催化学报 ›› 2023, Vol. 47: 243-253.DOI: 10.1016/S1872-2067(23)64395-5

• 论文 • 上一篇    下一篇

TiO2/TiN纳米管异质结用于光电催化CO2还原: 氮辅助活性氢机制

魏艳a,1, 段睿智b,c,1, 张巧兰a,b, 曹有智a, 王金圆a, 王冰a, 万雯瑞a, 刘春燕a, 陈加藏d, 高红a,b,*(), 景欢旺a,b,d,*()   

  1. a兰州大学化学化工学院, 功能有机分子化学国家重点实验室, 甘肃兰州730000
    b兰州大学化学化工学院, 甘肃省先进催化中心, 功能有机分子化学国家重点实验室, 甘肃兰州730000
    c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
    d中国科学院山西煤炭化学研究所, 煤转化国家重点实验室, 山西太原030001
  • 收稿日期:2022-11-22 接受日期:2023-01-09 出版日期:2023-04-18 发布日期:2023-03-20
  • 通讯作者: *电子信箱: gaoh@lzu.edu.cn (高红),hwjing@lzu.edu.cn (景欢旺).
  • 作者简介:1共同第一作者.
  • 基金资助:
    甘肃省自然科学基金(21JR7RA466);煤转化国家重点实验室开放基金(J21-22-913);中央高校基本科研业务费(lzujbky-2021-sp55)

Photoelectrocatalytic reduction of CO2 catalyzed by TiO2/TiN nanotube heterojunction: Nitrogen assisted active hydrogen mechanism

Yan Weia,1, Ruizhi Duanb,c,1, Qiaolan Zhanga,b, Youzhi Caoa, Jinyuan Wanga, Bing Wanga, Wenrui Wana, Chunyan Liua, Jiazang Chend, Hong Gaoa,b,*(), Huanwang Jinga,b,d,*()   

  1. aState Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, Gansu, China
    bKey Laboratory of Advanced Catalysis, Gansu Province, State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, Gansu, China
    cState Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian National Laboratory for Clean Energy, Dalian 116023, Liaoning, China
    dState Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, Shanxi, China
  • Received:2022-11-22 Accepted:2023-01-09 Online:2023-04-18 Published:2023-03-20
  • Contact: *E-mail: gaoh@lzu.edu.cn (H. Gao),hwjing@lzu.edu.cn (H. Jing).
  • About author:1 Contributed equally to this work.
  • Supported by:
    Natural Science Foundation of Gansu Province(21JR7RA466);Foundation of State Key Laboratory of Coal Conversion(J21-22-913);Fundamental Research Funds for Central Universities(lzujbky-2021-sp55)

摘要:

利用太阳能将CO2转换为高附加值的化学品是解决化石燃料消耗过快与CO2排放过度问题的可行性方案. 光电催化CO2还原可以模拟自然光合作用将CO2还原为多碳产物(C2+). 然而, 光电催化剂的带隙与太阳辐射光谱不匹配以及载流子的快速复合是限制人工光合作用效率的关键因素. 前期研究表明, 缺陷工程可有效地增加催化剂活性位点, 减小半导体的带隙并增强对光子的捕获能力; 而异质结的构筑则可有效提升载流子的分离效率. 因此, 构建具有较好可见光响应的高效半导体异质结催化剂有望实现催化材料对CO2还原能力和产物选择性的提升.

本文通过对金属钛板进行电化学阳极氧化, 氨气气氛煅烧得到TiN, 然后原位进行部分氧化构筑出结构新颖的TiO2/TiN纳米管异质结材料, 再进行配体和钯量子点修饰, 得到更加高效的催化电极材料Pd/R-TiO2/TiN, 并在三电极系统中研究了其光电催化CO2还原的性能. 通过扫描隧道电子显微镜、透射电子显微镜、X射线粉末衍射、X射线光电子能谱、电子顺磁共振谱、X射线吸收近边结构光谱及莫特肖特基曲线等系统考察了催化剂的结构与光电催化性能, 证明了n-n同型异质结的成功构筑, 且纳米管状的异质结含有丰富的Ti3+和氧空位, 具有较好的太阳光捕获能力, 保留了间隙金属材料TiN良好的电荷传输能力, 提高了光生载流子的分离效率. 光电催化CO2还原结果表明, 纳米管状Pd/R-TiO2/TiN异质结材料具有较好的CO2还原能力. 其中Pd/R-TiO2/TiN-30电极的碳基化合物的产率高达115.9 μmol L-1 h-1 cm-2, 是纳米颗粒状Pd/R-TiO2/TiN-30异质结材料的2.2倍, 且具有最高的C2选择性(65.7%), 说明纳米管状结构为反应提供的有限空间有利于C-C耦联. 另外, 光电联合催化的产率是纯光催化的3.4倍, 纯电催化的3.3倍, 说明光电协同催化的重要作用. 此外, 该电极获得的总电池效率(Φ°)为6.0%, 远超过植物细胞光合作用的0.4%, 并通过13CO2同位素标记实验证实了所有产物均来自CO2气体. 原位实况傅里叶变换红外光谱分析结果表明, *COOH和*CHO活性物种是主要中间体. 需要强调的是, 在氩气饱和(无CO2参与)的条件下检测到了Ti-H振动吸收谱带, 且与密度泛函理论计算结果一致. 实验和计算相互印证表明, 高活性氢原子可以附着在异质结表面与Ti3+位点形成Ti-H物种. 此外, 计算结果还表明, 氮掺杂对催化剂的影响很大, 当N物种在晶格中存在可促使晶格氧发生迁移, 形成新的氧空位, 氧空位有利于CO2分子和中间体的吸附, 两者结合从而促进了中间体的生成, 加之纳米管的有限空间结构, 有助于C-C耦联反应的发生. 相反, 无N掺杂的纯TiO2锐钛矿不能促进最终Ti-H物种的形成, 其反应机理有利于生成CO. 结合中间体检测、理论计算结果以及H218O同位素标记实验, 提出了一种氮辅助活性氢反应机理. 综上, 本研究为理解CO2还原机理提供了有益的参考, 也为设计高活性和高C2+选择性的CO2还原光电催化剂提供了思路.

关键词: 光电催化, CO2还原, 异质结, 氮化钛, 原位红外

Abstract:

To address the over-emission of CO2, the construction of new heterojunction materials is a promising approach for the photoelectrocatalytic (PEC) conversion of CO2 into valuable chemicals. Herein, a series of heterojunctions of TiO2/TiN nanotube arrays were designed and fabricated by anodic oxidation of titanium plates, followed by in situ partial oxidation to form heterojunctions. The surface of the heterojunction with nitrogen instead of oxygen contained more active Ti3+ species, and the oxygen vacancies were able to harvest solar light and showed excellent performance in the PEC reduction of CO2. As a porous material, the TiO2/TiN nanotube supports good adsorption of CO2 as well as a confined space favoring C-C coupling. Operando Fourier transform infrared (FTIR) analysis revealed that the active species *COOḢ and *CHO were the major intermediates. Density functional theory (DFT) calculations revealed that the highly active hydrogen atoms could attach to the surface of the heterojunction to form Ti-H species with Ti3+, and the existence of nitrogen atoms could promote the migration of lattice oxygen to form new oxygen vacancies, which is conducive to the adsorption and coupling of CO2 and intermediates. The vibration frequency of Ti-H predicted by DFT calculations matches well with the operando FTIR observations. The PEC cell of Pd/R-TiO2/TiN-30|SCE|BiVO4 efficiently produced carbon-based chemicals at a rate of 115.9 μmol L-1 h-1 cm-2 with high selectivity for C2 products. The total efficiency of the PEC cell approached 6.0%, exceeding that of the plant cell by 0.4%. Isotopic labeling experiments of 13CO2 and H218O verified the elemental source and inferred the reaction pathway via highly active hydrogen.

Key words: Photoelectrocatalysis, CO2 reduction, Heterojunction, Titanium nitride, Operando FTIR