Trenker Stefan, Vignolo-Gonzalez Hugo A, Rodríguez-Camargo Andrés, Yao Liang, Zwijnenburg Martijn A, Lotsch Bettina V
Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569 Stuttgart, Germany.
Department of Chemistry, University of Munich (LMU), Butenandtstr. 5-13, 81377 Munich, Germany.
Chem Mater. 2025 Jun 4;37(12):4463-4474. doi: 10.1021/acs.chemmater.5c00804. eCollection 2025 Jun 24.
Covalent organic frameworks (COFs) have emerged as promising semiconducting materials for photocatalytic applications due to their large surface area, high crystallinity, and vast synthetic tunability. This is especially noticeable in the context of photocatalytic water splitting, where many COFs have been employed for the hydrogen evolution half-reaction. There, sacrificial reagents typically replace the kinetically demanding oxygen evolution half-reaction. On the contrary, only few reports focus on (sacrificial) water oxidation with COF photocatalysts. In most of these cases, cobalt species are employed as oxygen evolution cocatalyst, often with limited insight into their structure and detailed role in the catalysis. Herein, we use heterogenization of a molecularly defined iridium half-sandwich complex onto a bipyridine-based COF (Ir@TAPB-BPY COF) and provide detailed structural insights ensuring the integrity of the targeted cocatalyst. First, we demonstrate the retained catalytic activity of the anchored Cp*Ir-(III) motifs in chemical water oxidation experiments. In contrast, subsequent photocatalytic and electrocatalytic tests indicate that Ir@TAPB-BPY COF does not evolve oxygen and that careful control experiments have to be conducted in order to avoid false positive results, caused for example by the sacrificial electron acceptor. Using computational methods, we trace back the missing performance to thermodynamic and kinetic limitations of the employed systems. This work demonstrates the pitfalls associated with low-performing oxygen evolution photocatalysts as well as the indispensability of control experiments and their careful evaluation.
共价有机框架（COFs）因其大表面积、高结晶度和巨大的合成可调性，已成为用于光催化应用的有前景的半导体材料。在光催化水分解的背景下，这一点尤为明显，其中许多COFs已被用于析氢半反应。在那里，牺牲试剂通常替代了动力学上要求苛刻的析氧半反应。相反，只有少数报道关注COF光催化剂的（牺牲性）水氧化。在大多数这些情况下，钴物种被用作析氧共催化剂，通常对其结构及其在催化中的详细作用了解有限。在此，我们将分子定义的铱半夹心配合物异质化到基于联吡啶的COF（Ir@TAPB-BPY COF）上，并提供详细的结构见解以确保目标共催化剂的完整性。首先，我们在化学水氧化实验中证明了锚定的Cp*Ir-(III)基序保留的催化活性。相比之下，随后的光催化和电催化测试表明Ir@TAPB-BPY COF不会析氧，并且必须进行仔细的对照实验以避免例如由牺牲电子受体引起的假阳性结果。使用计算方法，我们将缺失的性能追溯到所用体系的热力学和动力学限制。这项工作展示了与低性能析氧光催化剂相关的陷阱以及对照实验及其仔细评估的必要性。
