【作者】 李晓敏；

【导师】 许春建；

【作者基本信息】 天津大学 ， 化学工程与技术， 2022， 硕士

【摘要】 随着能源危机以及环境问题的日益加重,可再生清洁能源的开发、储存与转化成为目前全球关注的焦点。氢气作为具有最高质量能量密度的清洁能源,其制备方式成为研究重点。其中,电解水制氢被认为是生产高纯度氢气的有效途径之一,然而该技术存在的高成本以及低效率等问题阻碍了其大规模应用。不仅如此,相较于析氢反应（HER）,涉及四电子转移过程的析氧反应（OER）的动力学更加迟缓,导致电解水过程的能耗较高。因此,设计高活性的OER以及HER催化剂可以促进电解水制氢的发展与应用。本文提出了一个简便的策略制备富硫缺陷的尖晶石Co₃S₄催化剂,探究了合成催化材料的OER和HER的催化活性,并重点研究了缺陷浓度对其电化学性能的贡献。本文以空心结构的尖晶石Co₃O₄为前躯体,利用热解硫脲产生的H₂S的还原性与阴离子交换能力,制备出由富硫缺陷的尖晶石Co₃S₄纳米颗粒构建的空心十二面体（H-V_S-Co₃S₄）。通过对合成材料的形态、组成和电子结构进行系列表征测试,结果表明在H₂S气氛中阴离子交换和缺陷引入可以同时完成,并且调节硫脲的剂量可以控制引入硫缺陷的浓度。随着硫缺陷浓度逐渐增加,H-V_S-Co₃S₄系列样品的电子离域程度增强。不仅如此,硫缺陷引入会使部分Co³⁺价态降低以平衡表面缺陷的产生,进而暴露出更多的Co²⁺位点。本文通过一系列电化学测试对合成材料进行了催化性能的研究,结果表明H-V_S-Co₃S₄系列样品在1.0M KOH条件下对OER以及HER均表现出优异的催化活性。针对OER过程,具有合理硫缺陷浓度的H-V_S-Co₃S₄样品仅需要270 m V的低过电位(在10 m A cm^-2下)和59 m V dec^-1的低Tafel斜率。针对HER过程,此样品需要290 m V的过电位(在-10 m A cm^-2下)和56 m V dec^-1的Tafel斜率。对合成样品的结构与电催化性能建立联系发现,H-V_S-Co₃S₄系列样品的电子离域程度的提高降低了电荷转移阻力,提高了电荷转移速率,促进了OER和HER过程。此外,经过OER预氧化过程,H-V_S-Co₃S₄系列样品发生了结构重构,并且引入硫缺陷而暴露的Co²⁺转换为更多利于OER的高价Co³⁺活性位点,使得具有合理硫缺陷的H-V_S-Co₃S₄样品展现出优于商用催化剂（Ru O₂）的催化活性。更多还原

【Abstract】 The development,storage and conversion of renewable and clean energy sources is the focus of global attention with the increasing energy crisis and environmental problems.Hydrogen acts as a clean energy with the highest mass energy density,and the preparation has been the important topic of research.Among them,electrochemical water splitting is considered as one of the most efficient ways to produce high-purity hydrogen,however,the high cost and low efficiency of this technology hinder the large-scale application.In addition,compared to hydrogen evolution reaction（HER）,the kinetics of the oxygen evolution reaction（OER）,a four-electron transfer process,is slower,resulting in a high energy consumption in the process of electrochemical water splitting.Therefore,the design of high-active OER as well as HER catalysts could promote the development and application of hydrogen production from electrochemical water splitting.This paper proposes a facile strategy to prepare sulfur-vacancy-rich spinel Co₃S₄ catalysts,and investigates the catalytic activities of synthesized catalyst materials for OER and HER,and focuses on the contribution of defect introduction on the electrochemical performance.In this paper,the hollow structure constructed with spinel Co₃O₄ are acted as the precursor,and a hollow dodecahedron constructed with spinel Co₃S₄ nanoparticles rich in sulfur vacancies（H-V_S-Co₃S₄）is prepared by using the reduction and anion exchange capacity of H₂S generated by pyrolysis of thiourea.A series of characterization tests were performed on the morphology,composition and electronic structure.The results show that the anion exchange and vacancy introduction could accomplish simultaneously in the H₂S atmosphere,and the concentration of sulfur defects can be controlled by adjusting thiourea dose.With an increased sulfur defect concentration,the degree of electron delocalization for the series H-V_S-Co₃S₄ samples is enhanced.Moreover,the introduction of sulfur defects could decrease part of Co³⁺to balance the generation of surface vacancies,thereby exposing more Co²⁺sites.In this paper,the catalytic properties of the synthesized materials were investigated through a series of electrochemical tests,and the results showed that a series of H-V_S-Co₃S₄ samples exhibited excellent catalytic activity for OER and HER in 1.0 M KOH.According to OER,H-V_S-Co₃S₄ sample with reasonable sulfur defect concentration only requires a low overpotential of 270 m V(at 10 m A cm^-2)and a low Tafel slope of59 m V dec^-1.According to HER,this sample requires an overpotential of 290 m V(at-10 m A cm^-2)and a Tafel slope of 56 m V dec^-1.By establishing a connection between the structure and electrocatalytic performance of the synthesized samples,the result shows that the increase in the degree of electron delocalization reduces charge transfer resistance and increases the charge transfer rate,which in turn exhibits the excellent OER and HER performance.Moreover,after the OER pre-oxidation process,the H-V_S-Co₃S₄ sample underwent structural reconfiguration,and Co²⁺sites exposed by introducing sulfur vacancies converted to more OER-friendly high-valent Co³⁺active sites,leading the H-V_S-Co₃S₄ sample with reasonable sulfur vacancies exhibits the better catalytic activities than those of commercial catalysts（RuO₂）.更多还原