铱系氧化物纳米晶涂层电极电催化合成绿色硝化剂N2O5的作用机制

In order to overcome the disadvantages of traditional nitration process, the novel nitration technology using dinitrogen pentoxide(N2O5) is becoming the main method to synthesize the organic materials and energetic materials and the synthesis of N2O5 is crucial for this technology.Nowadays the electrochemical route has been focused on the synthesis of N2O5.However,the development of this electrochemical process has been limited by the critical materials- electrode materials. Up to now, the understandings on the effects of anode materials and the electrode reaction mechanism are still ambiguous, which severely affect the developments of novel electrode materials and electrosynthesis routes. In this work, the preparation method of the shape-,oriention- and size-controlled iridium and ruthenium binary oxide nanocrystal electrodes will be developed by investigating the mechanism of shape-evolution and crystal growth of IrRu oxides as well as the pre-treatment method of Ti substrate by coating gradient IrRu oxides. The structry-activity relationship of iridium oxide-based nanocrystal will be constituted by preparation of different shapes of IrRu oxides nanocrystal electrode and by investigating the electrocatalytic oxidation of N2O4 on the obtained electrodes. The reaction mechanism of electrocatalytic oxidation of N2O4 will be obtained by exploring electrochemical behaviours of N2O4 on the optimum IrRu oxides nanocrystal electrode in N2O4/HNO3 solution. Therefore, the activation mechanism of electrocatalytic oxidation of N2O4 on the IrRu oxides nanocrystal electrodes can be developed. The aim of this work is to reveal the nature of electrocatalytic oxidation of N2O4 by Ir-based oxides nanocrystal coated electrodes, so as to provide some valuable theoretical guidance and new kwnoledge on developing novel high performance DSA-type electrode materials and on their applications.

为克服传统硝化的缺点，基于N2O5的新型硝化技术是未来合成有机原料和含能材料的主要方法，N2O5合成是其关键。目前，电化学法是合成N2O5的研究热点，而该过程受到电极材料发展的制约。由于对电极材料的影响规律及反应机理目前尚不清晰，严重影响了新型电极材料及电化学合成N2O5过程的开发。本工作拟通过研究钌铱氧化物纳米晶的析形和生长机理以及钛基体梯度化涂层的预处理技术，建立晶体形貌、取向和大小可控的高稳定钌铱氧化物纳米晶涂层电极制备技术；开展不同形貌钌铱纳米晶电极制备及电催化N2O4氧化性能研究，构建铱系氧化物纳米晶的形貌与其电催化性能的构效关系；研究铱系纳米晶涂层电极在N2O4/HNO3溶液中的电化学特性，建立电催化N2O4氧化反应机理，获得纳米晶电极材料的电催化N2O4氧化作用机制。本研究旨在揭示铱系氧化物涂层电极的电催化本质，以期为新型高效DSA类电极材料的设计、开发及应用提供理论指导。

五氧化二氮(N2O5)被公认为是硝化性能优异的绿色硝化剂，电化学合成五氧化二氮是目前制备五氧化二氮最具有工业化前景的技术，为了获得适用于电化学合成N2O5的新型高效电极材料，本研究主要从形貌和晶面可控的纳米晶制备技术研究—IrRu氧化物纳米晶制备、高稳定性钛基体预处理研究—梯度IrRu纳米氧化物涂层及其稳定性研究、构效关系研究—生长可控IrRu氧化物纳米晶涂层电极制备及其电催化性能等方面开展研究。.通过研究建立了形貌、尺寸可控的(111)取向铱纳米晶制备方法，获得了铱纳米晶(nanoIr)析形和取向生长Ostwald机理，提出了铱纳米晶合成中的“阴离子限域效应”；研究了钛基体预处理对基层涂层的形貌和组成的影响，获得了梯度涂层基层合成条件和组成(处理温度、时间、基层元素和SiO2参杂)对其结构和稳定性的影响，SiO2参杂可改善铱纳米晶形貌和取向，提高稳定性7.4倍；建立了梯度IrRu纳米氧化物涂层基层预处理方法；研究了铱含量及其铱梯度分布对IrRu氧化物梯度涂层相结构、结晶度及晶体粒径组成及其稳定性的影响规律；通过强化电极寿命实验和失效机理分析，获得了梯度涂层结构与其电催化稳定性关系，以及强化电极稳定性机理，适宜的铱梯度分布为4层(内层为IrO2，表层为Ir0.5Ru0.5O2)，电极寿命提高2.5倍。研究了制备方法、铱含量、制备温度和溶液浓度等对钌铱氧化物纳米晶生长的影响，结合电催化氧化N2O4性能对其工艺进行了优化，建立了IrRu氧化物纳米晶生长可控的涂层钛电极制备技术；获得了不同形貌和尺寸nanoIr的析氧性能以及不同形貌和尺寸、晶面取向的IrRu氧化物纳米晶涂层对析氧和电催化氧化N2O4性能（过电位、Tafel行为）的影响规律，并运用循环伏安法获得了不同涂层表面N2O4吸附量（伏安电荷q）与其催化性能的关系。nanoIr尺寸对析氧历程影响显著，形貌影响不大；梯度涂层表面发生元素偏析，形成缺陷位氧化物；梯度涂层电极在N2O4/HNO3溶液中q*有不同程度下降，铱4层梯度变化电极的电化学活性表面积最大，其交换电流密度与非梯度涂层相当；不同电极表面N2O4氧化还原过程受表面吸附N2O4层扩散控制。 .研究结果为电化学合成N2O5过程提供一种高效催化电极材料，解决了N2O5合成中的关键基础问题；同时也为高效DSA电极制备提供借鉴。