非对称电子结构二维钴基电解水催化剂的设计与同步辐射解析

Water electrolysis is one of the most promising technologies to convert renewable energy, but is limited by the sluggish electrochemical reactions. It is necessary to use catalysts to promote the occurrence of the water electrolysis reactions. The development of low-cost nano-materials with high catalytic activity and stability to replace commercial noble-metal-based catalysts is the goal of current catalyst research. Accurately analyzing the structure of the catalyst and revealing the catalytic active sites can not only clarify the catalytic mechanism, but also provide theoretical guidance for the design of the catalyst, which is always been a hot spot of catalyst research and a core problem to be solved. In this project, ultrathin α-phase cobalt hydroxide nanosheet is proposed as the construction substrate. The ultrathin two-dimensional cobalt-based electrolysis water catalyst with asymmetrical electron distribution Pt(Ir)-Co-O structure will be designed and constructed by vacancy defects fabrication and refilling process. Based on the analysis of synchrotron radiation X-ray absorption spectroscopy and high resolution electron microscopy, the fine structure information of the catalyst can be revealed at the atomic scale. The catalyst structure and catalytic reaction models can be established by combining the first principle calculations with structure characterizations. The research results of this project can not only help to understand the true mechanism of action of asymmetric electronic structures in electrocatalysts in catalytic reactions, but also hope to provide reference for the study of other catalysts.

电解水是最有前景的可持续能量转换技术之一，但受限于缓慢的电化学反应，需要使用催化剂来促进电解水反应的发生。开发具有高催化活性和稳定性的低成本纳米材料替代商用贵金属基电解水催化剂，是当前催化剂研究的目标。精确解析催化剂的结构、揭示催化活性位点，不仅能阐明催化机理，还可为催化剂的设计提供理论指导，一直以来都是催化剂研究的热点和需要解决的核心问题。本项目拟将超薄α相氢氧化钴纳米片作为构筑基底，通过空位缺陷构筑及再填充工艺，设计和制备具有非对称电子分布Pt(Ir)-Co-O结构的超薄二维钴基电解水催化剂。利用同步辐射X射线吸收谱和高分辨电镜技术，从原子尺度揭示催化剂的精细结构信息，并结合第一性原理计算对催化剂结构进行模拟，从而建立催化反应模型。本项目的研究结果不仅可以有助于理解电催化剂中非对称电子结构在催化反应中的真正作用机制，也有望为其它催化剂的研究提供参考。

氢气由于具有能量密度高、燃烧零排放等优点，被认为是最理想的替代化石燃料的清洁能源，在可持续能源发展战略中被寄予厚望。以水作为原料，通过电催化水分解转化为氢气和氧气，是制取氢气的重要途径，同时也是众多能量转换技术的关键步骤，是实现清洁电能存储最理想的方法之一。本项目基于前期关于超薄二维钴基纳米片的研究基础，从含有缺陷结构超薄二维α相氢氧化钴（α-Co(OH)2）纳米片的制备、表面活性单原子位点的引入修饰等方面入手提高α-Co(OH)2的电催化性能。首先，通过共沉淀法制备富含空位缺陷结构的超薄二维Co(OH)x纳米片，分析了其形貌结构和晶体结构。利用电子顺磁共振测试证实纳米片中含有大量的氧空位。然后，通过光沉积的方法将Ir以单原子形式负载到该纳米片模板上，形成Ir-Co(OH)x。基于球差电镜HAADF-STEM和同步辐射X射线吸收精细结构（XAFS）表征证实Ir的单原子结构。该材料在碱性电解液中显示出优异的电催化OER性能和长时间稳定性。另一方面，以单原子Ir纳米团簇负载的α-Co(OH)2纳米片（Ir-Co(OH)2）为模板，通过外包覆聚多巴胺后高温碳化以及酸浸的策略，合成了Ir和Co双单原子修饰的多孔氮掺杂碳（IrCo-pNC）纳米片材料。球差电镜和XAFS表征指出了其中的双单原子结构，理论计算证实了Ir和Co之间的电荷转移。该材料在酸性电解液中展示出与商用Pt/C催化剂相媲美的电催化HER活性。此外，围绕电催化剂纳米材料中的界面结构以及电催化剂在电催化反应过程中的动态结构原位研究，根据团队研究基础和国内外研究最新进展，撰写了两篇综述论文。本项目的研究结果不仅有助于理解电催化剂中非对称电子结构在催化反应中的作用，也有望为其它催化剂的研究提供参考。