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

Abstract

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 (Td10: 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.