【作者】 李波；

【导师】 徐航勋；

【作者基本信息】 中国科学技术大学 ， 高分子化学与物理， 2017， 博士

【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。更多还原

【Abstract】 Efficient and durable oxygen evolution electrocatalysts are necessary for a wide range of clean energy technologies,with RuO2 and IrO2 as benchmark catalysts.However,RuO2 and IrO2 catalysts suffer from their high costs and instability,so nonprecious metal oxygen evolution electrocatalysts have been developed,such as Ni-,Fe-or Co-based oxides.It’s important to explore various methods to enhance catalytic performance with Ni-,Fe-and Co-based structures as model.The key to efficient and durable oxygen evolution electrocatalysts is abundant catalytic active sites,superior conductivity and stable catalytic active structure.Based on this design key,this thesis mainly focuses on:1.Efficient and durable amorphous NiFeOx/C oxygen evolution electrocatalysts synthesized by a sonochemical method.Amorphous catalysts are a series of less studied catalysts.However,amorphous materials feature in homegeneously dispersed compositions and abundant defects,which are beneficial as oxygen evolution electrocatalysts.That is to say,compared with crystalline catalysts,amorphous catalysts usually possess more catalytic active sites.It’s reported that amorphous catalysts generally possess superior catalytic performance when compared with their crystalline counterparts.However,amorphous catalysts usually suffer low conductivity and unstable structures,which are unfavourable to electocatalysis.Moreover,preparation methods for amorphous electrocatalysts are rather limited.Herein,we find that the feature of somochemistry enables it a convinient method for preparing amorphous NiFeOx/C hybrid oxygen evolution electrocatalysts with tunable compositions.The products not only exhibit prominent OER performance(including activity and stability),but also circumvent demerits of amorphous catalyst——low conductivity and instability.Synchrotron-based X-ray characterizations reveal that superior activities arise from abundant oxygen vacancies,cooperatively unsaturated metal sites,efficient charge transfer induced by homegeneously dispersed Ni/Fe,inner Ni(0)and simultaneously formed carbon scaffold.2.Unique Co4+-containing layered sodium cobaltatc oxygen evolution elcctrocatalysts.Co4+ is reported to be the real active site for Co-based oxygen evolution elcctrocatalysts.Soime studies revealed that increasing Co4+ contents in electrocatalysts can enhance their calalytic activities.However,pure Co4+ is unstable,and the absorption energy of O-containing intermediates is not optium when bound to a pure Co4+ site.So exploring mixed-valent Co-based electrocatalysts containing more and stable Co4+ should be a better way.Moreover,electronic properties can influence catalytic performance.Herein,a facile oxidation of layered sodium cobaltates,maintaing layered structure and stable Co4+,can synergistically enhance oxygen evolution activities through dual engineering of electronic properties including oxidation state,oxygen vacancies,conductivity,Co-O covalency.Synchrotron-based X-ray characterizations reveal that enhanced Co-O covalency and conductivity are the keys to superior oxygen evolution activities.3.HCl oxidative etching method can tune the size of metal nanocrystals with unchanged shapes and further tune their size-dependent plasmonic and catalytic properties.The effects of HC1 oxidative etching include removing twinned seeds and oxidizing metal atoms back to ions so as to decrease the reduction rate of metal ions,thus tuning the size of metal nanocrystals kinetically.This study provides a versatile,simple and effective method for size control of metal nanocrystals.更多还原