Sunlight-driven hydrogen production has been considered as one of the most important renewable energy sources, while active photocatalyst is a prerequisite for efficient hydrogen production. 2D covalent organic frameworks (COFs) could have well-defined arrangements of photo- and electro-active units that serve as electron or hole transport channels for solar energy harvesting and conversion, however, their insufficient charge transfer and rapid charge recombination impede the sunlight-driven photocatalytic performance. 

Motivated by such a challenge, a research team led by Prof. WEN Ke and Prof. YANG Hui at the Shanghai Advanced Research Institute (SARI), collaborating with Prof. ZHANG Yuebiao at ShanghaiTech University, reported a novel photoactive 2D COF from donor pyrene (Py) and acceptor Tz building units, which enabled remarkable photogenerated charge separation and efficient charge migration. The research results were featured on front cover of Angewandte Chemie International Edition. 

Based on physical structural characterizations, the researchers conjectured that Thiazolo[5,4-d]Thiazole might help to boost photo-absorbing ability of previously reported TpTz COF. They constructed the new donor-acceptor system from the electron-rich Py and electron-deficient thiazolo[5,4-d]thiazole (Tz).

According to the researchers, the PyTz-COF demonstrates high photocatalytic activitity for sustainable and efficient water splitting with a photocurrent up to 100 uA cm-2 at 0.2 V vs. RHE and could reach a hydrogen evolution rate of 2,072.4 umolg-1 h-1, which exceeds the values of many previously reported COFs. 

This study not only realizes the effective separation and migration of photogenerated electrons and holes, but also reveals a new mechanism of COF photocatalysis. More importantly, it would inspire future development of sunlight-driven photocatalysts for solar energy harvesting and conversion.