物理化学学报 >> 2023, Vol. 39 >> Issue (6): 2209037.doi: 10.3866/PKU.WHXB202209037

所属专题： S型光催化剂

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光激发电荷在光催化氧化还原反应中的全利用

王中辽, 汪静, 张金锋(), 代凯()   

  • 收稿日期:2022-09-26 录用日期:2022-10-26 发布日期:2022-11-01
  • 通讯作者: 张金锋,代凯 E-mail:jfzhang@chnu.edu.cn;daikai940@chnu.edu.cn
  • 作者简介:第一联系人：

    †These authors contributed equally to this work.

Overall Utilization of Photoexcited Charges for Simultaneous Photocatalytic Redox Reactions

Zhongliao Wang, Jing Wang, Jinfeng Zhang(), Kai Dai()   

  • Received:2022-09-26 Accepted:2022-10-26 Published:2022-11-01
  • Contact: Jinfeng Zhang, Kai Dai E-mail:jfzhang@chnu.edu.cn;daikai940@chnu.edu.cn

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摘要：

光催化转化CO2为碳氢燃料，分解水产氢，选择性有机合成，还原N2为NH3，降解毒害的有机污染物等对解决能源环境问题有重要意义。早在1972年，研究者利用TiO2通过光催化实现了全面分解水产氢和产氧。由于低的可见光利用率，严重的载流子复合和过高的水氧化能垒导致光催化全面水分解的效率极低。由于氢相对于氧更具有经济价值，因此牺牲剂辅助的光催化产氢被大量研究。由于牺牲剂可以快速的消耗光生空穴，有效降低了氧化端的能垒，光催化产氢的效率相比于光催化水分解的效率提高了3–4个量级。然而，牺牲剂的使用不仅导致了光生空穴的浪费，成本的提高，还导致了潜在的环境问题。近些年，研究者通过将光催化还原反应和光催化氧化反应结合在一起实现了电子空穴的全面利用，并改进了氧化和还原的效率。同时，电子空穴的全面利用也有效的促进了电荷的分离并提高了催化剂的稳定性。然而，由于全面氧化还原的设计难度大，反应过程复杂，因此光催化全面氧化还原的机理尚不够明确，仍然需要大量的探索。在这篇综述中，首先从光捕获、光激发电荷分离、氧化还原反应的热力学和动力学过程等角度讨论了光催化的基本原理。然后根据不同的光催化氧化反应和光催化还原反应的耦合，比如光催化整体水分解、光催化产H2与有机氧化耦合、光催化CO2还原与有机氧化耦合、光催化产H2O2与有机氧化耦合、光催化N2还原与N2氧化耦合、光催化有机还原与有机氧化耦合等光催化全面氧化还原反应进行了系统分类。随后，从光催化材料的设计、反应条件、反应物和产物的多样性等方面详细考虑了光催化氧化还原反应的设计要点。此外，通过功函数、电子密度差、Bader电荷、吸附自由能的变化，讨论了密度泛函理论(DFT)计算在揭示光激发电荷转移、中间体转变过程中的速率决定步骤和氧化还原反应势垒方面的重要作用。然后，结合典型案例，尽可能通过原位表征和DFT计算，详细分析了各种光催化氧化还原反应的活性和机理。最后，从构建S型异质结光催化剂、合理负载助催化剂、设计光催化剂形貌、开发新型光催化剂、合理选择氧化半反应和还原半反应耦合、原位表征和DFT计算的结合等角度对光催化全面氧化还原反应的应用进行了总结和展望。该工作为光催化整体氧化还原反应的设计策略和机理洞察提供了参考。

关键词: 光催化, 整体氧化还原反应, 太阳能利用, 电荷分离, 协同效应

Abstract:

The photoconversion of CO2 to carbon-containing fuels, splitting water into H2, selective organic synthesis, reduction of N2 to NH3, and hazardous organic contaminant degradation represent feasible schemes for solving environmental and energy issues. In 1972, TiO2 was applied for decomposing water into H2 and O2 via photocatalysis. Owing to its the low visible-light utilization, fast charge recombination, and high energy barrier for water oxidation, overall photocatalytic water-splitting efficiency is extremely low. Because H2 is more economically valuable than O2, sacrificial agent-assisted photocatalytic H2 evolution has been extensively investigated. Because the sacrificial agent can quickly consume photoexcited holes and effectively reduce the water oxidation energy barrier, photocatalytic H2 evolution efficiency can be increased by 3–4 orders of magnitude compared to photocatalytic water splitting. However, the overuse of sacrificial agents contributes to wasted photoexcited holes and expensive processes, while presenting potential environmental issues. Recently, overall charge utilization and improved redox efficiency have been achieved by coupling photocatalytic reduction with oxidation reactions. Moreover, overall charge utilization can boost charge separation and increase photocatalyst durability. However, the photocatalytic mechanism of the overall redox reactions remains unclear, owing to the complex reaction processes and design difficulties. Herein, the basic principles of photocatalysis are discussed from the perspective of light harvesting, photoexcited charge separation, thermodynamics, and redox reaction kinetics. Photocatalytic redox reactions, including overall water photodecomposition, photocatalytic H2 evolution coupled with organic oxidation, photocatalytic CO2 reduction coupled with organic oxidation, photocatalytic H2O2 production coupled with organic oxidation, photocatalytic N2 reduction coupled with N2 oxidation, and photocatalytic organic reduction coupled with organic oxidation, can be systematically classified according to the coupling of photocatalytic oxidation reactions with photocatalytic reduction reactions. Subsequently, the design of photocatalytic redox reactions is considered in terms of the modulation of photocatalyst materials, reaction conditions, and diversity of reactants and products. In addition, the vital role of density functional theory (DFT) calculations for unveiling photoexcited charge transfer, rate-determining steps, and redox reaction barriers are discussed in the context of the work function, electron density difference, Bader charge, and variation in the intermediate adsorption free energy profiles. The activity and mechanism of various photocatalytic redox reactions were elaborately analyzed through in situ characterizations and DFT calculations using representative cases. Finally, the overall photocatalytic redox reactions were summarized with a focus on the construction of an S-scheme heterojunction photocatalyst, reasonable loading of co-catalysts, photocatalyst morphology regulation, novel photocatalyst development, reasonable selection of the oxidation half-reaction and reduction half-reaction for coupling, and combined in situ characterization and DFT calculations. This work provides a reference for promising design strategies and insight into the mechanism of overall photocatalytic redox reactions.

Key words: Photocatalysis, Overall redox reaction, Solar utilization, Charge separation, Synergistic effect