催化学报 ›› 2021, Vol. 42 ›› Issue (8): 1338-1344.DOI: 10.1016/S1872-2067(20)63729-9

• 论文 • 上一篇    下一篇

缓冲溶液阴离子对三价铜催化剂催化水氧化过程的影响

陈齐发, 杜昊易, 章名田*()   

  1. 清华大学化学系基础分子科学中心, 北京 100084
  • 收稿日期:2020-09-05 接受日期:2020-09-05 出版日期:2021-08-18 发布日期:2020-12-10
  • 通讯作者: 章名田
  • 作者简介:*. 电话: (010)62783624; 电子信箱: mtzhang@mail.tsinghua.edu.cn
  • 基金资助:
    国家自然科学基金(21661132006);国家自然科学基金(219330007)

Buffer anion effects on water oxidation catalysis: The case of Cu(III) complex

Qifa Chen, Haoyi Du, Mingtian Zhang*()   

  1. Center of Basic Molecular Science (CBMS), Department of Chemistry, Tsinghua University, Beijing 100084, China
  • Received:2020-09-05 Accepted:2020-09-05 Online:2021-08-18 Published:2020-12-10
  • Contact: Mingtian Zhang
  • About author:*. Tel: +86-10-62783624; E-mail: mtzhang@mail.tsinghua.edu.cn
  • Supported by:
    This work was supported by the National Natural Science Foundation of China(21661132006);This work was supported by the National Natural Science Foundation of China(219330007)

摘要:

水氧化是光解水制氢气的瓶颈反应, 认识和理解水氧化机制并研发廉价稳定的催化剂对解决这一问题尤为重要. 自1982年Meyer课题组报道了第一例分子型双核钌水氧化催化剂(blue dimer)以来, 过渡金属配合物被广泛应用于探索这一氧化过程的规律和机理, 特别是近几年廉价金属配合物在水氧化领域的应用也备受关注. 由于水氧化一般在苛刻的氧化条件下才可以实现, 如何提高过渡金属配合物在催化条件下的稳定性一直是分子催化剂结构设计的一个难点. 利用部分分子催化剂的不稳定性, 将其作为前体制备非均相金属氧化物催化剂, 广泛用于水氧化研究. 然而, 对于催化水氧化过程中造成分子催化剂不稳定的因素却鲜有探讨. 因此, 了解分子催化剂和异相活性物种之间原位转化的机理对于分子催化剂设计至关重要.
本文考察了大环配体(TAML)的三价铜配合物(TAML-CuIII)的氧化还原性质及其电催化水氧化的反应性能. 实验结果表明, TAML-CuIII的催化水氧化活性与缓冲溶液种类有关, 在磷酸盐溶液与碳酸氢钠溶液中均无催化活性, 而在硼酸溶液中表现出较高的催化活性. 此外, TAML-CuIII具有与本课题组之前报道的TAML-CoIII截然不同的电化学行为. TAML-CuIII只能发生配体的单电子氧化生成TAML•+-CuIII, 且该物种无法实现对水分子的活化. 进一步实验结果表明, 生成的TAML•+-CuIII在硼酸根的协助下可以发生进一步氧化和配体的水解, 从而生成具有高活性的非均相物种. 研究表明该活性物种为含硼的氧化铜物种(B/CuOx). 通过本文研究可得出两个结论: (1)具有平面四方构型的三价铜配合物不是一种有效催化水氧化的分子型催化剂; (2)缓冲阴离子在分子催化剂的分解中起到了关键作用. 因此, 缓冲溶液的选择对催化剂的电化学行为以及稳定性有着重要的影响.

关键词: 人工光合作用, 水氧化, 氧化还原活性配体, 铜催化剂, 缓冲溶液阴离子效应

Abstract:

Water oxidation is the bottleneck of artificial photosynthesis. Since the first ruthenium-based molecular water oxidation catalyst, the blue dimer, was reported by Meyer’s group in 1982, catalysts based on transition metals have been widely employed to explore the mechanism of water oxidation. Because the oxidation of water requires harsh oxidative conditions, the stability of transition complexes under the relevant catalytic conditions has always been a challenge. In this work, we report the redox properties of a CuIII complex (TAML-CuIII) with a redox-active macrocyclic ligand (TAML) and its reactivity toward catalytic water oxidation. TAML-CuIII displayed a completely different electrochemical behavior from that of the TAML-CoIII complex previously reported by our group. TAML-CuIII can only be oxidized by one-electron oxidation of the ligand to form TAML•+-CuIII and cannot achieve water activation through the ligand-centered proton-coupled electron transfer that takes place in the case of TAML-CoIII. The generated TAML•+-CuIII intermediate can undergo further oxidation and ligand hydrolysis with the assistance of borate anions, triggering the formation of a heterogeneous B/CuOx nanocatalyst. Therefore, the choice of the buffer solution has a significant influence on the electrochemical behavior and stability of molecular water oxidation catalysts.

Key words: Artificial photosynthesis, Water oxidation, Redox-active ligand, Copper catalyst, Buffer anion effect