催化学报 ›› 2021, Vol. 42 ›› Issue (9): 1439-1444.DOI: 10.1016/S1872-2067(20)63762-7

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碱金属阳离子对铁卟啉电催化CO2还原的影响

郭凯a, 雷海涛a, 李夏亮a, 张宗尧b, 王亚博a, 郭鸿波a, 张伟a, 曹睿a,*()   

  1. a陕西师范大学化学与化工学院, 应用表面与胶体化学教育部重点实验室, 陕西西安710119, 中国
    b牛津大学化学系, 化学研究实验室, 牛津, 英国
  • 收稿日期:2020-12-19 接受日期:2021-01-11 出版日期:2021-09-18 发布日期:2021-05-16
  • 通讯作者: 曹睿
  • 基金资助:
    霍英东青年教师基金;国家自然科学基金(21573139);国家自然科学基金(21773146);中央高校基本科研基金;陕西师范大学研究经费

Alkali metal cation effects on electrocatalytic CO2 reduction with iron porphyrins

Kai Guoa, Haitao Leia, Xialiang Lia, Zongyao Zhangb, Yabo Wanga, Hongbo Guoa, Wei Zhanga, Rui Caoa,*()   

  1. aKey Laboratory of Applied Surface and Colloid Chemistry, Ministry of Education, School of Chemistry and Chemical Engineering, Shaanxi Normal University, Xi’an 710119, Shaanxi, China
    bChemistry Research Laboratory, Department of Chemistry, University of Oxford, Mansfield Road, Oxford, OX1 3TA, UK
  • Received:2020-12-19 Accepted:2021-01-11 Online:2021-09-18 Published:2021-05-16
  • Contact: Rui Cao
  • About author:* Tel: +86-29-81530726; Fax: +86-29-81530727; E-mail: ruicao@snnu.edu.cn
    Rui Cao (College of Chemistry and Chemical Engineering, Shaanxi Normal University) received the SPP/JPP Young Investigator Awards from International Society of Porphyrins and Phthalocyanines in 2020. Professor Rui Cao received his B.S. degree (2003) in chemistry from Peking University in Beijing, China and his Ph.D. degree (2008) from Emory University in Atlanta, Georgia, USA with Professor Craig L. Hill. He worked as a Postdoctoral Fellow (2008-2009) at Emory University and as the Dreyfus Postdoctoral Fellow (2009-2011) at Massachusetts Institute of Technology with Professor Stephen J. Lippard. In 2011, he became a professor at Renmin University of China, and transferred to Shaanxi Normal University in 2014. His main research interests include bioinorganic chemistry and molecular electrocatalysis for energy-related small molecule activation reactions. Some of his recent progresses using metal porphyrins as catalysts include: (1) demonstrating and controlling homolytic versus heterolytic hydrogen evolution reaction through steric effects, (2) developing porphyrin-appended water-soluble polymers as bioinspired catalysts for both electro- and photocatalytic hydrogen evolution reactions, (3) achieving low overpotential water oxidation at neutral pH and controlling water oxidation selectivity to either O2 or H2O2 with a copper porphyrin, (4) developing an asymmetrical dinuclear cobalt porphyrin for highly efficient and selective oxygen reduction, and (5) engineering carbon materials and metal oxides with molecular catalysts for efficient molecular electrocatalysis. Since 2011 when starting his independent research, Professor Cao has published more than 100 peer-reviewed papers. He joined the editorial Board of Chin. J. Catal. since 2020, Chem. Soc. Rev. since 2019, and Chin. Chem. Lett. since 2017.
  • Supported by:
    Fok Ying-Tong Education Foundation for Outstanding Young Teachers in University;National Natural Science Foundation of China(21573139);National Natural Science Foundation of China(21773146);Fundamental Research Funds for the Central Universities;Research Funds of Shaanxi Normal University

摘要:

电催化CO2还原反应(CO2RR)可以有效地将温室气体转化为燃料或高附加值的化学品, 从而缓解目前人类所面临的环境问题和能源危机, 其中开发高效的电催化剂是至关重要的环节. 近年来, 研究者设计了多种高效的过渡金属配合物(包括Mn, Fe, Co, Ni和Cu)用作CO2RR分子电催化剂, 并研究了其中的构效关系, 例如, 在分子内修饰质子给体取代基或电荷取代基可以显著提高CO2RR的催化效率. 而电催化CO2RR的实际应用要在含有碱金属阳离子(例如, Na+和K+)的电解质水溶液中进行, 但在已有报道中, 很少有关于碱金属阳离子对CO2RR的影响. 在众多的分子催化剂中, 铁卟啉可以以较高的催化活性和选择性实现CO2到CO的转化. 重要的是, 卟啉环的刚性结构、稳定的配位环境及其骨架上官能团的易于修饰性成为研究CO2RR的构效关系的理想分子模型. 基于以上考虑, 本文以铁卟啉配合物为分子模型, 研究了碱金属阳离子Na+和K+对电催化CO2RR的影响.
首先, 本文合成了简单的A4型铁卟啉化合物四-(3,4,5-三甲氧基苯基)-铁卟啉(FeP). 并采用核磁共振、质谱分析、单晶衍射等表征手段对化合物进行了表征, 在含有电解质的DMF溶液中测试其电催化CO2还原性能. 实验结果表明, FeP可以实现高效的电催化CO2还原, 催化电流随FeP的浓度呈线性增加, 说明催化反应速率与催化剂浓度呈一级反应速率关系. 较长时间的恒电压电解实验以及电解前后化合物的紫外-可见光谱证实了FeP的稳定性. 通过气相色谱对产物进行分析, CO为主要产物, 法拉第效率为95%. 以上结果均表明, FeP是一个优良的分子催化剂. 在此基础上, 本文还发现加入Na+和K+均可以显著提升催化活性, 而K+的加入使催化电流的提升更加显著, 这可能是由于K+在溶液中的迁移速度比Na+更快. 基于此实验现象, 本文通过在FeP的第二配位层修饰1-氨-18-冠-6-醚官能团(N18C6), 合成了N18C6-FeP化合物. 结果表明, 由于N18C6与Na+/K+之间的配位作用, 使得N18C6-FeP比FeP具有更好的电催化CO2RR活性. 研究表明, 催化活性的提升归因于碱金属阳离子能够通过静电相互作用稳定Fe-CO2中间体.1H NMR谱证实了N18C6基团的确能够螯合碱金属阳离子. 本文研究证明了碱金属阳离子对改善电催化CO2RR的积极作用, 对于进一步深入了解CO2RR催化反应机理和未来合理的设计高效催化剂也都具有重要意义.

关键词: 二氧化碳还原, 分子电催化, 碱性金属阳离子效应, 铁卟啉, 构效关系

Abstract:

The electrocatalytic CO2 reduction reaction (CO2RR) has attracted increasing attention in recent years. Practical electrocatalysis of CO2RR must be carried out in aqueous solutions containing electrolytes of alkali metal cations such as sodium and potassium. Although considerable efforts have been made to design efficient electrocatalysts for CO2RR and to investigate the structure-activity relationships using molecular model complexes, only a few studies have been investigated the effect of alkali metal cations on electrocatalytic CO2RR. In this study, we report the effect of alkali metal cations (Na+ and K+) on electrocatalytic CO2RR with Fe porphyrins. By running CO2RR electrocatalysis in dimethylformamide (DMF), we found that the addition of Na+ or K+ considerably improves the catalytic activity of Fe chloride tetrakis(3,4,5-trimethoxyphenyl)porphyrin (FeP). Based on this result, we synthesized an Fe porphyrin N18C6-FeP bearing a tethered 1-aza-18-crown-6-ether (N18C6) group at the second coordination sphere of the Fe site. We showed that with the tethered N18C6 to bind Na+ or K+, N18C6-FeP is more active than FeP for electrocatalytic CO2RR. This work demonstrates the positive effect of alkali metal cations to improve CO2RR electrocatalysis, which is valuable for the rational design of new efficient catalysts.

Key words: CO2 reduction, Molecular electrocatalysis, Alkali metal cation effect, Iron porphyrin, Structure-activity relationship