非贵金属铁基限域电催化剂：分辨限域组分氧还原活性位点

Confined iron based non-precious metal catalysts have recently been disclosed as an interesting type of highly active electrocatalysts for the oxygen reduction reaction (ORR). However, the complex composition of the metal-containing components and their contributions in catalysis remain unclear. We previously developed a high-pressure pyrolysis approach to prepare a series of confined iron based catalysts with uniform and essentially identical morphologies but varied compositions. The catalysts exhibited good ORR activity and stability in acid media. By 57Fe-Mössbauer spectroscopy a few iron containing components were identified. The ORR kinetic current density showed positive correlation with encapsuated Fe3C, indicating its active site among confined Fe-containing components. However, it remians no direct evidence for confirmation of Fe3C. In addition, trace FeNx/C may also contributed to the ORR. In this project, we use high-vaccum sputter technique to prepare confined iron based catalysts from bottom to up. This technique can control individually confined and pure phase Fe components. The carbon layer can also be sputtered with precisely controlling the thickness. Through this project, we aim at offering a clear conclusion for the active sites and open an avenue for the development of confined iron-based NPMCs.

非贵金属铁基限域催化剂是近年来氧还原（ORR）电催化领域一种新型的高活性电催化剂。由于其活性组分被表面碳层所限域，避免了直接与电解液接触，同时展现出良好的ORR稳定性。但其复杂的结构组成及活性位点目前仍然不明确。前期我们采用高压固相热解的方法合成了一系列结构均一，组成可调的碳层限域铁基催化剂，在酸性介质中展现出良好的活性和稳定性。我们采用57Fe穆斯堡尔谱鉴别了其复杂的多种铁组分，并得到ORR动力学电流密度与Fe3C含量呈现正相关，暗示Fe3C为限域ORR活性组分。但我们仍然缺乏直接的证据确证其活性位点，特别是表面痕量FeNx/C也参与了ORR活性贡献，进一步复杂了该体系。在本项目中，我们将使用超高真空溅射技术，由于其精确的厚度控制能力，自下而上制备单一纯相限域铁组分及其碳层。通过本项目，我们期望能清晰地阐明其限域活性中心，促进非贵金属铁基限域氧还原催化剂的发展。

氧还原（ORR）作为燃料电池的阴极反应，一直以来备受关注。而其高的过电位和动力学迟缓是限制燃料电池快速发展的主要因素。Fe/N/C材料被认为是最有潜力的非贵金属ORR催化剂之一。对于其活性中心的辨别是进一步提高催化剂性能的主要依据与基础，更是一直以来困扰该领域的难题。本项目主要针对铁基非贵金属催化剂的活性位点辨别展开，在此基础上扩展体系至对ORR电子转移路径的可控调节，利用其成功实现电化学法制备过氧化氢（H2O2），并应用于水体中有机污染物降解等。主要结果如下：（1）通过三聚氰胺为构架，成功合成表面氮掺杂的Fe/N/C催化剂，并对其ORR四电子转移催化活性及活性位点进行探索，实验证明ORR电化学催化活性与Fe/N/C组分及其表面吡咯氮含量呈线性相关。（2）通过含硫组分对铂基催化剂的表面吸附，合成一系列PtSCNx/C和PtSx/C 催化剂，并对其ORR电化学催化性能展开研究。发现其成功实现对ORR电子转移路径从4e-到2e-的可控调节。（3）利用PtSCNx/C和PtSx/C催化剂对ORR2e-转移反应的高选择性，实现了电化学方法合成H2O2。进一步对催化剂的活性及稳定性优化提高，设计实验室小规模电化学合成H2O2装置，并将其应用于水体有机物降解领域，实现了有机污染物的快速降解。该体系的开发与利用，有望为医疗消杀，家用清洁等终端用户提供灵活、在线的H2O2合成装置。