非贵金属氧化物的设计、合成与电催化析氧反应研究

发布时间：2017-12-27 22:31

本文关键词：非贵金属氧化物的设计、合成与电催化析氧反应研究　出处：《中国科学技术大学》2017年博士论文　论文类型：学位论文

【摘要】：广泛的清洁能源技术需要高效、耐用的析氧反应电催化剂,其中以RuO2和IrO2为代表。但RuO2和IrO2具有昂贵和不稳定的缺点,因此非贵金属析氧反应电催化剂受到重视和发展,如基于镍、铁、钴的氧化物。以这三种过渡金属为模型,探索增强析氧反应电催化剂性能的方法,十分重要。而设计高效、耐用的析氧反应电催化剂的关键原则在于大量的活性位点、优异的导电性以及稳定的催化活性结构。围绕以上几点设计原则,本文的主要研究内容如下:1、超声化学法合成的高效、耐用的非晶镍铁氧化物/碳杂化析氧反应电催化剂。非晶催化剂是一类研究较少的催化剂。但非晶材料具有成分分布均匀、缺陷多等特点,作为析氧反应电催化剂十分有利。即非晶催化剂与对应的晶体催化剂相比,具有更多的催化活性位点。据报道,与晶体催化剂相比,非晶催化剂通常拥有更好的催化性能。然而,非晶催化剂一般导电性差,结构也不稳定,对电催化不利。而且非晶电催化剂的制备方法十分有限。有鉴于此,我们发现,超声化学的特点使其可以用来制备组成可调控的非晶镍铁氧化物/碳杂化析氧反应电催化剂。产物不仅具有优异的析氧反应性能(包括催化活性与稳定性),而且在一定程度上克服了非晶催化剂导电性差和不稳定的缺点。基于同步辐射的X射线表征揭示了,非晶镍铁氧化物/碳杂化催化剂中,优异的性能来自于其中大量的氧空位、金属配位不饱和位点、均相分散的镍与铁带来的高效电荷传递、内部的镍单质以及同时形成的碳骨架。2、独特的含有高价态Co4+的层状钴酸钠析氧反应电催化剂。Co4+据报道是钴基析氧反应电催化剂真正的活性位点。有研究表明,增加催化剂中Co4+的含量可以提高其催化活性。但纯Co4+不稳定,而且理论计算研究表明Co4+在OER中并不具有最优的吸附能。因此开发含有较多稳定的Co4+的混合价态钴基电催化剂应该是一种较好的方式。另外,电子性质可以影响催化剂的性能。本文通过对一种层状钴酸钠进行简单的氧化,在保持层状结构不变和高价态Co4+相对稳定的情况下,同时实现了对多种电子性质包括氧化态、氧空位、导电性、钴氧共价性的调控,从而协同增强了析氧反应活性。基于同步辐射的X射线表征揭示了,层状钴酸钠中钴氧共价性的增强和导电性的提高是提升钴酸钠析氧反应催化活性的关键。3、盐酸氧化刻蚀法可以在保持金属纳米晶体外形不变的情况下,实现其尺寸调控,从而进一步调控其尺寸依赖的表面等离激元及催化性质。盐酸氧化刻蚀的作用包括去除孪晶晶种和将金属原子氧化回离子以降低离子的还原速率,从而在动力学上实现对金属纳米晶体的尺寸调控。这为调控金属纳米晶体的尺寸提供了一种通用、简单、有效的方法。
[Abstract]:A wide range of clean energy technologies require an efficient and durable electrocatalyst for oxygen evolution reaction, which is represented by RuO2 and IrO2. However, RuO2 and IrO2 are expensive and unstable. Therefore, the electrocatalysts for non noble metal oxygen evolution have been emphasized and developed, such as oxides based on nickel, iron and cobalt. Taking these three transition metals as the model, it is very important to explore the method of enhancing the performance of the electrocatalyst for the enhanced oxygen evolution reaction. The key principles of designing highly effective and durable oxygen evolution reaction electrocatalysts are large number of active sites, excellent electrical conductivity and stable catalytic activity. Based on the above design principles, the main contents of this paper are as follows: 1. An efficient and durable amorphous nickel iron oxide / carbon hybrid oxygen evolution electrocatalyst synthesized by sonochemical method. Amorphous catalyst is a kind of less research catalyst. However, the amorphous material has the characteristics of homogeneous distribution and many defects. It is very beneficial to be used as an electrocatalyst for oxygen evolution reaction. That is, the amorphous catalyst has more catalytic activity sites than the corresponding crystal catalyst. It is reported that the amorphous catalyst usually has better catalytic performance compared with the crystal catalyst. However, the amorphous catalyst is generally poor in electrical conductivity, and the structure is unstable, which is unfavorable to electrocatalysis. Moreover, the preparation method of the amorphous electrocatalyst is very limited. In view of this, we found that the characteristics of ultrasonic chemistry can be used to prepare a controllable amorphous nickel iron oxide / carbon hybrid oxygen evolution electrocatalyst. The product not only has excellent oxygen evolution performance (including catalytic activity and stability), but also overcomes the shortcomings of poor conductivity and instability of amorphous catalyst to a certain extent. X - ray characterization based on synchrotron radiation reveals that amorphous iron nickel oxide / carbon hybrid catalyst, excellent performance from the high nickel and iron charged oxygen vacancy, a large number of metal coordination sites, unsaturated homogeneous dispersion of the transmission, the Ni internal and with the formation of the carbon skeleton. 2. A unique electrocatalyst with a high valence state of Co4+ in the stratified sodium cobalt acid oxygen evolution reaction. Co4+ is reported to be the real active site of the Co based oxygen evolution electrocatalyst. Some studies have shown that increasing the content of Co4+ in the catalyst can increase the catalytic activity of the catalyst. But the pure Co4+ is unstable, and the theoretical calculation shows that Co4+ does not have the best adsorption energy in OER. Therefore, it should be a better way to develop a mixed valence cobalt based electrocatalyst containing more stable Co4+. In addition, the properties of the catalyst can be affected by the electronic properties. Based on the simple oxidation of a layered cobalt acid sodium in the lamellar structure remains unchanged and valence Co4+ is relatively stable, while achieving the regulation of oxidation state, including oxygen vacancies, conductivity, cobalt oxide covalency for various electronic properties, thus synergistically enhanced the oxygen evolution reaction activity. The X ray characterization based on synchrotron radiation reveals that the enhancement of covalence and the conductivity of cobalt oxide in layered sodium carbonate is the key to enhance the catalytic activity of sodium cobaltate in oxygen evolution reaction. 3, HCl oxidation etching can keep the size of metal nanocrystal unchanged, and further regulate its size dependent surface plasmon and catalytic properties. The role of hydrochloric acid oxidation etching includes removing twin crystal seeds and oxidizing metal atoms back to ions to reduce the reduction rate of ions, thus realizing the size control of metal nanocrystals in dynamics. This provides a general, simple and effective method for the control of the size of metal nanocrystals.
【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O643.36

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