物理化学学报 >> 2021, Vol. 37 >> Issue (7): 2009043.doi: 10.3866/PKU.WHXB202009043

所属专题: 电催化

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非金属电催化剂环境条件下氮还原反应的研究进展

许桐1, 马奔原1, 梁杰1, 岳鲁超1, 刘倩1, 李廷帅1, 赵海涛1, 罗永岚1, 卢思宇2, 孙旭平1,*()   

  1. 1 电子科技大学,基础与前沿研究院,成都 610054
    2 郑州大学,化学学院与绿色催化研究中心,郑州 450001
  • 收稿日期:2020-09-11 录用日期:2020-11-18 发布日期:2020-11-24
  • 通讯作者: 孙旭平 E-mail:xpsun@uestc.edu.cn
  • 作者简介:Xuping Sun received his Ph.D. degree in Changchun Institute of Applied Chemistry (CIAC), Chinese Academy of Sciences in 2006. During 2006–2009, he carried out postdoctoral researches at Konstanz University, University of Toronto, and Purdue University. In 2010, he started his independent research career as a full Professor at CIAC and then moved to Sichuan University in 2015. In 2018, he joined University of Electronic Science and Technology of China where he found the Research Center of Nanocatalysis & Sensing. He was recognized as a highly cited researcher (2018 & 2019) in both areas of chemistry and materials science by Clarivate Analytics. He published over 470 papers with total citations over 40000 and an h-index of 106. His research mainly focuses on rational design of functional nanostructures toward applications in electrochemistry for energy conversion and storage, sensing, and environment

Recent Progress in Metal-Free Electrocatalysts toward Ambient N2 Reduction Reaction

Tong Xu1, Benyuan Ma1, Jie Liang1, Luchao Yue1, Qian Liu1, Tingshuai Li1, Haitao Zhao1, Yonglan Luo1, Siyu Lu2, Xuping Sun1,*()   

  1. 1 Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China, Chengdu 610054, China
    2 Green Catalysis Center and College of Chemistry, Zhengzhou University, Zhengzhou 450001, China
  • Received:2020-09-11 Accepted:2020-11-18 Published:2020-11-24
  • Contact: Xuping Sun E-mail:xpsun@uestc.edu.cn
  • About author:Xuping Sun, Email: xpsun@uestc.edu.cn

摘要:

在现代社会中氨是一种重要的工业原料,广泛应用于化工业、塑料制造,炸药以及染料等行业。由于氨气中不含碳,氢容量大、能量密度高且易于运输,已经被视为一种绿色能源替代品。Haber-Bosch方法在全球合成氨中起着主导作用,但其过程在高温高压条件下进行,且伴随着高能耗和CO2排放的问题。电催化氮还原反应(NRR)有望成为常规条件下低成本且环境无害的替代方法,且具有太阳能、风能和其他可再生能源相同的应用潜力。然而,由于惰性的N≡N键,它需要有效的电催化剂来驱动氮气-氨气的转化。迄今为止,人们一直在努力探索高性能催化剂,以实现高效率和选择性。通常,贵金属催化剂具有较高的NRR效率,但是稀缺性和高成本限制了它们的大规模应用。因此,人们将注意力集中在丰富的过渡金属(TM)催化剂上,该催化剂可以通过空的轨道接受氮气分子的孤对电子,同时提供丰富的d-轨道电子进入氮气的反键轨道。然而,这些催化剂可能释放金属离子,导致环境污染,并且大多数金属电催化剂也可能促进金属与氢成键,从而在电催化反应过程中促进了析氢反应(HER)。近年来,非金属催化剂已经成为一个研究热点。非金属催化剂主要包括碳基催化剂(CBC)以及一些硼基和磷基催化剂。通常,碳基催化剂具有多孔结构和较大的表面积,这有利于暴露更多的活性位点,并为质子和电子的传递提供了丰富的通道。本文总结了近期非金属电催化剂(MFCs)在电化学NRR中的设计和发展状况,包括碳基、硼基和磷基催化剂。此外,大多数非金属化合物的路易斯酸位也可以接受氮气的孤对电子并通过形成非金属和氮成键来吸附氮气分子,从而进一步扩大了它们在电催化NRR中的潜力。与金属基催化剂相比,非金属催化剂的占据轨道只能形成共价键或共轭π键,从而阻碍了电子从催化剂到氮气分子的转移以及分子的活化。我们重点讨论了掺杂型催化剂(N,O,S,B,P,F掺杂以及共掺杂)、有机聚合物、氮化碳及缺陷和表面修饰催化剂。最后,我们还讨论了提高NRR性能的方法,展望了非金属电催化剂的发展前景。

关键词: 电化学, 非金属催化剂, 环境条件, 氮还原反应, 氨合成

Abstract:

NH3 plays an important role in modern society as an essential building block in the manufacture of fertilizers, aqueous ammonia, plastics, explosives, and dyes. Additionally, it is regarded as a green alternative fuel, owing to its carbon-free nature, large hydrogen capacity, high energy density, and easy transportation. The Haber-Bosch process plays a dominant role in global NH3 synthesis; however, it involves high pressure and temperature and employs N2 and H2 as feeding gases, thus suffering from high energy consumption and substantial CO2 emission. As a promising alternative to the Haber-Bosch process, electrochemical N2 reduction enables sustainable and environmentally benign NH3 synthesis under ambient conditions. Moreover, its applied potential is compatible with intermittent solar, wind, and other renewable energies. However, efficient electrocatalysts are required to drive N2-to-NH3 conversion because of the extremely inert N≡N bond. To date, significant efforts have been made to explore high-performance catalysts with high efficiency and selectivity. Generally, noble-metal catalysts exhibit efficient performance for the NRR, but their scarcity and high cost limit their large-scale application. Therefore, considerable attention has been focused on earth-abundant transition-metal (TM) catalysts that can use empty or unoccupied orbitals to accept the lone-pair electrons of N2, while donating the abundant d-orbital electrons to the antibonding orbitals of N2. However, these catalysts may release metal ions, leading to environmental pollution. Most of these TM electrocatalysts may also favor the formation of TM—H bonds, facilitating the hydrogen evolution reaction (HER) during the electrocatalytic reaction. Recent years have seen a surge in the exploration of metal-free catalysts (MFCs). MFCs mainly include carbon-based catalysts (CBCs) and some boron-based and phosphorus-based catalysts. Generally, CBCs exhibit a porous structure and high surface area, which are favorable for exposing more active sites and providing rich accessible channels for mass/electron transfer. Moreover, the Lewis acid sites of most metal-free compounds could accept the lone-pair electron of N2 and adsorb N2 molecules by forming nonmetal—N bonds, further widening their potential for electrocatalytic NRR. Compared with metal-based catalysts, the occupied orbitals of metal-free catalysts can only form covalent bonds or conjugated π bonds, hindering electron donation from the electrocatalyst to N2 and molecular activation. In this review, we summarize the recent progress in the design and development of metal-free electrocatalysts (MFCs) for the ambient NRR, including carbon-based catalysts, boron-based catalysts, and phosphorus-based catalysts. In particular, heteroatom doping (N, O, S, B, P, F, and co-dopants), organic polymers, carbon nitride, and defect engineering are highlighted. We also discuss strategies to boost NRR performance and provide an outlook on the development perspectives of MFCs.

Key words: Electrochemistry, Metal-free catalysts, Ambient condition, N2 reduction reaction, NH3 synthesis

MSC2000: 

  • O643