Unexpected effect of second-shell defect in iron-nitrogen-carbon catalyst for electrochemical CO_(2)reduction reaction:A DFT study  

第二壳层的碳缺陷调控CO_(2)电催化还原的理论研究

作　　者：Mengna Wang Qi Wang Tianfu Liu Guoxiong Wang 王梦娜;王琪;刘天夫;汪国雄(大连交通大学材料科学与工程学院,辽宁大连116028;中国科学院大连化学物理研究所催化基础国家重点实验室,辽宁大连116023;中国科学院大学,北京100039)

机构地区：[1]School of Materials and Engineering,Dalian Jiaotong University,Dalian 116028,Liaoning,China [2]State Key Laboratory of Catalysis,Dalian National Laboratory for Clean Energy,Dalian Institute of Chemical Physics,Chinese Academy of Sciences,Dalian 116023,Liaoning,China [3]University of Chinese Academy of Sciences,Beijing 100039,China

出　　处：《Chinese Journal of Catalysis》2024年第11期247-256,共10页催化学报(英文)

基　　金：国家重点研发计划(2023YFA1508002);国家自然科学基金(22002158,22172009,22125205,92045302);大连化物所创新研究基金(DNL201924,DNL202007);中国科学院碳中和光子科学中心项目.

摘　　要：Metal-nitrogen-carbon catalysts(M-N-C)with single-atom active site are highly efficient catalysts for electrochemical CO_(2)reduction reactions(CO_(2)RR).Abundant M-N-C catalysts have been developed,and the coordinated adjacent nitrogen atoms as first-shell environment have been the focus of research of activity-tuning.However,the effect of second-shell carbon environment around the metal-nitrogen moiety is still unclear.Moreover,it is confusing for the discrepancy between the experimental onset potential of around–0.2 V(vs.reversible hydrogen electrode,RHE,unless otherwise noted)and theoretical predictions of–0.5 V or higher by the widely-used computational hydrogen electrode(CHE)model.Herein,using the explicit solvent model and constant potential method(CPM),the electrochemical interface on Fe-N-C is simulated for CO_(2)RR.It reveals that the*COOH formation is facilitated in water solvent environment,while the CO_(2)adsorption is potential-dependent.The predicted onset potential of around–0.2 V on Fe-N-C is consistent with experimental results.The sp2 non-hexatomic defects introduced into second-shell carbon environment are significantly influential for the CO_(2)RR.The double five-seven ring(5577)defect is the most active,compared to that with triple five-seven ring(55577)or five-eight ring(58)defects.The highly flexible structure and altered density of states of Fe site induced by 5775 defects are key to CO_(2)adsorption.This study provides new insights into the role of second-shell carbon environment for effective CO_(2)RR,and underlines the importance of CPM and solvent environment in accurate simulation for electrochemical interface.CO_(2)电催化还原提供了一种利用可再生能源将CO_(2)转化为燃料和化学品的负碳技术,对于实现双碳目标具有重要意义.单原子金属-氮-碳催化剂在CO_(2)电催化还原反应中展现了将CO_(2)高效还原为CO的性能.目前关于金属-氮-碳催化剂的研究大多集中在对于金属种类、氮配位等结构与性能之间的关系.但是对于金属-氮-碳催化剂结构中的第二壳层碳缺陷的研究很少.在理论计算中广泛使用的计算氢电极模型是一种恒电荷模型,与实验中实际采用的恒电位条件相差很大.值得注意的是,在铁-氮-碳(Fe-N-C)催化剂中的pH无关效应显示,限速步骤可能不是质子-电子耦合转移,而是质子-电子分步骤转移,文献中常见报道的*COOH生成并不是速控步骤,而CO_(2)吸附可能更加重要.本文利用恒电位方法,计算了Fe-N-C催化剂中第二壳层的三种碳缺陷(5577,55577,58)对CO_(2)电催化还原反应的影响,并与恒电荷方法比较,进而揭示*COOH的生成、CO_(2)吸附与电催化性能之间的关系.研究结果表明,加入碳缺陷并没有显著改变Fe-N-C的结构稳定性,说明其可以在Fe-N-C催化剂中的第二壳层稳定存在.恒电荷方法计算中得到的CO_(2)电催化限制电位约为–0.5 V(vs.RHE,下同),与实验中得到的–0.2 V相比有很大的误差,而且恒电荷方法无法描述Fe-N-C催化剂上的pH无关效应.利用恒电位与显式溶剂环境结合的方法发现,*COOH的生成在H2O溶剂分子网络存在下非常容易发生,而且在负电位下进一步降低了反应能垒,说明*COOH生成不是速控步骤.利用恒电位和显式溶剂化方法研究不同电位条件下的CO_(2)在Fe-N-C催化剂上的吸附过程,发现CO_(2)吸附是一个随电位变负而增强的过程,CO_(2)可以在恒电位在Fe位点上形成稳定的吸附构型.在–0.2 V的施加电位下,Fe-N-C催化剂上CO_(2)吸附能开始变负,与实验结果一致.加入第二壳层碳缺陷之后,CO_(2)吸

关 键 词：Iron-nitrogen-carbon catalysts Electrochemical CO_(2)reduction reaction Defect engineering Constant potential method Density functional theory calculations 

分 类 号：O643.3[理学—物理化学]