【作者】 陈硕；

【导师】 刘小鹤；

【作者基本信息】 中南大学 ， 材料科学与工程， 2023， 硕士

【摘要】 面对日益严峻的能源危机和环境污染的挑战,推进氢能高质量发展有重要意义。电化学制氢被认为理想的制氢途径,高活性水分解催化剂是实现其工业化的关键。目前,商用的阳极析氧（Oxygen evolution reaction,OER）催化剂和阴极析氢（Hydrogen evolution reaction,HER）催化剂多以贵金属为主,高昂的价格和较低的平均丰度限制了其大规模应用。相比之下,过渡金属催化剂凭借其能带结构合适、电子结构易调控、成本低廉等优点,在能源转化领域扮演着重要角色,然而由于电荷转移电阻等不利因素的存在,往往需要较高的过电位来克服能量转移壁垒,另外,过渡金属催化剂的稳定性相对贵金属也较差。鉴于此,本论文以过渡金属纳米催化剂为研究对象,采取了多种策略,包括稀土元素掺杂、相变调控、贵金属与过渡金属复合、调控活性位点电荷分布、优化表面重构过程策略等,成功制备了三种高效的电催化水分解催化剂,并探究其催化性能增强机理。具体研究内容如下:（1）稀土元素掺杂调节活性位点的电子结构。为了实现对Ni Fe催化体系的电子调控,将稀土元素富含空轨道的Ce引入到柠檬酸根插层的Ni Fe层状氢氧化物中。柠檬酸根的引入导致材料呈现多孔自支撑的纳米结构,更多的活性位点被暴露处出来。电子结构表征和理论计算结果表明Ce掺杂通过3d-4f作用调节了Ni、Fe原子周围的电荷分布,优化了OER过程中不同中间体的吸附能。当体系Ni:Fe:Ce的摩尔比例为2:0.7:0.3时,催化剂表现出最佳的OER性能,电流密度达到20 m A cm^-2时所需的过电位仅为224 m V,在100 m A cm^-2的电流密度下,负载催化剂的电极可以稳定运行160 h以上。（2）控制硒化物的相变过程进而优化表面重构过程。为了实现对材料体相结构的调控,将Fe原子引入到正交相Co Se₂,造成材料局部的晶格畸变,实现了从正交相到立方相的转变。通过对材料的体相和电子结构进行表征,发现在阳极电流下,Fe掺杂的立方相Co Se₂更容易在其表面形成具有一定厚度的活性（氧）氢氧化物层,并且Fe会迁移至催化剂表面参与活性层的形成。Fe掺杂立方相Co Se₂达到10 m A cm^-2时所需的过电位仅为254.7 m V,Tafel斜率仅仅为48.0 m V dec^-1,与铁掺杂正交相Co Se₂以及单一正交相的Co Se₂相比,分别降低了66.9 m V和79.9 m V,同时Fe掺杂的立方相Co Se₂表现出更加优异的稳定性。（3）构造贵金属与过渡金属异质结构。为了降低催化剂的成本同时实现催化剂的双功能,本章将少量的Ru引入Co氢氧化物纳米片中,随后制备了双金属磷化物纳米片。通过对其进行详细的表征,发现了体相结构、电子结构随温度变化的规律,提出了Co和Ru与非金属元素P结合时存在一定的竞争关系。电化学测试表明催化剂的析氢性能与材料电子结构存在很强的相关性,在双金属体系中,Co-P键在400℃时强度较弱,电流密度达到10 m A cm^-2时所需过电位仅为54.2 m V,这与工业Pt/C催化剂活性相当。同时,双金属磷化物纳米片也显示出优异的OER活性,用作全水解催化剂时,电流密度为20 m A cm^-2时,所需电位仅为1.55 V。更多还原

【Abstract】 In the context of increasingly severe energy crises and environmental pollution,the high-quality development of hydrogen energy is of great significance.Electrocatalytic hydrogen production is considered as an ideal way of hydrogen production.High-activity water splitting catalysts are crucial for industrialization.Currently,commercial anode and cathode catalysts are mainly based on precious metals,whose high price and low average abundance limit their large-scale application.Transition metal catalysts play an important role in energy conversion due to their suitable band structure,flexible electronic structure,and low cost.However,due to the charge transfer resistance,a large overpotential is often required to overcome the energy transfer barrier.Additionally,the stability of transition metal catalysts is relatively poor compared to precious ones.Accordingly,this thesis takes transition metal nanocatalysts as the research object.Several strategies were taken to enhance water splitting ability,such as rare earth element doping,optimizing phase transition,integrating precious and transition metals,turning charge redistribution,and regulating the surface reconstruction process.Three efficient electrocatalysts were prepared for water splitting,of which corresponding performance enhancement mechanisms were investigated.The specific research content is as follows:（1）Rare earth doping modulates the electronic structure of the active site.To optimize the electronic structure of the Ni Fe-base catalysts,the rare earth element Ce was introduced into the Ni Fe layer double hydroxide with interlayer citrate.Thanks to the introduction of citrate,catalysts exhibit porous,self-supporting nanostructure with significant active sites.Electronic structure characterization and theoretical calculations illustrate that the doped Ce could modify the charge redistribution around Ni and Fe atoms through the 3d-4f interaction mechanism.The ideal electronic structure optimizes the adsorption and desorption energy of the intermediate during the OER process.When the molar ratio of Ni:Fe:Ce was 2:0.7:0.3,the catalyst showed the best OER performance,with an overpotential of 224 m V at the current density of 20 m A cm^-2.More importantly,the catalyst possessed outstanding durability with more than160 hours at the high current density of 100 m A cm^-2.（2）Controlling the phase structures of selenide and optimizing the surface reconstruction process.In order to tune the bulk structure of selenide,we introduced Fe atoms into orthorhombic Co Se₂,which causes local lattice distortion and finally results in a phase transition from orthorhombic to cubic.Phase and electronic structure characterizations exhibit that,under anodic current,Fe-doped cubic Co Se₂ will be prone to forming an active（oxy）hydroxide layer with a certain thickness.Fe atoms will migrate to the catalyst surface and participate in the formation of the active layer.Fe-doped cubic Co Se₂ exhibited outstanding OER activity with an overpotential of 254.7 m V at the current density of 10 m A cm^-2,which was smaller by 66.9 m V and 79.9 m V than that of Fe-doped orthorhombic Co Se₂ and pristine orthorhombic Co Se₂ respectively.The Tafel slope of Fe-doped cubic Co Se₂ was just 48.0 m V dec^-1.Furthermore,Fe-doped cubic Co Se₂ demonstrated superior stability.（3）Constructing heterostructures between noble and transition metals.A small amount of Ru was introduced into Co hydroxide nanosheets to reduce the cost of ingredients and obtain bifunctional catalysts,and then bimetallic phosphide nanosheets were prepared.Phase and electronic structure characterizations reveal the regulations of phase transition evolution along with temperature and the electronic structure.We suggest there is a competitive relationship between Co and Ru bonding with the non-metallic element P.The HER performance of the catalyst is strongly related to its electronic structure.In this bimetallic system,the Co-P bond was weakest at 400℃.At this temperature,the nanosheets only needed a small overpotential of 54.2 m V to achieve a current density of 10 m A cm^-2,which was equivalent to the activity of industrial Pt/C catalyst.At the same time,bimetallic phosphide nanosheets showed excellent OER performance.When it was used as an overall water splitting catalyst,the electrolytic cell needed a potential of 1.55 V at a current density of 20 m A cm^-2.更多还原