催化学报 ›› 2023, Vol. 48: 205-213.DOI: 10.1016/S1872-2067(23)64413-4

• 论文 • 上一篇    下一篇

电催化硝酸盐还原合成氨电势相关性的计算见解

井会娟a,b, 龙军a, 李欢a,b, 傅笑言a, 肖建平a,b,*()   

  1. a中国科学院大连化学物理研究所, 催化国家重点实验室, 大连洁净能源国家实验室(筹), 辽宁大连116023
    b中国科学院大学, 北京100049
  • 收稿日期:2022-12-14 接受日期:2023-02-13 出版日期:2023-05-18 发布日期:2023-04-20
  • 通讯作者: * 电子信箱: xiao@dicp.ac.cn (肖建平).
  • 基金资助:
    国家重点研发计划(2021YFA1500702);国家重点研发计划(22YFE0108000);国家自然科学基金(22172156);中国科学院洁净能源创新研究院合作基金资助项目(DNL202003);中国科学院战略先导计划(XDB36030200);中国科学院大连清洁能源国家实验室榆林分中心人工智能科技计划(DNL-YLA202205)

Computational insights on potential dependence of electrocatalytic synthesis of ammonia from nitrate

Huijuan Jinga,b, Jun Longa, Huan Lia,b, Xiaoyan Fua, Jianping Xiaoa,b,*()   

  1. aState Key Laboratory of Catalysis, Dalian National Laboratory for Clean Energy, Dalian Institute of Chemical Physics, Chinese Academy of Sciences,Dalian 116023, Liaoning, China
    bUniversity of Chinese Academy of Sciences, Beijing 100049, China
  • Received:2022-12-14 Accepted:2023-02-13 Online:2023-05-18 Published:2023-04-20
  • Contact: * E-mail: xiao@dicp.ac.cn (J. Xiao).
  • Supported by:
    National Key Research and Development Program of China(2021YFA1500702);National Key Research and Development Program of China(22YFE0108000);National Natural Science Foundation of China(22172156);DNL Cooperation Fund, CAS(DNL202003);Strategic Priority Research Program of the Chinese Academy of Sciences(XDB36030200);AI S&T Program of Yulin Branch, Dalian National Laboratory for Clean Energy, CAS(DNL-YLA202205)

摘要:

人类活动和工业生产导致全球氮循环严重失衡, 对生命系统的健康造成了一定威胁. 因此, 开发高效、环保的NOx脱除技术具有重要意义. 其中, 电化学硝酸盐还原反应(eNO3RR)是反向人工氮循环的重要组成部分, 同时也被认为是一种非集成式合成氨(NH3)的可行途径. NH3是生产肥料的重要原料之一, 传统哈伯法(H-B)合成氨能耗高, 且会排放大量温室气体CO2, 由可再生电力驱动的电催化氮气还原(eNRR)合成氨被认为是一条更环保和可持续的路线. 目前, 一些研究表明电催化硝酸盐还原具有比eNRR更高的产氨活性和选择性. 然而, 一个主要的挑战是在低过电位下产物的选择性, 即亚硝酸盐(HNO2)和NH3之间的竞争.
本文选择了六个具有MN4单元的石墨烯负载的过渡金属单原子催化剂(SACs)作为模型, 通过密度泛函理论(DFT)计算研究eNO3RR机理. 采用本课题组开发的反应相图分析(RPD)方法从全局热力学最优的角度构建了六个MN4催化剂的二维准活性和选择性相图, 其中FeN4催化剂展示出较高的准活性和适当的选择性. DFT计算结果表明, 产生HNO2和NH3的最优路径共享一个关键中间体(NO2*), 其吸附结构和在后续转化中的偏好决定了产物选择性. 结合电势相关性动力学势垒计算和微观动力学模拟结果, 动力学研究表明, 理论上两种产物不同电压下的法拉第效率(FE)趋势会发生反转, 与FeN4催化剂上实验测得的HNO2和NH3的FE趋势和反转电压吻合, 这归因于两个重要的基元步骤(R4: NO2* → cisHNO2*和R7: NO2* → HNO2 + *)具有不同的电荷转移系数(β), 前者(R4)具有更大的电荷转移系数, 使得生成NH3的动力学能垒随电压的降低而下降得更快, 这就把NH3从低过电势下的低选择性到高过电势下的高选择性归因到动力学问题, 较好地理解了两种产物的FE发生发转的原因. 最后, 从电子结构方面对R4和R7两个关键基元步骤的初态和过渡态进行了电子局域化函数和晶体轨道哈密顿布居分析.
综上, 理论计算的机理研究很好地解释实验观察的结果, 其机理方面的理解对于将来理性设计高效的eNO3RR合成NH3催化剂具有一定的指导意义.

关键词: 电催化合成氨, 密度泛函理论计算, 反应相图分析, 活性, 选择性

Abstract:

Electrochemical nitrate reduction reaction (eNO3RR) has been considered as an alternative route for decentralized ammonia (NH3) synthesis. However, a major challenge is products selectivity at low overpotentials, namely, the competition between nitrite (HNO2) and ammonia. Herein, we employed a single-atom catalyst (FeN4) as model to study the competitive mechanism of NH3 and HNO2 by density functional theory calculations. It was found the optimal paths for ammonia and nitrite productions share a key intermediate (NO2*), whose adsorption structures and preference in the following conversion determines the selectivity. We have incorporated potential-dependent barriers and microkinetic modeling to understand the Faradaic efficiency at different potentials. Our results are in good agreement with the experimental trend of Faradaic efficiencies of NH3 and HNO2, which can be rationalized well by the charge transfer coefficient (β) for NO2* protonation to cisHNO2* with respect to that to HNO2. A low selectivity of ammonia production at small overpotentials can be ascribed to a kinetic issue. The electron localization function and crystal orbital Hamilton population were analyzed on the initial and transition states for NO2* protonation to cisHNO2* and HNO2. The computational mechanistic insights can help to design new catalyst for eNO3RR highly active and selective to NH3.

Key words: Electrochemical ammonia synthesis, Density functional theory calculation, Reaction phase diagram, Activity, Selectivity