Donor-acceptor carbazole-based conjugated microporous polymers as photocatalysts for visible-light-driven H₂ and O₂ evolution from water splitting

Although novel donor–acceptor conjugated microporous polymers (D-A CMPs) that absorb visible light broadly and allow the efficient isolation of photoinduced electrons and holes are being sought for water splitting photocatalysis, their elusive energy band structures have made it a challenge to produce both H₂ and O₂ simultaneously. In this paper, for the first time, we develop a series of semiconducting D-A CMPs with various sulfur and nitrogen contents and degrees of conjugation for effective photocatalytic H₂ and O₂ generation from water. Here, we used a carbazole (Cz) moiety as the donor, and pyrene (Py), triphenyltriazine (TPT), benzothiadiazole (BT), and thiazolylthiazole (TzTz) as the acceptors. The resulting D-A CMPs had large surface areas (up to 1530 m² g^–1) and high thermal stabilities (T_d10: up to 623 °C; char yield: up to 83 wt%). Moreover, the Cz-TzTz CMP provided an excellent hydrogen evolution rate (HER), reaching 15.3 mmol g^–1 h^–1 in the presence of ascorbic acid as the sacrificial electron donor, but without the need for an additional Pt co-catalyst. Interestingly, the Cz-TPT CMP provided an excellent oxygen evolution rate (OER) of 3.38 mmol g^–1 h^–1 when using AgNO₃ as a sacrificial electron acceptor; this value is competitive with those of most previously reported organic photocatalysts. These highly active CMP-based photocatalysts appear to be useful materials for solar energy harvesting and conversion.