【作者】 王杨；

【导师】 邓意达；

【作者基本信息】 天津大学 ， 材料科学与工程， 2022， 博士

【摘要】 随着经济的发展和对能源需要的不断增加,导致了严重的能源和环境问题,驱使着人们不断寻求绿色可持续发展能源。氢能来源广泛、高能量密度和零污染等优点,被认为是最有应用前景的能源之一。电解水制氢具有高纯、高效和绿色环保等优势,因此受到广泛关注。析氧（oxygen evolution reaction,OER）和析氢（hydrogen evolution reaction,HER）是电解水制氢的两个半反应,但因其受反应动力学的限制而导致能源大量损耗。目前,常用的电解水制氢催化剂有Ir O₂、Ru O₂和Pt/C,但由于受到储量低、成本高和稳定性差等因素影响,限制其产业化应用。过渡金属硫族化合物（transition metal dichalcogenides,TMDs）具有储量丰富、成本低和结构稳定等特点,成为电解水产氢催化剂的研究热点。然而,TMDs催化剂在电解水反应过程中具有较大的活化能垒,严重的限制其催化活性。提高催化剂电催化活性的主要途径为增加催化剂活性位点数目和提高催化剂活性位点的本征活性。因此,本论文以TMDs为基础,通过调控催化材料的应变、单原子掺杂和非晶相等三个方面,改变材料的电子结构和配位环境,实现增加活性位点数目和优化本征活性的目的,提升TMDs电催化性能,并对其催化性能的提升机理进行分析与讨论。首先,通过一步水热法合成晶格应变参数可控且不引入其他因素（如异质结构、空位或基底）的TMDs,用于揭示应变对TMDs电子结构和催化性能的影响。分析表明,晶格应变可导致金属d电子态的重叠减小,d带变窄和d带中心更靠近费米能级。晶格应变约为2.7%的NiS_0.5Se_0.5纳米片@纳米棒(NiS_0.5Se_0.5)表现出良好的H吸附能,同时具有较低的OER决速步能垒。实验结果表明,NiS_0.5Se_0.5表现出优异的HER和OER双功能催化性能,呈现出低的过电位和优异的稳定性。尤其在大电流密度下,连续催化反应300 h仍未出现明显衰减,优于贵金属催化剂。其次,利用简单的一步水热法制备了一种W单原子掺杂NiS_0.5Se_0.5纳米片@NiS_0.5Se_0.5纳米棒(W-NiS_0.5Se_0.5)电催化剂,用于深入研究单原子掺杂对金属活性位的影响和相关电催化性能的提升机制。研究结果表明,W单原子掺杂导致Ni原子的自旋离域,增加Ni的d电子态密度,增强水吸附能,降低水解能垒,优化H吸附动力学,降低OER决速步（O*→OOH*）自由能。电化学测试表明,W-NiS_0.5Se_0.5表现出优异的HER和OER催化性能,超低的过电位和超高的稳定性,其催化活性和稳定性均优于商业贵金属和多数过渡金属化合物（transition metal compounds,TMCs）催化剂。最后,采用调控还原剂法合成了一种Mo-NiS_0.5Se_0.5非晶纳米片@NiS_0.5Se_0.5纳米棒(Am-Mo-NiS_0.5Se_0.5)电催化剂,用于揭示非晶相对TMDs电子结构的影戏和催化性能增强机理。实验和DFT计算结果表明,非晶结构致使Am-Mo-NiS_0.5Se_0.5存在高密度的缺陷,改变金属原子的局部电子结构,增加Ni周围的电子态密度,增强水吸附能,优化H的吸附/脱附能,降低了OER决速步能垒。Am-Mo-NiS_0.5Se_0.5在中性电解液中表现出优异的HER/OER双功能催化活性,具有超低的过电位和超长的稳定性,优于商业贵金属和多数文献报道的TMCs电催化剂。本工作研究表明,通过对催化材料应变、单原子掺杂和非晶相等三方面的调控,能够显著优化TMDs催化材料的电子结构和HER/OER吸附能,增加活性位点数目和优化本征活性,提高其催化活性和稳定性,为设计高效稳定的TMDs催化材料提供理论参考和实验依据。更多还原

【Abstract】 With the development of economy and the increasing demand for energy,serious energy and environmental problems have been caused,driving people to seek green and sustainable energy.Hydrogen is considered as one of the most promising energy sources due to its wide source,high energy density and no pollution.Electrocatalytic water splitting has been given much attention in hydrogen generation due to its high conversion efficiency,environmentally friendly and high purity hydrogen production.In the process of electrocatalytic water splitting,there are two reactions:oxygen evolution and hydrogen evolution reaction（OER/HER）,which are limited by reaction kinematics and cause great energy wasting.Ir O₂,Ru O₂ and Pt/C are the benchmark catalysts for water electrolysis,but their large-scale applications are limited by their earth scarcity,high cost and poor stability.Transition metal dichalcogenides（TMDs）have become a hot topic in the field of electrocatalysis OER/HER due to their rich resources,low cost and stable structure.However,TMDs catalyst has a large activation energy barrier during water electrolysis,which severely limits its catalytic activity.Increasing the number of active sites and the intrinsic activity of active sites are two of the most effective strategies to improve the electrocatalytic activities.This thesis focuses on improving the electrocatalytic performances of TMDs by regulating the strain,doping single-atom,and amorphous of the catalytic material,which will modify the electronic structure and coordination environments of the material,increase the active sites and optimize the intrinsic activity of catalytic sites,thus improve the electrocatalytic performance of TMDs.The enhancement mechanism of the electrocatalytic performance are analyzed and discussed.Firstly,in order to further clarify the effect of lattice strain on the catalytic performance and electronic structure of TMDs,we synthesized TMDs with one step hydrothermal method,which has tunable lattice strain without introducing other factors（such as heterostructure,vacancy,and substrate）.The analyses showed that the lattice strain decreased the metal d-orbital overlap,leading to a narrower bandwidth and a closer d-band center towards the Fermi level.The NiS_0.5Se_0.5 nanosheet@nanorod(NiS_0.5Se_0.5)sample with a lattice strain of～2.7%exhibits favorable H*adsorption kinetics for HER and lower rate-determining step energy barriers for OER.The experiment result shows that NiS_0.5Se_0.5 exhibits efficient bifunctional activity for HER/OER,presenting ultral-low overpotential and outstanding long-term durability.Specialy,at high current density,there is no obvious attenuation after 300 h reaction,which is much better than noble metal catalysts.Secondly,we prepared a W single-atoms doped NiS_0.5Se_0.5 nanosheet@NiS_0.5Se_0.5nanorod(W-NiS_0.5Se_0.5),which is used to study the impact of single atom doping on metal active sites and the improvement mechanism of related electrocatalytic performance.Experimental results show that the single-atom W doping would lead to the delocalization of Ni spin states,which increases the Ni d-electronic states,enhances the water adsorption energy,reduces water splitting barrier,optimizes H*adsorption kinetics,significantly reducing the energy barrier for the rate-determining step（O*→OOH*）of OER.Electrochemical results show that W-Nis_0.5Se_0.5exhibits superior catalytic activity for HER and OER with an ultralow overpotential and excellent long-term durability,superior to commercial noble metal catalysts and transition metal compounds（TMCs）catalysts reported in most literatures.Finally,Mo-NiS_0.5Se_0.5 nanosheet@NiS_0.5Se_0.5 nanorod(Am-Mo-NiS_0.5Se_0.5)was synthesized by regulating reducing agent,so as to reveal the influence of amorphous on the electronic structure and the enhancement mechanism of catalytic performance.Experiment and DFT calculations results show that amorphous structure results in high density defect of Am-Mo-NiS_0.5Se_0.5,modifying the local electronic structure of the metal atom,increasing the electron state density of Ni and strengthening the water molecule binding energy,optimizing H adsorption/desorption energy,reducing the adsorption energy of OER determining step.Am-Mo-NiS_0.5Se_0.5 exhibits excellent bi-functional HER/OER catalytic activity in neutral electrolytes,with ultralow overpotential and favorable stability,which are highly superior to commercial noble metal catalysts and many reported TMCs catalysts.This study shows that regulating the lattice strain,doping single-atom,and amorphous can optimize the electronic structure and OER/HER free energy of TMDs catalyst,increase the number of active sites and optimize the intrinsic activity,thus improve the catalytic performance,which provides theoretical reference and experimental basis for the design of efficient and stable TMDs catalytic materials.更多还原