4异质结光电极体系的构建大大提高了光生电子空穴对的分离效率,使得其具有优异的光电化学阴极保护性能。具有最优性能的WO3/ZnIn2S4-0.75异质结光电极体系在纯NaCl溶液中可以为偶联的304 SS提供332.8 mV的阴极极化。此外,ZnIn2S4的复合可以在光照下为WO3充电,供其在无光状态下对304 SS进行阴极保护。光照时间为2 h时,WO3/ZnIn2S4-0.75异质结光电极可以储存0.17 C的电量,足够在暗态下为304 SS提供11.88 h的阴极保护,这实现了在暗态下的阴极保护,为光电化学阴极保护技术的实际应用提供了可能性。

5.采用恒电流沉积法通过控制不同的沉积时间在TiO2纳米管表面沉积不同量的Cu2O纳米颗粒制得了Cu2O/TiO2-X 复合材料。研究表明,Cu2O纳米颗粒的沉积不仅可以增加TiO2对可见光的吸收,还可以与TiO2形成异质结,提高光生载流子的分离效率。可见光下的光电化学阴极保护性能表明,沉积不同量的Cu2OCu2O/TiO2-X光电极均可对316 L SS进行阴极保护,而且沉积时间为20 minCu2O/TiO2-20光电极对316 L SS具有最优的光电化学阴极保护性能和最高的光生电流密度,这归因于Cu2OTiO2纳米管之间的p-n异质结间内建电场的建立加速了光生载流子的分离,使更多的光生电子转移到316 L SS上,对316 L SS进行光电化学阴极保护。总之,Cu2O/TiO2是一种可行的可见光驱动光电化学阴极保护复合材料,这将为Cu2O纳米颗粒沉积到纳米管或其它高取向的n型半导体(如WO3ZnO纳米棒)上,以增加光活性位点的数量,进一步增强可见光下的光电化学或光电化学阴极保护性能提供新的思路。

综上所述,通过元素掺杂、形貌调控及相结的构建和复合导带电位较负的半导体等改性策略,达到了拉负WO3的导带电位,加速光生载流子的迁移和分离效率,从而提升光电化学阴极保护性能的目的。同时,通过光照前后的X射线衍射及X射线光电子能谱等研究了WO3/ZnIn2S4复合光电极的延时阴极保护机理,为进一步提升WO3的光电化学阴极保护性能及延时阴极保护性能提供了理论基础,也为光电化学阴极保护技术的实际应用奠定了理论基础。

Other Abstract

In recent years, with the rapid development of China's marine industry, the corrosion of steel materials serving in the marine environment has attracted more and more attention. As a new corrosion protection technology, photoelectrochemical cathodic protection technology has attracted extensive attention. It only needs to use the photoelectric conversion effect of semiconductor under sunlight to transfer the photogenerated electrons excited on the semiconductor to the protected metal, so that the metal can be protected by cathodic polarization. In this process, the semiconductor itself will not be consumed and will not cause harm to the environment. It has the advantages of cleanness, high efficiency and no pollution, and has a very broad application prospect. Tungsten oxide (WO3) is considered as a potential photochemical cathodic protection material because of its high electron mobility, wide light response range, simple preparation method, non-toxic and low cost. However, WO3 has the disadvantages of insufficient reduction ability of photogenerated electrons and low separation efficiency of photogenerated carriers, which greatly limits its application in the field of photoelectrochemical cathodic protection. In this paper, the conduction band potential of WO3 is negatively shifted by doping molybdenum (Mo) to improve the reduction ability of photogenerated electrons of WO3. Then, through the construction of phase junction and the modification of semiconductor materials with negative conduction band potential, the quasi Fermi level of the composite photoelectrode is shifted negatively, the separation of photogenerated carriers is promoted, and finally the photoelectrochemical cathodic protection is provided for the protected metal in NaCl solution. The specific research contents include:

1. Mo doping is used to regulate the energy band of WO3. Mo doping does not change the morphology and light absorption characteristics of WO3, but makes the conduction band of WO3 move negatively, which improves the reduction ability of photogenerated electrons, so as to solve the problem of insufficient reduction ability of photogenerated electrons. At the same time, the doping of Mo greatly improves the conductivity of WO3, which greatly improves the migration ability of photogenerated electrons and the separation ability of photogenerated carriers, thereby increasing its photoelectric conversion efficiency. Therefore, the photochemical cathodic protection performance of 0.3%Mo-WO3 for 304 SS is greatly improved compared with pure WO3, and the photogenerated current density can reach 38.0 μA·cm-2, providing 234.5 mV cathodic polarization for 304 SS.

2. The morphology and crystal phase composition of WO3 were regulated by controlling the amount of sodium tungstate (Na2WO4) in the hydrothermal process. With the increase of Na2WO4, the morphology of WO3 changes from smooth nano sheet structure to porous nanoplate structure, then a porous nanorod structure, and finally a sugar-like structure. At the same time, the proportion of monoclinic phase in mixed phase (hexagonal phase and monoclinic phase) also increases with the increase of Na2WO4. WO3-3 has the best photoelectrochemical cathodic protection performance for 304 SS when the addition amount of Na2WO4 is 0.56 g. It can provide a photoinduced current density of approximately 32.1 μA·cm-2 and a cathodic polarization of approximately 369.1 mV for the 304 SS. The reasons for the improvement of photoelectrochemical cathodic protection performance are as follows: On the one hand, the WO3-3 porous nanorod photocathode has a large specific surface area, which leads to an increase in exposed reactive sites; On the other hand, the hexagonal phase and monoclinic phase of WO3-3 will form a phase junction, which can effectively accelerate the directional separation of photogenerated electrons and holes; In addition, the nanorod structure nearly perpendicular to the titanium (Ti) substrate is conducive to the directional transmission of photogenerated electrons along the nanorod, which shortens the transmission path of photogenerated carriers and reduces the possibility of photogenerated carrier recombination.

3. Although the photoelectrochemical cathodic protection performance of WO3 photoelectrode has been greatly improved through morphology control and Mo element doping, it still can not achieve cathodic protection in pure NaCl solution. Therefore, Mo-WO3 was first modified with CdZnS with a relatively negative conduction band potential. The recombination of CdZnS can greatly broaden the light absorption threshold of Mo-WO3/CdZnS photoelectrode, so that it can absorb more energy in the solar spectrum. At the same time, the heterojunction electric field formed between them can accelerate the separation of photogenerated carriers, so that more photogenerated electrons can migrate to the protected metal for cathodic protection. In addition, CdZnS has a negative conduction band potential, which is conducive to the migration of photogenerated electrons to coupling metals. Therefore, Mo-WO3/CdZnS photoelectrode can realize photoelectrochemical cathodic protection in pure NaCl solution. Under simulated sunlight irradiation, Mo-WO3/CdZnS-2 photoelectrode with optimal performance can provide a photogenerated current density of about 39.5 μA cm-2 to coupled 304 SS and the supplied electrons will achieve approximately 334.3 mV cathodic polarization for 304 SS.

4. Because the toxic and photocorrosion prosperities of Cd element in CdZnS, ZnIn2S4 with negative conduction band potential is further selected to modify WO3, and the time-delay cathodic protection performance of WO3/ZnIn2S4 composite photoelectrode is further studied. The outer layer of ZnIn2S4 can enhance the light absorption performance. At the same time, the construction of the WO3/ZnIn2S4 heterojunction system greatly improves the separation efficiency of photogenerated electron-hole pairs, making it have excellent photoelectrochemical cathodic protection performance. When the WO3/ZnIn2S4 heterojunction system is coupled with the 304 SS electrode, the photoinduced potential drop in NaCl solution can reach 332.8 mV without adding any hole scavenger, which is significantly better than those of the single WO3 and single ZnIn2S4 photoelectrodes. At the same time, compounding ZnIn2S4 on WO3 can charge WO3 under light illumination, so that the WO3/ZnIn2S4 composite system can continue to provide cathodic protection for the coupled 304 SS after switching off the light. When the light illumination time is 2 h, the WO3/ZnIn2S4 heterojunction photoelectrode can store 0.17 C electrons, which is enough to provide the coupled 304 SS for 11.88 h of CP in the dark state after switching off the light, which realizes the continuous cathodic protection for the whole night in the dark. The design and fabrication of the WO3/ZnIn2S4 heterojunction photoelectrode provide the feasibility for the application of the photoelectrochemical cathodic protection technology.

5. Cu2O/TiO2-X composites were prepared by galvanostatic deposition method to deposit different amounts of Cu2O nanoparticles on the surface of TiO2 nanotubes by controlling different deposition time. The deposition of Cu2O nanoparticles can not only increase the absorption of visible light of TiO2, but also form a heterojunction with TiO2 to improve the separation efficiency of photogenerated carriers. The photoelectrochemical cathodic protection performance under visible light indicates that the Cu2O/TiO2-X photoelectrode deposited with different amounts of Cu2O can protect 316 L SS from corroded, and the Cu2O/TiO2-20 photoelectrode has the best photoelectrochemical cathodic protection performance and the highest photocurrent density, which is attributed to the establishment of the built-in electric field between the p-type Cu2O and n-type TiO2 that accelerates the separation of photogenerated carriers and makes more photogenerated electrons transferred to 316 L SS for photoelectrochemical cathodic protection. In summary, Cu2O/TiO2 is a feasible visible light-driven photoelectrochemical cathodic protection composite that will provide a new idea for the deposition of Cu2O nanoparticles onto nanotubes or other highly oriented n-type semiconductors (such as WO3 or ZnO nanorods) to increase the number of photoactive sites and further enhance the photoelectrochemical or photoelectrochemical cathodic protection performance under visible light illumination.

In summary, the energy band structure of WO3 is regulated by the above energy band regulation methods, so as to pull the conduction band potential of WO3 negative, accelerate the migration and separation efficiency of photogenerated carriers, and improve the performance of photoelectrochemical cathodic protection. At the same time, the time-delay protection mechanism of WO3/ZnIn2S4 composite photoelectrode is studied by X-ray diffraction and X-ray photoelectron spectroscopy before and after illumination, which not only provides a theoretical basis for further improving the photoelectrochemical cathodic protection performance and time-delay cathodic protection performance of WO3, but also lays a theoretical foundation for the practical application of photoelectrochemical cathodic protection technology.

Subject Area海洋科学
MOST Discipline Catalogue理学 ; 理学::化学 ; 理学::海洋科学
Language中文
Table of Contents

1 绪论... 1

1.1 引言... 1

1.2 金属防腐蚀技术... 1

1.2.1 涂层保护法... 2

1.2.2 阳极保护法... 2

1.2.3 阴极保护法... 2

1.2.4 缓蚀剂保护法... 3

1.3 光电化学阴极保护技术... 3

1.3.1 光电化学阴极保护技术的定义... 3

1.3.2 光电化学阴极保护技术的原理... 3

1.3.3 光电化学阴极保护技术的影响因素... 4

1.4 光电化学阴极保护研究进展... 5

1.4.1 TiO2材料在光电化学阴极保护领域的研究进展... 5

1.4.2 SrTiO3材料在光电化学阴极保护领域的研究进展... 8

1.4.3 ZnO材料在光电化学阴极保护领域的研究进展... 8

1.4.4 g-C3N4材料在光电化学阴极保护领域的研究进展... 9

1.5 WO3纳米材料研究进展... 10

1.5.1 形貌调控... 10

1.5.2 元素掺杂... 11

1.5.3 半导体复合... 12

1.6 选题意义及研究内容... 13

1.6.1 选题意义... 13

1.6.2 研究内容... 14

2 Mo-WO3光电极的制备及光电化学阴极保护性能的研究... 17

2.1 引言... 17

2.2 材料与方法... 18

2.2.1 材料与试剂... 18

2.2.2 仪器与设备... 19

2.2.3 材料制备... 19

2.2.4 材料的表征... 20

2.2.5 光电化学阴极保护性能的测试... 20

2.2.6 光电化学性能的测试... 21

2.3 结果与讨论... 21

2.3.1 化学组成、形貌和光吸收性能分析... 21

2.3.2 光电化学阴极保护性能分析... 24

2.3.3 光电化学性能和电化学性能分析... 26

2.3.4 光电化学阴极保护性能提升的机制分析... 28

2.4 本章小结... 29

3 双相WO3纳米棒光电极的制备及其光电化学阴极保护性能的研究... 31

3.1 引言... 31

3.2 材料与方法... 31

3.2.1 材料与试剂... 32

3.2.2 仪器与设备... 32

3.2.3 材料制备... 33

3.2.4 材料的表征... 33

3.2.5 光电化学阴极保护性能的测试... 33

3.2.6 光电化学性能和电化学性能的测试... 34

3.3 结果与讨论... 34

3.3.1 化学组成、形貌和光吸收性能分析... 34

3.3.2 光电化学阴极保护性能分析... 37

3.3.3 光电化学性能和电化学性能分析... 38

3.3.4 光电化学阴极保护性能提升的机制分析... 39

3.4 本章小结... 40

4 Mo-WO3/CdZnS的异质结的制备及光电化学阴极保护性能的研究... 43

4.1 引言... 43

4.2 材料与方法... 44

4.2.1 材料与试剂... 44

4.2.2 仪器与设备... 44

4.2.3 材料制备... 45

4.2.4 材料的表征... 46

4.2.5 光电化学阴极保护性能的测试... 46

4.2.6 光电化学性能和电化学性能的测试... 46

4.3 结果与讨论... 47

4.3.1 化学组成、形貌和光吸收性能分析... 47

4.3.2 光电化学阴极保护性能分析... 50

4.3.3 光电化学性能和电化学性能分析... 52

4.3.4 光电化学阴极保护性能提升的机制分析... 54

4. 4 本章小结... 56

5 WO3/ZnIn2S4异质结的制备及其光电化学阴极保护性能及储电性能的研究    57

5.1 引言... 57

5.2 材料与方法... 58

5.2.1 材料与试剂... 58

5.2.2 仪器与设备... 59

5.2.3 材料制备... 60

5.2.4 材料的表征... 61

5.2.5 光电化学阴极保护性能的测试... 62

5.2.6 光电化学性能和电化学性能的测试... 62

5.3 结果与讨论... 62

5.3.1 化学组成、形貌和光吸收性能分析... 62

5.3.2 光电化学阴极保护性能分析... 68

5.3.3 光电化学性能和电化学性能分析... 71

5.3.4 储电性的分析... 75

5.3.5 光电化学阴极保护性能提升的机制分析... 77

5.4 本章小结... 81

6 Cu2O/TiO2 p-n异质结的制备及其光电化学阴极保护性能的研究... 83

6.1 引言... 83

6.2 材料与方法... 84

6.2.1 材料与试剂... 84

6.2.2 仪器与设备... 85

6.2.3 材料制备... 85

6.2.4 材料的表征... 87

6.2.5 光电化学阴极保护性能的测试... 87

6.2.6 光电化学性能和电化学性能的测试... 87

6.3 结果与讨论... 88

6.3.1 化学组成、形貌和光吸收性能分析... 88

6.3.2 光电化学阴极保护性能分析... 93

6.3.3 光电化学性能和电化学性能分析... 96

6.3.4 光电化学阴极保护性能提升的机制分析... 99

6.4 本章小结... 100

7 结论及展望... 101

7.1 结论... 101

7.2 创新点... 102

7.3 展望... 103

参考文献... 105

  ... 117

作者简历及攻读学位期间发表的学术论文与研究成果... 119

 

Document Type学位论文
Identifierhttp://ir.qdio.ac.cn/handle/337002/177040
Collection中国科学院海洋研究所
Recommended Citation
GB/T 7714
田景. WO3的能带调控与改性及其光电化学阴极保护性能的研究[D]. 中国科学院海洋研究所. 中国科学院大学,2021.
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