Benefiting from their modular nature and tunable optoelectronic properties, two-dimensional (2D) covalent organic frameworks (COFs) have emerged as promising candidates for photocatalytic overall water splitting (OWS). However, the rapid recombination of photogenerated carriers usually results in poor photocatalytic performance in many of these COFs. Herein, we propose that introducing in-plane polarity in COFs with homogeneous cores can effectively address this challenge. Using first-principles calculations, we designed two types of 2D imine-linked COF monolayers (Im-TPB and Im-TPP) for OWS. Interestingly, both COFs exhibit type-II-like band alignments induced by polarized imine linkages, which significantly inhibit electron–hole recombination. This advantageous characteristic was further confirmed in ten additional COFs. The predicted lifetimes of photogenerated carriers for Im-TPB and Im-TPP are 13.5 and 8.7 times longer than those of non-polar azo-linked TPB and TPP, respectively. Furthermore, the band edges of Im-TPB and Im-TPP not only straddle the water redox potentials at pH = 7 and pH = 14, but also afford a sufficiently high driving force and enhanced light absorption ability. Of particular note is Im-TPB's capability to spontaneously split pure water into hydrogen and oxygen under visible light without the need for cocatalysts and sacrificial reagents. Our results highlight the role of in-plane polarity in the polarized-bond-linked COFs and open a promising avenue to design efficient COF-based photocatalysts for OWS.

中文翻译：

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面内极性促进具有极化连接的二维共价有机框架中的光催化整体水分解


得益于其模块化性质和可调光电特性，二维（2D）共价有机骨架（COF）已成为光催化整体水分解（OWS）的有希望的候选者。然而，光生载流子的快速复合通常会导致许多COF的光催化性能较差。在此，我们建议在具有同质纤芯的 COF 中引入面内极性可以有效解决这一挑战。利用第一性原理计算，我们设计了两种用于 OWS 的二维亚胺连接 COF 单层膜（Im-TPB 和 Im-TPP）。有趣的是，两种 COF 均表现出由极化亚胺键引起的类 II 型能带排列，显着抑制电子空穴复合。这一有利的特性在另外十个 COF 中得到了进一步证实。 Im-TPB 和 Im-TPP 的光生载流子寿命预计分别比非极性偶氮连接的 TPB 和 TPP 长 13.5 倍和 8.7 倍。此外，Im-TPB和Im-TPP的带边不仅跨越pH = 7和pH = 14时的水氧化还原电位，而且还提供足够高的驱动力和增强的光吸收能力。特别值得注意的是 Im-TPB 能够在可见光下自发地将纯水分解为氢气和氧气，而无需助催化剂和牺牲试剂。我们的结果强调了面内极性在极化键连接的COF中的作用，并为设计高效的基于COF的OWS光催化剂开辟了一条有前途的途径。