电催化硝酸盐还原合成氨电势相关性的计算见解  

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

作　　者：井会娟 龙军 李欢 傅笑言 肖建平 Huijuan Jing;Jun Long;Huan Li;Xiaoyan Fu;Jianping Xiao(State Key Laboratory of Catalysis,Dalian National Laboratory for Clean Energy,Dalian Institute of Chemical Physics,Chinese Academy of Sciences,Dalian 116023,Liaoning,China;University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]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 [2]中国科学院大学,北京100049

出　　处：《Chinese Journal of Catalysis》2023年第5期205-213,共9页催化学报（英文）

基　　金：国家重点研发计划(2021YFA1500702,22YFE0108000);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-YL A202205).

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NO_(x)脱除技术具有重要意义.其中,电化学硝酸盐还原反应(eNO_(3)RR)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(NH_(3))的可行途径.NH_(3)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CO_(2),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(HNO_(2))和NH_(3)之间的竞争.本文选择了六个具有MN_(4)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eNO_(3)RR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MN_(4)催化剂的二维准活性和选择性相图,其中FeN_(4)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HNO_(2)和NH_(3)的最优路径共享一个关键中间体(NO_(2)*),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FeN_(4)催化剂上实验测得的HNO_(2)和NH_(3)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:NO_(2)*-→cisHNO_(2)*和R7:NO_(2)*→HNO_(2)+*)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NH_(3)的动力学能垒随电压的降低而下降得更快,这就把NH_(3)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�Electrochemical nitrate reduction reaction(eNO_(3)RR)has been considered as an alternative route for decentralized ammonia(NH_(3))synthesis.However,a major challenge is products selectivity at low overpotentials,namely,the competition between nitrite(HNO_(2))and ammonia.Herein,we employed a single‐atom catalyst(FeN_(4))as model to study the competitive mechanism of NH_(3)and HNO_(2)by density functional theory calculations.It was found the optimal paths for ammonia and nitrite productions share a key intermediate(NO_(2)*),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 NH_(3)and HNO_(2),which can be rationalized well by the charge transfer coefficient(β)for NO_(2)*protonation to cisHNO_(2)*with respect to that to HNO_(2).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 NO_(2)*protonation to cisHNO_(2)*and HNO_(2).The computational mechanistic insights can help to design new catalyst for eNO3RR highly active and selective to NH_(3)。

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 

分 类 号：TQ113.26[化学工程—无机化工] TQ426