Abstract：
Covalent organic frameworks (COFs) are promising photocatalysts for H2O2 production from water via oxygen reduction reaction (ORR). The design of COFs for efficient H2O2 production indubitably hinges on an in-depth understanding of their ORR mechanisms. In this work, taking an imine-linked COF as an example, we demonstrate that protonation of the functional units such as imine, amine, and triazine, is a highly efficient strategy to upgrade the activity levels for H2O2 synthesis. The protonation not only extends the light absorption of the COF but also provides proton sources that directly participate in H2O2 generation. Notably, the protonation simplifies the reaction pathways of ORR to H2O2, i.e. from an indirect superoxide radical ( O 2 • - ${{O}_{2}^{\\bullet -}}$ ) mediated route to a direct one-step two-electron route. Theoretical calculations confirm that the protonation favors H2O2 synthesis due to easy access of protons near the reaction sites that removes the energy barrier for generating *OOH intermediate. These findings not only extend the mechanistic insight into H2O2 photosynthesis but also provide a rational guideline for the design and upgradation of efficient COFs.
摘要：
共价有机骨架（COF）是通过氧还原反应（ORR）从水中生产H2O2的有前途的光催化剂。用于高效H2O2生产的COF的设计无疑取决于对其ORR机制的深入理解。在这项工作中,以亚胺连接的COF为例，我们证明了诸如亚胺之类的功能单元的质子化，胺,和三嗪,是提高H2O2合成活性水平的高效策略。质子化不仅扩展了COF的光吸收,而且提供了直接参与H2O2生成的质子源。值得注意的是,质子化简化了ORR到H2O2的反应途径，即从间接超氧化物自由基（[[方程]]）介导的途径到直接一步两电子途径。理论计算证实，质子化有利于H2O2的合成，因为易于接近反应位点的质子，从而消除了产生*OOH中间体的能垒。这些发现不仅扩展了对H2O2光合作用的机理见解，而且为高效COF的设计和升级提供了合理的指导。
